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Orthopaedic Proceedings
Vol. 106-B, Issue SUPP_5 | Pages 21 - 21
23 Apr 2024
Brown N King S Taylor M Foster P Harwood P
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Introduction

Traditionally, radiological union of fractures treated with an Ilizarov frame is confirmed by a period of dynamization - destabilisation of the frame for a period prior to removal. Reduced clinic availability during the COVID-19 pandemic caused a shift to selective dynamisation in our department, whereby lower risk patients had their frames removed on the same day as destabilisation. This study investigates the effects of this change in practice on outcomes and complication rates.

Materials & Methods

Adult patients treated with circular frames between April 2020 and February 2022 were identified from our Ilizarov database. Patients were divided into 2 groups: - “dynamised” if their frame was destabilised for a period to confirm union prior to removal; or “not dynamised” if the decision was taken to remove the frame without a period of dynamisation, other than a short period in the clinic. A retrospective review of clinical notes was conducted to determine outcome.


Bone & Joint Open
Vol. 4, Issue 1 | Pages 3 - 12
4 Jan 2023
Hardwick-Morris M Twiggs J Miles B Al-Dirini RMA Taylor M Balakumar J Walter WL

Aims

Iliopsoas impingement occurs in 4% to 30% of patients after undergoing total hip arthroplasty (THA). Despite a relatively high incidence, there are few attempts at modelling impingement between the iliopsoas and acetabular component, and no attempts at modelling this in a representative cohort of subjects. The purpose of this study was to develop a novel computational model for quantifying the impingement between the iliopsoas and acetabular component and validate its utility in a case-controlled investigation.

Methods

This was a retrospective cohort study of patients who underwent THA surgery that included 23 symptomatic patients diagnosed with iliopsoas tendonitis, and 23 patients not diagnosed with iliopsoas tendonitis. All patients received postoperative CT imaging, postoperative standing radiography, and had minimum six months’ follow-up. 3D models of each patient’s prosthetic and bony anatomy were generated, landmarked, and simulated in a novel iliopsoas impingement detection model in supine and standing pelvic positions. Logistic regression models were implemented to determine if the probability of pain could be significantly predicted. Receiver operating characteristic curves were generated to determine the model’s sensitivity, specificity, and area under the curve (AUC).


Orthopaedic Proceedings
Vol. 103-B, Issue SUPP_2 | Pages 43 - 43
1 Mar 2021
Casper-Taylor M Wilkinson G Fermor H Wilcox R Mengoni M
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Abstract

Objectives

Osteochondral grafting (OCG) is one treatment strategy for osteoarthritis with good clinical results. Decellularised tissues provide a promising alternative to standard autografts or allografts. This study aimed to compare the stability of traditional OCG and decellularised scaffolds upon initial implantation.

Methods

Host cubes (N=16) were extracted from porcine femoral condyles around an artificial defect hole. Grafts (N=11) were harvested from the trochlear groove; porcine decellularized osteochondral scaffold (N=5) were prepared. Each host was secured in fixtures and submerged in PBS at 37 ºC. Each graft or scaffold was press fit into one of the hosts, then pushed in for 5 mm, using an indenter (Instron3365) and pushed out in the opposite direction for 10 mm. Parameters analysed were the force required to initiate movement (Dislodging Force) and the maximum force (Max Force).


The Bone & Joint Journal
Vol. 103-B, Issue 2 | Pages 279 - 285
1 Feb 2021
Ferguson D Harwood P Allgar V Roy A Foster P Taylor M Moulder E Sharma H

Aims

Pin-site infection remains a significant problem for patients treated by external fixation. A randomized trial was undertaken to compare the weekly use of alcoholic chlorhexidine (CHX) for pin-site care with an emollient skin preparation in patients with a tibial fracture treated with a circular frame.

