Introduction

The input mechanical properties of knee replacement bearing materials, such as elastic modulus and Poisson's ratio, significantly contribute to the accuracy of computational models. They should therefore be determined from independent experimental studies, under similar test conditions to the clinical and experimental conditions, to provide reliability to the models. In most cases, the reported values in the literature for the elastic modulus and Poisson's ratio of the bearing materials have been measured under tensile test conditions, in contrast to the compressive operating conditions of the total knee replacements (TKR). This study experimentally determined the elastic modulus and Poisson's ratio of conventional and moderately cross-linked ultra-high molecular weight polyethylene (UHMWPE) under compressive test conditions. These material parameters will be inputs to future computational models of TKR.

Materials/Methods

To determine the Poisson's ratio of the conventional and moderately cross-linked UHMWPE, contact areas of 12mm diameter cylindrical specimens of 10.2mm length were measured experimentally under a compressive displacement of 1mm, at a strain rate of 12mm/min that was held for 10minutes. A computational model was developed in Abaqus, 6.14–1, to simulate this experimental test assuming different values for the Poisson's ratio of the UHMWPE cylindrical specimens. The curve fitted relationship between the computationally predicted contact area and Poisson's ratio was used to calculate the Poisson's ratio of the UHMWPE specimens, using the experimentally measured contact areas. Using a similar approach, the equivalent elastic modulus of the UHMWPE was calculated using the computationally calculated curve fitted contact area-elastic modulus relationship, from the computational simulation of a ball-on-flat compression test, and the experimentally measured contact area from a ball-on-flat dynamic compression test. This experiment used 10mm thick UHMWPE flat specimens against a 63.5mm rigid ball, under a compressive dynamic sinusoidal loading of 250N average load, and 6000 cycles. The applied test conditions maintained the stress level within the reported range for the TKR.

Introduction

Surface wear of polyethylene is still considered a long-term risk factor for clinical success, particularly as life expectancy and activity levels increase. Computational models have been used extensively for preclinical wear prediction and optimization of total knee replacements (TKR). In most cases, the input wear parameters (wear factors and coefficients) to the computational models have been experimentally measured under average contact stresses to simulate standard activities. These wear studies are not therefore applicable for more adverse conditions that could lead to edge loading and high stress conditions, including higher levels of activities and severe loading conditions. The current study investigated the multidirectional pin-on-plate wear performance of moderately cross-linked ultra-high molecular weight polyethylene (UHMWPE) under high applied nominal contact stress, to be used as inputs to a computational model investigating adverse high stress conditions.

Materials/Methods

Moderately cross-linked UHMWPE (GUR_1020,5Mrad gamma irradiation) pins were tested against cobalt–chrome alloy (CoCr) plates in a multidirectional pin-on-plate wear simulator. The CoCr metallic plates were polished to an average surface roughness of 0.01μm. The pin rotation and the plate reciprocation of ±30º and 28mm were in phase, having a common frequency of 1Hz, and resulted in a multidirectional motion at the pin-plate contact surface in a flat-on-flat configuration. Six different pin diameter and applied load combinations were tested, resulting in applied nominal contact stresses from 4 to 80[MPa](Fig.1). Each set was run for 1million cycles in 25% bovine serum as a lubricant. The volumetric wear was calculated from the weight loss measurements using a density 0.93mg/mm³ for the UHMWPE material. The wear factor and wear coefficient were calculated as (volumetric wear/(load x sliding distance)) and (volumetric wear/(contact area x sliding distance)) respectively[1]. Statistical analysis of the data was performed in ANOVA and significance was taken at p<0.05.

Introduction

The mobile-bearings were introduced in total knee arthroplasty (TKA) to improve the knee performance by simulating more closely ‘normal’ knee kinematics, and to increase the longevity of TKA by reducing the polyethylene wear and periprosthetic osteolysis. However, the superiority between posterior-stabilized mobile-bearing and fixed-bearing designs still remains controversial. The objective of the present study was to compare the mid-term results of Scorpio + Single Axis system (Stryker Howmedica Osteonics, Allendale, New Jersey) for the mobile-bearing knees and Duracon system (Stryker Howmedica Osteonics, Allendale, New Jersey) for the fixed bearing design with regard to clinical and roentgenographic outcome with special reference to any complications and survivorship.

Methods

Prospective, randomized, double-blinded controlled study was carried out on 56 patients undergoing primary, unilateral total knee arthroplasty for osteoarthritis, who were divided into two groups. Group I received mobile-bearing knee prosthesis (29 patients) and Group 2 received fixed-bearing prosthesis (27 patients). The patients were assessed by a physical examination and knee scoring systems preoperatively, at a follow-up of three months, six months, and one year after surgery by independent researcher who was not part of the operating team, and was blinded as to the type of implant inserted. We used the Oxford knee score (OKS) and Knee society score (KSS), with Knee Society Knee Score (KSKS) and Knee Society Functional Score (KSFS) being the subsets. The questionnaire for OKS was printed in our national language, and handed over to the patient at each visit.

Background

Total hip arthroplasty (THA) has become one of the most commonly performed elective procedures. Today, there are nearly 50 000 annual hospitalizations for hip replacement surgery in Canada. This number is projected to increase significantly with the aging population. Periprosthetic joint infection (PJI) is the 3rd leading cause of failure following THA and is reported to occur at an incidence of 1–3%. A two-stage revision THA is the current gold standard treatment and this has a tremendous economic impact on the healthcare system. The purpose of this study is to create an accurate cost estimate of two-stage revision THA and, in turn, evaluate the economic burden of PJI as it compares to primary THA in a Canadian healthcare context.

Methods

We conducted a retrospective review of primary THA cases and two-stage revision THA for PJI at our institution. Patients were matched for age and BMI. We recorded all costs associated with each procedure, including: OR time, equipment, length of hospital stay, readmission rates, and any other inpatient resource use. Unit costs were obtained using administrative data from the case costing department at London Health Sciences Centre. Billing fees associated with the procedure were obtained from the Ontario Schedule of Benefits. Descriptive statistics were used to summarize the demographic characteristics of patients, hospital costs and resource use data. Patients with PJI were compared to the matched cohort of primary THA using the t-test (for continuous variables), and the chi-square test (for categorical variables).

Introduction

Successful designs of total hip replacement need to be robust to surgery-related variability. Until recently, only simple parametric studies have explored the influence of surgical variability [1]. This study presents a systematic method for quantifying the effect of variability in positioning on the primary stability of femoral stems using finite element (FE) models.

Methods

Patient specific finite element models were generated of two femurs, one male and one female. An automated algorithm positioned and sized a Corail stem (DePuy Synthes, Warsaw) into each of the femurs to achieve maximum fill of the medullary canal without breaching into the cortical bone boundaries.. Peak joint contact and muscle forces associated with level gait were applied[2] and scaled to the body mass of each subject, whilst the distal femur was rigidly constrained. The space prone to surgical variation was defined by the “gap” between the stem and the inner boundary of the cortical bone. The anterior/posterior and the varus/valgus alignment of the stem within this “gap” was controlled by varying the location of the points defining the shaft axis. The points were taken at 20% and 80% of the stem length (Figure 1). The anteversion angle as well as the vertical and the medial position of the stem were controlled by changing the location of the head centre within the femoral head radius. The location of these points was varied using Latin Hypercube sampling to generate 200 models per femur, each with a unique stem position. The risk of failure was evaluated based on stem micromotion, equivalent strains, and percentage of the bone-prosthesis contact area experiencing more than 7000 µstrains [3].

Introduction

Pre-clinical testing of orthopaedic devices could be improved by comparing performance with established implants with known clinical histories. Corail and Summit (DePuy Synthes, Warsaw) are femoral stems with proven survivorship of 95.1% and 98.1% at 10 years [1], which makes them good candidates as benchmarks when evaluating new stem designs. Hence, the aim of this study was to establish benchmark data relating to the primary stability of Corail and Summit stems.

Methods

Finite Element (FE) simulations were run for 34 femurs (from the Melbourne femur collection) for a diverse patient cohort of joint replacement age (50 – 80 yrs). To account for the diversity in shape, the cohort included femurs with the maxima, minima and medians for 26 geometric parameters. Subject-specific FE models were generated from CT scans. An in-house developed algorithm positioned idealized versions of Corail and Summit (Figure 1) into each of the femur models so that the stem and femur shaft axes were aligned, and the vertical offset between the trunnion centre and the femoral head centre was minimised. For such a position, the algorithm selected the size that achieved maximum fill of the medullary canal without breaching the cortical bone boundaries.

Joint contact and muscle forces were calculated for level gait and stair climbing[2] and scaled to the body mass of each subject. Femurs were rigidly constrained at the condyles. Risk of failure was assessed based on (i) stem micromotion, (ii) equivalent strains (iii) percentage of the bone-prosthesis contact area experiencing micromotions < 50 μm, micromotions > 150 μm and strains > 7000 μstrains [3].

Introduction

Previous studies have shown that third body damage to the femoral head in metal-on-polyethylene hip replacement bearings can lead to accelerated wear of the polyethylene liners. The resulting damage patterns observed on retrieved metal heads are typically scratches and scrapes. The damage created in vitro must represent the third body damage that occurs clinically. A computational model was developed to predict the acceleration of wear of polyethylene articulating against in vitro damaged femoral heads. This involved using a damage registry from retrieval femoral heads to develop standardized templates of femoral head scratches statistically representative of retrieval damage

The aim of this study was to determine the wear rates of polyethylene liners articulating against retrievals and artificially damaged metal heads for the purpose of validating a computational wear prediction model; and to develop and validate an in vitro standardised femoral head damage protocol for pre-clinical testing of hip replacements.

Materials and Methods

Twenty nine, 32mm diameter, metal-on-moderately cross-linked polyethylene bearings (Marathon^TM) inserted into Ti-6Al-4V shells (Pinnacle^®) were tested in this study. All products were manufactured by DePuy Synthes, Warsaw, Indiana, USA. Following a retrieval study seven different damage patterns were defined, and these were applied to the femoral heads using a four-degree-of-freedom CNC milling machine (Figure 1). The ProSim 10-station pneumatic hip joint simulator (Simulation Solutions, UK) was used for experimental wear simulation using standard gait cycles and testing each experimental group for 3 million cycles. The acetabular cups were inclined at 35° on the simulator (equivalent to 45° in vivo). The wear volumes were determined using a microbalance (Mettler-Toledo XP205, Switzerland) at one million cycle intervals. Statistical analysis used was one way ANOVA followed by a post hoc analysis with significance taken at p<0.05.

INTRODUCTION

Due to increasing interest into taper corrosion observed primarily in hip arthroplasty devices with modular tapers, efforts towards characterizing the corrosion byproducts are prevalent in the literature [1–4]. As a result of this motivation, several studies postulate cellular induced corrosion due to the presence of remarkable features in the regions near taper junction regions and articulating surfaces [3–5]. Observations made on explanted devices from a retrieval database as well as laboratory tests have led to the alternative proposal of electrocautery-electrosurgery damage as the cause of these features. These surgical instruments are commonly used for hemostasis or different degrees of tissue dissection.

METHODS

Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to evaluate the features observed on retrieved devices. Retrieved devices consisted of OXINIUM and cobalt-chromium-molybdenum (CoCrMo) femoral implants, a Titanium-alloy hip stem, and a CoCrMo metal-on-metal femoral head. Electrocautery-electrosurgery damage was created using a SurgiStat II (Valleylab, Colorado) onto various components (CoCrMo, OXINIUM femoral heads as well as Ti-6Al-4V and CoCrMo alloy test stem constructs). Test components were evaluated using the same methods as the retrieved devices.

Introduction

Patellar resurfacing affects patellofemoral (PF) kinematics, contact mechanics, and loading on the patellar bone. Patients with total knee arthroplasty (TKA) often exhibit adaptations in movement patterns that may be linked to quadriceps deficiency and the mechanics of the reconstructed knee [1]. Previous comparisons of PF kinematics between dome and anatomic resurfacing have revealed differences in patellar sagittal plane flexion [2], but further investigation of PF joint mechanics is required to understand how these differences influence performance. The purpose of this study was to compare PF mechanics between medialized dome and medialized anatomic implants using subject-specific computational models.

Methods

A high-speed stereo radiography (HSSR) system was used to capture 3D sub-mm measurement of bone and implant motion [3]. HSSR images were collected for 10 TKA patients with Attune® (DePuy Synthes, Warsaw, IN) posterior-stabilized, rotating-platform components, 5 with medialized dome and 5 with medialized anatomic patellar components (3M/7F, 62.5±6.6 years, 2.2±0.6 years post-surgery, BMI: 26.2±3.5 kg/m²), performing two activities of daily living: knee extension and lunge (Figure 1). Relative motions were tracked using Autoscoper (Brown University, Providence, RI) for implant geometries obtained from the manufacturer. A statistical shape model was used to predict the patella and track motions [4].

Subject-specific finite element models of the experiment were developed for all subjects and activities [5]. The model included implant components, patella, quadriceps, patellar tendon, and medial and lateral PF ligaments (Figure 2a). While tibiofemoral kinematics were prescribed based on experimental data, the PF joint was unconstrained. A constant 1000N quadriceps load was distributed among four muscle groups. Soft tissue attachments and pre-strain in PF ligaments were calibrated to match experimental kinematics [5]. Model outputs included PF kinematics, patellar and contact force ratios, patellar tendon angle, and moment arm.

Objectives

Modularity in total knee arthroplasty, particularly in revisions, is a common method to fit the implants to a patient's anatomy when additional stability or fixation is needed. In such cases, it may be necessary to employ multiple points of modularity to better match the anatomy. Taper junction strength at each of these levels is critical to maintain the mechanical stability of the implant and minimize micromotion. This effect of distributed assembly loads through multiple tapers and the resulting strength of the construct have not been previously evaluated on this revision tibial implant. The purpose of this study was to evaluate the possible dissipation of impaction force through multiple taper connections as compared to a single connection.

Methods

Two different constructs representative of modular implants were studied: a construct with a single axial taper connection (Group A; representing implant-stem) was compared to a construct with an adaptor that included two, offset, modular taper connections (Group B; representing implant-adapter-stem). For Group A, the stem taper was assembled and impacted through the stem. For Group B, the two tapers of the adapter and stem were hand assembled with the mating components and impacted simultaneously through the stem. Assembly load for each construct was recorded. As shown in Figure 1, the constructs were then fixed in a mechanical test frame and an axial distraction force was applied to the end of the stem at a constant displacement rate of 0.075 mm/sec until taper separation or mechanical failure occurred. Force and displacement data were recorded at 50 Hz. Disassembly force was normalized to assembly force for each component. Minitab software was used to analyze the data using a t-test.

Introduction

Edge loading of hip replacements may result in plastic deformation, creep and wear at the rim of the cup and potentially fatigue failure. Variations in component positioning can lead to dynamic separation and edge loading [1]. The aim of this study was firstly to investigate the effects of translational and rotational positioning on the dynamic separation and severity of edge loading, and secondly to determine the wear rates of metal-on-polyethylene bearings under the more severe separation and edge loading conditions.

Materials and Methods

A hip joint simulator (ProSim EM13, Simulation Solutions, UK) was set up with 36mm diameter metal-on-polyethylene hip replacements (Marathon™, DePuy Synthes Joint Reconstruction, Leeds, UK). This study was in two parts. I) A biomechanical test was carried out at 45° (n=3) and 65° (n=3) cup inclination angles with 1, 2, 3 and 4 (mm) medial-lateral translational mismatch between the head and cup centres. The severity of edge loading was calculated from the area under the axial force and medial-lateral force outputs during the time of separation when the load was acting on the edge of the cup [2]. II) For two conditions (two million cycles), the head and cup were concentric for cups inclined equivalent clinically to 45° (n=3) and 65° (n=3). For two further conditions (three million cycles), 4mm medial-lateral translational mismatch between centres was applied for cups inclined equivalent clinically to 45° (n=6) and 65° (n=6). Volumetric wear measurements were undertaken at one million cycle intervals. The lubricant was diluted new-born calf serum (25% v/v). Plastic deformation and wear were determined using a coordinate measurement machine. Mean values were calculated with 95% confidence limits. Statistical analysis was carried out using ANOVA and a t-test with significance levels taken at p<0.05.

Introduction

Variations in component position can lead to dynamic separation and edge loading conditions. In vitro methods have been developed to simulate edge loading conditions and replicate stripe wear, increased wear rate, and bimodal wear debris size distribution, as observed clinically [1, 2]. The aim of this study was to determine the effects of translational and rotational positioning on the occurrence of dynamic separation and severity of edge loading, and then investigate the wear rates under the most severe separation and edge loading conditions on an electromechanical hip joint simulator.

Materials and Methods

A hip joint simulator (ProSim EM13, Simulation Solutions, UK) was set up with 36mm diameter ceramic-on-ceramic (BIOLOX®delta, PINNACLE®, DePuy Synthes, UK) hip replacements. Three axes of rotation conditions (ISO 14242-1 [3]) was applied to the femoral head. This study was in two parts. I) A biomechanical test was carried out at 45° (n=3) and 65° (n=3) cup inclination angles with 1, 2, 3 and 4 (mm) medial-lateral translational mismatch between the centres of the head and cup. The amount of dynamic separation displacement between the head and cup was measured using a position sensor. The severity of edge loading was determined from the area under the axial force and medial-lateral force outputs during the time of separation [4]. II) A wear test was carried out at 45° (n=6) and 65° (n=6) cup inclination angles for three million cycles with translational mismatch of 4mm between the head and cup. The lubricant used was diluted new-born calf serum (25% v/v). Volumetric wear measurements were undertaken at one million cycle intervals and mean wear rates were calculated with 95% confidence limits. Statistical analysis was carried out using ANOVA and a t-test with significance levels taken at p<0.05.

INTRODUCTION

Dislocation is one of the most frequent complications in total hip arthroplasty (THA), affecting an estimated 1% to 5% of THA patients. Malposition of the acetabular cup is thought to be a likely contributor. As the field searches for solutions, new experimental methods can help engineers, scientists, and surgeons better understand the problem as well as evaluate novel techniques and products.

OBJECTIVES

Create a laboratory simulation to assess patient positioning and pelvic motion during THA. Apply this simulation to assess (1) variation in patient positioning; (2) various methods to identify the pelvic plane via palpated anatomic landmarks.

INTRODUCTION

The alignment of components in total knee arthroplasty (TKA) is perceived to be one of the most influential factors in determining the long-term outcomes. A contemporary debate exists regarding the choice of the alignment method. As a vast majority of the surgeons support the basis of the mechanical alignment philosophy (MA), others believe in the concept of anatomical alignment theory (AA) to closely match the anatomy of the femur and the tibia of the native knee [1]. This study was intended to evaluate the accuracy of achieving a planned tibial resection target using either the MA or AA methods.

