The increasing incidence of periprosthetic femoral fractures (PFF) after total hip arthroplasty presents growing concerns due to challenges in treatment and increased mortality. PFF are often observed when the prosthesis is implanted in varus, especially with blade-type stems. To help elucidate its impact on the PFF risk, the specific research question is: What is the effect of misalignment of a blade-type stem (resulting in down-sized prosthesis) on 1)the distribution and magnitude of cortical stresses and 2)implant-bone micromotion. We developed two finite element models consisting of an average female femur implanted within a generic blade-type stem prosthesis, (i)in neutral alignment, and (ii)oriented in 5° of varus, coupled with corresponding down-sizing of the prosthesis. Each model consisted of 1.1million elements, while the average mesh length at the implant-bone interface was 0.4mm. Elastic moduli of 15GPa(cortex), 150MPa(trabecular bone), and 121GPa(implant), and Poisson's ratio of 0.3 were assumed. The distal end was fixed and the interface was defined as a surface-to-surface contact with friction coefficients (dynamic 0.3; static 0.4). Walking and stair-climbing were simulated by loading the joint contact and muscle forces after scaling to the subjects’ body weight. The peak von Mises stress and the average stress within the surface having 1cm diameter and the center at where the peak stress occurred at each contacting area, the interfacial micromotion along medial, lateral side were analyzed. For statistical analysis, two-tailed t-test was performed between the neutral and varus cases over four loading cycles with significance level of p<0.05.INTRODUCTION
METHOD
In theory, Finite Element Analysis (FEA) is an attractive method for elucidating the mechanics of modular implant junctions, including variations in materials, designs, and modes of loading. However, the credence of any computational model can only be established through validation using experimental data. In this study we examine the validity of such a simulation validated by comparing values of interface motion predicted using FEA with values measured during experimental simulation of stair-climbing. Two finite element models (FEM) of a modular implant assembly were created for use in this study, consisting of a 36mm CoCr femoral head attached to a TiAlV rod with a 14/12 trunnion. Two head materials were modelled: CoCr alloy (118,706 10-noded tetrahedral elements), and alumina ceramic (124,710 10-noded tetrahedral elements). The quasi-static coefficients of friction (µs) of the CoCr-TiAlV and Ceramic-TiAlV interfaces were calculated from uniaxial assembly (2000N) and dis-assembly experiments performed in a mechanical testing machine (Bionix, MTS). Interface displacements during taper assembly and disassembly were measured using digital image correlation (DIC; Dantec Dynamics). The assembly process was also simulated using the computational model with the friction coefficient set to µs and solved using the Siemens Nastran NX 11.0 Solver. The frictional conditions were then varied iteratively to find the value of µ providing the closest estimate to the experimental value of head displacement during assembly. To validate the FEA model, the relative motion between the head and the trunnion was measured during dynamic loading simulating stair-climbing. Each modular junction was assembled in a drop tower apparatus and then cyclically loaded from 230–4300N at 1 Hz for a total of 2,000 cycles. The applied load was oriented at 25° to the trunnion axis in the frontal plane and 10° in the sagittal plane. The displacement of the head relative to the trunnion during cyclic loading was measured by a three-camera digital image correlation (DIC) system. The same loading conditions were simulated using the FEA model using the optimal value of µ derived from the initial head assembly trials.INTRODUCTION
MATERIALS and METHODS
The demands placed upon joint surgeons are perhaps greatest when treating the revision arthroplasty patient, who present with complications demanding skill in diagnosis and evaluation, interpersonal communication and the technical aspects of the revision procedure. However, little information exists identifying which specific tasks in revision arthroplasty are most difficult for surgeons to master, and whether the greatest challenges arise from clinical, cognitive or technical facets of patient treatment. This study was undertaken to identify which tasks associated with revision total knee replacement (TKR) are perceived as most challenging to young surgeons and trainees to guide future efforts in surgical training and curriculum development. We developed an online survey instrument consisting of 69 items encompassing pre-operative, intraoperative, and post-operative tasks that preliminary studies identified as the essential components of revision TKR. These tasks encompassed 4 domains: clinical decision-making skills (n=9), interpersonal assessment and communication (n=7), surgical decision-making (n=35) and procedural surgical tasks (n=18). Respondents rated the difficulty of each item on a 5-level Likert scale, with an ordinal score ranging from 1 (“very easy”) to 5 (“very difficult”. The survey instrument was administered to a cohort of 109 US surgeons: 31 trainees enrolled in a joint fellowship program (Fellows) and 78 surgeons who had graduated from a joint fellowship program within the previous 10 years (Joint Surgeons). Using appropriate parametric and non-parametric tests, the responses were analyzed to examine the variation of reported difficulty of each of the 69 items, in addition to the nature of the task (cognitive, surgical, clinical and interpersonal), and differences between Fellows and Surgeons.Introduction
Methods
Most patients presenting with loss of hip motion secondary to FAI have a combination of cam and pincer morphology. In this study, we present a composite index for predicting joint ROM based on anatomic parameters derived from both the femur and acetabulaum using a single reformatted CT slice. Computer models of the hip joint were reconstructed from CT scans of 31 patients with mixed-type FAI (Average alpha angle: 73.6±11.1°, average LCE: 38.9±7.2°). The internal rotation of the hip at impingement was measured at 90° flexion using custom software. With the joint in neutral, a single slice perpendicular to the acetabular rim was taken at the 2 o'clock position. A set of 11 femoral and acetabular parameters measured from this slice were correlated with hip ROM using stepwise logistic regression. Three anatomic parameters provided significant discrimination of cases impinging at <15 and >15 degrees IR: femoral anteversion (28%, p=0.026), the arc of anterior femoral head sphericity (10%, p=0.040), and the LCE in the 2 o'clock plane (10%, p=0.048). This led to the following definition of the Impingement Index: 0.16*(fem version) +0.11*(ant arc)−0.17*(LCE) which correctly classified 82% of cases investigated. None of the traditional parameters (e.g. alpha angle) were significantly correlated with ROM. Our study has identified alternative morphologic parameters that could act as strong predictors of FAI in preoperative assessments. Using this information, each patient's individual risk of impingement may be estimated, regardless of the relative contributions of deformities of the femur and the acetabulum.