Methods

Patients were randomized to use either 0.5% CHX or Dermol (DML) 500 emollient pin-site care. A skin biopsy was taken from the tibia during surgery to measure the dermal and epidermal thickness and capillary, macrophage, and T-cell counts per high-powered field. The pH and hydration of the skin were measured preoperatively, at follow-up, and if pin-site infection occurred. Pin-site infection was defined using a validated clinical system.


The Bone & Joint Journal
Vol. 101-B, Issue 4 | Pages 415 - 425
1 Apr 2019
Thewlis D Bahl JS Fraysse F Curness K Arnold JB Taylor M Callary S Solomon LB

Aims

The purpose of this exploratory study was to investigate if the 24-hour activity profile (i.e. waking activities and sleep) objectively measured using wrist-worn accelerometry of patients scheduled for total hip arthroplasty (THA) improves postoperatively.

Patients and Methods

A total of 51 THA patients with a mean age of 64 years (24 to 87) were recruited from a single public hospital. All patients underwent THA using the same surgical approach with the same prosthesis type. The 24-hour activity profiles were captured using wrist-worn accelerometers preoperatively and at 2, 6, 12, and 26 weeks postoperatively. Patient-reported outcomes (Hip Disability and Osteoarthritis Outcome Score (HOOS)) were collected at all timepoints except two weeks postoperatively. Accelerometry data were used to quantify the intensity (sedentary, light, moderate, and vigorous activities) and frequency (bouts) of activity during the day and sleep efficiency. The analysis investigated changes with time and differences between Charnley class.


Orthopaedic Proceedings
Vol. 100-B, Issue SUPP_8 | Pages 12 - 12
1 May 2018
Anathalee Y Foster P Taylor M Wilks D Wiper J Harwood P
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Background

To improve patient pathways we have, in selected patients, begun to acutely apply circular (rather than temporary monolateral) fixators with simultaneous or subsequent soft tissue closure. We present early results.

Methods

Adult patients treated using an Ilizarov frame prior to soft tissue management were identified from our Ilizarov database. This data was supplemented by medical record review.


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_20 | Pages 59 - 59
1 Dec 2017
Theodore W Little J Liu D Bare J Dickison D Taylor M Miles B
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Despite of the high success of TKA, 20% of recipients remain dissatisfied with their surgery. There is an increasing discordance in the literature on what is an optimal goal for component alignment. Furthermore, the unique patient specific anatomical characteristics will also play a role. The dynamic characteristic of a TKR is a product of the complex interaction between a patient's individual anatomical characteristics and the specific alignment of the components in that patient knee joint. These interactions can be better understood with computational models. Our objective was to characterise ligament characteristics by measuring knee joint laxity with functional radiograph and with the aid of a computational model and an optimisation study to estimate the subject specific free length of the ligaments.

Pre-operative CT and functional radiographs, varus and valgus stressed X-rays assessing the collateral ligaments, were captured for 10 patients. CT scan was segmented and 3D–2D pose estimation was performed against the radiographs. Patient specific tibio-femoral joint computational model was created. The model was virtually positioned to the functional radiograph positions to simulate the boundary conditions when the knee is stressed. The model was simulated to achieve static equilibrium. Optimisation was done on ligament free length and a scaling coefficient, flexion factor, to consider the ligaments wrapping behaviour.

Our findings show the generic values for reference strain differ significantly from reference strains calculated from the optimised ligament parameters, up to 35% as percentage strain. There was also a wide variation in the reference strain values between subjects and ligaments, with a range of 37% strain between subjects. Additionally, the knee laxity recorded clinically shows a large variation between patients and it appears to be divorced from coronal alignment measured in CT. This suggests the ligaments characteristics vary widely between subjects and non-functional imaging is insufficient to determine its characteristics. These large variations necessitate a subject-specific approach when creating knee computational models and functional radiographs may be a viable method to characterise patient specific ligaments.