Materials and Methods

Five healthy cadaveric knees (tibia and foot only) were studied. Four surgeons were independently asked to position a tibial cutting block (without pinning) using conventional extramedullary mechanical instrumentation (Exactech LPI instrumentation, Gainesville, FL, USA). Surgeons were asked to target a predefined proximal tibial cut according to MA (Varus= 0°, posterior slope= 3°, resection level= 10 mm) or to AA (Varus= 3°, posterior slope= 6°, resection level= 9 mm). Once the surgeon expressed satisfaction with the achieved position of the tibial cutting block, the planned resection was recorded using an imageless guidance system (ExactechGPS^®, Blue-Ortho, Grenoble, FR). Surgeons completed at least three positioning trial for each alignment method on each cadaver. The accuracy and outliers (deviated more than 2°/mm from the target [2]) of resection planning were compared between the MA and AA methods. Statistical significance was defined as p< 0.05.

Background

Long term success of any shoulder joint reconstruction procedure involving subscapularis attachment take down is dictated by the way one chooses to release and repair/reconstruct the subscapularis insertion. There are several methods that were reported in the literature without any preset guidelines which are easily reproducible.

Methods

5 specimens of fresh cadaver shoulder joints dissected and the subscapularis footprint insertion involving the tendon and muscle exposed. We intend to preserve subscapularis tendon footprint along with the lesser tuberosity by performing the footprint osteotomy fashioned step wise in the following manner.

Introduction

Magnetic resonance imaging with intraarticular contrast (arthro-MRI) and radial cuts is the gold standard to quantify labral and chondral lesions in the setting of femoroacetabular impingement. To date, no study exists that has evaluated these findings as potential predictors of outcome for the long term follow-up after surgical treatment of FAI.

Objectives

The purpose of this study was to detect potential predictors for failure after surgical hip dislocation for FAI based on specific preoperative arthro-MRI of the hip at a minimum follow-up of 10 years.

Introduction & Objective

Labral refixation has established as a standard in open or arthroscopic treatment for femoroacetabular impingement (FAI). The rationale for this refixation is to maintain the important suction seal in the hip. To date, only few short-term results are available which indicate a superior result in FAI hips with labral refixation compared to labral resection. Scientific evidence of a beneficial effect of labral refixation in the long-term follow-up is lacking.

Aim of this study was to evaluate if labral refixation can improve the cumulative 10-year survivorship in hips undergoing surgical hip dislocation for FAI compared to labral resection.

Methods

We performed a retrospective comparative study of 59 patients treated with surgical hip dislocation for symptomatic FAI between December 1998 and January 2003. We analyzed two matched groups: The ‘resection’ group consisted of 25 hips that were treated consistently by excision of the damaged labrum. The ‘refixation’ group consisted of 34 hips that were treated with labral reattachment. Correction of the osseous deformity (rim trimming/femoral osteochondroplasty) did not differ between the two groups. We then evaluated the clinical (Merle d'Aubigné score) and radiographical results (according to Tönnis) at a follow-up of ten years.

We calculated a cumulative Kaplan-Meier survivorship curve with the following factors as endpoints: conversion to total hip arthroplasty (THA), radiographic evidence of osteoarthritis progression, or a poor clinical result (defined as Merle d'Aubigné score of less than 15). The two curves were compared using the Log-rank test.

Introduction

Previous studies of CoCr alloy femoral components for total knee arthroplasty (TKA) have identified 3^rd body abrasive wear, and apparent inflammatory cell induced corrosion (ICIC) [1] as potential damage mechanisms. The association between observed surface damage on the femoral condyle and metal ion release into the surrounding tissues is currently unclear. The purpose of this study was to investigate the damage on the bearing surface in TKA femoral components recovered at autopsy and compare the damage to the metal ion concentrations in the synovial fluid.

Methods

12 autopsy TKA CoCr femoral components were collected as part of a multi-institutional orthopedic implant retrieval program. The autopsy components included Depuy Synthes Sigma Mobile Bearing (n=1) and PFC (n=1), Stryker Triathlon (n=1) and Scorpio (n=3), and Zimmer Nexgen (n=4) and Natural Knee (n=2). Fluoro scans of all specimens prior to removal was carried out to assure no signs of osteolysis or aseptic loosening were present.

Third-body abrasive wear of CoCr was evaluated using a semi-quantitative scoring method similar to the Hood method [2]. ICIC damage was reported as location of affected area and confirmed using a digital optical microscope with 4000X magnification.

Synovial fluid was aspirated from the joint capsule prior to removal of the TKA device. The synovial fluid was spun at 1600 rpm for 20 minutes in a centrifuge with the cell pellet removed. The supernatant was analyzed in 1 mL quantities for ICP-MS (inductively coupled plasma mass spectrometry) by Huffman Hazen Laboratories. Data was expressed as ppb.

Introduction

There is little information available to surgeons regarding how the lateral soft-tissue structures prevent instability in knees implanted with total knee arthroplasty (TKA). The aim of this study was to quantify the lateral soft-tissue contributions to stability following cruciate retaining (CR) TKA.

Methods

Nine cadaveric knees with CR TKA implants (PFC Sigma; DePuy Synthes Joint Reconstruction) were tested in a robotic system (Fig. 1) at full extension, 30°, 60°, and 90° flexion angles. ±90 N anterior-posterior force, ±8 Nm varus-valgus and ±5 Nm internal-external torque were applied at each flexion angle. The anterolateral structures (ALS, including the iliotibial band, anterolateral ligament and anterolateral capsule), the lateral collateral ligament (LCL), the popliteus tendon complex (Pop T) and the posterior cruciate ligament (PCL) were then sequentially transected. After each transection the kinematics obtained from the original loads were replayed, and the decrease in force / moment equated to the relative contributions of each soft-tissue to stabilising the applied loads.

Background

Osteoarthritis and the pain associated with it result in gait pattern alteration, in particularly gait asymmetry when the disease is unilateral [1–2]. The quantification of such asymmetry could assist with the diagnosis and follow up. Various asymmetry indices have been proposed to compare the spatiotemporal, kinematic and kinetic parameters of lower limbs during the gait cycle. One, the Continuous Relative Phase [3] compares the joints angle and its derivatives to assess the gait asymmetry during the gait cycle. However, the indices rely on marker based gait measurement systems that are costly and generally require manual examination, calibration procedures and the precise placement of sensors/markers on the body of the patient.

Aim

Create an automatic method to assess gait asymmetry with low cost depth camera system like Kinect.

Introduction

Because of the low cost and easy access, surgical video has become a popular method of acquiring surgical skills outside operating rooms without disrupting normal surgical flow. However, currently existing video systems all use a single point of view (POV). Some complex orthopedic procedures, such as joint replacement, require a level of accuracy in several dimensions. So single and fixed POV video may not be enough to provide all the necessary information for educational and training purposes. The aim of our project was to develop a novel multiple POV video system and evaluate its efficacy as an aid for learning joint replacement procedure compared with traditional method.

Materials and Methods

Based on the videos of a hip resurfacing procedure performed by an expert orthopedic surgeon captured by 8 cameras fixed all around the operating table, we developed a novel multiple POV video system which enables users to autonomously switch between optimal viewpoints (Figure 1). 30 student doctors (undergraduate years 3–5 and naive to hip resurfacing procedure) were recruited and randomly allocated to 2 groups: experiment group and control group, and were assigned to learn the procedure using multiple or single POV video systems respectively. Before learning they were first asked to complete a multiple choicetest designed using a modified Delphi technique with the advice and feedback sought from 4 experienced orthopedic surgeons to test the participants' baseline knowledge of hip resurfacing procedure. After video learning, they were asked to answer the test again to verify their gained information and comprehension of the procedure, followed by a 5-point Likert-scale questionnaire to demonstrate their self-perception of confidence and satisfaction with the learning experience. The scores in the 2 tests and in the Likert-scale questionnaire were compared between 2 groups using Independent-Samples t-test (for normally distributed data) or Mann-Whitney U test (for non-normally distributed data). Statistical significance was set as p<0.05.

Background/Purpose

Total hip arthroplasties (THAs) with ceramic bearings are widely performed in young, active patients and thus, long-term outcome in these population is important. Moreover, clinical implication of noise, in which most studies focused on ‘squeaking’, remains controversial and one of concerns unsolved associated with the use of ceramic bearings. However, there is little literature regarding the long-term outcomes after THAs using these contemporary ceramic bearings in young patients. Therefore, we performed a long-term study with a minimum follow-up of ¹5 years after THAs using contemporary ceramic bearings in young patients with osteonecrosis of the femoral head (ONFH) less than fifty.

Materials and Methods

Among sixty patients (71 hips) with a mean age of 39.1 years, 7 patients (7 hips) died and 4 patients (4 hips) were lost before 15-year follow-up. The remaining 60 hips were included in this study with an average follow-up period of 16.3 years (range, 15 to 18). All patients underwent cementless THA using a prosthesis of identical design and a 28-mm third-generation alumina head by single surgeon. The clinical evaluations included the modified Harris hip score (HHS), history of dislocation and noise around the hip joint: Noise was classified into squeaking, clicking, grinding and popping and evaluated at each follow-up. Snapping was excluded through physical examination or ultrasonography. Radiographic analysis was performed regarding notching on the neck of femoral component, loosening and osteolysis. Ceramic fracture and survivorship free from revision were also evaluated.

Introduction

Femoral heads made from zirconia-toughened alumina (ZTA) are the most advanced bioceramic available for total hip arthroplasty. ZTA's superior mechanical properties result from the polymorphic transformation of its zirconia (ZrO₂) phase in the presence of a propagating crack. In vitro derived activation energies predict that several human lifetimes are needed to reach a state of significant transformation;¹ but in vivo confirmation of material stability is still lacking. This investigation determined if transition metal ions might be responsible for triggering the tetragonal to monoclinic (t®m-ZrO₂) phase transformation in this bioceramic.

Materials and Methods

BIOLOX^®delta femoral heads (CeramTec GmbH, Plochingen, Germany) were acquired and characterized for their surface monoclinic content, V_m, using Raman spectroscopy. Then they were physiologically scratched with different metals (i.e., Ti, CoCr, and Fe, n=3 each) to simulate in vivo staining as a result of acetabular shell impingement due to subluxation or dislocation. They were subsequently hydrothermally aged for up to 100 h in an autoclave at 98∼132^°C and 1 bar pressure. Raman maps, each consisting of 120 spectra, were compiled and monoclinic contents, V_m, calculated for zones adjacent to and away from the metal stains.² Activation energies for the t®m transformation in stained and non-stained zones were derived and compared to retrieved heads having service lives of between ∼45 days and ∼8 years.

Introduction

The longevity of highly cross-linked polyethylene (XLPE) bearings is primarily determined by its resistance to long-term oxidative degradation. Addition of vitamin E to XLPE is designed to extend in vivo life, although it has unintended consequences of inducing higher frictional torque and increased wear when articulating against metallic femoral heads.^1–3 Conversely, lower friction was observed when oxide ceramic heads were utilized.³ Previous studies suggest that oxide ceramics may contribute to XLPE oxidation, whereas a non-oxide ceramic, silicon nitride (Si₃N₄), might limit XLPE's degradation.⁴ To corroborate this observation, an accelerated hydrothermal ageing experiment was conducted using static hydrothermal contact between XLPE and commercially-available ceramic femoral heads.

Materials and Methods

Two sets of four types of ceramic femoral heads, consisting of three oxides (Al₂O₃ BIOLOX^®forte, and ZTA BIOLOX^®delta, CeramTec, GmbH, Plochingen, Germany; and m-ZrO₂ OXINIUM^TM, Smith & Nephew, Memphis, TN, USA) and one non-oxide (MC^2®Si₃N₄, Amedica Corp., Salt Lake City, UT, USA) were cut into hemispherical sections. Six highly crosslinked polyethylene liners (X3^TM Stryker Orthopedics, Inc., Mahwah, New Jersey, USA) were also sectioned, gamma irradiated (32 kGy), and mechanically clamped (25 kN) to the convex surfaces of the ceramic heads (Figure 1(a)). All surfaces were dipped in water and placed into an autoclave at 121°C under adiabatic conditions for 24 hr. The test was repeated three times using two couples for each material along with XLPE-on-XLPE controls. Each XLPE sample was characterized before and after ageing using Raman spectroscopy for variations in their crystalline phase and oxidation indices using the intensities of unpolarized vibrational bands at 1296, 1305, and 1418 cm⁻¹. Significance (p<0.05) was determined using Student's t-test with a sample size of n=18.

Introduction

Advancements in knee surgery require a profound understanding of knee mechanics. However, there are seemingly contradicting reports regarding certain aspects of normal knee function, such as the location of the pivot of internal-external rotation in the transverse plane. Among others, it has been suggested to be located close to the knee center or in the medial compartment.

We hypothesized that this apparent contradiction is a result of different studied knee motions and that it can be explained by the underlying envelopes of motion. The study objective was to characterize normal knee behavior in-vitro with an emphasis on pivot location.

Methods

Thirty-four cadaveric human knee specimens (Age: 61±8 years, BMI: 25±7) underwent CT and MR imaging and load controlled in-vitro testing using an industrial robot (KUKA, Augsburg, Germany). The robot simulated passive knee flexion and assessed the envelopes of motion through anterior-posterior (AP, ±100 N), medial-lateral (ML, ±100 N) and internal-external (IE, ±6 Nm) laxity testing at five flexion angles. Kinematics were expressed by the femoral flexion facet centers (FFC). The pivot location was determined for IE laxity testing and passive flexion by computing the center of transverse femoral rotation in a least squares sense. Groups were compared by one-way ANOVA (α = 0.05). Results are stated as average ± standard deviation.

Introduction

Cementless acetabular components are commonly used in primary and revision total hip arthroplasty, and most designs have been successful despite differences in the porous coating structure. Components with 2D titanium fiber mesh coating (FM) have demonstrated high survivorships up to 97% at 20 years¹. 3D tantalum porous coatings (TPC) have been introduced in an attempt to improve osseointegration and therefore implant fixation. Animal models showed good results with this new material one year after implantation², and clinical and radiographic studies have demonstrated satisfactory outcomes³. However, few retrieval studies exist evaluating in vivo bone ingrowth into TPC components in humans. We compared bone ingrowth between well-fixed FM and TPC retrieved acetabular shells using backscatter scanning electron microscopy (BSEM).

Methods

16 retrieved, well-fixed, porous coated acetabulum components, 8 FM matched to 8 TPC by gender, BMI and age, all revised for reasons other than loosening and infection, were identified from our retrieval archive (Fig. 1). The mean time in-situ was 42 months for TPC and 172 for FM components. Components were cleaned, dehydrated, and embedded in PMMA. They were then sectioned, polished, and examined using BSEM. Cross-sectional slices were analyzed for percent bone ingrowth and percent depth of bone ingrowth (Fig. 2). Analysis was done using manual segmentation and grayscale thresholding to calculate areas of bone, metal, and void space. Percent bone ingrowth was determined by assessing the area of bone compared to the void space that had potential for bone ingrowth.

Background

The use of tranexamic acid (TEA) can significantly reduce the need for allogenic blood transfusions in elective primary joint arthroplasty. Revision total hip arthroplasty requires increased utilization of post-operative blood transfusions for acute blood loss anemia compared to elective primary hip replacement. There is limited literature to support the routine use of TEA in revision THA.

Methods

We performed a retrospective review of 161 consecutive patients who underwent revision total hip arthroplasty from 2012–14 at a single institution by two fellowship-trained surgeons. We compared the transfusion requirements and the post-operative hemoglobin drop of the TEA Group (109 patients, 114 hips) versus the No TEA group (52 patients, 56 hips). Our standard protocol for administering TEA is 1000mg IV at incision, and the same dose repeated two hours later. The No TEA group did not receive the medication because of previous hospital contraindication criteria.

Introduction

With the introduction of minimally invasive surgery techniques and improved polyethylene wear properties, there has been a renewed interest in Unicondylar Knee Replacements (UKR). Customized, Individually Made (CIM) UKR have been in the market for some time, and have shown to provide improved coverage and fit. The purpose of this study was to assess clinical and patient-reported outcomes utilizing CIM-UKR prostheses.

Methods

A prospectively recruited cohort of 118 patients was implanted with 120 CIM-UKR (110 medial/10 lateral) at multiple centers across the US. Patients were diagnosed with uni-compartmental osteoarthritis of the medial or lateral compartment. Patients with compromised cruciate or collateral ligaments or having a varus/valgus deformity <15^° were excluded. Patients were assessed for Knee Society Knee and Function Scores, WOMAC & ROM pre-operatively (120 patients), at 6-weeks post-op (119), 6-months post-op (71 optional visit), 1 year post-op (113) and 2 years post-operatively (96). For the 3 and 4 year post-operative time points, patients were contacted to report on any possible adverse events.

Introduction

When performing a total hip arthroplasty (THA), some surgeons routinely perform an intraoperative anteroposterior (AP) pelvis radiograph to assess components. The purpose of this study was to evaluate the reliability of the intraoperative radiograph to accurately reflect acetabular inclination, leg length, and femoral offset as compared to the immediate postoperative supine AP radiograph.

Methods

The intraoperative (lateral decubitus position) and immediate postoperative (supine position) AP pelvis x-rays of 100 consecutive patients undergoing primary THA were retrospectively reviewed. Acetabular inclination, leg length, and femoral offset were measured on both radiographs. We analyzed the correlation coefficient of the recorded measurements between the two films as well as the interobserver reliability of each measurement obtained.

INTRODUCTION

Utilization of a patient management support system in our clinical pathway has been successfully demonstrated to both reduce the length of hospital stay after primary THA, as well as reducing the number of hospital readmissions. While successful in a general patient population, the ability of a patient management support system to reduce readmissions in subsets of high risk THA patients has not been evaluated.

METHODS

We identified all primary THAs performed at a single institution between 2013 and 2015. Patient sex, age at the time of surgery, race, ASA grade, and 120-day readmissions were retrieved from the patient medical record. Similar to previous studies, the patient's home address was used as a proxy for socioeconomic status, with the estimated median income of a given patient being estimated as the median household income for patients of similar ethnicity living within their zip code as reported in the 2014 U.S. Census. A binary regression was used to determine if a model of patient factors (age, sex, race, socioeconomic status, and/or ASA grade) could accurately predict 120-day readmission after primary THA. Age and socioeconomic status were treated as a continuous variable and all other factors were categorical in nature, and the individual effects of each categorical factor on readmissions were also assessed.

Introduction

In vitro studies showed that the anti-oxidative properties of vitamin E stabilize free radicals while retaining the mechanical strength of UHMWPE. The purpose was to evaluate vitamin E diffused polyethylene (VEPE) wear and stability of femoral components using RSA. Patient reported outcome measures (PROMs) were evaluated to determine the clinical outcome at 5 years.

Methods

48 patients (52 hips), with osteoarthritis, participated in a 5 year RSA study. Each patient received a VEPE liner, a porous titanium coated shell, and an uncemented stem with a 32mm head. Tantalum beads were inserted into the VEPE and the femur to measure head wear and stem stability using RSA. RSA and PROM follow-up was obtained postoperatively, 6 months, 1, 2, 3, and 5 years after surgery. The Wilcoxon signed-ranks test determined if changes in penetration or migration were significant (p≤0.05).