Stable fixation of cementless tibial trays remains a challenge due bone density variability within the proximal tibia and the spectrum of loads imposed by different activities. This study presents a novel approach to measuring the interface motion of cementless tibial components during functional loading and tests whether interface motion of cementless tibial trays varies around the implant periphery. We developed a method to measure relative displacement of a tibial tray relative to the underlying bone using 3D digital image correlation (DIC) and multi-camera stereo photogrammetry. A clinically successful design of cementless total knee prosthesis (Zimmer Inc, Warsaw, IN) was implanted in 6 fresh cadaveric knees. A black-on-white stochastic pattern was applied to the outer surface of the tibia and the cementless prosthesis. High resolution digital images were prepared of the interface region and divided into 25 × 25 pixel regions of interest (ROI). Stereo images of the same ROI were generated using two cameras angled at 60 degrees using image correlation techniques. All specimens were mounted in a custom-built functional activity simulator and loaded with the forces and moments recorded during three common functional activities (standing from a seated position, walking, and stair descent), as reported in the Orthoload database, scaled by 50% for application to cadaveric bone. Prior to functional testing, each implant-tibia construct was preconditioned with 500 cycles of flexion from 5–100 degrees under a vertical tibial load of 1050 N at a frequency of 0.2 Hz. During loading, image data was acquired simultaneously (±20 μs) from the entire circumference of the tibial interface forming 4 stereo images using 8 cameras spaced at 90 degree intervals (Allied Vision Technologies, Exton, PA) using custom image acquisition software (Mathworks, Natick, MA) (Figure 1). The multiple stereo images were registered using the surface topography of each specimen as measured by laser scanning (FARO Inc., Montreal) (Figure 2). During post-processing, the circumferential tray/tibia interface was divided into 10 zones for subsequent analysis (Figure 3). Interface displacements were measured on a point-to-point basis at approximately 700 sites on each specimen using commercial DIC software (Dantec Dynamics, Skovlunde, Denmark) (Figure 4).INTRODUCTION
METHODS
Cementless tibial trays commonly fail through failure of fixation due to excessive interface motion. However, the specific combination of axial and shear forces precipitating implant failure is unknown. This has led to generic loading profiles approximating walking to perform pre-clinical assessment of new designs, even though telemetric data demonstrates that much larger forces and moments are generated during other functional activities. This study was undertaken to test the hypotheses: (i) interface motion of cementless tibial trays varies as a function of specific activities, and (ii) the response of the cementless tibial interface to walking loading is not representative of other functional activities. Six fresh-frozen cadaveric tibias were tested using a custom designed functional activity simulator after implantation of a posterior stabilized total knee replacement (NexGen LPS, Zimmer, Warsaw IN). Activity scenarios were selected using force (Fx, Fy, Fz) and moment (Mx, My, Mz) data from patients with instrumented tibial trays (E-tibia) published by Bergmann et al. A pattern of black and white spray paint was applied to the surface of the specimen including the tibial tray and bone. Each specimen was preconditioned through application of a vertical load of 1050N for 500 cycles of flexion-extension from 5–100°. Following preconditioning, each tibia was loaded using e-tibia values of forces and moments for walking, stair-descent, and sit-to-stand activities. The differential motion of the tibial tray and the adjacent bony surface was monitored using digital image correlation (DIC) (resolution: 1–2 microns in plane; 3–4 microns out-of-plane). Four pairs of stereo-images of the tray and tibial bone were prepared at sites around the circumference of the construct in both the loaded and unloaded conditions: (i) before and after pre-conditioning and (ii) before and after the 6 functional loading profiles. The images were processed to provide circumferential measurements of interface motion during loading. Differences in micromotion and migration were evaluated statistically using step-wise multivariate regression.INTRODUCTION
MATERIALS and METHODS
Numerous factors have been hypothesized as contributing to mechanically-assisted corrosion at the head-neck junction of total hip prostheses. While variables attributable to the implant and the patient are amenable to investigation, parameters describing assembly of the component parts can be difficult to determine. Nonetheless, increasing evidence suggests that the manner of intraoperative assembly of modular components plays a critical role in the fretting and corrosion of modular implants. This study was undertaken to measure the magnitude and direction of the impaction forces applied by surgeons in assembling modular head-neck junctions under operative conditions where both the access and visibility of the prosthesis may potentially compromise component fixation. A surrogate consisting of the lower limb with overlying soft tissue was developed to simulate THR performed via a 10cm incision using the posterior approach. The surrogate was modified to match the resistance of the body to retraction of the incision, mobilization of the femur and hammering of the implanted femoral component. An instrumented femoral stem (SL PLUS) was surgically implanted into the bone after attachment of 3 miniature accelerometers (Dytran Inc) in an orthogonal array to the proximal surface of the prosthesis. A 32mm cobalt chrome femoral head was mounted on the trunnion (12/14 taper, machined) of the femoral stem. 15 Board-certified and trainee surgeons replicated their surgical technique in exposing the femur and impacting the modular head on the tapered trunnion. Impaction was performed using an instrumented hammer (5000 Lbf Dytran impact hammer) that provided measurements of the magnitude and temporal variation of the impact force. The components of force acting along the axis aof the neck and in the AP and ML directions were continuously samples using the accelerometers.Introduction