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_13 | Pages 15 - 15
1 Jun 2017
Messner J Johnson L Perera N Taylor M Harwood P Britten S Foster P
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We analysed the functional and psychological outcomes in children and adolescents with complex tibial fractures treated with the Ilizarov method at our frame unit.

An observational study with prospective data collection and retrospective analysis of clinical data was undertaken. Patients younger than 18 years and an open physis were included. The Ilizarov method (combined with percutaneous screw fixation in physeal injuries) was applied and immediate weightbearing recommended.

Sixty four patients (50 male, 14 female) aged between 4 and 17 years were admitted to our Major Trauma Centre from 2013 until 2016 (25 tertiary referrals). Thirty one (48%) patients were involved in road traffic accidents, 12 (19%) sustained injuries in full contact sports. The average weight was 51 kg (range 16–105 kg). Twenty three open tibial fractures (14 Gustilo 3A and 9 Gustilo 3B) and 15 associated physeal injuries were treated among a cohort of closed tibial fractures with significant displacement (10 failed conservative treatment prior to frame treatment).

We report a 100% union rate with a median hospital stay of 4 days (range 2–19) and a median frame time of 105 days (range 62–205 days). Malunions (> 5 degrees in any plane) were not observed. Three patients required bone transport. At the time of submission, 70% of patients and their parents reported functional outcomes using the Paediatric Quality of Life Inventory (PedsQL) at minimum six months post frame. The PedsQLTM 4.0 Generic Core Scales are comprised of parallel child self-report and parent proxy-report formats. Children's physical average scores were 79 out of 100 and average psychosocial scores were 80 out of 100 and for parent average physical scores were 78 out of 100 and the same for parent average psychosocial scores. These results suggest high levels of quality of life on the PedsQL. The median visual analogue health score (0–100) was 81 out of 100 (71–100), median Lysholm knee scores 98 (range 49–100) and median Olerud & Molander ankle scores 75 (range 40 – 100).

Regardless of age, weight and soft tissue damage and complexity of fracture pattern, the Ilizarov method has shown to be safe and effective treating tibial fractures in the paediatric and adolescent population admitted to our Major Trauma Centre. Furthermore, patients reported high physical and psychosocial functioning following treatment.

Level of evidence: IV (case series)


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_13 | Pages 16 - 16
1 Jun 2017
Giannoudis V Ewins E Foster P Taylor M Harwood P
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Introduction

Distal tibial fractures are notoriously difficult to treat and a lack of consensus remains on the best approach. This study examined clinical and functional outcomes in such patients treated definitively by circular external fixation (Ilizarov). Patients and Methods: Between July 2011 and May 2016, patients with fractures extending to within 1 muller square of the ankle were identified from our prospective Ilizarov database. Existing data was supplemented by review of clinical records. Fractures were classified according to the AO/OTA classification. Functional outcome data, including general measures of health related quality of life (SF-12 and Euroqol) and limb specific scores (Olerud and Molander Score and Lysholm scores) had been routinely collected for part of the study period. Patients in whom this had not been collected were asked to complete these by post. Adverse events were documented according to Paley's classification of: problems, obstacles and complications.

Results

142 patients with 143 fractures were identified, 40 (28%) were open, 94 (66%) were intra-articular, 85 (59%) were tertiary referrals. 32% were type 1, 28%, type 2 and 40% type 3 AO/OTA severity. 139 (97%) of the fractures united (2 non-unions, 1 amputation and 2 delayed unions who remain in frames), at a median of 165 days (range 104 to 429, IQR 136 to 201). 62% united by 6 months, 87% by 9 months and 94% by 1 year. Both non-unions have united with further treatment. Closed fractures united more rapidly than open (median 157 vs 185 days; p=0.003) and true Pilon (43C3) fractures took longer to unite other fractures (median 156 vs 190 days; p<0.001).