Introduction

Total hip arthroplasty (THA) is a common operation. Different operative approaches have specific benefits and compromises. Soft tissue injury occurs in total hip arthroplasty. This prospective study objectively measured muscle volume changes after direct anterior and posterior approach surgeries.

Methods

Patients undergoing Direct Anterior Approach (DAA) and Posterior Approach (PA) THA were prospectively evaluated. 3 orthopaedic surgeons performed all surgeries. Muscle volumes of all major muscles around the hip were objectively measured using preoperative and 2 different postoperative follow-up MRIs. 2 independent measurers performed all radiographic volume measurements. Repeated-measures ANOVA was used to compare mean muscle volume changes over time. Student's t-test was used to compare muscle volumes between groups at specific time intervals.

Abstract

A number of postoperative complications of navigated total knee arthroplasty have been discussed in the literature, including tracker pin site infection and fracture. In this paper we discuss the low postoperative complication rate in a series of 3100 navigated total knee arthroplasties and the overall complication rate in a systematic analysis of the literature.

Methods

3100 consecutive patients with navigated total knee arthroplasties from 2001 to 2016 were retrospectively evaluated for complications specific to navigation. We discuss the two cases of postoperative fracture through tracker pin sites that we experienced and compare this systematically to the literature.

Introduction

Revision Total Hip Arthroplasties (THA) have a significantly higher failure rate than primary THA's and the most common cause is aseptic loosening of the cup. To reduce this incidence of loosening various porous metal implants with a rough surface and a porous architecture have been developed which are said to increase early osteointegration. However, for successful osteointegration a minimal micromotion between the implant and the host bone (primary stability) is beneficial. It has not been previously determined if the primary stability for the new Gription® titanium cup differs from that of the old Porocoat® titanium cup.

Material and Methods

In 10 cadaveric pelvises, divided into 20 hemipelvises, bilateral THA's were performed by an experienced surgeon (RGB) following the implant manufacturer's instructions and with the original surgical instruments provided by the company. In randomized fashion the well established Porocoat® titanium implant was implanted on one side of each each hemipelvis whereas on the corresponding opposite side the modified implant with a Gription® coating was inserted. Radiographs were taken to confirm satisfactory operative results. Subsequently, the hemipelvis and cups were placed in a biomechanical testing machine and subjected to physiological cyclic loading.

Three-dimensonal loading corresponded to 30% of the load experienced in normal gait was imposed reflecting the limited weight bearing generally prescribed postoperatively. The dynamic testing took place in a multi-axial testing machine for 1000 cycles. Relative motion and micromotion were quantified using an optical measurement device (Pontos, GOM mbh, Braunschweig, Germany). Statistical evaluation was performed using the Wilcoxon signed-rank test.

Purpose

Current methods for inserting a press fit hemispherical metal-backed acetabular component within the acetabula are uncontrolled, relying on the surgeon to generate the necessary forces required for sufficient introduction. While previous studies have recorded impact forces of 2–3 kN necessary to seat an acetabular cup using visual observation[1], some researchers have observed users imparting as high as 8.9 kN of force[2]. The aim of this study is to quantify the forces required to generate optimal implant primary stability, as well as compare force delivery methods.

Method

The experiments were carried out using prepared bone substitute. A high frequency force sensor was rigidly mounted under the substitute to measure impact force and duration. An acetabular cup was inserted using successive reproducible impacts of varying magnitude (2.5 kg falling 17, 34, 43, 51, 68, or 85 mm). Impacts were repeated until the cup was no longer advancing. Each test recorded the number of impacts, maximum impact force, impact duration, and extraction force of the cup after insertion. The results were then compared against manual insertion (tapping) and high frequency vibratory insertion (50–500 Hz).

Background

Proper femoral component placement plays a key role in the success of a total knee replacement (TKR). Controversy exists on which technique should be used to ensure proper femoral component placement. This two-part study compares gap balancing (GB) and measured resection (MR) techniques used in TKR, investigating femoral component position and early clinical outcomes.

Methods

Femoral component position was analyzed in 95 consecutive knees that underwent primary TKR. Both GB and MR cutting blocks from the same knee system were sequentially placed on the operative knee, marking the pin sits. A standardized photograph (Figure) was taken prior to making final femoral cuts. Relative rotation was determined based on measurements made from a commercially available software. Clinical comparison was made using 50 consecutive GB patients and 50 consecutive MR patients. Clinical outcome measures were Knee Society Scores (KSS), knee range of motion (ROM), functional ROM (FROM), tourniquet time, and patients having manipulations under anesthesia (MUA).

Introduction

Revision for instability has supplanted revision for aseptic loosening and revision for osteolysis since the advent of improved polyethylene inserts with changes in both sterilization techniques and cross-linking. Having the ability to judiciously choose a higher level of constraint may be beneficial in complex primary total knee arthroplasty (TKA) scenarios which can not be balanced through traditional surgical methods. The purpose of this work was to investigate short term outcomes and survivorship in cases where a greater stabilizing insert was used with a posterior stabalizing (PS) femur to address instability in flexion or extension.

Methods

Two high volume TKA centers retrospectively reviewed cases in which a greater stabilizer insert was used with a primary PS knee system. The studied insert had +/− 2 degrees of varus-valgus coronal restraint as opposed the standard with no coronal constraint. The study inserts had 7 degrees of transverse plane rotational freedom. The inserts were used when extension balance was not achieved despite the usual soft tissue releases and a thicker insert resulted in a flexion contracture statically during the procedure. This situation typically occurred in the following patient groups: valgus knees with medial collateral (MCL) stretching, iatrogenic MCL injury, varus knees with lateral ligament complex stretching, the “double-varus” knee, and patients with a previous high tibial osteotomy.

Intra-operatively patients were taken through a range of motion and trial implants were then placed. A cruciate retaining trial insert was then used to assess stability so that a true assessment could be made of ligament balance. Bone cuts were checked before ligament release. The usual releases were then performed to achieve balance including subperiosteal releases medially and laterally and pie-crusting when indicated. Repeat trial reductions were then performed once the final implants were cemented in place again using the cruciate retaining insert. If the soft tissue releases did not achieve balance and a thicker insert resulted in a flexion contracture then the greater stabilizer insert was selected over the PS insert. Knee Society Score and plain radiographs were collected at pre-op, 2 year and 5 year follow-up.

Introduction

We have previously demonstrated that peroxide crosslinked vitamin E-blended UHMWPE maintains its clinically-required wear and mechanical properties [1]. This material can potentially be used as an irradiation-free bearing surface for TJA. However, using organic peroxides in medical devices requires a thorough examination of tissues in contact with the implant. For this study we crosslinked polyethylene using five times the needed concentration of peroxide (2,5-Dimethyl-2,5-di(t-butylperoxy)-hexyne-3 or P130), followed by implantation to determine implant biocompatibility, and pre and post implant peroxide residual contents.

Methods

The study was performed after institutional approval following ISO standard 10993–6. Study groups: not crosslinked (0.2 (1050) VE), crosslinked (0.2 VE (1050)/5% P130) and crosslinked-high temperature melted (HTM) (0.2 VE (1050)/5% P130). Materials were blended and consolidated, machined (2.5 diameter × 2.5 cm height), sterilized and implanted in the dorsum New Zealand white rabbits. Pre and post implantation FTIR was performed. Two samples were implanted in each rabbit; n=6 samples were included for each group. After 4 weeks, samples were explanted, analyzed using FTIR, and subcutaneous tissues processed for histological analysis.

Introduction/Purpose

Total ankle replacement (TAR) success has improved since first-generation implants, but patient satisfaction continues to be less than knee and hip replacements. Little is known about variations in distal tibia anatomy between genders and across ethnicities; therefore it is unclear the extent to which current TAR prostheses accommodate variability in patient size and shape. This study quantified distal tibia morphometrics relevant to TAR design, and assessed differences between ethnicities and genders. The hypotheses were: (1) The anterior-posterior (AP) location of the dwell point of the tibia is centralized; (2) The sagittal radius of curvature of the tibial articulation increases with bone size; (3) Differences in dwell point location or sagittal radii between genders and ethnicities can be attributed to size differences between those populations.

Methods

Tibial CT scans were obtained from cadavers or individuals of various ethnicities (Table 1). Landmarks were defined on digital models created from the scans, including medial and lateral edges of the distal tibial articulation (Figure 1a), and sagittal contours of the articulation (Figure 1b). The articulation center was defined as the average center point of all contours (Figure 1c). The AP center and AP length at the level of a distal tibial resection for TAR were determined, and the AP offset of the articulation center was calculated (Figure 1c). Differences in metrics for each ethnic and gender group were determined using a one-way Anova (P<.05) with Tukey's method for differentiating groups. Regression fits of AP offset, average medial radius, and average lateral radius were determined. Utilizing AP length as a covariate, ANCOVA was utilized to assess differences in AP offset and sagittal radii between gender and ethnic groups (P<.05).

Introduction

Inadequate stability of the baseplate is a leading cause of revision within reverse total shoulder arthroplasty (rTSA). Micromotion between baseplate and bone is commonly used as a pre-clinical indicator for clinical stability (ASTM F2028-14). Finite element analysis (FEA) has been shown to accurately predict baseplate-bone micromotion, but results may be critically dependent on several modeling assumptions. Here, FEA was used to assess the impact of key modeling assumptions related to screw-bone interactions on various rTSA configurations.

Methods

FEA with Ansys ver. 16 was used to simulate a fixation experiment. Baseplates of two different sizes (25mm and 28mm diameter), each with a central screw and four peripheral screws, were virtually implanted in a synthetic bone block. Each baseplate was analyzed using 1.5mm and 3.5mm superior-inferior (SI) offsets of the glenosphere center, as well as using four (‘4S’) and two (‘2S’) peripheral screws. A clinically relevant loading of 756N was applied in compression as well as in inferior-to-superior shear direction through the glenosphere (Figure 1A, 1B).

Screw-bone block interactions were modeled in three different ways: (1) Threads were defeatured from the peripheral screws, which were bonded to the bone block (b-nt); (2) Threads were modeled, while still assuming bonded contact (b-t); (3) Threads were modeled, with frictional contact between threads-bone block (f-t). Micromotion results (Figure 1C) from all 24 simulations (3 screw-bone interactions × 2 baseplate diameters × 2 SI offsets × 2 screw configurations) were compared.

Introduction

Fretting corrosion of the modular taper junction in total hip arthroplasty has been studied in several finite element (FE) investigations. In FE analyses, different parameters can be varied to study micromotions and contact pressures at the taper interface. However, to truly study taper wear, the simulation of micromotions and contact pressures in non-adaptive FE models is insufficient, as over time these can change due to interfacial changes caused by the wear process.

In this study we developed an FE approach in which material removal during the wear process was simulated by adaptations to the taper geometry. The removal of material was validated against experiments simulating the clinical fretting wear process.

Method

Experimental test: An accelerated fretting screening test was developed that consistently reproduced fretting wear features observed in retrievals. Biomet Type-1 (4°) tapers and +9 mm offset adaptors were assembled with a 4 kN force (N=3). A custom head fixture was used to create an increased offset and torque. The stems were potted in accordance with ISO 7206–6:2013. The set-up was submerged in a 37°C PBS solution with a pH adjusted to 3 using HCL and NaCl concentration of 90gl⁻¹. The components were cyclically loaded between 0.4 – 4 kN for 10 million cycles. After completion, the volumetric and linear wear was measured using a Talyrond-585 roundness measurement machine.

FE model: This was created to match the experimental set up (Figure 1). Taper geometry and experimental material data were obtained from the manufacturer (Zimmer Biomet). The coefficient of friction of the studied combination of components was based on previous experiments (Bitter, 2016). After each change in load the geometry was updated by moving nodes inwards perpendicular to the taper surface. Archard's Law (Archard, 1953) was used to calculate the wear with the following equation: H=k*p*S. Where H is the linear wear depth in mm, k is a wear factor (mm³/Nmm), p is the contact pressure (MPa) and S is the sliding distance (mm). The 10 million experimental cycles were simulated using a range of 5 to 200 computational cycles. For this purpose, the wear factor (k) was scaled for each simulation to match the volumetric wear found in the experiments.

Introduction

Due to its remarkable stoichiometric flexibility and surface chemistry, hydroxyapatite (HAp) is the fundamental structural material in all vertebrates. Natural HAp's properties inspired an investigation into silicon nitride (Si₃N₄) to see if similar functionality could be engineered into this bioceramic. Biological and in situ spectroscopic analyses were used to monitor the response of osteosarcoma cells (SaOS-2) to surface-modulated Si₃N₄ and a titanium alloy after long-term in vitro exposure.

Materials and Methods

Four groups of Si₃N₄ discs, Ø12.7×1.0mm, (Amedica Corporation, Salt Lake City, UT USA) were subjected to surface treatments: (i) “As-fired;” (ii) HF-etched (5% HF solution for 45 s); (iii) Oxidized (1070°C for 7 h); and (iv) Nitrogen-annealed (1400°C for 30 min, 1.1 bar N₂ gas).¹ Titanium alloy discs (Ti6Al4V, ASTM F136) were used as a control group. SaOS-2 cells cultured for 24 h at 37^°C were deposited (5×10⁵ cells/ml) and incubated on the UV sterilized discs in an osteogenic medium for 7 days at 37°C. Cell proliferation was monitored using scanning electron and laser microscopy. The Receptor Activator of NF-kB Ligand (sRANKL) and the insulin growth factor 1 (IGF-1) were used to evaluate osteoclast formation and cell proliferation efficiency, respectively. In situ Raman spectroscopy was employed to monitor metabolic cell activity. Statistics (n≥3) were analyzed using the Student's t-test or one-way Analysis of Variance with p<0.05 considered significant.

Introduction

The reconstruction of the knee in growing children considers many options and the chosen solution is often patient (or surgeon) based. Megaprostheses represent a reliable solution but quite expensive in the non-invasive growing version and not free from complications. In an Italian reference center for Bone and Soft tissue sarcomas, following the experience of Rizzoli Institute in Bologna, we performed the reconstruction with a resurfaced allograft for the distal femur or the proximal tibia in selected patients. The aim of the study is to confirm the reliability of this technique and to identify its potential advantages and indications.

Methods

Among 60 children below 16 years old with bone sarcomas (39 osteosarcomas, 21 Ewing's sarcomas, age range 4–16) treated since 2007, 35 cases were around the hip and the knee. 7 pediatric knees (age range 5–12 ys) with the tumor involving the epiphysis were reconstructed using a resurfaced allograft for distal femur (2) or proximal tibia (6) leaving intact the other half of the joint. Functional outcome (MSTS score), complication rate, and oncologic follow up were evaluated.

Purpose

Analysis of the morphology of the distal femur, and by extension of the femoral components in total knee arthroplasty (TKA), has been related to the aspect ratio, which represents the width of the femur. Little is known about variations in trapezoidicity (i.e whether the femur is more rectangular or more trapezoidal). This study aimed to quantify additional morphological characteristics of the distal femur and identify anatomical features associated with higher risks of over- or under-sizing of components in TKA.

Method

We analyzed the shape of 114 arthritic knees at the time of primary TKA using the pre-operative CT scans. The maximum AP dimension was measured. The mediolateral dimensions were measured on the theoretical distal resection slice at three levels: the posterior region (MLP), the central region (MLC) and the anterior region (MLA) (Fig 1). The ‘aspect’ ratio (MLC/AP) ratio quantified how wide or narrow the shape is. The ‘trapezoidicity’ ratio (MLP/MLA) ratio quantified how rectangular or trapezoidal the shape is. We also quantified the medial and lateral ‘narrowing angles’ in the anterior and central zones (α and β) (Fig 2).

The post-operative prosthetic overhang was calculated from CT-scan.

We compared the morphological characteristics with those of twelve TKA models scanned using a three-dimensional optical scanning machine (ATOS II, GOM mbH, Braunschweig, Germany) and its photogrammetric analysis software (TRITOP, GOM mbH, Braunschweig, Germany).

Introduction

The increase in revision joint replacement surgery and fractures of bone around orthopaedic implants may be partly addressed by keeping bone healthy around orthopaedic implants by inserting implants with mechanical properties closer to the patient's bone properties. We do not currently have an accurate way of calculating a patient's bone mechanical properties. We therefore posed a simple question: can data derived from a micro-indenter be used to calculate bone stiffness?

Methods

We received ethical approval to retrieve femoral heads and necks from patients undergoing hip replacement surgery for research. Cortical bone from the medial calcar region of the femoral neck was cut into 3×3×6mm cuboid specimens using a diamond wafering blade. Micro-indentation testing was performed in the direction of loading of the bone using a MicroMaterials (MicroMaterials, UK) indenter, using the high load micro-indentation stage (see Figure 1). To simulate in vivo testing, the samples were kept hydrated and were not fixed or polished. From the unloading curve after indentation, the elastic modulus was calculated, using the Oliver-Pharr method using the indentation machine software. To assess which microindentation machine settings most precisely calculate the elastic modulus we varied the loading and unloading rates, load and indenter tip shape (diamond Berkovich tip, 1mm diameter Zirconia spherical tip and 1.5mm diameter ruby spherical tip).

Following this, for 11 patients' bone, we performed compression testing of the same samples after they were indented with the 1.5mm diameter ruby spherical tip to assess if there was a correlation between indentation values of apparent elastic modulus and apparent modulus values calculated by compression testing (see Figure 2). Platens compression testing was performed using an Instron 5565 (Instron, USA) materials testing machine. Bluehill compliance correction software (Instron, USA) was used to correct for machine compliance. The strain rate was set at 0.03mm/s. The apparent elastic modulus was calculated from the slope of the elastic region of the stress-strain graph. The correlation between values of apparent modulus from compression testing and indentation were analyzed using IBM SPSS Statistics 22.

Introduction

The first highly crosslinked and melted polyethylene acetabular component for use in total hip arthroplasty was implanted in 1998 and femoral heads larger than 32mm in diameter introduced 2004.

The purpose of this study was to re-assemble a previous multi-center patient cohort in order to evaluate the radiographic and wear analysis of patients receiving this form of highly crosslinked polyethylene articulating against large diameter femoral heads at a minimum of 10 years follow-up.

Methods

Two centers contributed patients to this ongoing clinical study. Inclusion criteria for patients was: primary THR; femoral heads greater than 32mm; minimum 10 year follow-up. 69 hips have been enrolled with an average follow-up of 11.2 years (10–15), 32 females (50%). Wear analysis was performed using the Martell Hip Analysis software. Radiographic grading was performed on the longest follow-up AP hip films. The extent of radiolucency in each zone greater than 0.5mm in thickness was recorded along with the presence of sclerotic lines and osteolysis.