Methods
Restoration of knee function after total knee arthroplasty (TKA) often entails a balance between normal kinematics and normal knee stability, especially in performing demanding physical activities. The ultra-congruent (UC) knee design prioritizes stability over kinematics through close conformity between the femoral component and the tibial insert in extension. This configuration is intended to provide AP stability in the absence of the posterior cruciate ligament during activities that would otherwise cause anterior femoral subluxation. In this study we examine the kinematics of an ultra-congruent knee design in comparison with the intact knee and with conventional articulations used in PCL-retaining (CR) and PCL-substituting (PS) TKR designs. The 3D tibio-femoral kinematics of 6 fresh frozen cadaveric human knees were tested during loaded simulation of squatting in a computer-controlled knee testing rig. Muscle forces were simulated by loading rectus femoris and vastus intermedius (150N), vastus lateralis (100N), vastus medialis (75N), and the hamstring muscles (60N) (total: 385N). Testing was performed on the intact knee, and after implanting a standard design of total knee prosthesis with the posterior cruciate ligament intact (CR-TKA), resected (PCL-substituting insert; PS-TKA), and a UC insert (UC-TKA group). The 3D positions of the tibia and femur were tracked with a high resolution 12 camera motion analysis system (Motion Analysis Inc.) and used to position 3D CT reconstructions of each bone. The translation and rotation of the femur with respect to the tibia were calculated by projecting the femoral transcondylar axis onto a plane normal to the longitudinal anatomical axis of the tibia coincident with the transverse axis of the tibial plateau.Introduction
Materials and Methods
The success of knee replacement surgery depends, in part, on restoration of the correct alignment of the leg with respect to the load-bearing vector passing from the hip to the ankle (the mechanical axis). Conventional thinking is that the correct angle of resection of the distal femur (Valgus Cut Angle, VCA) depends on femoral length or femoral offset, though femoral bowing, in addition to length and medial offset, may also have a significant influence on the VCA. We hypothesized that femoral bowing has a strong effect on the VCA necessary to restore physiologic alignment after arthroplasty or osteotomy. A total of 102 long-leg radiographs were obtained from patients scheduled for primary total knee arthroplasty. The patients on average were 41% male 59% female, 67.9 ± 11.1 years, 67.0 ± 4.7 in, 192 ± 43 lbs, and had a BMI of 29.7 ± 4.8. All radiographs were prepared with the feet placed in identical rotation and the patellae pointing forward, and were excluded if there was evidence of malrotation, as defined by (i) a difference in the medial head offsets of the right and left femur of >3mm, (ii) a difference in the width of the tibiofibular syndesmoses, or (iii) a difference in the rotation of one foot compared to the other. The following anatomic variables were measured on each radiograph: (i) the neck shaft angle (NSA) of the femur, (ii) the length of the femur, (iii) the length of the femoral shaft, (iv) the medial head offset, (v) the medial-lateral bow of the distal femur, (vi) the hip- knee axis angle, (vii) the mechanical axis deviation of the extremity at the knee, (viii) the medio-lateral bow of the tibia, and (ix) the valgus cut angle required to restore the mechanical axis to the center of the knee during surgery (VCA). Bivariate plots were constructed using the measurements thought to influence the VCA: femoral bowing, femoral offset, and length of femur. Multivariate regression was then used to find the variable that had the strongest effect on the VCA.Introduction
Methods
Relative motion at the modular head-neck junction of hip prostheses can lead to severe surface damage through mechanically-assisted corrosion. One factor affecting the mechanical performance of modular junctions is the frictional resistance of the mating surfaces to relative motion. Low friction increasing forces normal to the head-neck interface, leading to a lower threshold for slipping during weight-bearing. Conversely, a high friction coefficient is expected to limit interface stresses but may also allow uncoupling of the interface in service. This study was performed to examine this trade-off using finite element models of the modular head-neck junction A finite element model (FEM) of the trunnion/ head assembly of a total hip prosthesis was initially created and experimentally validated. CAD models of a stem trunnion (taper size: 12/14mm) and a prosthetic femoral head (diameter: 28mm) were discretized into elements for finite element analysis (FEA). The trunnion (Ti6Al4V) was modelled with a hexahedral mesh (33,648 elements) and the femoral head (CoCrMo) with a tetrahedral mesh (51,182 elements). A friction-based sliding contact interface was defined between the mating surfaces. The model was loaded in 2 stages: (i) an assembly load of 4000N applied along the trunnion axis, and (ii) 500N applied along the trunnion axis in combination with a torque of 10Nm. A linear static solution was set up using Siemens NX-Nastran solver. Multiple simulations were executed by modulating the frictional coefficient at the taper-bore interface from 0.05 to 0.15 in increments of 0.01, the coefficient of 0.1 serving as the control case (Swaminathan and Gilbert, 2012).Introduction
Methods
Patients who undergo hip resurfacing, total hip arthroplasty (THA), and total knee arthroplasty (TKA) are frequently assessed post-operatively using objective scoring indices. A small yet significant percentage of these patients report specific unfulfilled functions following surgery, indicating unmet expectations. The purpose of this study was to examine the types of functional deficits reported for each class of surgery, how frequently these limitations occur, and the demographic of patients who experience/report these limitations. Four groups of subjects were enrolled in this study: (i) 111 hip resurfacing patients at an average of 14 months after resurfacing, (ii) 170 patients at an average of 16 months post-primary THA, (iii) 61 patients at an average of 12 months post-primary TKA, and (iv) 64 control subjects with no history of hip or knee surgery or pathology. Each participant completed a self-administered Hip Function Questionnaire, Knee Function Questionnaire, or Hip Resurfacing Questionnaire which assessed each subject's overall satisfaction and expectations following surgery. The questionnaires included numerical scores of post-operative function as well as an open-ended question which inquired “Is there anything your knee/hip keeps you from doing?”Introduction