34% of patients encountered a problem, 12% an obstacle and 10% a complication. Of the complications, 6 (4%) were minor, 5 (3.5%) major not interfering with the goals of treatment and 4 (3%) major interfering with treatment goals (including the 2 patients with non-union and 1 who underwent amputation as well as 1 significant mal-union). This will increase to 4% if the 2 delayed unions fail to unite. Overall 56% reported good or excellent ankle scores at last report, 28% fair and 16% poor. Closed, extra-articular and non-43C3 fractures had better functional outcome scores than open, intra-articular and 43C3 fractures respectively.


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_3 | Pages 6 - 6
1 Feb 2017
Al-Dirini R Huff D Taylor M
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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].


Orthopaedic Proceedings
Vol. 99-B, Issue SUPP_3 | Pages 7 - 7
1 Feb 2017
Al-Dirini R Huff D O'Rourke D Taylor M
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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].


Orthopaedic Proceedings
Vol. 98-B, Issue SUPP_7 | Pages 12 - 12
1 May 2016
Al-Dirini R Taylor M O'Rourke D Huff D
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Introduction

Primary stability is essential for long-term performance of cementless femoral components. There is debate as to whether collars contribute to primary stability. The results from experimental studies and finite element (FE) analysis have been variable and contradictory. Subtle differences in performance are often swamped by variation between cadaveric specimens in vitro, whereas FE studies tend to be performed on a single femur. However, FE studies have the potential to make comparisons of implant designs within the same cohort of femurs, allowing for subtle performance differences to be identified if present. This study investigates the effect of a collar on primary stability of a femoral prosthesis across a representative cohort of femurs.

Materials and Methods

FE models were generated from QCT scans of eight cadaveric femurs taken from the Melbourne Femur Collection (4 male and 4 female; BMI: 18.7 – 36.8 kg.m-2; age: 59 – 80 years) which were of joint replacement age. Heterogeneous bone material properties were assigned based on the CT greyscale information. Each femur was implanted with the collared and collarless version of Corail femoral stem (DePuy, Leeds, United Kingdom). The stems were sized and positioned so that the prosthesis filled the medullary canal with minimal gap between the prosthesis and the inner boundary of the cortical bone. The peak muscle and joint contact forces associated with level gait were applied and the distal femur was rigidly fixed. The forces were scaled based on the body weight for each subject. Micromotion, as well as microstrains at the bone-prosthesis interface were measured for each subject. Paired t-test was run to compare the micromotion and the microstrains measured for the collared and collarless prosthesis.


Orthopaedic Proceedings
Vol. 98-B, Issue SUPP_4 | Pages 95 - 95
1 Jan 2016
Teeter M Parikh A Taylor M Vandekerckhove P Sprague J Naudie D
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We sought to determine what dimensional changes occurred from wear testing of a total knee implant, as well as whether any changes developed within the polyethylene subsurface. Three fixed bearing implants underwent wear simulator testing to 6.1 million cycles. Gravimetric analysis and micro-CT scans were performed pre-test, mid-test, and post-test. Wear volume and surface deviations were greater during 0–3.2 million cycles (91±12 mm3) than from 3.2–6.1 million cycles (52±18 mm3). Deviations (wear and creep) occurred across all surfaces of the tibial inserts, including the articular surface, backside surface, sides, and locking mechanism. No subsurface changes were found. The micro-CT results were a useful adjunct to gravimetric analysis, better defining the dimensional changes that occurred with testing and ruling out subsurface fatigue.


Orthopaedic Proceedings
Vol. 95-B, Issue SUPP_34 | Pages 57 - 57
1 Dec 2013
Fitzpatrick CK Hemelaar P Taylor M
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Introduction:

Primary stability is crucial for long-term fixation of cementless tibial trays. Micromotion less than 50 μm is associated with stable bone ingrowth and greater than 150 μm causes the formation of fibrous tissue around the implant [1, 2]. Finite element (FE) analysis of complete activities of daily living (ADL's) have been used to assess primary stability, but these are computationally expensive. There is an increasing need to account for both patient and surgical variability when assessing the performance of total joint replacement. As a consequence, an implant should be evaluated over a spectrum of load cases. An alternative approach to running multiple FE models, is to perform a series of analyses and train a surrogate model which can then be used to predict micromotion in a fraction of the time. Surrogate models have been used to predict single metrics, such as peak micromotion. The aim of this work is to train a surrogate model capable of predicting micromotion over the entire bone-implant interface.