Introduction

The first highly crosslinked and melted polyethylene acetabular component for use in total hip arthroplasty was implanted in 1998. Numerous publications have reported reduced wear rates and a reduction in particle induced peri-prosthetic osteolysis at short to mid-term follow-up.

The purpose of this study was to re-assemble a previous multi-center patient cohort in order to evaluate the radiographic and wear analysis of patients receiving this form of highly crosslinked polyethylene articulating against 32mm femoral heads or less at a minimum of 13 years follow-up.

Methods

Inclusion criteria for patients was a primary THR with femoral heads 32mm or less and a minimum 13 year follow-up. 139 hips have been enrolled with an average follow-up of 13.7 years (13–16), 80 females (57%). Wear analysis was performed using the Martell Hip Analysis software. Radiographic grading was performed on the longest follow-up AP hip films. The extent of radiolucency in each zone greater than 0.5mm in thickness was recorded along with the presence of sclerotic lines and osteolysis.

Introduction

A modern total knee replacement system was introduced in 2012 in order to improve the mechanics of total knee replacement (TKR). The purpose of this study was to assess the early clinical and radiographic outcomes of patients who have been treated with this modern TKR system at two years postoperatively.

Methods

Patients who received this TKR system between June of 2012 and September of 2014 were included in this prospective registry-based follow-up study. Demographics, component, and surgical data were collected. Radiographic outcomes were also assessed. Patient reported outcome measures (PROMs) of all patients with 2-year follow-up data were collected. Reasons for revision and overall survival at 2-years were evaluated.

Background

Fifteen to twenty percent of patients presenting for total hip arthroplasty (THA) have bilateral disease. While simultaneous bilateral THA is of interest to patients and surgeons, debate persists regarding its merits. The majority of previous reports on simultaneous bilateral THA involve patients in the lateral decubitus position, which require repositioning, prepping and draping, and exposure of a fresh wound to pressure and manipulation for the contralateral THA. The purpose of this study was to compare complications, component position, and financial parameters for simultaneous versus staged bilateral THAs using the direct anterior approach (DAA).

Methods

Medical records were reviewed for patient demographics, medical history, operative time, estimated blood loss (EBL), change in hemoglobin, transfusion, tranexamic acid (TXA) use, length of stay (LOS), discharge disposition, leg length discrepancy, acetabular cup position, and perioperative complications. Cost and reimbursement data were analyzed.

INTRODUCTION

As the demographic of the patient population requiring revision total knee arthroplasty (rTKA) continues to expand, varying preoperative conditions and activity levels need to be taken into consideration when analyzing postoperative outcomes. Factoring in preoperative activity levels can help manage the expectations of patients. The purpose of this study was to analyze the outcomes of low and high activity patients receiving a contemporary rTKA.

METHODS

One hundred and eighty rTKA patients enrolled in a prospective, multicenter study were evaluated through 2 years postoperative. Patients were divided into groups based on preoperative activity level using the Lower Extremity Activity Scale (LEAS). Patients scoring between 1–7 were classified as ‘Low Activity’ (LA, N=104) and patients scoring 8–18 were classified as ‘High Activity’ (HA, N=76). Clinical and patient-reported outcomes were evaluated, with an additional quality of life analysis completed utilizing SF-6D scores obtained by transforming SF-36 scores through a method described by Brazier et al. and analyzed for effect size.

Introduction

The use of cementless TKA's has been gradually increasing over the past several years given the increasing life expectancy of our patient population. Cementless TKA's have not been rapidly adopted due to the challenges and uncertainty of tibial fixation especially in elderly patients. With the advent of new technologies, the results of cementless TKA's with the potential for long term biologic fixation may now be equivalent or better than cemented TKA's. A highly porous tibial baseplate was developed based on proximal tibial anatomy using CT scans using 3D printing technology with focus on length, location and design of press-fit pegs.

Objectives

The purpose of this study was to review the early results with respect to fixation and complications using a new, highly porous cementless tibial baseplate designed for biologic fixation.

Methods

A polished cobalt-chromium disk (40 mm diameter, 8 mm thick) was marked into 8 sections for various testing conditions (Figure 2a). A stainless steel Bovie tip with a unipolar electrocautery machine (SYSTEM 5000, ConMed, USA) was used at typical surgical coagulation conditions: (70 volt, 120 watts, 562 KHz frequency). We mimicked three types of surgical techniques with the electrocautery: “Dotting” was repeated, on and off, direct surface contact; “Dragging” was constant, direct surface contact; “Hovering” was pausing several millimeters above the surface. We also examined the interplay of these practices on diamond-tip-induced scratches and either dry or wet (normal saline) conditions. High magnification images (Keyence VHX-2000E) were taken after the disk was cleaned with laboratory soap, light mechanical scrubbing, and formalin soak.

Results

Coagulation mode generated electrical sparks when dotting/dragging and electrical arcs when hovering. These left seared marks that persisted even after cleaning (Figure 2b). At higher magnification, the surface features were comparable in size and shape to those attributed to ICI (1, 2). Areas wet with saline (Figure 3a) showed an abundance of ringed pits with raised edges that closely resembled those observed in Figure 1. Furthermore we obtained images similar to the phenomenon of “cellular tracks” (Figure 3b) (1). Premade scratches did not influence the pit arrangement but scratches made by the Bovie tip produced the characteristic scratch-associated ICI features as observed on implant retrievals in the past (Figure 3c) (4).

Methods

The study included all of the MoM HRA devices in our collection. Of the 284 hip resurfacing devices with complete clinical information, 131 were from male and 153 from female patients. Femoral sizes ranged from 36 – 58mm, median and mode 46mm; median size in females was 44 and 50mm in males. Time to failure ranged from 1 to 178 months, median 24 mos. Seven designs were represented but the majority were Conserve Plus (n=105 WMT, USA) and BHR (n=78 Smith & Nephew, USA) which differ in cementing technique. 131 femoral components were sectioned and the width of the cement mantle and the amount of cement in the head were measured. Where available, the amount of bone attached to the cup porous surface (n=91), tissue ALVAL scores (n=75) and bearing wear depth (n=138) were included in the multivariate analysis.

Results

As a function of gender, there were no significant differences in time to revision, cement measurements or ALVAL scores. Wear depth was significantly higher in females (femoral 41um vs 21um; cup 50um vs 16um, p=0.05). As a function of size (46 and less = small), the <46mm group had a slightly shorter time to revision, 30 vs 38 months, p=0.04). Bone ingrowth ranged from 0 to 60% (Figure 1) and significantly less bone attachment was noted in both the smaller and larger components (p = 0.001). Other characteristics were similar in both groups. When wear-related failure modes (cup malposition, lysis, high ions) were compared, no differences between male and female or large vs small were found. The amount of cement in the femoral heads covered a wide range but femoral loosening or fracture rates were not different as a function of size or gender.

Introduction

Cementless tapered wedge stems have shown excellent results over the last decade. Distal potting with inadequate proximal fit, as well as failure to achieve biologic fixation has led to thigh pain, loosening and implant failure. To support a variety of patient morphologies a novel tapered wedge stem was designed with reduced distal morphology, maximizing the proximal contact of the grit blasted surface. The objective of the study was to analyze the clinical outcomes of this stem design.

Methods

Three hundred and nineteen patients enrolled into prospective, post-market multicenter studies received a novel tapered wedge stem. Clinical and patient-reported outcomes including the Harris Hip Score (HHS), Lower Extremity Activity Scale (LEAS), Short Form 12 (SF12), and Euroqol 5D Score (EQ-5D) were evaluated preoperative through two years postoperative.

Introduction

Acetabular revision surgery remains a technically demanding procedure with higher failure rates than primary total hip arthroplasty (THA). An acetabular component with three dimensional porous titanium and anatomic screw holes (Figure 1) was designed to allow the cup to be positioned anatomically and provide reliable fixation.

Methods

A prospective multicenter study of 193 cases (190 patients) was conducted to assess the midterm clinical outcomes of the revision titanium acetabular shell. Radiographs, demographics, Harris Hip Score (HHS), and Short Form 36 (SF-36) were collected preoperatively, at 6 weeks, 3 months, and annually thereafter to 5 years. The mean duration of follow-up was 3.36 years. The Paprosky classification was assessed intraoperatively. Short Form 6D (SF-6D) utility values were obtained by transforming SF-36 scores through the Brazier method and were analyzed for effect size.

1) INTRODUCTION

Acetabular fixation in cementless total hip arthroplasty (THA) relies on new technology for stability and survivorship of the implant. A highly porous 3D titanium coating was developed with a biologically inspired pore structure to improve initial friction fixation with mechanical stability and long term biological fixation. Ongoing research is investigating potential radiographic phenomenons these coatings produce, resulting in the presence of lucent lines. The purpose of this study was to evaluate clinical and radiographic outcomes of a 3D highly porous-coated titanium acetabular shell.

2) METHODS

One hundred and sixty-two cases as part of a non-randomized, post-market, multicenter study received a primary cementless THA. Clinical outcomes including the Harris Hip Score (HHS), Lower Extremity Activity Scale (LEAS), Short Form 12 (SF12), and EuroQol 5D Score (EQ-5D) were collected preoperatively and at six weeks, one year postoperative. Additionally, radiographs, radiographic parameters and techniques were analyzed for institutional differences.

Introduction

Accurate component placement in total hip arthroplasty (THA) improves post-operative stability and reduces wear and aseptic loosening. Methods for achieving accurate stem placement have not been as extensively studied as cup placement.

Objectives

The purpose of this study is to determine how consistently femoral stem version can be corrected to an ideal of 15 +/− 5 degrees using robotic guidance. Furthermore, the study aims to identify other factors related to approach and patient demographics, which may influence the degree of correction obtained.

Introduction

Subluxation and dislocation are frequently cited reasons for THA revision. For patients who cannot accommodate a larger femoral head, an offset liner may enhance stability. However, this change in biomechanics may impact the mechanical performance of the bearing surface. To our knowledge, no studies have compared wear rates of offset and neutral liners. Herein we radiographically compare the in-vivo wear performance of 0mm and 4mm offset acetabular liners.

Methods

Two cohorts of 40 individuals (0mm, 4mm offset highly crosslinked acetabular liners, respectively) were selected from a single surgeon's consecutive caseload. All patients received the same THA system via the posterior approach. AP radiographs were taken at 6-week (‘pre’) and 5-year (‘post’) postoperative appointments. Patients with poor radiograph quality were excluded (n_0mm=5, n_4mm=4). Linear and volumetric wear were quantified according to Patent US5610966A. Briefly, images were processed in computer aided design (CAD) software. Differences in vector length between the center of the femoral head and the acetabular cup (pre- and post-vector, Figure 1) allow for calculation of linear wear and wear rate. The angle (β) between the linear wear vector and the cup inclination line was quantified (Figure 1). Patients with negative β were excluded from volumetric analyses (n_0mm=11, n_4mm=7). Volumetric wear was accordingly calculated accounting for wear vector direction. The results from three randomly selected patients were compared to results achieved using the “Hip Analysis Suite” software package (UChicagoTech).

Introduction

For nearly 58% of total knee arthroplasty (TKA) revisions, the reason for revision is exacerbated by component malalignment. Proper TKA component alignment is critical to functional outcomes/device longevity. Several methods exist for orthopedic surgeons to validate their cuts, however, each has its limitations. This study developed/validated an accurate, low-cost, easy to implement first-principles method for calculating 2D (sagittal/frontal plane) tibial tray orientation using a triaxial gyroscope rigidly affixed to the tibial plateau of a simulated leg jig and validated 2D tibial tray orientation in a human cadaveric model.

Methods

An initial simulation assessed error in the sagittal/frontal planes associated with all geometric assumptions over a range of positions (±10°, ±10°, and −3°/0°/+3° in the sagittal, frontal, and transverse planes, respectively). Benchtop experiments (total positions - TP, clinically relevant repeated measures - RM, novice user - NU) were completed using a triaxial gyroscope rigidly affixed to and aligned with the tibial tray of the fully adjustable leg-simulation jig. Finally, two human cadaveric experiments were completed. A similar triaxial gyroscope was mounted to the tibial tray of a fresh frozen human cadaver to validate sagittal and frontal plane tibial tray orientation. In cadaveric experiment one, three unique frontal plane shims were utilized to measure changes in frontal plane angle. In cadaveric experiment two, measurements using the proprosed gyroscopic method were compared with computer navigation at a series of positions. For all experiments, one rotation of the leg was completed and gyroscopic data was processed through a custom analysis algorithm.

Objective

Compare the safety and effectiveness of different anesthetic technique used in the simultaneous bilateral total knee arthroplasty (BTKA).

Methods

Medical records of patients admitted for simultaneous BTKA between January 1, 2014 and September 1, 2015 in ‘The safety and effect evaluation of joint arthroplasty’ database were analyzed. The general anesthesia (GA) and neuraxial anesthesia (NA) group were identified. Patient preoperative characteristics were compared. Perioperative outcomes measured included operating time, blood loss, transfusion requirement, length of hospitalization, joint range of motion at discharge, complications.

Objective

To investigate the effectiveness of applying fast track surgery concept in primary total hip arthroplasty.

Methods

The data of patients with primary total hip arthroplasty in our department from January 1, 2013 to October 1, 2015 were retrospectively analyzed. The patients were divided into traditional recovery group, enhanced recoverygroup and update enhanced recovery group according to different interventions. The blood loss, transfusion rate, complications rate, postoperative function, length of stay, hospitalization expense and readmission rate were compared between three groups.

Introduction

Periprosthetic joint infection (PJI) and particle-induced osteolysis are closely related to peri-implant local immunity and macrophage function. We previously demonstrated that titanium particles attenuate the immune response of macrophages caused by chronic inflammation [1]. In a separate study, we have determined that UHMWPE wear particles containing vitamin E (VE) induce less osteolysis compared to HXL UHMWPE wear particles in a murine calvarium model [2]. For this study we hypothesized that macrophages exposed to HXL UHMWPE particles containing VE would better maintain their ability to respond to S. aureus compared to HXL UHMWPE without VE.

Methods

A gamma-sterilized, HXL UHMWPE tibial bearing containing VE (E1, Biomet, “VE-PE”) and 100kGy irradiated and melted UHMWPE (“CISM 100”) were cryomilled to particles by Bioengineering Solutions (Oak Park, IL). In the first in vitro study, RAW 264.7 mouse macrophages were exposed (inverted co-culture) to either VE-PE particles or CISM100 particles and lipopolysaccharide (LPS) for 1–7 days. Macrophage viability was measured using a cell counting kit (CCK-8). Control group with no particles and a LPS group were also included. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining was performed to determine macrophage apoptosis rate in response to particle exposure over time. In the second study, macrophages were exposed to VE-PE or CISM100 particles for 48h, then exposed to LPS for 30 min. Subsequently, reactive oxygen species (ROS) generation and extracellular regulated protein kinase (ERK) phosphorylation were measured. In a third study, after exposure to particles for 48h, fatigued macrophages were co-cultured with bioluminescent S. aureus strain Xen29 for 3h and 6h. Bioluminescence signal was determined to measure the total amount of bacteria. Bacterial live/dead staining and optical density at 600 nm (OD 600) were also performed to determine S. aureus viability. Statistical analysis was performed using one-way or two-way ANOVA with a post hoc examination. *indicates p<0.05.

Background

The Perioperative Surgical Home (PSH) is a physician-led, patient centered, rapid recovery care delivery model that includes multi-specialty care teams and cost-efficient use of resources developed to deliver patient centered value based care. The purpose of this study was to compare a group of patients undergoing primary total hip arthroplasty (THA) managed in the PSH model to a matched group managed in a more traditional fashion with respect to clinical outcomes, complications, and costs.

Methods

We prospectively followed the first 180 THA patients from the PSH group, comparing them to a group matched for age, Body Mass Index (BMI), American Society of Anesthesiologists (ASA) Score, and Charlson Comorbidity Index (CCI) that was treated prior to implementation of the PSH. A combination of regional anesthesia and multi-modal pain control was used to minimize patient narcotic consumption. There was a rapid de-escalation of care post-operatively. Weekly multi disciplinary meetings were held where advanced discharge planning was discussed and we evaluated successes and areas of improvement of the prior week in an effort to continuously improve. We used Wilcoxon, Chi square, and multivariate regression analysis to compare the groups for length of stay (LOS), total direct cost (TDC), complications, 30-day readmissions, and discharge location.

Purpose

We evaluated the clinical and radiographic outcomes of cementless bipolar hemiarthroplasty using rectangular cross-section stem for femoral neck fracture in elderly patients more than 80 years of age with osteoporosis.

Material and Methods

76(cemented 46, cementless 30) bipolar hemiarthroplasties for femur neck fracture were performed in elderly patients more than 80 years old. The mean follow-up period was 4.3 years (2 to 7 years). The Harris hip score at last follow-up and pre-postoperative daily living activity scale according to Kitamura methods were analyzed clinically. The radiological results were assessed using stability of femoral stem and other complications were evaluated. Results: At last follow-up, there were no significant differences of Harris hip score and daily living activity between two groups. Stem loosening and instability were not observed in cementless arthroplasty. There were 18 cases of osseous fixation in radiologic study. There were 1 case of dislocation and 1 case of superficial infection in cemented arthroplasty and 1 case of deep infection in cementless arthroplasty.

Background

Hard-on-hard bearings showed advantages of reduction of wear rates, osteolysis and aseptic loosening in total hip arthroplasty (THA). A new combination of ceramic-on-metal (COM) was developed to compensate the disadvantages of MOM and COC. COM showed good short-term results in vitro and in vivo studies. There was no report of stripe wear and metal ion level elevation. Our study was designed to evaluate the wear pattern of this bearing in early loosening THA.

Methods

During January 2009 to December 2010, 121 primary THAs were performed at our institution by single-surgeon, using the same acetabular component and same uncemented femoral stem with a 32-mm modular head. All patients received the information of the bearing couples and made their own decision to choose one of the following bearings: COM, MOP and MOM. The functional outcomes (Harris Hip Score), Serum Co and Cr levels and survival rates were compared between groups at 5 years. The retrievals were tested by optical microscopy and Raman spectroscopy to evaluate the wear pattern in the cases those need revision.

Background

Both minimally invasive surgery(MIS) and computer-assisted surgery(CAS) in total knee arthroplasty have been scientifically linked with surgical benefits. However, the long-term results of these techniques are still controversial. Most surgeons assessed the surgical outcomes with regard to knee alignment and range of motion, but these factors may not reflect subjective variables, namely patient satisfaction

Purpose

To compare satisfaction and functional outcomes between two technical procedures in MIS total knee arthroplasty, namely computer-assisted MIS and conventional MIS procedure, operated on a sample group of patients after 10 years.

Introduction

Total hip replacement (THR) is one of the most successful orthopedic surgeries performed today. Long term success of THR has been well established, but there remains significant room to improve early outcomes (e.g. pain, length of hospital stay, readmissions). The surgical technique is a key variable affecting these early outcomes. The objective of the current study was to evaluate outcomes for over 1,000 consecutive THRs using the supercapsular percutaneously-assisted total hip (SuperPath) approach.