Methods
Patients who undergo hip resurfacing, total hip arthroplasty (THA), and total knee arthroplasty (TKA) are frequently assessed post-operatively using objective scoring indices. A small yet significant percentage of these patients report pain and discomfort related to specific physical activities following surgery. The purpose of this study was to examine the types of activities which prove difficult for patients for each class of surgery, how important these activities are to the individual patients, and the demographic of patients who experience/report these limitations. Four groups of subjects were enrolled in this study: (i) 111 hip resurfacing patients at an average of 14 months after resurfacing, (ii) 170 patients at an average of 16 months post-primary THA, (iii) 61 patients at an average of 12 months post-primary TKA, and (iv) 64 control subjects with no history of hip or knee surgery or pathology. Each participant completed a self-administered Hip Function Questionnaire, Knee Function Questionnaire, or Hip Resurfacing Questionnaire which assessed each subject's overall satisfaction and expectations following surgery. The questionnaires included a section with 58 physical activities and asked the patients to rate the activities based on frequency of participation, importance of the activity, and how much their knee or hip bothered them when performing the activity.Introduction
Methods
There is tremendous variability amongst surgeons' ability to reference anatomic landmarks. This may suggest the necessity of other objective methods in determining femoral alignment and rotation. Despite the durability of total knee arthroplasty, there is much room for improvement with regards to functional outcome and patient satisfaction. One important factor contributing to poor outcomes after TKA is malrotation of the femoral component. It has been postulated that this is due to failure of surgeons to correctly reference bony landmarks, principally the femoral epicondyles, however, this is unproven. The purpose of this study was to evaluate the accuracy of joint surgeons and trainees in identifying anatomic landmarks for positioning the femoral component and to determine the effect of prior training and experience.Summary
Introduction
With the rising demand for primary total hip arthroplasty (THA), there has been an emphasis on reducing the revision burden and improving patient outcomes. Although studies have shown that primary THA effectively minimizes pain and restores normal hip function for activities of daily living, many younger patients want to participate in more demanding activities after their operation. With IRB approval, 2 groups of subjects were enrolled in this study: (i) 143 patients at an average of 25 months (range 10–69 months) post-primary THA, and (ii) 165 control subjects with no history of hip surgery or hip pathology. All subjects were assigned to one of four categories according to their age and gender: Group A: 40–60 year old males (31 THA; 42 Controls), Group B: 40–60 year old females (25 THA; 53 Controls), Group C: 60–80 year old males (35 THA; 25 Controls), and Group D: 60–80 year old females (36 THA; 23 Controls). Each patient completed a self-administered Hip Function Questionnaire (HFQ) which assessed each subject's satisfaction, expectations, symptoms and ability to perform a series of 94 exercise, recreational and daily living activities. These included participation in work-out activities, adventure and water sports, running and biking, and contact and team sports. Each participant was also asked their activity frequency, symptom prevalence and satisfaction with their hip in performing each activity.Background
Methods
Knee pain and instability during high demand activities such as stair descent are reported by patients after TKA. Previous studies theorized that this pain is from increased demand on the quadriceps required to stabilize the femur on the tibia. In this study we explore the relationship between implant design, the posterior cruciate ligament (PCL), and AP stability of the knee during stair descent. CTs of 6 fresh-frozen human cadaveric knees (average age: 61 ± 6.5 years) with functioning cruciates were prepared. All specimens were mounted in a computer controlled, 6 DOF simulator programed to apply physiologic muscle loads and flexion/extension moments simulating the highest demand phase of stair descent (terminal swing to initial contact). A contemporary design of TKA was implanted in each specimen by an experienced surgeon. Testing was repeated after implantation of tibial inserts of the CR, CS with and without a PCL and PS designs.Purpose:
Methods:
With the growing emphasis on the cost of medical care, there is renewed interest in the productivity and efficiency of surgical procedures. We have developed a method to systematically examine the efficiency of the surgical team during primary total knee replacement (TKR). In this report, we present data derived from a series of procedures performed by different joint surgeons. This data demonstrates a variation between the duration and efficiency of each step in this procedure and its relationship to the experience and coordination of the surgeon working with the scrub team. After consent was achieved, videotaped recordings were prepared of ten primary TKR procedures performed by five highly experienced joint surgeons. For quantitative analysis, each procedure was divided into 7 principal tasks from initial incision to wound closure. In order to quantify efficiency, we recorded the occurrence of events leading to delays in each step of the procedure (Table 1). Starting with a total score of 100 points, deductions were made, based on the number of delaying events and its impact on the efficiency of the procedure. A final score for the surgery was then determined using the individual scores from each principal task. The experience of each member of the surgical team in participating in TKR, and in working with the surgeon, were recorded and correlated with the total efficiency score for the entire procedure.Introduction:
Methods:
The failure rate of Total Hip Replacement (THR) has been shown to be strongly influenced by the nature of the articulating interfaces, with Metal-on-Metal (MoM) articulations having three times the failure rate of Metal-on-Polyethylene (MoP) components. It has been postulated that this observation is related to edge wear and increased bearing torque of large MoM heads, which would lead to increased loading and wear at the head taper junction and, subsequently, to the release of metal ions and corrosion products. This suggests that taper wear and corrosion should not be as prevalent in large head MoP implants as in large head MoM implants. This study was undertaken to test the hypotheses that: (i) MoM implants exhibit higher rates of corrosion and fretting at the head taper junction than MoP implants, and that (ii) the severity of corrosion and fretting is greater in components of larger head diameter. Our study included 90 modular implants (41 MoM; 49 MoP) retrieved during revision hip arthroplasties performed between 1992 and 2012. Only retrievals with head diameters greater than 32 mm were included, and trunnion sizes ranged from 10/12 mm to 14/16 mm with 12/14 mm being the most common size. The stem trunnion and head taper surfaces were examined under stereomicroscope by a single observer. Each surface was scored for both corrosion (using a modified Goldberg scoring system) and fretting (using the standard Goldberg scoring system). For both the trunnion and head tapers, the student's t-test was used to determine if differences exist in the severity of corrosion or fretting between the MoM and MoP groups and between different head sizes of the same articulation type.Introduction
Materials and Methods
Tribo-chemical damage of modular taper junctions is often observed at revision THR and may be a contributing factor to chronic inflammation of peri-prosthetic tissues through generation of chromium rich corrosion products. At the time of revision, surgeons may elect to leave the primary femoral stem in situ and replace the original femoral head with a new component. This decision is based on the assumption that the interface formed between the original trunnion and the new bore is capable of withstanding the loads and torques applied during use, without failure of the new interface. This study was performed to determine the extent to which the mechanical properties of the taper interface are degraded with varying degrees of tribo-chemical damage secondary to prior implantation. Fifteen CoCr femoral heads (DePuy: 6, Smith & Nephew: 5; Zimmer: 4) were retrieved at revision THR and were examined with stereomicroscopy. The surface of each bore was scored for the presence of fretting and corrosion using the grading system of Goldberg et al. Nine additional heads in original (unimplanted) condition (3 per manufacturer) were also selected to act as controls. Each head was manually assembled on a matching unimplanted TiAlV trunnion in a mechanical testing machine (MTS Bionix) and loaded at 500N/sec to a maximum assembly load of 4000N. The head/trunnion specimen was then mounted in a torsional loading fixture and immersed in bovine serum. A cyclic torque was applied to the head with an initial maximum value of 2 Nm. The specimen was unloaded and held for a 30 sec wait period and the torsional loading was repeated to a peak value of 4 Nm. With each torsional cycle the peak torque was increased by 2 Nm until the taper junction underwent rotational failure. During testing, relative motion between the femoral head and the trunnion was measured with a displacement transducer (DVRT-3, MicroStrain, accuracy = ± 0.1%, resolution = 1.5 μm, hysteresis & repeatability = ± 1 μm). A separate disassembly test was performed by first assembling each specimen with 4000N and then applying a distraction force at 0.008 mm/sec until separation.Introduction
Materials and Methods
Dual mobility total hip arthroplasty (DM-THA) allows for very large femoral head size, which may be beneficial for hip range of motion (ROM). No clinical study has objectively compared ROM in patients with DM-THA and large (36-mm head) total hip arthroplasty (36-THA). The aim of this prospective case-control study is to test the hypotheses that DM-THA provides superior hip ROM compared to 36-THA by dynamic radiography, and that surgical approach (posterolateral [PL] versus modified anterolateral [AL]) has effect on post-operative hip ROM. Sixteen patients (11 males, 5 females) who had undergone DM-THA with a minimum follow up of one year were age, sex and body mass index (BMI) matched to twenty patients (12 males, 8 females) with 36-THA, all operated upon by the senior author. Maximum hip-trunk flexion, extension and total hip-trunk ROM was calculated on standing lateral digital radiographs of the lower lumbar spine, pelvis and hip, using commercially available software (TraumaCad®, BrainLab, Munich, Germany) from three upright positions; standing neutral, standing with maximum hip flexion and standing with maximum hip extension. Contributions to motion from lumbo-sacral spine (LSS) and pelvic tilt were calculated and subtracted from hip-trunk measurements to quantify true hip flexion, extension and total true hip ROM. Statistical analysis (SPSS software, Chicago, IL) was performed on all radiographic measurements to detect difference in ROM between DM-THA and 36-THA, and to detect difference in ROM between THAs performed through posterolateral (THA-PL) and anterolateral (THA-AL) approaches.Introduction:
Materials and Methods:
Malrotation of the tibial component is a common error in TKR, and has been frequently cited as the cause of clinical symptoms. Correct rotational orientation of the tibial tray is difficult to achieve because the resected surface of the tibia is internally rotated and is not symmetrical in shape. This suggests that anatomically contoured components may lead to improved rotational positioning. This study was undertaken to test the hypotheses:
Use of an anatomically shaped tibial tray can reduce the prevalence of malrotation and cortical over-hang in TKA while increasing coverage of the resected tibial surface, and Component shape has more influence on the results of surgical trainees compared to experienced surgeons. A standard symmetric design of tibial tray was developed from the profiles of 3 widely used contemporary trays. Corresponding asymmetric profiles were generated to match the average shape of the resected surface of the tibia based on a detailed morphometric analysis of anatomic data. Both designs were proportionally scaled to generate a set of 7 different sizes. Computer models of eight tibias were selected from a large anatomic collection. The proximal tibia was resected perpendicular to the canal axis with a posterior slope of 5 degrees at a depth of 5 mm (medial). Eleven experienced joint surgeons and twelve trainees individually determined the ideal size and placement of each tray on each of the 8 resected tibias. The rotational alignment, coverage of the resected bony surface, and extent of overhang of the tray beyond the cortical boundary were measured for each implantation. Differences in the parameters defining the implantations of the surgeons and trainees were evaluated statistically.Introduction:
Materials and Methods:
Proper rotational alignment of the tibial component is a critical factor in the outcome of total knee arthroplasty (TKA), and misalignment has been implicated as a major contributing factor to several mechanisms of TKA failure. In this study we examine the relationship between bony and soft tissue tibial landmarks against the knee motion axis (plane that best approximates tibiofemoral motion through range of motion). The kinematic motions of 16 fresh-frozen lower limb specimens were analyzed in simulated lunging and squatting. All the tendons of the quadriceps and hamstrings were independently loaded to simulate a lunging or squatting maneuver. All specimens underwent CT scan and the 3D position of the knee was virtually reconstructed. Ten anatomic axes were identified using both the intact tibia and the resected tibial surface. Two axes were normal vectors to either the medial-lateral plateau center or the posterior tibial surface. Seven axes were defined between the tibial tubercle (the most prominent point, center of the tubercle, or medial third of the tubercle) and soft tissue landmarks of the tibia (the medial insertion of the patellar tendon, the center of the PCL and ACL, and the tibial spines). The last axis was the Knee Motion Axis (KMA), which was defined as the longitudinal axis of the femur from 30 to 90 degrees of flexion.Introduction:
Methods:
Malpositioning of the tibial component is a common error in TKR. In theory, placement of the tibial tray could be improved by optimization of its design to more closely match anatomic features of the proximal tibia with the motion axis of the knee joint. However, the inherent variability of tibial anatomy and the size increments required for a non-custom implant system may lead to minimal benefit, despite the increased cost and size of inventory. This study was undertaken to test the hypotheses:
That correct placement of the tibial component is influenced by the design of the implant. The operative experience of the surgeon influences the likelihood of correct placement of contemporary designs of tibial trays. CAD models were generated of all sizes of 7 widely used designs of tibial trays, including symmetric (4) and asymmetric (3) designs. Solid models of 10 tibias were selected from a large anatomic collection and verified to ensure that they encompassed the anatomic range of shapes and sizes of Caucasian tibias. Each computer model was resected perpendicular to the canal axis with a posterior slope of 5 degrees at a depth of 5 mm distal to the medial plateau. Fifteen joint surgeons and fourteen experienced trainees individually determined the ideal size and placement of each tray on each resected tibia, corresponding to a total of 2030 implantations. For each implantation we calculated: (i) the rotational alignment of the tray; (ii) its coverage of the resected bony surface, and (iii) the extent of any overhang of the tray beyond the cortical boundary. Differences in the parameters defining the implantations of the surgeons and trainees were evaluated statistically.Introduction
Materials and Methods
After TKR, excessive tension within the lateral retinaculum can lead to joint instability, component wear, stiffness and pain. The spatial distribution of strain in the lateral retinculum is unknown, both in the native knee and after TKR. In this study we measure the magnitude and distribution of mechanical strain in the lateral retinaculum with knee flexion, both in the native knee and after TKR. We hypothesize that:
Strain in the lateral retinaculum will increase as a function of flexion. Some regions of the lateral retinaculum experience greater strain than others. TKR will affect the magnitude and location of strain during knee flexion. A fiduciary grid of approximately 40–70 markers was attached to the exposed lateral retinacula of five fresh frozen cadaveric knees in order to allow tracking of soft-tissue deformation. Each knee was flexed from 0–120° in a 6 degree-of-freedom custom activity simulator that physiologically loaded the knee during a squatting maneuver. During simulation, the displacement of each fiduciary point was measured using visible-light stereo-photogrammetry. The fiduciary grid divided into four distinct regions for strain analysis. Using the grid of the native knee in full extension as the initial state, the average principal strain in each region was calculated as a function of flexion. Measurements were repeated after TKR was performed using a contemporary implant system.Introduction
Materials and Methods
A disturbing prevalence of painful inflammatory reactions has been reported in metal-on-metal (MoM) hip resurfacing arthroplasty. A contributing factor is localized loading of the acetabular shell leading to “edge wear” which is often seen after precise measurement of the bearing surfaces of retrieved components. Factors contributing to edge wear include adverse cup orientation leading to proximity (<10 mm) of the hip reaction force to the edge of the acetabular component. As this phenomenon is a function of implant positioning and patient posture, this study was performed to investigate the occurrence of edge loading during different functional activities as a function of cup inclination and version. We developed a computer model of the hip joint through reconstruction of CT scans of a proto-typical pelvis and femur and virtually implanting a hip resurfacing prosthesis in an ideal position. Using this model, we examined the relationship between the resultant hip force vector and the edge of the acetabular shell during walking, stair ascent and descent, and getting in and out of a chair. Load data was derived from 5 THR patients implanted with instrumented hip prostheses (Bergmann et al). We calculated the distance from the edge of the shell to the point of intersection of the load vector and the bearing surface for cup orientations ranging from 40 to 70 degrees of inclination, and 0 to 40 degrees of anteversion.Introduction:
Methods:
Increasing attention to the functional outcome of total knee arthroplasty (TKA) has demonstrated that many patients experience limitations when attempting to perform demanding activities that are normal for age-matched peers, primarily because of knee symptoms. Episodes of instability following TKA are most commonly reported during activities in which significant transverse or torsional forces are supported by the joint with relatively low joint compression forces, including stair-descent and walking on sloped or uneven surfaces. This study was performed to examine the influence of conformity between the femoral and tibial components on the Antero-Posterior (AP) stability of knee during stair descent. Six cadaveric knees were loaded in a six degree-of-freedom joint simulator, with the application of external forces simulating the action of the quadriceps and hamstring muscles and the external loads and moments occurring during stair descent, including the stages of terminal swing phase, weight-acceptance phase (prior to and after quadriceps contraction) and mid-stance. During these manoeuvres, the displacement and rotation of the femur and the tibia were measured with a multi-camera high resolution motion analysis system (Fig. 1). Each knee was tested in the intact and ACL deficient condition – and after implantation of total knee prosthesis with Cruciate-Retaining (CR), Cruciate-Sacrificing with an intact PCL (CS + PCL), Cruciate-Sacrificing with an absent PCL (CS-PCL) and Posterior-Stabilizing (PS) tibial inserts (Figs 2 and 3).Introduction
Methods
Despite all the attention to new technologies and sophisticated implant designs, imperfect surgical technique remains a obstacle to improving the results of total knee replacement (TKR). On the tibial side, common errors which are known to contribute to post-operative instability and reduced function include internal rotation of the tibial tray, inadequate posterior slope, and excessive component varus or valgus. However, the prevalence of each error in surgeries performed by surgeons and trainees is unknown. The following study was undertaken to determine which of these errors occurs most frequently in trainees acquiring the surgical skills to perform TKR. A total of 43 knee replacement procedures were performed by 11 surgical trainees (surgical students, residents and fellows) in a computerized training center. After initial instruction, each trainee performed a series of four TKR procedures in cadavers (n = 2) and bone replicas (n = 2) using a contemporary TKR instrument set and the assistance of an experienced surgical instructor. Prior to each procedure, computer models of each cadaver and/or bone replica tibia were prepared by reconstructing CT scans of each specimen. All training procedures were performed in a navigated operating room using a 12 camera motion analysis system (Motion Analysis Inc.) with a spatial resolution in all three orthogonal directions of ± 0.15 mm. The natural slope, varus/valgus alignment, and axial rotation of the proximal tibial surface were recorded prior to surgery and after placement of the tibial component. For evaluation of all data, acceptable limits for implantation were defined as: posterior slope: 0–10°; varus/valgus inclination of tibial resection: ± 3°; and external rotation: 0–10°.Introduction:
Materials and Methods:
A disturbing prevalence of short-term failures of metal-on-metal (MoM) hip resurfacings has been reported by joint registries. These cases have been primarily due to painful inflammatory reactions and, in extreme cases, formation of pseudotumors within periarticular soft-tissues. The likely cause is localized loading of the acetabular shell leading to “edge wear” which is often seen after precise measurement of the bearing surfaces of retrieved components. Factors contributing to edge wear of metal-on-metal arthroplasties are thought to include adverse cup orientation, patient posture, and the direction of hip loading. The purpose of this study was to investigate the role of different functional activities in edge loading of hip resurfacing prostheses as a function of cup inclination and version. We developed a computer model of the hip joint through reconstruction of CT scans of a proto-typical pelvis and femur and virtually implanting a hip resurfacing prosthesis in an ideal position. Using this model, we examined the relationship between the resultant hip force vector and the edge of the acetabular shell during walking, stair ascent and descent, and getting in and out of a chair. Load data was derived from 5 THR patients implanted with instrumented hip prostheses (Bergmann et al). We calculated the distance from the edge of the shell to the point of intersection of the load vector and the bearing surface for cup orientations ranging from 40 to 70 degrees of inclination, and 0 to 40 degrees of anteversion.Introduction
Methods
With the growing emphasis on the cost of medical care, there is renewed interest in the productivity and efficiency of surgical procedures. We have developed a method to systematically examine the efficiency of the surgical team during primary total knee replacement (TKR). In this report, we present data derived from a series of procedures performed by different joint surgeons. This data demonstrates a variation between the duration and efficiency of each step in this procedure and its relationship to the experience and coordination of the surgeon working with the scrub team. After consent was achieved, videotaped recordings were prepared of ten primary TKR procedures performed by five highly experienced joint surgeons. For quantitative analysis, each procedure was divided into 7 principal tasks from initial incision to wound closure. In order to quantify efficiency, we recorded the occurrence of events leading to delays in each step of the procedure. Starting with a total score of 100 points, deductions were made, based on the number of delaying events and its impact on the efficiency of the procedure. A final score for the surgery was then determined using the individual scores from each principal task. The experience of each member of the surgical team in participating in TKR, and in working with the surgeon, were recorded and correlated with the total efficiency score for the entire procedure.Introduction