Methods:

A FE model of an implanted proximal tibia was analysed [3] (Fig. 1). A statistical model of knee kinetics, incorporating subject-specific variability in all 6-DOF joint loads [4], was used to randomly generate loading profiles for 50 gait cycles. A Latin Hypercube (LH) sampling method was applied to sample 6-DOF loads of the new population throughout the gait cycle. Kinetic data was sampled at 10, 50 and 100 instances and FE predictions of micromotion were calculated and used to train a surrogate model capable of describing micromotion over the entire bone-implant interface. The surrogate model was tested for an unseen gait cycle and the resulting micromotions were compared with FE predictions.


Orthopaedic Proceedings
Vol. 95-B, Issue SUPP_34 | Pages 183 - 183
1 Dec 2013
Teeter M Parikh A Taylor M Sprague J Naudie D
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BACKGROUND:

Implant wear continues to be a limitation of total knee replacement (TKR). Wear simulator studies are a valuable screening tool in new implant development. The purpose of this study was to determine the ability of micro-CT to prospectively measure wear in TKR implants during a wear simulator trial.

METHODS:

Three identical cruciate-retaining, fixed bearing cobalt-chromium-molybdenum (CoCrMo) on conventional EtO-sterilized polyethylene TKA implants underwent wear simulator testing up to 3.2 million cycles using gait inputs; loaded-soaks were used to correct for fluid absorption. The implants were weighed and scanned with micro-CT (at 50 micron resolution) before and after testing. The gravimetric mass was converted to volume based on the density of polyethylene. Volume change due to wear was calculated from both the gravimetric and micro-CT methods. The pre- and post-wear test micro-CT geometries were co-registered and the deviations between the two were measured.


Orthopaedic Proceedings
Vol. 95-B, Issue SUPP_13 | Pages 7 - 7
1 Mar 2013
Worsley P Whatling G Holt C Bolland B Barrett D Stokes M Taylor M
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The aim of this study was to perform a comprehensive evaluation of the changes in function from pre- to post-surgery in total and unilateral knee arthroplasty (UKA/TKA) patients. Twenty healthy (age 62.4 ±5.9, 11 male), 14 UKA (age 60.9 ±10.1, 8 male) and 17 TKA (age 67.2 ±8.1, 9 male) patients were studied. KA patients were assessed four weeks pre- and six months post-operation. Measures of perceived pain and function were collected using Oxford Knee Score (OKS) questionnaire. Tests of objective function included joint range of motion (RoM), ultrasound imaging, and 3-D motion analysis/inverse modelling from gait and sit-stand. An optimal set of variables was used to classify KA function using the Cardiff DST method. Pre-KA and healthy individuals were accurately classified (96%). Post-operation questionnaire measures of function improved for both UKA and TKA groups. However, observed measures of RoM, muscle atrophy and gait had only limited gains. This resulted in 57% of UKA and only 27% of TKA patients being classified as healthy post-operation. The results of this study show that 6 months post-surgery UKA patients had higher function than TKA. Using statistical approaches to combine functional assessments has provided an accurate platform to classify function and estimate changes from pre- to post-surgery. The clinical application of this tool requires further investigation and comparison to commonly used clinical techniques.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXVIII | Pages 48 - 48
1 Jun 2012
Marsh A Knox D Murray O Taylor M Bayer J Hendrix M
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Post-operative regimes involving the use of intra-articular local anaesthetic infiltration may allow early mobilisation in patients undergoing total knee arthroplasty. Few studies have evaluated such regimes outside specialist arthroplasty units. We aimed to determine whether an enhanced recovery programme including the use of local anaesthetic administration could be adapted for use in a district general setting.