Patients and Methods

Between September 2008 and April 2015, one surgeon performed 1,074 consecutive primary THRs using the SuperPath surgical technique. All THRs were performed without local anesthesia, patient controlled analgesia (PCA), or postoperative hip precautions. Surgical outcomes including operative time, blood loss, incision length, length of stay (LOS), and complications were collected as part of this IRB approved study. Harris Hip Scores (HHS) and UCLA scores were obtained preoperatively and at 6 and 12 months postoperatively.

Intro

Across much of medicine, activity levels predict life expectancy, with low levels of activity being associated with increased mortality, and higher levels of activity being associated with longer healthier lives. Resurfacing is a technically demanding procedure that has suffered significant fallout from the failure of a couple of poorly performing designs. However strong evidence associates resurfacing with improved life expectancy in both the short and longer term following surgery.

We wondered if there was any relationship between the function of hips following surgery and the extent of that surgery. Could a longer stem inside the femur be the reason for a slightly reduced step length? We proposed the nul hypothesis that there was no clinically relevant difference between stem length and gait.

Method

After informed consent each subject was allowed a 5 minute acclimatisation period at 4km/hr on the instrumented treadmill (Kistler Gaitway, Amherst, NY). Their gait performance on an increasing incline at 5, 10 and 15%. At all 0.5km incremental intervals of speed, the vertical component of the ground reaction forces, center of pressure and temporal measurements were collected for both limbs with a sampling frequency of 100Hz over 10sec.

They were also asked to log onto our JointPRO website and report their function using Oxford, EQ5D, and Imperial scores.

Owing to current restrictions in indications, the patient groups selected were not comparable. However, from our database of over 800 patients who have been through the gait lab. 82 subjects were tested from 2 diagnostic groups (29 conventional THR, 27 hip resurfacing) and compared with a slightly younger group of 26 healthy controls. Patients were excluded if less than 12 months postop, or with any other documented joint disease or medical comorbidities which might affect gait performance.

Body weight scaling was also applied to the outputted mechanical data to correct for mass differences. All variables for each subject group were compared to each other using an analysis of variance (ANOVA) with Tukey post hoc test with significance set at α=0.05.

Introduction

The Accolade II taper stem incorporates design features which maximize proximal stem fit and bone contact and avoids more distal taper engagement which has been shown to be problematic. RSA was used in this study to analyze stem micromotion to 2 years post-surgery, providing an indication of long-term fixation. Pain, function and health-related quality of life were also compared before and after total hip arthroplasty (THA.)

Method

This prospective, single centre case-series enrolled 35 patients into Parts A and B. The first 5 subjects were recruited to Part A of the study (learning curve), the subsequent 30 patients to part B. Radiopaque tantalum beads were inserted intra-operatively into each patient, with RSA radiographs taken immediately post-operatively, and at 3, 6, 12 and 24 months. These radiographs were digitized to DICOM file format and exported, allowing for independent analysis using the UmRSA system. Three Patient Reported Outcome Measurements; WOMAC, EQ-5D-3L and VAS pain were collected pre-operatively and at 6, 12 and 24 month intervals for all patients.

Introduction

Symptomatic instability following total knee arthroplasty (TKA) is a leading cause of early failure. Despite numerous reports on instability, standardized diagnostic and treatment protocols for these patients continue to remain unclear. Most reports recommend component revision as the preferred treatment, because of poor outcomes and high failure rates associated with isolated tibial polyethylene insert exchange (ITPIE). However, modern implant systems and standardized protocols may potentially change this teaching.

Methods

We performed an IRB-approved, retrospective review of 90 consecutive patients with minimum 2 years follow-up who underwent revision TKA for instability by one of four arthroplasty surgeons at a single institution. Mean age was 62.0 years (range, 41 to 83 years), and 73% of patients were women. Charts were reviewed for relevant preoperative clinical and physical exam findings, as well as pertinent intraoperative findings. Radiographs were analyzed for femoral and tibial component positioning. Pre- and post-operative Knee Society Scores (KSS) were calculated.

Introduction

Prosthetic replacement remains the treatment of choice for displaced femoral neck fractures in the elderly population, with recent literature demonstrating significant functional benefits of total hip arthroplasty (THA) over hemiarthroplasty. Yet the fracture population also has historically high rates of early postoperative instability when treated with THA. The direct anterior approach (DAA) may offer the potential to decrease the risk of postoperative instability in this high-risk population by maintaining posterior anatomic structures. The addition of intraoperative fluoroscopy can improve precision in component placement and overcome limitations on preoperative planning due to poor preoperative radiographs performed in the emergency setting.

Methods

We retrospectively reviewed clinical and radiographic outcomes of 113 consecutive patients with displaced femoral neck fractures treated by two surgeons over a five-year period. All underwent surgery via the DAA using fluoroscopic guidance, and were allowed immediate postoperative weight bearing without any hip precautions or restrictions. Charts were reviewed for relevant complications, while radiographs were reviewed for component positioning, sizing, and leg length discrepancy. Mean follow-up was 8.9 months.

Introduction

Computer-assisted navigation is an established tool in hip and knee arthroplasty. This technology was introduced with the goals of greater precision in bone preparation and implant placement, potentially leading to improved clinical outcomes. Various navigation protocols exist, many of which require placement of temporary percutaneous pins in the operative field. Risks of pin placement have not been described.

Methods

We conducted a retrospective review of 352 consecutive patients undergoing elective hip and knee surgery using computer-assisted navigation between January 2013 and December 2015, all with a minimum follow-up of 90 days. Navigation pins were placed using a standardized protocol into the iliac crest for hip arthroplasty or into the femoral and tibial diaphysis for knee arthroplasty. Postoperatively, all patients were allowed to weight bear as tolerated. Patient records were reviewed for operative details and clinical outcomes. Outcome measures included any pin site complications including direct neurovascular damage, fracture through a pin site, and pin site infection.

Introduction

Alternative payment models, such as bundled payments, aim to control rising costs for total knee (TKA) and total hip arthroplasty (THA). Without risk adjustment for patients who may utilize more resources, concerns exist about patient selection and access to care. The purpose of this study was to determine whether lower socioeconomic status (SES) was associated with increased resource utilization following TKA and THA.

Methods

Using the Michigan Arthroplasty Registry Collaborative Quality Initiative (MARCQI) database, we reviewed a consecutive series of 4,168 primary TKA and THA patients over a 3-year period. We defined lowest SES based upon the median household income of the patient's ZIP code. An a prioripower analysis was performed to determine the appropriate sample size. Demographics, medical comorbidities, length of stay, discharge destination, and readmission rates were compared between patients of lowest SES and higher SES.

Introduction

Calcium sulfate bone void fillers (CS-BVF) are increasingly being used for dead space management in infected arthroplasty revision surgery. The use of loose beads of CS-BVF close to the articulating surfaces of an implant means there is potential for them to migrate between the articulating surfaces acting as a third body particle. The aim of this study was to investigate the influence of CS-BVF on the third body wear of total knee replacements.

Methods

The influence of CS-BVF on wear was investigated using the commercially available CS-BVF ‘Stimulan’ (Biocomposites Ltd., UK) and posterior stabilised U2 total knee replacement system implants (United Orthopaedic Corp., Taiwan). The experimental wear simulation was performed using a six station ProSim electropneumatic knee simulator (Simulation Solutions, UK) running the Leeds intermediate kinematics input profile [1]. To investigate the damage that could be caused by the third body particles, 5cc of CS-BVF beads (excess) were placed on the tibial component of the implant, the simulator was run dry for 60 cycles before adding lubricant (25% bovine serum supplemented with 0.03% sodium azide) and running for an additional 115,000 cycles representative of the 6–8 weeks the CS-BVF are present in the body prior to their resorption. The surface topography of the cobalt chrome femorals was analysed using contacting profilometry to ascertain whether the third body particles of CS-BVF had damaged the surfaces. To investigate the influence of CS-BVF on the third body wear of the UHMWPE tibials, 3 million cycles (MC) of wear simulation was subsequently carried out. The wear of the UHMWPE tibials was assessed gravimetrically and the wear of implants tested with CS-BVF was compared to the wear against negative controls (initial Ra∼0.02µm) and positive controls (initial Ra ∼0.4µm) damaged with a diamond stylus. N=6 was completed for each condition, statistical analysis was carried out using ANOVA with significance taken at p<0.05.

Background

Posterior referencing (PR) total knee arthroplasty (TKA) aims to restore posterior condylar offset. When a symmetric femoral implant is externally rotated (ER) to the posterior condylar axis, it is impossible to anatomically restore the offset of both condyles. PR jigs variously reference medially, laterally, or centrally. The distal femoral cutting jigs typically reference off the more distal medial condyle, causing distal and posterior resection discrepancies. We used sawbones to elucidate differences between commonly used PR cutting jigs with regards to posterior offset restoration.

Materials/Methods

Using 32 identical sawbones, we performed distal and posterior femoral resections using cutting guides from 8 widely available TKA systems. 6 systems used a central-referencing strategy, 1 system used a lateral-referencing strategy, and 1 system used a medial-referencing strategy with implants of asymmetric thickness. Distal femoral valgus resection was set at 5 degrees for all specimens. Rotation was set at 3 degrees for 2 sawbones and 5 degrees for 2 sawbones with each system. We measured the thickness of all bone resections, and compared those values to known implant thickness.

Background

Instability and dislocation are some of the most important postoperative complications and potential causes of failure that dual mobility total hip arthroplasty (THA) systems continue to address. Studies have shown that increasing the relative head size provides patients implanted with smaller and larger cups increased stability, greater ROM and a lesser incidence of impingement, without compromising clinical results. The purpose of the current study was to review clinical outcomes in three groups of primary THA patients receiving a dual mobility acetabular shell.

Methods

In two US based, post-market, multicenter studies, 450 patients received a primary cementless dual mobility THA. Patients were split into three groups based on cup size: ≤ 50mm, 52mm–56mm, and ≥ 58mm. Harris Hip Scores (HHS), Short Form 12 Physical Components (SF12 PCS), Lower Extremity Activity Scores (LEAS), and Euroqol 5D Score (EQ-5Ds) were collected preoperatively and through 2 years postoperative.

Introduction

The optimum UHMWPE orthopaedic implant bearing surface must balance wear, oxidation and fatigue resistance. Antioxidant polyethylene addresses free radicals, resulting from irradiation used in cross-linking, that could oxidize and potentially lead to fatigue damage under cycles of in vivo use. Assessing the effectiveness of antioxidant (AO) polyethylene compared to conventional gamma-sterilized or remelted highly cross-linked (HXL) polyethylene is necessary to set realistic expectations of the service lifetime of AO polyethylene in the knee. This study evaluates what short-term antioxidant UHMWPE retrievals can reveal about: (1) oxidation-resistance, and (2) fatigue-resistance of these new materials.

Methods

An IRB-approved retrieval laboratory received 25 AO polyethylene tibial insert retrievals from three manufacturers with in vivo time of 0–3 years. These were compared with 20 conventional gamma-inert sterilized and 30 HXL (65-kGray, remelted) tibial inserts of the same in vivo duration range. The retrievals were

(1) analyzed for oxidation and trans-vinylene index (TVI) using an FTIR microscope, and (2) inserts of sufficient size and thickness were evaluated for mechanical properties by uniaxial tensile testing using an INSTRON load frame. Oxidation was reported as maximum oxidation measured in the scan from the articular surface to the backside of each bearing. TVI was reported as the average of all scans for each material. Average ultimate tensile strength (UTS), ultimate elongation (UE), and toughness were the reported mechanical properties for each material.

Methods

We retrospectively reviewed 301 consecutive primary TKA cases performed by a single surgeon. The first 102 consecutive cases were performed with a femur-first measured resection technique using computer navigation. The femoral component was positioned in neutral mechanical alignment and at 3° of external rotation relative to the posterior condylar axis. The tibia was resected perpendicular to the mechanical axis and ligaments were released as required until the soft tissues were sufficiently balanced. The subsequent 199 consecutive cases were performed with a tibia-first ligament balancing technique using a robotic-assisted TKA system. The tibia was resected perpendicular to the mechanical axis, and the relative positions of the femur and tibia were recorded in extension and flexion by inserting a spacer block of appropriate height in the medial and lateral compartments. The position, rotation, and size of the femoral component was then planned in all planes such that the ligament gaps were symmetric and balanced to within 1mm (Figure 1). Bone resection values were used to define acceptable limits of implant rotation: Femoral component alignment was adjusted to within 2° of varus or valgus, and within 0–3° of external rotation relative to the posterior condyles. Component flexion, anteroposterior and proximal-distal positioning were also adjusted to achieve balance in the sagittal plane. A robotic-assisted femoral cutting guide was then used to resect the femur according to the plan (Figure 2).

CPT billing codes were reviewed to determine how many patients in each group underwent post-operative MUA. Post-operative mechanical alignment was measured in a subset of 50 consecutive patients in the ligament balancing group on standing long-leg radiographs by an independent observer.

Results

Post-operative MUA rates were significantly lower in the ligament balancing group (0.5%; 1/199) than in the measured resection group (3.9%; 4/102), p=0.051. 91.3% (42/46) of knees were within 3° and 100% (46/46) were within 4° of neutral alignment to the mechanical axis post-operatively in the ligament balancing group.

Background

Dislocation is a common complication after proximal and total femur prosthesis reconstruction for primary bone sarcoma patients. Expandable prosthesis in children puts an additional challenge due to the lengthening process. Hip stability is impaired due to multiple factors: Resection of the hip stabilizers as part of the sarcoma resection: forces acts on the hip during the lengthening; and mismatch of native growing acetabulum to the metal femoral head. Surgical solutions described in literature are various with reported low rates of success.

Objective

Assess a novel 3D surgical planning technology by use of 3D models (computerized and physical), 3D planning, and Patient Specific Instruments (PSI) in supporting correction of young children suffering from hip instability after expandable prosthesis reconstruction following proximal femur resection. This innovative technology creates a new dimension of visualization and customization, and could improve understanding of this complex problem and facilitate the surgical decision making and procedure.

INTRODUCTION

While multiple factors contribute to the variability of prosthesis placement during total knee arthroplasty (TKA), the accuracy of the surgeon's resection planning (positioning of the cutting block) is arguably the most critical. One may postulate that proper training, including enabling the surgeon to passively receive quantitative feedback on the cutting block position, may help him/her improve resection accuracy. The purpose of this study was to test the hypothesis that passive reception of feedback on cutting block position improves the accuracy of the successive TKA resection planning.

Materials and Methods

Five cadaveric knees (tibia and foot only) were studied. After arthrotomy, the tracker of an imageless navigation system (ExactechGPS^®, Blue-Ortho, Grenoble, FR) was attached to the tibia. A navigated TKA procedure was initiated starting with registration of anatomical landmarks. Four surgeons then positioned the tibial cutting block (without pinning) on each knee using standard extramedullary mechanical instruments. The planned target resection was neutral varus/valgus, 3° posterior slope, and 10mm resection depth referencing the lateral plateau. Each surgeon performed 3 planning trials on each of the 5 knees, removing the cutting block between attempts. The planned resections were measured using an instrumented checker provided with the navigation system, referencing the cutting block. Surgeons were informed of the resection parameters measured by the navigation system after each planning trial. The deviations in resection parameters between the resection target and the cutting block position were calculated for each planning trial. The effect of receiving passive feedback on the accuracy of successive placement of the cutting block was assessed by comparing the deviations between each surgeon's 3 trials on the same cadaver (paired-t test). Statistical significance was defined as p<0.05.

INTRODUCTION

Studies have reported that only 70–80% of the total knee arthroplasty (TKA) cases using conventional instruments can achieve satisfactory alignment (within ±3° of the mechanical axis). Computer-assisted orthopaedic surgery (CAOS) has been shown to offer increased accuracy and precision to the bony resections compared to conventional techniques [1]. As the early adopters champion the technology, reservation may exist among new CAOS users regarding the ability of achieving the same results. The purpose of this study was to investigate if there are immediate benefits in the accuracy and precision of achieving surgical goals for the novice surgeons, as compared to the experienced surgeons, by using a contemporary CAOS system.

Materials and Methods

Two groups of surgeons were randomly selected from TKAs between October 2012 and January 2016 using a CAOS system (ExactechGPS, Blue-Ortho, Grenoble, FR), including:

Novice group (7 surgeons): no navigation experience prior to the adoption of the system and have performed ≤20 CAOS TKAs. To investigate the intra-group variation, this group was further divided into surgeons with extensive experience in conventional TKA (novice-senior), and surgeons who were less experienced (novice-junior).

All the surgeries from the novice group (86 cases) and the most recent 20 cases from each surgeon in the experienced group (120 cases) were studied. Deviations in the resection parameters between the following were investigated for both tibia and femur: 1) planned resection, resection goals defined prior to the bone cuts; 2) checked resection, digitization of the realized bone cuts. The deviations were compared within the novice group (novice-senior vs novice-junior), as well as between the novice and experience groups. Knees with optimal resection (deviation<2°/mm, without clinically alter the joint mechanics [2]) and acceptable resection (deviation<3°/mm, as commonly adopted) were identified. Significance was defined as p<0.05.

Introduction

Successful cementless acetabular designs require sufficient initial stability between implant and bone (with interfacial motions <150 μm) and close opposition between the porous coating and the reamed bony surface of the acetabulum to obtaining bone ingrowth and secondary stability. While prior generations of cementless components showed good clinical results for long term fixation, modern designs continue to trend toward increased porosity and improved frictional characteristics to further enhance cup stability.

Objectives

We intend to experimentally assess the differences in initial stability between a hemispherical acetabular component with a highly porous trabecular tantalum fixation surface (Continuum^® Acetabular System, Zimmer Inc, Warsaw, IN)(Fig 1) and a hemispherical component with the new highly porous Trabecular Titanium^® surface (Delta TT, Lima Corporate, Italy)(Fig 2) manufactured by electron beam melting.

Introduction

Pain control following total knee arthroplasty (TKA) heavily influences timing of mobilization and rehabilitation postoperatively as well as length of hospital stay. Recently, periarticular injection of liposomal bupivacaine (EXPAREL®; Pacira Pharmaceuticals, Inc., San Diego, California) has demonstrated pain relief comparable to femoral nerve block for postoperative analgesia in TKA with earlier mobilization and shortened hospital stay. In order to better explore the use of EXPAREL® in TKA, we standardized the postoperative analgesia to intraoperative periarticular injection of multimodal pain management, which is a recommended postoperative method of pain control in TKA. We studied the effectiveness of periarticular EXPAREL® in TKA postoperative pain control, including impact on early mobilization and length of hospital stay, compared to another local analgesic (Ropivacaine) when both are used as part of a multimodal pain management approach.