Methods
Although the “learning curve” in surgical procedures is well recognized, little data exists documenting the accuracy of surgeons in performing individual steps of orthopedic procedures. In this study we have used a validated computer-based training system to measure variations instrument placement and alignment in TKA, specifically those relating to tibial preparation. Eleven trainees (surgical students, residents and fellows) were recruited to perform a series of 43 knee replacement procedures in a computerized training center. After initial instruction, each trainee performed a series of four TKA procedures in cadavers (n=2) and bone replicas (n=2) using a contemporary TKA instrument set and the assistance of an experienced surgical instructor. The Computerized Bioskills system was utilized to monitor the placement and orientation of the proximal tibial osteotomy and the tibial tray.Introduction
Methods
Proper rotational alignment of the tibial component is a critical factor affecting the outcome of TKA. Traditionally, the tibial component is oriented with respect to fixed landmarks on the tibia without reference to the plane of knee motion. In this study, we examined differences between rotational axes based on anatomic landmarks and the true axis of knee motion during a functional activity. 24 fresh-frozen lower limb specimens were mounted in a joint simulator which enable replication of lunging and squatting through application of muscle and body-weight forces. Kinematic data was collected using a 3D motion analysis system. Computer models of the femur and tibia were generated by CT reconstruction. The motion axis of each knee (TFA) was defined by the 3D path of the femur with respect to the tibia as the knee was flexed from 30 to 90 degrees. The orientation the TFA was compared to 5 different anatomic axes commonly proposed for alignment of the tibial component.Introduction
Materials and Methods
Several studies have suggested that, in TKR, gender specific-prostheses are needed to accommodate anatomic differences between males and females. This study was performed to examine whether gender is a factor contributing to the variability of the size, shape and orientation of the patellofemoral sulcus. 3D computer models of the femur were reconstructed from CT scans of 20 male and 20 female femora. The patellofemoral groove was quantified by measuring landmarks at 10 degree increments around the epicondylar axis. The orientation of the groove was defined by the tracking path generated by a sphere moving from the top of the groove to the intercondylar notch. To assess the influence of gender on the shape of the distal femur, all morphologic parameters were normalized for differences in bone size. Overall, the distal femur was 15% larger in males compared to females. The male condyles were 4% wider than the female for constant AP depth (p=0.13). When normalized for bone size, there was no gender difference in most patello-femoral dimensions, including the length, width, angle or tilt of the sulcus. Female femora had a less prominent medial anterior ridge (p=0.07), and a larger normalized radius of curvature of the tracking path (p=0.03). In addition, the orientation of the sulcus differed by 1–2 degrees in both the coronal and axial planes. Overall, gender explained 4.7% of the anatomic variation of the parameters examined, varying from 0 to 15.9%. The size, shape and orientation of the patello-femoral groove are highly variable. While the patello-femoral morphology of male and female femora are very similar, some of the anatomic variability is related to gender, particularly the prominence of the medial ridge and the sulcus radius of curvature. The biomechanical and clinical significance of these differences after TKA have yet to be determined.
Wear of the underside of modular tibial inserts (“backside wear”) has been reported by several authors. However, the actual volume of material lost through wear of the backside surface has not been quantified. This study reports the results of computerized measurements of tibial inserts of one design known to have a high incidence of backside wear in situ. A series of retrieved TKA components of one design (AMK, Depuy) with evidence of severe backside wear and extrusions of the polyethylene insert were examined. The three-dimensional surface profile of the backside of each insert was digitized and reconstructed with CAD software (UniGraphics). The volume of material removed was calculated from the volume between the worn backside surface and an “initial” surface defined by unworn areas. Computer reconstructions showed that in all retrievals, the unworn surface of the remaining pegs, the rim of material extruded over the medial edge and unworn surfaces on the anterior-lateral edge all lie in a single plane. This demonstrates that the “pegs” present on the backside of these inserts correspond to residual, unworn protrusions remaining on each retrieved component and do not represent cold flow extrusions through the base plate holes. The average volume of material lost due to backside wear was 608mm^3 ± 339mm^3 (range:80–1599 mm^3). This corresponds to an average loss of 569mg and an average linear wear rate of 103mg/year, based on the time in situ for each implant. The volume of material removed due to backside wear is significant and is of a magnitude large enough to generate osteolysis. Our results indicate that the appearance of pegs on the underside of components with screw holes on the baseplate are not due to creep, but instead are due to severe wear of the insert. The mechanisms of material removed due to pitting and burnishing actually produce debris of a size more damaging in terms of osteolysis than wear at the articulating surface making it clear that significant improvements in implant design are needed to prevent backside wear and osteolysis.