Following introduction of this regime to our unit, 100 consecutive patients undergoing primary total knee arthroplasty were reviewed. 56 patients underwent a standard analgesic regime involving a general or spinal anaesthetic and oral analgesics post operatively (group1). 48 patients underwent the newly introduced regime, which included pre-operative counselling, peri-articular local anaesthetic infiltration at operation and intra-articular local anaesthetic top-up administration post-operatively for 24 hours (group 2). Length of stay, post-operative analgesic requirements, and range of knee motion post-operatively were compared.

Median length of stay was less for patients in group 2 compared with those in group 1 (4 days compared to 5 days, p<0.05). Patients in group 2 required lower total doses of opiate analgesia post-operatively. 90% of patients in group 2 were ambulant on the first post operative day, compared with less than 25% of patients in group 1. Mean knee flexion on discharge was greater in patients in group 2 compared with those in group 1 (85 degrees compared with 75 degrees). No infective complications from intra-articular catheter placement were observed. However, technical difficulties were encountered during the introduction period, including loss of catheter placement, leakage of local anaesthetic and adaptation of nursing time for top-up anaesthetic administration.

A rehabilitation regime involving local anaesthetic infiltration for total knee arthroplasty can successfully be adapted for use in a district general setting. Our results suggest if initial technical difficulties are overcome, this regime can provide effective postoperative analgesia, early mobilisation and reduced hospital stay.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXV | Pages 241 - 241
1 Jun 2012
Taylor M
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Introduction

Cementless tibial fixation has been used for over 30 years. There are several potential advantages including preservation of bone stock and ease of revision. More importantly, for young active patients there is the potential for increased longevity of fixation. However, the clinical results have been variable, with reports of extensive radiolucent lines, rapid early migration and aseptic loosening. Problems appear to stem from a failure to become sufficiently osseointegrated, which in turn suggests a lack of primary stability. In order to achieve boney ingrowth, interface micromotions should be less than 50 microns, whereas fibrous tissue formation is known to occur if micrmotions are in excess of 150 microns. The degree of micromotion at the bone-implant interface are dependent on the kinematics and kinetics of the replaced joint. Finite element analyses has been used to assess primary stability, however, it is becoming increasing difficult to differentiate performance. The aim of this study was too examine the micromotion for a variety of different activities for three commercially available tibial tray designs.

Methods

A finite element model of the implanted proximal tibia was generated form CT scans of a 72 year old male and material properties were assigned based on the Hounsfield units. Three tray designs were evaluated: LCS, Duofix and Sigma (DePuy Inc, Warsaw USA). The implants were assumed to be debonded, with a coefficient of friction of 0.4 applied to the bone-implant interface except for the porous coated region of the Duofix design, which was assumed to be 0.6. The distal portion the tibia was rigidly constrained. Five activities were simulated based on data from Orthoload.com (patient K1L) including walking, stair ascent, stair descent, sitting down and a deep knee bend. The three force and three moment time histories were discritised to give between 44 and 48 individual load steps. Custom written scripts were used to generate composite peak micromotion plots, which report the peak micromotion that occurs at each point of the contact surface during the gait cycle. The primary stability was then assessed by reporting the maximum micromotion, the average peak micromotion and the percentage of the contact area experiencing micromoitons less than 50 microns.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXV | Pages 69 - 69
1 Jun 2012
Galloway F Seim H Kahnt M Nair P Worsley P Taylor M
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Introduction

The number of total knee joint replacements has increased dramatically, from 28,000 in 2004 to over 73,000 in 2008 in the UK. This increase in procedures means that there is a need to assess the performance of an implant design in the general population. For younger, more active patients, cementless tibial fixation is an attractive alternative means of fixation and has been used for over 30 years. However, the clinical results with cementless fixation have been variable, with reports of extensive radiolucent lines, rapid early migration and aseptic loosening [1]. This study investigates the inter-patient variability of bone strain at the implant-bone interface of 130 implanted tibias over a full gait cycle.