Methods

We performed a double blind, randomized, controlled, prospective, IRB-approved study that enrolled 96 participants who underwent a unilateral TKA by one surgeon between May 2014 and March 2015. The two randomized groups were as follows: group 1 (control group) was given the standard intra-articular “pain cocktail” injection, consisting of ropivacaine, ketorolac, morphine, and epinephrine mixed with saline into a 100cc preparation and group 2 (study group) was given a similar intra-articular injection consisting of bupivacaine, ketorolac, morphine, and epinephrine mixed with saline into an 80cc preparation as well as an injection of EXPAREL®, 20cc of 1.3% EXPAREL®, to total 100cc. All patients included in the study were determined to be opioid naïve as described by the Food and Drug Administration criteria. Patients were treated with the same postoperative pain management protocol as well as the same post-operative physical therapy program. The consumption of oral and intravenous narcotics at specific time points as well as total use was recorded during hospital stay. We recorded Visual Analog Pain scores, hours to ambulate 100 feet and length of hospital stay (hours). Both the investigator and the patient were blinded as to which group the patient was randomized, making this a double blind study.

Introduction

A common problem for patients receiving total knee arthroplasty (TKA) is postoperative functional impairment of the joint. This is minimized in bicruciate-retaining (ACL preserving) knee replacements, due to the important role of the anterior cruciate ligament (ACL) in normal kinematic patterns of the knee. We explore ACL sparing TKA by estimating the fraction of osteoarthritic TKA patients with a compatible ACL (assessed intraoperatively), while also examining potential preoperative indicators of ACL status.

Method

We retrospectively examined 498 patients with a primary diagnosis of osteoarthritis who underwent a TKA by one surgeon between September 2013 and March 2015. Exclusion criteria included a prior TKA, a unicompartmental knee replacement, or inflammatory arthritis. Extensive preoperative data (within four months of surgery) for each patient was collected (anatomical alignment, extension, flexion, range of motion (ROM), Lachman test, and BMI) in addition to de-identified demographic data. The intraoperative assessment of ACL status (normal/functionally intact, compromised/deficient, or absent) was then obtained from our local database and compared with the preoperative data. IRB exemption was obtained to retrospectively collect data.

Background

Spinal deformity has a known deleterious effect upon the outcomes of total hip arthroplasty and acetabular component positioning. This study sought to evaluate the relationship between severity of spinal deformity parameters and acetabular cup position, rate of dislocation, and rate of revision among patients with total hip arthroplasties and concomitant spinal deformity.

Methods

A prospectively collected database of patients with spinal deformity was reviewed and patients with total hip arthroplasty were identified. The full body standing stereoradiographic images (EOS) were reviewed for each patient. From these images, spinal deformity parameters and acetabular cup anteversion and inclination were measured. A chart review was performed on all patients to determine dislocation and revision arthroplasty events. Statistical analysis was performed to determine correlation of deformity with acetabular cup position. Subgroup analysis was performed for patients with spinal fusion, dislocation events, and revision THA.

Introduction

Tibiofemoral constraint in patients with total knee replacements (TKR) is dependent on both implant geometry and the surrounding soft tissue structures. Choosing more highly constrained geometries can reduce the contribution of soft tissue necessary to maintain joint stability [1]. Often when knee revision surgeries are required, the soft tissue and bone are compromised leading to the use of more constrained implants to ensure knee stability [2]. The current study quantifies the differences in varus-valgus (VV) and internal-external (IE) constraint between two types of total knee revision systems: SIGMA® TC3© and ATTUNE® REVISION.

Methods

Nine cadaveric knees (7 male, age 64.0 ± 9.8 years, BMI 26.28 ± 4.92) were implanted with both fixed-bearing SIGMA TC3 and ATTUNE REVISION knee systems. Five knees received the TC3 implant first, while the remaining 4 received the ATTUNE implant first. The knees were mounted in an inverted position, and a six degree-of-freedom force-torque sensor (JR3, Woodland, CA) was rigidly secured to the distal tibia (Fig. 1). A series of manual manipulations applying IE and VV torques was performed through the flexion range [3]. Each specimen was then revised to the alternate revision system, and the manual manipulations were repeated. Joint loads were calculated, and tibiofemoral kinematics were described according to the Grood-Suntay definition [4]. VV and IE kinematics were calculated as a function of flexion angle, VV torque, and IE torque as has been described previously [3]. The knees were analysed at ±6 Nm VV and ±4 Nm IE, and the kinematics were normalized to the zero load path. A paired t-test (p < .05) was employed to identify significant differences between the kinematics of the two knee systems at 10º flexion increments.

Introduction

When following patients with metal-on-metal (MoM) hip replacements, current evidence suggests that orthopaedic surgeons should avoid reliance on any single investigative tool. In 2014, guidelines for stratifying patients with MoM hip replacement into groups of low, medium, and high risk of failure based on multiple criteria were published. However, such risk stratification guidelines can be difficult to interpret due to the numerous risk factors related to MoM hip replacements. This is especially true for patients with various (high and low) risk levels for different criteria within the guidelines.

The first purpose of this study was to assess if a scoring system can be applied to the current MoM guidelines. The second purpose was to test, using this scoring system, how the contemporary guidelines would classify a cohort of patients with a recalled MoM hip replacement system.

Methods

The study population consisted of 1301 patients (1434 hips) enrolled from September 2012 to June 2015 in a multicenter follow-up study of a recalled MoM hip replacement system at a mean of 6.2 (range 2.4 – 11.2) years from index surgery. Eleven required scoring criteria were determined based on existing follow-up algorithm recommendations and consisted of patient factors, symptoms, clinical status, implant type, metal ion levels, and radiographic imaging results. Criteria considered ‘low’ risk were given 1 point, 2 points for ‘moderate’ risk, and 3 points for the ‘high’ risk group. Forward stepwise logistic regression was conducted to determine the minimum set of predictive variables for risk of revision and assign variable weights. The MoM risk score for each hip was then created by averaging the weighted values of each predictive variable.

Introduction

Complication and revision rates have shown to be high for all metal-on-metal (MoM) bearings, especially for the ASR Hip System (ASR hip resurfacing arthroplasty (HRA) and ASR XL total hip arthroplasty (THA)). This prompted the global recall of the ASR Hip System in 2010. Many studies have previously explored the association between female gender and revision surgery MoM HRA implants; yet less research has been dedicated to exploring this relationship in MoM THA.

The first purpose of this study was to assess the associations between gender and implant survival, as well as adverse local tissue reaction (ALTR), in patients with MoM THA. Secondly, we sought to report the differences between genders in metal ion levels and patient reported outcome measures (PROMs) in patients with MoM THA.

Methods

The study population consisted of 729 ASR XL THA patients (820 hips) enrolled from September 2012 to June 2015 in a multicenter follow-up study at a mean of 6.4 (3–11) years from index surgery. The mean age at the time of index surgery was 60 (22–95) years and 338 were women (46%). All patients enrolled had complete patient and surgical demographic information, blood metal ion levels and PROMs obtained within 6 months, and a valid AP pelvis radiograph dating a maximum of 2 years prior to consent. Blood metal ion levels and PROMs were then obtained annually after enrollment. A sub-set of patients from a single center had annual metal artifact reduction sequence (MARS) MRI performed and were analyzed for the presence of moderate-to-severe ALTR.

Introduction

Self tapping bone screw has been widely used in the fixation of Arthroplasty implants and bone graft. But the unwanted screw or driver breakage can be a direct result of excessive driving torque due to the thread cutting resistance. Previous studies showed that bone drill bit cutting rake angle was a critical factor and was inversely related to the bone cutting efficiency.^{1, 2, 3, 4} (Figure 1) However to date there was no data for how the rake angle could influence the performance of self tapping bone screw. The purpose of this study was to investigate the torque generated by the self tapping cortical screw in simulated bone insertion as a function of the screw tip cutting flute rake angle.

Methods

Two 5 mm thick BM5166 polyurethane block were stacked together and drilled through with 2.5mm diameter holes. Five 30mm long 3.5 mm diameter Ti6AL4V alloy self tapping cortical screws with 0°rake angle cutting flutes (Figure 2) were inserted in the holes and driven by the spanner attached to the test machine (Z5.0TN/TC-A-10) with a displacement control of 3 revolutions/min and 30N constant axial loading. The screws were driven into the stacked polyurethane block for 8mm depth. The maximum driving torque was recorded. Procedure was repeated for five same screws but with 7° rake angle cutting flutes. (Figure 2) The driving torqueses were compared. Student t test was performed with confidence level of 95% was assumed.

Background

Recent advances in materials and manufacturing processes for arthroplasty have allowed fabrication of intricate implant surfaces to facilitate bony attachment. However, refinement and evaluation of these new design strategies is hindered by the cost and complications of animal studies, particularly during early iterations in development process. To address this problem, we have constructed and validated an ex-vivo bone bioreactor culture system to enable empirical testing of candidate structures and materials. In this study, we investigated mineralization of a titanium wire mesh scaffold under both static and dynamic culturing using our ex vivo bioreactor system.

Methods

Cancellous cylindrical bone cores were harvested from bovine metatarsals and divided into five groups under different conditions. After incubation for 4 & 7 weeks, the viability of each bone sample was evaluated using Live-Dead assay and microscopic anatomy of cells were determined using histology stain H&E. Matrix deposits on the scaffolds were examined with scanning electron microscopy (SEM) while its chemical composition was measured using energy-dispersive x–ray spectroscopy (EDX).

Background

Total knee arthroplasty (TKA) is a routine, cost-effective treatment for end-stage arthritis. While the evidence for good-to-excellent patient-reported outcomes and objective clinical data is present, approximately 20% of patients continue to be dissatisfied with results of their surgery. Dissatisfaction is strongly correlated with unmet patient expectations, and these patients may experience a higher cost of care due to recurring office and emergency visits. Therefore, this survey asked a large group of United States (U.S) and international surgeons to prioritize areas of opportunity in primary TKA. Specifically, we compared surgeon responses regarding: 1) the top 5 areas needing improvement; which were stratified by: 2) surgeons' years of experience; and 3) surgical case volume.

Methods

A total of 418 orthopaedic surgeons were surveyed. Two hundred U.S. surgeons and 218 international surgeons participated from 7 different countries including: The United Kingdom (40), France (40), Germany (43), Italy (40), Spain (38), and Australia (17). To participate, surgeons had to be board certified, in practice for 2 years, spend 60% of their time in clinical practice, and perform a minimum of 25 joint arthroplasties per year. Surgeons were asked to choose the top 5 areas of improvement for TKA from a list of 17 attributes including clinical and functional outcomes, procedural workflow and economic variables. Surgeons were able to specify additional options if needed. Results were stratified by annual case volume (25 to 50; 51 to 100; greater than 100 cases) and years of experience (1 to 10; 11 to 20; greater than 20). Single-tail proportion tests were used to compare results between cohorts, where an alpha of 0.05 was set as significant.

Introduction

In the evaluation of patients with pre-arthritic hip disorders, making the correct diagnosis and identifying the underlying bone pathology is of upmost importance to achieve optimal patient outcomes. 3-dimensional imaging adds information for proper preoperative planning. CT scans have become the gold standard for this, but with the associated risk of radiation exposure to this generally younger patient cohort.

Purpose

To determine if 3D-MR reconstructions of the hip can be used to accurately demonstrate femoral and acetabular morphology in the setting of femoroacetabular impingement (FAI) and development dysplasia of the hip (DDH) that is comparable to CT imaging.

Introduction

PSI technology have proved helpful in difficult primary Total Knee Replacement. However applying it to revision was impossible due to multiple factor. To Start with the landmark We usually destroy it. There is an extensive damage at the bone at the epiphysis, the implant prevent an accurate visualization and debridement usually change the surface of the bone as well which make applying the psi dyed impossible, we are proposing a new way of using psi in revision where we don't depend on the all masses adjusted in primary. However we depend on the metaphysical area of the bone.

Material & method

We have reviewed 56 MRI &CT scans for cases posted for revision and showed clearly that in spite of the extensive bony destruction and metal presence the MRI / CT scan we were able to visualize well the metaphysical area in the intramedullary canal in both tibial and femoral · we have established a special external guide that depends on the outside surface of the metaphysis of the femur. We have tried this model on six plastic bone and showed that this external guide can give the accurate details that the surgeon is looking for in a revision surgery

Introduction

Malpositioning of the acetabular cup during total hip arthroplasty increases the risk of dislocation, edge loading, squeaking and can be responsible for early wear and loosening. We hypothesized that the use of three-dimensional visualization tools showing during surgery the planned cup position relatively to the acetabular edge would increase the accuracy of cup orientation. The purpose of this study was to compare 3D planning-assisted with freehand insertion of the acetabular cup.

Methods

A randomized, controlled, prospective study of two groups of twenty eight patients each was performed. In the first group, cup positioning was guided by 3D views of the cup within the acetabulum based on a three-dimensional preoperative planning (Figure 1). In the control group, the cup was placed freehand. All of the patients were operated on by the same surgeon through a direct anterior approach in supine position. Cup anteversion and abduction angles were measured on three-dimensional computed tomography reconstructions for each patient by an independent observer. We analyzed the accuracy of both methods. The main evaluation criterion was the percentage of outliers according to the Lewinneck safe zone.

Introduction

Lateralizing the center of rotation (COR) of reverse total shoulder arthroplasty (rTSA) has the potential to increase functional outcomes of the procedure, namely adduction range of motion (ROM). However, increased torque at the bone-implant interface as a result of lateralization may provoke early implant loosening, especially in situations where two, rather than four, fixation screws are used. The aim of this study was to utilize finite element (FE) models to investigate the effects of lateralization and the number of fixation screws on micromotion and adduction ROM.

Methods

Four patient-specific scapular geometries were developed from CT data in 3D Slicer using a semi-automatic threshold technique. A generic glenoid component including the baseplate, a lateralization spacer, and four fixation screws was modelled as a monoblock. Screws were simplified as 4.5 mm diameter cylinders. The glenoid of each scapula was virtually reamed after which the glenoid component was placed. Models were meshed with quadratic tetrahedral elements with an edge length of 1.3 mm.

The baseplate and lateralization spacer were assigned titanium material properties (E = 113.8 GPa and ν = 0.34). Screws were also assigned titanium material properties with a corrected elastic modulus (56.7 GPa) to account for omitted thread geometry. Cortical bone was assigned an elastic modulus of 17.5 GPa and Poisson's ratio of 0.3. Cancellous bone material properties in the region of the glenoid were assigned on an element-by-element basis using previously established equations to convert Hounsfield Units from the CT data to density and subsequently to elastic modulus [1].

Fixed displacement boundary conditions were applied to the medial border of each scapula. Contact was simulated as frictional (μ = 0.8) between bone and screws and frictionless between bone and baseplate/spacer. Compressive and superiorly-oriented shear loads of 686 N were applied to the baseplate/spacer. Lateralization of the COR up to 16 mm was simulated by applying the shear load further from the glenoid surface in 4 mm increments (Fig. 1A). All lateralization levels were simulated with four and two (superior and inferior) fixation screws.

Absolute micromotion of the baseplate/spacer with respect to the glenoid surface was averaged across the back surface of the spacer and normalized to the baseline configuration considered to be 0 mm lateralization and four fixation screws. Adduction ROM was measured as the angle between the glenoid surface and the humeral stem when impingement of the humeral cup occurred (Fig. 1B).

Introduction

Reverse total shoulder arthroplasty (RTSA) can partially restore lost range of motion (ROM). Active motion restoration is largely a function of RTSA joint constraint, limiting impingement, and muscle recruitment; however, it may also be a function of implant design. The aim of this computational study was to examine the effects of implant design parameters, such as neck-shaft (N-S) angle and glenoid lateralization, on impingement-free global circumduction range of motion (GC-ROM). GC-ROM summarizes the characteristically complex, wide-ranging envelope of glenohumeral motion into a single quantity for ease of comparison.

Methods

Nine computational models were used to investigate implant parameters. The parameters examined were N-S angles of 135°, 145°, and 155° in combination with glenoid lateralizations (0, 5, and 10 mm). Static positioning of the humerus was defined by an elevation direction angle, elevation angle, and rotation. The humerus was rotated from the neutral position (0° of rotation and elevation), and then elevated in different elevation directions until impingement was detected. Abduction occurred at an elevation direction angle of 0°, while flexion and extension occurred at elevation direction angles of 90° and −90°, respectively. Elevation direction angles ranged from −180° to 180°. Elevation ranged from 0° and 180°. Rotations ranged from −45° to 90°, where negative and positive rotations represented external and internal rotation, respectively. For each rotation angle, a plot of maximum elevation in each elevation plane was created using polar coordinates (radius = elevation, angle = elevation direction). The area enclosed by the resulting points, normalized with respect to the implant with a 145° N-S angle and 5 mm lateralization, was calculated. The sum of these areas defined the GC-ROM.

Introduction

Various 2D and 3D surfaces are available for cementless fixation of acetabular cups. The goal of these surface modifications is to improve fixation between the metallic cups and surrounding bone. Radiographs have historically been used to evaluate the implant-to-bone fixation around the acetabular cups. In general, a well fixed cup shows no gaps or radiolucency around the cup's outer diameter. In post-operative radiographs, the presence of progressive radiolucent zones of 2mm or more around the implant in the three radiographic zones is indicative of aseptic loosening, as described by DeLee and Charnley [1]. In this cadaveric study, we investigated the X-ray image characteristics of two different types of acetabular shell surfaces (2D and 3D) to evaluate the implant-to-bone interface in the two designs.

Methods

Six human cadavers were bilaterally implanted with acetabular cups by an orthopaedic surgeon. 2D surface cups (Trident, Stryker, Mahwah, NJ) and 3D surface cups (Tritanium, Stryker, Mahwah, NJ) were randomized between the left and right acetabula. The surgeon used his regular surgical technique (1 mm under reaming) to implant the acetabular cups. The cadavers were sent for X-ray imaging after the operation, Figure 1A. Following the X-ray imaging, the acetabular cups were carefully resected from the cadavers. Enough bone around the cups was retained for analysis of the implant-to-bone interface by contact X-ray. The acetabular cups with the surrounding bone were fixed in 70% isopropyl alcohol for about a week and subsequently embedded in polymethyl methacrylate. The embedded cups were sectioned at 30° intervals using a diamond saw in the coronal plane, as recommended by Engh et al [2], Figure 1B. The sectioning of the samples produced 6 slices of each cup where the implant-bone interface could easily be visualized for evaluation with contact X-ray.

Introduction

Reverse total shoulder arthroplasty (RTSA) is a commonly performed operation for a variety of pathologies. Despite excellent short-term outcomes, complications are commonly encountered. Recurrent instability occurs in up to 31% of cases, often due to components placed with too little tension. Acromial stress fractures can occur in up to 7% of cases, often due to components placed in too much tension. Despite these concerns, there is little evidence evaluating the intraoperative tension and glenohumeral contact forces (GHCF) during RTSA. The purpose of this study was to measure the intraoperative GHCF during RTSA.

Methods

26 patients were enrolled after obtaining IRB approval. Inclusion criteria were patients undergoing primary RTSA. An instrumented strain gauge implant was designed to attach to an Exactech Equinoxe (Gainesville, FL) baseplate during RTSA. A specially designed trial glenosphere was then attached to the instrumented baseplate. Wires from the strain gauges were connected to a 24-bit analog input and placed outside the operative field to a computer that measure the forces. After joint reduction, GHCF were measured in neutral, passive flexion, passive abduction, passive scaption and passive external rotation (ER). Five patients were excluded due to wire calibration issues.

INTRODUCTION

Aseptic loosening is the most common failure mode for Total Elbow Arthroplasty (TEA) and is considered to be associated with accelerated polyethylene bearing wear [1, 2]. This study aimed to evaluate three commercially available implant designs under loads associated with daily living. The hypothesis was that more recent designs (Discovery and Nexel) provide greater articular contact areas resulting in lower polyethylene stresses compared to the Coonrad/Morrey (CM).

METHODS

Motion tracking was performed on a healthy volunteer during elbow flexion at 0, 45, and 90° shoulder abduction because most daily activities occur with some shoulder abduction [3] resulting in varus stress about the elbow. This kinematic data was used in an OpenSim upper extremity musculoskeletal model [4] to estimate muscle and joint reaction loads with 5lb in hand, consistent with the common clinical restrictions following TEA.

Computer aided assemblies of the smallest size implants for each system were imported to ANSYS for finite element analysis. Metallic components were treated as rigid and polyethylene components were modeled using a nonlinear elastoplastic constitutive model calibrated to material data. Articular contacts were frictional. Physiologic joint reaction forces and moments quantified in OpenSim were applied and the resulting peak articular contact area and peak bearing von Mises stresses were assessed.

INTRODUCTION

Total knee arthroplasty (TKA) is typically performed using cement to secure the prosthesis to bone. There are complications associated with cementing that include intra-operative hypotension, third-body abrasive wear, and loosening at the cement interfaces. A cementless prosthesis using a novel keeled trabecular metal tibial baseplate was developed to eliminate the need for cementing the tibial component in TKA.

METHODS

A retrospective chart review was performed on patients who underwent TKA using cementless tibial and femoral components between August, 2013 and January, 2014. Patients with minimum two-year follow-up including radiographs were included in the analysis. Patient demographics as well as preoperative and postoperative range of motion (ROM) and function were measured using the Knee Society Scoring system (KSS). Post-operative radiographs were assessed for signs of osteolysis, loosening, or subsidence. Paired T-tests were used to identify differences in preoperative and postoperative ROM and KSS.

Background

The transverse acetabular ligament (TAL) has been described as an anatomic landmark to guide in the positioning of the acetabular component during total hip arthroplasty. On plain films, the radiographic teardrop (RT) has similarly been utilized as a measure of appropriate cup positioning. The goal of this study is to quantify the distance and location between the anatomic TAL and RT landmarks to aid in the positioning of acetabular component.

Methods

Sixteen randomly selected cadaveric pelvises (eight male, eight female) underwent dissection. Radiographic markers were placed bilaterally at the anteromedial insertions of the TAL, and true anteroposterior (AP) pelvic radiographs of the cadavers were obtained. Distances between the markers and the lateral borders of the RT were measured.

Objectives

Total hip replacement is increasingly being conducted in younger and more active patients, so surgeons often use bearing surfaces with improved wear characteristics, such as ceramic on ceramic. The primary objective of this study was to determine if survivorship for a BIOLOX® delta ceramic on delta ceramic couple used with the PROCOTYL® L acetabular cup is significantly different from all other cementless cups in a large arthroplasty registry. The secondary objective of this study was to analyze patient reported outcomes measures (PROMs) of the subject cup with a minimum five year follow-up.

Methods

Patient demographics and survivorship data was collected from the National Joint Registry of England, Wales, Northern Ireland, and the Isle of Man (NJR) database for all total hip replacements performed with the PROCOTYL® L cup used in combination with a delta-on-delta articulation, as well as for all other cementless cups. Survivorship data was compared for all revisions and cup revisions only and data was adjusted to exclude metal on metal articulations. The hazard ratio of the subject system to all cementless cups was also calculated with the Cox Proportional Hazards model. Patients with the subject components implanted for a minimum of five years completed Oxford Hip, EQ-5D, and EQ VAS score questionnaires.

Introduction

Patellar crepitus and clunk are tendofemoral-related complications predominantly associated with posterior-stabilizing (PS) total knee arthroplasty (TKA) designs [1]. Contact between the quadriceps tendon and the femoral component can cause irritation, pain, and catching of soft-tissue within the intercondylar notch (ICN). While the incidence of tendofemoral-related pathologies has been documented for some primary TKA designs, literature describing revision TKA is sparse. Revision components require a larger boss resection to accommodate a constrained post-cam and stem/sleeve attachments, which elevates the entrance to the ICN, potentially increasing the risk of crepitus. The objective of this study was to evaluate tendofemoral contact in primary and revision TKA designs, including designs susceptible to crepitus, and newer designs which aim to address design features associated with crepitus.

Methods

Six PS TKA designs were evaluated during deep knee bend using a computational model of the Kansas knee simulator (Figure 1). Prior work has demonstrated that tendofemoral contact predictions from this model can differentiate between TKA patients with patellar crepitus and matched controls [2]. Incidence of crepitus of up to 14% has been reported in Insall-Burstein® II and PFC® Sigma® designs [3]. These designs, in addition to PFC® Sigma® TC3 (revision component), were included in the analyses. Primary and revision components of newer generation designs (NexGen®, Attune® and Attune® Revision) were also included. Designs were evaluated in a patient model with normal Insall-Salvati ratio and a modified model with patellar tendon length reduced by two standard deviations (13mm) to assess worst-case patient anatomy.

Introduction

During primary total knee arthroplasty (TKA), surgeons occasionally encounter compromised bone and fixation cannot be achieved using a primary femoral component. Revision knee replacement components incorporate additional features to improve fixation, such as modular connection to sleeves or stems, and feature additional varus-valgus constraint in the post-cam mechanism to compensate for soft tissue laxity. The revision femoral component can be used in place of the primary femur to address fixation challenges; however, it is unclear if additional features of the revision femoral components adversely affect knee kinematics when compared to primary TKA components. The objective of this study was to compare weight-bearing tibiofemoral and patellofemoral kinematics between primary and revision femoral component with the primary tibial insert for a single knee replacement system. The hypothesis of the study was that kinematics for revision femoral components will be similar to kinematics of the primary femoral components

Methods

Eight cadaveric knees (age: 59±10 years, BMI 23.3±3.5) were implanted with a primary TKA system (ATTUNE™ Posterior Stabilized Total Knee Replacement System). Each knee was mounted and aligned in the Kansas Knee Simulator (Fig. 1) [1]. A deep knee bend was performed which flexed the knee from full extension to 110° flexion, while the medial-lateral translation, internal-external, and varus-valgus rotations at the ankle were unconstrained. The femoral component was then replaced with a revision femoral component of the same TKA system, articulating on the same primary insert component, and the deep knee bend was repeated. The translations of the lowest points (LP) of the medial and lateral femoral condyles along the superior-inferior axis of the tibia were calculated. In addition, tibiofemoral and patellofemoral kinematics were calculated for each cycle based on the Grood-Suntay coordinate system [2] [1]. The change in LP and patellofemoral kinematics from the primary to revision femurs were calculated. Student t-tests were performed at 5° increments of knee flexion to identify significant differences between the two implant types.

Introduction

CMS is now publicly reporting 30-day readmission rates following total joint replacement (TJR) by hospital and is planning the collection of patient-reported function and pain after TJR. Nationally, 5% of patients are readmitted to the hospital after TJR for both medical and orthopedic-related issues. However, the relationship between readmission and functional gain and pain relief after TJR has not been evaluated.

Methods

Clinical data on 2990 CMS patients from over 150 surgeons practicing in 22 US states who elected primary unilateral TJR in 2011–2012 were identified. Measures include pre-operative demographics, BMI, medical and musculoskeletal comorbidities, pain and function (KOOS/HOOS; SF36) and 6 month post-TJR pain and function. Data were merged with CMS claims to verify 30-day readmissions. Descriptive statistics and multivariate models adjusted for covariates and clustering within site were performed.

Introduction

Acetabular cup deformation is an important topic in today's THA and was investigated for a variety of metal cup designs (e.g. 1,2,3). Cup deformation caused by press-fit forces can have negative effects on the performance of such systems (e.g. high friction, metal ion release). When considering new materials for monolithic acetabular cups - such as ceramics - detailed knowledge about the deformation behaviour is essential to ensure successful performance. Therefore, the deformation behaviour of monolithic ceramic cups was investigated.

Materials and Methods

Testing was conducted with monolithic ceramic cups (under development, not approved) of size 46mm and 64mm. One cup design of each size had a constant wall thickness of 3.0mm and an offset of 0.0mm (center of rotation on front face level), the other design was lateralized with an offset of 3.5mm (46mm) or 5.0mm (64mm), leading to an increased wall thickness. First, 3 cups of each design were impacted into 1.0mm underreamed Sawbones® blocks (pcf 30, geometry: see (2)). Second, all cups were quasi-statically assembled into the Sawbones® blocks of the same design using a material testing machine. Third, the cups were placed in a two-point-loading frame (acc. to ISO/DIS 7206–12:2014(E)) and a load of up to 1kN was applied. The inner diameter of all cups was measured under unloaded and loaded conditions for all scenarios using a coordinate measurement machine at 9 locations of each cup, 1.5mm below the front face (Fig.1). As the diametrical deformation (unloaded inner diameter – loaded inner diameter) was not normally distributed a Wilcoxon test was performed to statistically analyse the deformation differences of the different cup designs (p<0.05).

Introduction

Recent literature demonstrates that the assembly load to connect ball head and femoral stem affects the taper junction fretting wear evolution in THR [1]. During assembly the surface profile peaks of the mostly threaded tapers are deformed. This contributes to the taper locking effect. Very little is known about this deformation process and its role in the evolution of fretting and wear. Therefore, this study aimed to experimentally determine the deformation of the profile peaks after the initial assembly process.

Materials and Methods

36 tapers of three different stem materials acc. to ISO5832-3 (titanium), ISO5832-9 (steel), ISO5832-12 (cobalt chromium) and 36 ceramic ball heads were tested under quasi-static (4kN) and dynamic (impaction) (3.7±0.3kN) axial assembly. Before and after loading 4 surface profiles in 90° offset were measured on each taper. Height differences of profile peaks and areas under profile curves were calculated and compared. Both parameters provide insights into the deformation behavior of the surface structure. Additionally, subsidence of tapers into ball heads was measured and subsidence rates were calculated with regard to varying impaction forces. Due to different thermal expansion coefficients tapers could be disconnected from ball heads by utilizing liquid nitrogen. Thus, further surface damage due to disassembly was avoided. Statistical analysis was performed using a Wilcoxon test (p<0.05).

Introduction

The use modular total hip arthroplasty is associated with potentially serious local and systemic complications. Each modular interface introduces a source for wear particle generation. Research suggests the etiology of wear particle generation and subsequent corrosion begins with mechanical fretting and disruption of the protective oxide layer leading to release of metal ions at the taper interface. The purpose of this study was to conduct three dimensional (3D) surface scans of the mating surfaces of the neck-stem taper to identify features that may contribute to the fretting and surface corrosion.

Methods

Eighteen modular hip implant components (9 stems and 9 necks) received 3D surface scans to examine the neck-stem taper junction. The study analyzed the neck-stem taper in an as assembled condition so relative surface positions and surface features could be studied. The 9 stems and 9 necks were scanned using an optical scanner. The implant image volume was resolved to a point spacing of 0.5 mm. Measurements were made to determine the normal distance between the surfaces of the neck taper as seated in the stem slot. These measurements were used to produce a color map of the contact proximity between the neck and stem surfaces (Figure 1). Circumferential surface points from the neck and stem at corresponding taper axis heights were used to create surface contour plots to identify surface shape variation and contact. The angle measurements and neck seated depth were analyzed by regression.

Introduction

CT-based navigation system in total hip arthroplasty (THA) is widely used to achieve accurate implant placement. Now, we developed our own CT-based navigation system originally, and since then we have been conducting various analysis in order to use the system more effectively. We compared the accuracy of registration with this navigation system and land mark matching type navigation system. In this study, we evaluated the influence of the surgical approach to the accuracy of registration.

Methods

Between June 2015 and February 2016, 28 consecutive uncemented THAs were performed in 26 patients. The preoperative diagnosis was osteoarthritis in 20 hips, osteonecrosis of the femoral hips in 5, and rheumatoid arthritis in 3. The newly developed navigation system was a CT based, surface matching type navigation system. We used newly developed navigation system and commercially available land-mark type CT-based navigation system in the setting of acetabular sockets under the same condition. After we fixed the cementless cup, we measured the cup setting angle of inclination and anteversion on each navigation system. Postoperative assessment was performed using CT one week after the operation, and measured the actual angle of the cup. Approach of operations were performed via posterolateral approach in 14 hips, and Hardinge approach in 14 hips. We calculated the absolute value of the cup angle difference between intra-operative value and post-operative value with each navigation system and compared the accuracy between each navigation system and surgical approach.

Objectives

Few reports were shown about the position of the cup in total hip arthroplasty (THA) with CT-based navigation system. We use minimally invasive surgery (MIS) technique when we perform cementless THA and the correct settings of cups are sometimes difficult in MIS. So we use CT-based navigation system for put implants with correct angles and positions. We evaluated the depth of cup which was shown on intra-operative navigation system.

Materials and Methods

We treated 30 hips in 29 patients (1 male and 28 females) by navigated THA. 21 osteoarthritis hips, 6 rheumatoid arthritis hips and 3 idiopathic osteonecrosis hips were performed THA with VectorVision Hip navigation system (BrainLAB). Implants were AMS HA cups and PerFix stems (Japan Medical Materials, Osaka). Appropriate angles and positions of cups were decided on the 3D model of pelvis before operation. According to the preoperative planning, we put the implants with navigation system. We correct the pelvic inclination angle and measured the depth of cups with 3D template software.

Introduction

Studies of metal-on-metal (MoM) hip resurfacing arthroplasty (HRA) have reported high complication and failure rates due to elevated metal ion levels. These rates were shown to be especially high for the Articular Surface Replacement (ASR) HRA, possibly due to its unique design. Associations between metal ion concentrations and various biological and mechanical factors have been reported. Component positioning as measured by acetabular inclination has been shown to be of especially strong consequence in metal ion production in ASR HRA patients, but few studies have evaluated acetabular anteversion as an independent variable.

The primary objective of this study was to evaluate the associations between component orientation, quantified by acetabular inclination and anteversion, and blood metal ions. Secondly, we sought to report whether conventional safe zones apply to MoM HRA implants or if these implants require their own positioning standards.

Methods

We conducted a multi-center, prospective study of 512 unilateral ASR HRA patients enrolled from September 2012 to June 2015. At time of enrollment our patients were a mean of 7 (3–11.5) years from surgery. The mean age at surgery was 56 years and 24% were female. All subjects had complete demographic and surgical information and blood metal ions. In addition, each patient had valid AP pelvis and shoot-though lateral radiographs read by 5 validated readers measuring acetabular abduction and anteversion, and femoral offset. A multivariate logistic regression was used with high cobalt or chromium (greater than or equal to 7ppb) as the dependent variable. The independent variables were: female gender, UCLA activity score, age at surgery, femoral head size, time from surgery, femoral offset, acetabular abduction, and acetabular anteversion.

Background and aim

Total hip replacement (THR) in young patients has been associated to higher revision rates than in older population. Different conditions may lead to end-stage arthritis of the hip in these patients.

We compared the clinical and radiological outcome of two different groups of young and very young patients who underwent a ceramic-on-ceramic THR.

Patients and Methods

120 hips were prospectively followed for a mean of 10.4 years (range, 5 to 17). 38 patients (46 hips) were less than 30 years old (group 1), and, 68 (74 hips) were between 31 and 40 years old (group 2). Weight (p<0.001) and physical activity level were greater in group 2 (p<0.001). Preoperative function (p=0.03) and range of mobility (p=0.03) were worse in group 1. Primary osteoarthritis was not found in any case. Rheumatoid juvenile arthritis was the most frequent diagnosis in group 1 and avascular necrosis of the femoral head in group 2. A femoral funnel-shaped type 1 according to Dorr was more frequent in group 2 (p=0.04). The same ceramic-on-ceramic uncemented THR was used in all cases. Screws for cup fixation were only used when strictly needed. We analysed the clinical results according to the Merle-D´Aubignè and Postel scale, the postoperative radiological reconstruction of the hip and the radiological appearance of cup loosening. Kaplan-Meier survivorship analysis was used to estimate the cumulative probability of not having a revision surgery.

Background and aim

Despite good survivorship analysis for most uncemented tapered straight stems, new proposals modifying stem design in total hip replacement (THR) are being introduced in order to facilitate femoral revision surgery.

We have evaluated the clinical and radiological results of four different designs of uncemented tapered straight stems implanted in our institution in order to assess: operative complications, clinical results, survivorship analysis for aseptic loosening and radiographic findings

Methods

1008 hips implanted from 1998 to 2006 were prospectively followed for a mean of 12 years (range, 10 to 17). Four uncemented femoral designs employing a tapered straight stem were included: 209 Alloclassic stems, 420 Cerafit, 220 SL-Plus and 159 Summit. All hips had a 28 or 32 mm femoral head, and polyethylene (PE)-on metal or ceramic-on-ceramic bearing surface. Radiological femoral type, stem position, femoral canal filling at three levels and the possible appearance of loosening and other bone remodelling changes were recorded in all hips.

Background and aim

A significant reduction in wear using Durasul highly cross-linked polyethylene (PE) versus Sulene polyethylene (sterilized with nitrogen) at 5 and 10 years have been reported previously. We ask if the improvement observed at the earlier follow-up continues at 15 years.

Methods

Between 1999 and 2001, 90 hips underwent surgery using the same cementless cup and stem: 45 received Allofit cups with a Sulene-PE liner and 45 Allofit cups with a Durasul-PE liner, both associated with an Alloclassic stem (28 mm metallic femoral head). 66 hips of this prospective comparative study were available over a minimum follow-up of 15 years. Linear femoral head penetration was estimated digitally at 6 weeks, at 6 and 12 months and annually thereafter, using the Dorr method, given the nonspherical cup shape. All radiographs were evaluated by the same author, who was not involved in surgery.

Introduction

With the increasing burden of geriatric population in India, TKR is a very common procedure done these days. But as compared to western population the expectations of the people are different in our country. Indian patients want to sit cross legged and squat but can tolerate pain and limp better. So our population has different satisfaction levels after surgery. Keeping this in mind, post op evaluation should also include the performance as well as satisfaction levels. The factors affecting these parameters need to be studied. The current trend is to operate on younger people with more life expectancy and lesser co-morbidities but they have higher demands. Thus it is important to follow TKR patients for an extended time and to study their performance and satisfaction levels and the effect of pre op factors on these parameters.