Methods

A large scale FE study of a full gait cycle was performed on 130 tibias implanted with a cementless tibia tray (PFC Sigma, DePuy Inc, USA). A population of tibias was generated from a statistical shape and intensity (SSI) model [2].

The tibia tray was automatically positioned and implanted using ZIBAmira (Zuse Institute Berlin, Germany). Cutting and implanting were performed using Boolean operations on the meshed surfaces of the tibia and implant. After generation of a volume mesh from the resulting surface, the bone modulus was mapped onto the new mesh.

The FE models were processed in Abaqus (SIMULIA, RI, USA). Associated force data (axial, anterior-posterior and medial-lateral forces and flexion-extension, varus-valgus and internal-external moments) was sampled from a statistical model of the gait cycle derived from musculoskeletal modelling of 20 elderly healthy subjects. Patient weight was estimated using the length of the tibia and a BMI sampled from NHANES data.

Loads were applied to four groups of nodes on the tibia tray (anterior, posterior, medial and, lateral) for 51 steps in the gait cycle. The bone and implant were assumed to be bonded, simulating the osseointegrated condition.


Orthopaedic Proceedings
Vol. 93-B, Issue SUPP_IV | Pages 473 - 473
1 Nov 2011
Mavrogordato M Taylor M Taylor A Browne M
Full Access

The Acoustic Emission (AE) technique has been described as possessing ‘many of the qualities of an ideal damage-monitoring technique’, and the technique has been used successfully in recent years to aid understanding of failure mechanisms and damage accumulation in bone cement during de-bonding of the cement-metal interface fatigue loading, pre-load cracking during polymerisation and to describe and locate damage within an entire stem construct. However, most investigations to date have been restricted to in-vitro testing using surface mounted sensors. Since acoustic signals are attenuated as they travel through a material and across interfaces, it is arguable that mounting the sensors on the bone surface to investigate damage mechanisms occurring within the bone cement layer is not ideal. However, since direct access to the bone cement layer is not readily available, the bone surface is often the only practical option for sensor positioning.

This study has investigated the potential for directly embedding AE sensors within the femoral stem itself. This enables a permanent bond between the sensor and structure of interest, allows closer proximity of the sensor to the region of interest, and eliminates potential complications and variability associated with fixing the sensor to the sample. Data is collected during in-vitro testing of nominal implanted constructs, and information from both embedded and externally mounted AE sensors are compared and corroborated by microComputed Tomography (micro-CT) images taken both before and after testing.

The use of multiple AE sensors permitted the location as well as the chronology of damage events to be obtained in real time and analysed without the need for test interruption or serial sectioning of the test samples. Parametric analysis of the AE signal characteristics enabled those events likely to be associated with cracking as opposed to interfacial rubbing or de-bonding to be differentiated and it was shown that the embedded sensors gave a closer corroboration to observed damage using micro-CT and were less affected by unwanted sources of noise.

The results of this study have significant implications for the use of AE in assessing the state of total hip replacement (THR) constructs both in-vitro and potentially in-vivo. Incorporating the sensors into the femoral stem during in-vitro testing allows for greater repeatability between tests since the sensors themselves do not need to be removed and re-attached to the specimen. To date, all in-vivo studies attempting to use the AE technique to monitor the condition of any replacement arthroplasty device have used externally mounted sensors and suffered from the attenuation of acoustic information through flesh and skin. It is hypothesised that the use of directly embedded AE sensors may provide the first steps towards an in-vivo, cost effective, user friendly, non-destructive system capable of continuously monitoring the condition of the implanted construct and locating the earliest incidences of damage initiation.