Objectives

Introduction

Detailed analysis of retrieved total hip replacements (THRs) is valuable for assessing implant and material successes and failures. Reduction of bearing wear and corrosion and fretting of the head-neck trunnion is essential to implant durability and patient health. This research quantifies and characterizes taper and bearing surface damage on retrieved oxidized zirconium THRs.

Methods

Initially, 11 retrieved oxidized zirconium femoral heads were examined along with their associated femoral stems. Relevant patient and retrieval data was collected from clinical charts and radiographs. Taper corrosion (Figure 1) and fretting damage (Figure 2) scoring was performed following the Dyrkacz [1] method. A coordinate measuring machine was used to obtain a detailed surface map of the male and female taper surfaces. Taper surface maps were best-fit with an idealized cone followed by volume subtraction to quantify the amount of material removed as a result of fretting and corrosion processes. Scanning electron microscopy was performed on select samples to identify specific damage modes.

Unique surface bumps were noted on the articular surface of select femoral heads (Figure 3). Seventeen femoral heads were added to the analysis specifically for identification of these bumps. Articular surfaces were searched under SEM magnification and bumps were identified and counted. Parametric statistical correlations were performed with SAS v9.3.

Introduction

Mechanically assisted crevice corrosion (MACC) of head-neck modular taper junctions is prevalent in virtually all head neck tapers in use today. To date, no clear in vitro tests of design, material or surgical elements of the modular taper system have been reported that show which factors principally affect MACC in these tapers. Possible elements include seating load, head-neck offset, surface roughness, taper engagement length, material combination, angular mismatch, and taper diameter. The goals of this study were to use an incremental fretting corrosion test method¹ to assess the above 7 elements using a design of experiments approach. The hypothesis is that only one or two principal factors affect fretting corrosion.

Methods

A 2^7-2 design of experiment test (7 factors, ¼ factorial, n=32 total runs, 16 samples per condition per factor) was conducted. Factors included: Assembly Force (100, 4000N), Head Offset (1.5, 12 mm), Taper Locking Position (Mouth, Throat), Stem Taper Length (0.44, 0.54 in), Stem Taper Roughness (Ground, Ridged), Taper Diameter (9/10, 12/14), and Stem Material (CoCrMo, Ti-6Al-4V). The heads were CoCrMo coupled with taper coupons (DePuy Synthes, Warsaw, IN). Test components were assembled wet and seated axially with 100 or 4000N assembly force. The assemblies were immersed in PBS and potentiostatically held at −50mV vs. Ag/AgCl. Incremental cyclic loads were applied vertically to the head at 3Hz until a 4000N maximum load was reached (See Fig. 1). Fretting currents at 4000 N cyclic load were used for comparisons while other parameters, including onset load, subsidence, micromotion and pull off load were also captured. Statistical analysis was performed using Pareto charts and Student's T-tests for single factor comparisons (P < 0.05 was statistically significant).

Introduction

Failure rates of Metal-on-Metal (MoM) ASR XL hip implants have been unacceptably high compared with other bearing surfaces, so patients must be monitored over the time checking for disorders in clinical condition, blood tests or in diagnostic imaging.

Objectives

We have carried out a continuing prospective investigation to evaluate the relationship between blood metal ions measurements and ultrasound levels and to evaluate if ultrasound score can predict a future indication to revision.

Introduction

Perioperative dexamethasone has been shown to effectively reduce post-operative nausea and vomiting and aide in analgesia after total joint arthroplasty (TJA), however systemic glucocorticoid therapy is carries the theoretical risk of increased susceptibility to prosthetic joint infection (PJI), increased white blood cell (WBC) counts, and increased blood glucose levels. The purpose of this study is to determine the effect of dexamethasone on PJI, WBC count, and blood glucose levels in diabetic and non-diabetic patients undergoing TJA.

Methods

A retrospective chart review of all patients receiving primary total joint (hip or knee) arthroplasty between January 1, 2013 and December 31, 2015 (n = 1818) was conducted. The patients were divided into two main cohorts: those receiving dexamethasone (n = 1426) and those not receiving dexamethasone (n = 392); these groups were further subdivided into diabetic (n = 428 dexamethasone; n = 129 no dexamethasone) and non-diabetic patients (n = 998 dexamethasone, n = 263 no dexamethasone). The primary outcome was PJI; secondary measures included in (WBC) count, glucose levels, and days to infection. Statistics were carried out using chi-squared or ANOVA tests.

Introduction

Total Knee Arthroplasty (TKA) is highly successful in treatment of end-stage degenerative arthritis of the knee. CT-based Patient-Specific Instrumentation (PSI) utilizes a CT scan of the lower extremity to create a three-dimensional model of the patient's anatomy, plan the surgery, and provide unique patient-specific resection blocks for the surgery.

There are few published studies utilizing CT-PSI. The present study prospectively evaluates clinical, operative, and radiographic outcomes from 100 CT-based TKAs using this technology (MyKnee®, Medacta International S.A., Castel San Pietro, Switzerland).

Materials and Methods

100 consecutive eligible knees (94 patients) of the senior author underwent TKA using CT-based PSI technology. The primary outcome of the study was to compare the planned pre-operative femoral and proximal tibial resections to the actual intra-operative measured resections. Clinical outcomes included pre- and post-operative Knee Society Scores, Range-of-Motion (ROM, measured by goniometer), and complication data.

Pre- and 6-week post-operative long-leg standing radiographs were obtained to assess HKA alignment. The femoral component angle (FCA) in the coronal plane, the tibial component angle (TCA), and posterior slope of the tibia were also assessed. Additionally, 10 patients were selected at random to undergo a post-operative CT scan for comparison to radiographic measurements.

Introduction

Each year, a large number of total hip arthroplasties (THA) are performed, of which 60 % use cementless fixation. The initial fixation is one of the most important factors for a long lasting fixation [Gheduzzi 2007]. The point of optimal initial fixation, the endpoint of insertion, is not easy to achieve, as the margin between optimal fixation and a femoral fracture is small. Femoral fractures are caused by peak stresses induced during broaching or by the hammer blows when the implant is excessively press-fitted in the femur. In order to reduce the peak stresses during broaching, IMT Integral Medizintechnik (Luzern, Switzerland) designed the Woodpecker, a pneumatic broach that generates impulses at a frequency of 70 Hz. This study explores the feasibility of using the Woodpecker for implant insertion by measuring both the strain in the cortical bone and the vibrational response. An in vitro study is presented.

Material and Methods

A Profemur Gladiator modular stem (MicroPort Orthopedics Inc. Arlington, TN, USA) and two artificial femora (composite bone 4th generation #3403, Sawbones Europe AB, Malmö, Sweden) were used. One artificial femur was instrumented with three rectangular strain gauge rosettes (Micro-Measurements, Raleigh, NC, USA). The rosettes were placed medially, posteriorly and anteriorly proximally on the cortical bone. Five paired implant insertions were repeated on both artificial bones, alternating between standard hammering and Woodpecker insertions. During the insertion processes the vibrational response was measured at the implant and Woodpecker side (fig. 1) using two shock accelerometers (PCB Piezotronics, Depew, NY, USA). Frequency spectra were derived from the vibrational responses. The endpoint of insertion was defined as the point when the static strain stopped increasing during the insertion.

INTRODUCTION

During activities of daily living (ADL), varus moments are experienced in the knee, which can result in frontal plane rotation, or liftoff, of the lateral femoral condyle with respect to the tibial plateau. An understanding of this rotation is valuable as it could potentially lead to contact between the femoral component and polyethylene post of a total knee replacement (TKR). Therefore, the purpose of this study was 1) to assess how much frontal plane rotation was achieved due to varus moments imposed on a total stabilized (TS) TKR from the stair ascent activity, and 2) to determine whether a TS TKR could withstand the contact stresses imposed by the varus loading for 1 million cycles without the post fracturing or plastically deforming.

METHODS

A PS femoral component paired with a TS polyethylene insert and baseplate (Triathlon, Stryker, Mahwah, NJ) were aligned on a multi-axis testing system (MTS Systems Corp, Eden Prairie, MN) (Figure 1). Size 1 components were used as they represented the worst-case size for testing. The femoral component was fixed at 60 degrees of flexion, representing an angle of peak varus moment during stair ascent [1]. The peak varus moment used in this study was determined by scaling the data from Orthoload.com for a 136 kg patient body weight (3 SD above average TKR patient body weight) [1, 2].

In order to evaluate the frontal plane rotation achieved due to the varus moment with minimal influence from other loads, an FEA model of the physical test setup was used to determine the lowest joint compressive load that would allow testing to be stable. Given this, testing was completed with a constant joint compressive load of 1500 N (33% of that reported by Orthoload.com) while sinusoidally applying a varus moment from 5Nm to 54.5Nm [1, 2]. The loads were applied to three samples for 1 million cycles to represent the number of stair ascent cycles experienced over 20 years [3].

Lastly, a validation test was run on a component with the polyethylene post notched at the medial distal aspect. The post fractured during testing indicating that the test could induce the clinical failure mode of interest.

INTRODUCTION

As computer navigated surgery continues to progress to the forefront of orthopedic care, the application of a navigated total shoulder arthroplasty has yet to appear. However, the accuracy of these systems is debated, as well as the dilemma of placing an accurate tool in an inaccurate hand. Often times a system's accuracy is claimed or validated based on postoperative imaging, but the true positioning is difficult to verify. In this study, a navigation system was used to preoperatively plan, guide, and implant surrogate shoulder glenoid implants and fiducials in nine cadaveric shoulders. A novel method to validate the position of these implants and accuracy of the system was performed using pre and post operative high resolution CT scans, in conjunction with barium sulfate impregnated PEEK surrogate implants.

METHODS

Nine cadaveric shoulders were CT scanned with .5mm slice thickness, and the digital models were incorporated into a preoperative planning software. Five orthopedic shoulder specialists used this software to virtually place aTSA and rTSA glenoid components in two cadavers each (one cadaver was omitted due to incomplete implantation), positioning the components as they best deemed fit. Using a navigation system, each surgeon registered the native cadaveric bone to each respective CT. Each surgeon then used the navigation system to guide him or her through the total shoulder replacement, and implant the barium sulfate impregnated PEEK surrogate implants. Four cylindrical PEEK fiducials were also implanted in each scapula to help triangulate the position of the surrogate implants. Previous efforts were attempted with stainless steel alloy fiducials, but position and image accuracy were limited by CT artifact. BaSO₄ PEEK provided the highest resolution on a postoperative CT with as little artifact as possible. All PEEK fiducials and surrogate implants were registered by probing points and planes with the navigation system to capture the digital position. A high resolution post operative CT scan of each specimen was obtained, and variance between the executed surgical plan and PEEK fiducials was calculated.

Background

The optimal surgical treatment for osteonecrosis of the femoral head has yet to be elucidated. To evaluate the role of femoral fixation techniques in hip resurfacing, we present a comparison of the results for two consecutive groups: Group 1 (75 hips) received hybrid hip resurfacing implants with a cemented femoral component; Group 2 (103 hips) received uncemented femoral components. Both groups received uncemented acetabular components.

Methods

We retrospectively analyzed our clinical database to compare failures, reoperations, complications, clinical results, metal ion test results, and x-ray measurements. Using consecutive groups caused time interval bias, so we required all Group 2 patients be at least two years out from surgery; we compared results from two years and final follow-up.

Purpose

Traditionally, an inpatient hospital stay has been required for joint replacement surgery. The three primary drivers of cost for joint replacement have been implant cost, other hospital charges and postoperative rehabilitation costs. The three primary reasons that have made hospitalization necessary are pain control, blood loss / transfusion, and monitoring patients with comorbidities. Advances in surgical technique, implants, comprehensive blood management, and multimodal pain management have allowed a marked reduction in the hospital stay required and have eliminated the need for extensive formal rehabilitation. The purpose of this study is to evaluate if hip resurfacing can be performed safely and cost-effectively as an outpatient procedure.

Methods

We present the short-term outcome of our first 125 hip resurfacings done as an outpatient procedure performed by two experienced surgeons. Young patients without major medical co-morbidities were selected. The average age was 53±7 years old (range: 38 to 66), there were 98 men and 27 women. The mean ASA score was 1.7±0.5 (range 1 to 3). The diagnosis was OA in 92, dysplasia in 22, and osteonecrosis in 9, and trauma in 2. There were no major complications noted in the first 6 weeks postoperative. There was one ER visit, and there were no hospitalizations required.

Introduction

Since the introduction of modular hip taper junctions, corrosion has been studied yet the clinical effect remains unclear. Mechanically assisted corrosion and crevice corrosion are thought to be the primary clinical processes driving taper corrosion. Like all corrosion reactions, these processes require the taper junction to be in contact with an electrolyte. This study investigates the effect of sealing the taper junction from the environment on the mechanically-induced corrosion of a modular hip taper junction.

Methods

A short-term corrosion fatigue test was conducted with Ti6Al4V 12/14 taper coupons coupled with CoCrMo 12/14 taper 28mm+12 heads (DePuy Synthes, Warsaw, IN). Ten specimens were assembled with a 1.1 kN press load and sealed with silicone sealant (Dow-Corning 732 Multi-Purpose Sealant). Prior to assembly five of these specimens were assembled with the taper junction having been wetted with phosphate buffered saline before assembly; the rest were assembled dry. Specimens were then immersed in phosphate buffered saline and a potentiostat was used to maintain the potential of the specimen at −50mV vs. Ag/AgCl. Incrementally larger loads were applied to the head of the specimen until a 4000N maximum load was reached. The average currents generated during this test was used to assess the corrosion performance of the specimens. The data from the sealed specimens was compared to a control group, which were wetted before assembly but not sealed.

Introduction

The corrosion of modular taper junctions in hip implants is becoming an area of increased research focus. Many design factors have been hypothesized to contribute to this kind of corrosion. The authors' previous research indicated femoral stem taper roughness may influence taper corrosion. The purpose of this study is to determine whether taper roughness significantly affects taper performance.

Methods

A 2² design of experiment was conducted with Ti6Al4V 12/14 taper coupons coupled with CoCrMo 12/14 taper 28mm+12 heads (DePuy Synthes, Warsaw, IN) with n=3 samples per test run for a total of 12 samples. The femoral heads and taper coupons were manufactured with “smooth” finishes ranging from R_t 100–200 µin and “rough” finishes ranging from R_t 900–1000 µin. Test components were assembled wet (dipped in saline solution and drained) and pressed together with a 4400 N assembly force. The assemblies were immersed in phosphate buffered saline and a potentiostat was used to maintain the potential of the specimen at −50mV vs. Ag/AgCl. Incrementally larger cyclic loads were applied vertically to the head at 3Hz until a 4000N maximum load was reached, then this cyclic load was maintained for an additional 1 million cycles.

Introduction

Geometric variations of the hip joint can give rise to abnormal joint loading causing increased stress on the articular cartilage, which may ultimately lead to degenerative joint disease. In-vitro simulations of total hip replacements (THRs) have been widely reported in the literature, however, investigations exploring the tribology of two contacting cartilage surfaces, and cartilage against metal surfaces using complete hip joint models are less well reported.

The aim of this study was to develop an in-vitro simulation system for investigating and comparing the tribology of complete natural hip joints and hemiarthroplasties with THR tribology. The simulation system was used to assess natural porcine hip joints and porcine hemiarthroplasty hip joints. Mean friction factor was used as the primary outcome measure to make between-group comparisons, and comparisons with previously published tribological studies.

Method

In-vitro simulations were conducted on harvested porcine tissue. A method was developed enabling natural acetabula to be orientated with varying angles of version and inclination, and natural femoral heads to be potted centrally with different orientations in all three planes. Acetabula were potted with 45° of inclination and in the complete joint studies, natural femoral heads were anatomically matched and aligned (n=5). Hemiarthroplasty studies (n=5) were conducted using cobalt chrome (CoCr) heads mounted on a spigot (Figure 1), size-matched to the natural head. Natural tissue was fixed using PMMA (polymethyl methacrylate) bone cement.

A pendulum friction simulator (Simulator Solutions, UK), with a dynamic loading regime of 25–800N, ± 15° flexion-extension (FE) at 1 Hertz was used. The lubricant was a 25% (v/v) bovine serum. Axial loading and motion was applied through the femoral head and frictional torque was measured using a piezoelectric transducer, from which the friction factor was calculated.

Introduction

Contact between the femoral head and rim of the acetabular liner in total hip replacements has been linked to adverse tribological performance that may potentially shorten the lifespan of the prosthesis. Predicting the size and location of the contact area can be done computationally, however, experimental validation of these models is challenging due to the conforming nature of the bearing surfaces.

This study aimed to develop a method of accurately determining the in-vitro contact area between the femoral head and acetabular cup in metal-on-polyethylene and ceramic-on-polyethylene bearings under different component orientations.

Method

Metal-on-polyethylene and ceramic-on-polyethylene samples, with a nominal diameter of 36mm (DePuy Synthes, Leeds, UK), were tested with the cups orientated using a combination of inclination (equivalent to 45°, 55° and 65° in-vivo) and version (−20°, 0°, 20° and 40°) angles. The liners, which were first gold hard-coated (EMSCOPE SC 500, Quarum Technologies, UK), were inserted into a Pinnacle^® titanium shell, and femoral heads were mounted on a vertical spigot (Figure 1). A single-station multi-axis electromechanical hip joint simulator (Prosim, Simulator Solutions, UK) was used to position the samples with 18.7° flexion, 6.2° adduction and 8.3° external rotation, congruous with just after heel strike (ISO 14242-1), and apply a 3kN static axial load through the centre of the femoral head.

The contact area was generated by manually turning the head about the vertical axis of the centre of rotation of the applied load, removing the gold hard-coating from the contacting areas. The contact area was determined from photographs of the acetabular cup using SolidWorks (Dassault Systèmes, US) and ImageJ (National Institutes of Health, US) software packages. Three repeats under each combination of cup angles were completed, and the mean contact area and 95% confidence limits were determined for each bearing under all cup angle combinations.

Introduction

It has been shown in vitro that human monocytes can phagocytose submicron polyethylene wear particles generated from total hip arthroplasties (THA) with highly cross-linked polyethylene inlays. The aim of our study was to detect the presence and possible phagocytosis of such particles in peripheral blood monocytes of patients with respective THA.

Patients and methods

All patients were operated using the same implant, the cementless SL Plus stem; Bicon cup and a cross-linked polyethylene insert Rexpol (Smith and Nephew). Besides clinical and radiographic check-up, blood samples were collected at follow-up and analyzed by flow cytometry. Polyethylene can be identified by its auto fluorescence when stimulated by a laser with the wavelength of fluorescein isothiocyanate (FITC). Presence of wear particles in monocytes was identified by determination of their size and granularity. Some samples were scrutinized by confocal laser scanning microscopy to correlate the intracellular position of the particles. Blood samples of patients without total joint replacement served as controls.