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
Mechanically-assisted corrosion of the head-neck junction present a dilemma to surgeons at revision THR whenever the femoral component is rigidly fixed to the femur. Many remove the damaged femoral head, clean the femoral taper and fix a new head in place to spare the patient the risks associated with extraction and replacement of the well-functioning femoral stem. This study was performed to answer these research questions:
Will new metal heads restore the mechanical integrity of the original modular junction after impaction on corroded tapers? Which variables affect the stability of the new interface created at revision THR? Twenty-two tapers (CoCr, n=12; TiAlV, n=10) were obtained for use in this study. Ten stems were in pristine condition, while 12 stems had been retrieved at revision THR and with corrosion damage to the trunnion (Goldberg scale 4). Twenty-two new metal heads were obtained for use in the study, each matching the taper and manufacturer of the original component. The following test states were performed using a MTS Machine: 1. Assembly, 2. Disassembly, 3. Assembly, 4. Toggling and 5. Disassembly. All head assemblies were performed wet using 50% calf serum in accordance to ISO 7206-10. During toggling, each specimen's loading axis was aligned 25° to the trunnion axis in the frontal plane and 10° in the sagittal plane (Figure 1). Toggling was performed at 1Hz for 2,000 cycles with a sinusoidal loading function (230N–4300N). During loading, 3D motion of the head-trunnion junction was measured using a custom jig rigidly attached to the head and the neck of each prosthesis. Relative displacement of the head with respect to the neck was continuously monitored using 6 high resolution displacement transducers with an accuracy of ±0.6µm. Displacement data was independently validated using FEA models of selected constructs.Introduction
Materials and Methods
Manifestation of high interface stresses coupled with micromotion at the interface can render the taper lock joint in a modular hip replacement prosthesis at risk for failure. Bending can lead to crevice formation between the trunnion and the head and can potentially expose the interface to the biological fluids, generating interface corrosion. Additionally, development of high stresses can cause the material to yield, ultimately leading to irreversible damage to the implant. The objective of this study is to elucidate the mechanical response of taper junction in different material combination assemblies, under the maximum loads applied during everyday activities. Computer simulations were executed using a verified FE model. A stable hexahedral mesh (33648 elements) was generated for the trunnion (taper size: 12/14mm) and a tetrahedral mesh (51182 elements) for the head (CoCr, size: 32mm). An assembly load of 4000N was applied along the trunnion axis followed by the application of a load of 230–4300N at 25° and 10° angle to the trunnion axis in the frontal and sagittal planes. A linear static solution was set up using Siemens NX Nastran. Two material combinations were tested - cobalt-chrome head with a titanium alloy trunnion and cobalt chrome head with a cobalt-chrome trunnion.Introduction
Methods
This data may help explain the variability in physical function after primary TKR as compared to primary THR. Total knee replacement (TKR) and total hip replacement (THR) reliably relieve pain, restore function, and ensure mobility in patients with advanced joint arthritis; however these results are not uniform across all patient populations. We compared baseline demographic and symptom profiles in patients from a US national cohort undergoing primary TKR and THR.Summary Statement
Introduction
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:
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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:
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Total knee replacement (TKR) and total hip replacement (THR) reliably relieve pain, restore function, and ensure mobility in patients with advanced joint arthritis; however these results are not uniform across all patient populations. Moreover, it is well established that knee replacement patients have outcomes inferior to those undergoing hip replacement procedures with lower rates of dissatisfaction with post-operative function and pain relief. We compared baseline demographic and symptom profiles in patients from a US national cohort undergoing primary TKR and THR to determine whether differences in demographic make-up, pre-operative symptoms, or pre-existing co-morbidities might contribute to these differences observed post-operatively. A cohort of 2375 patients undergoing primary TKR and THR was identified from the FORCE national research consortium from all surgeries performed between July 1st 2011 and March 30th 2012. This set of patients was derived from 120 contributing surgeons in 23 US states. Gathered data included patient demographics, comorbidity (Charlson Comorbidity Index), operative joint pain severity (Western Ontario and McMaster Universities Arthritis Index (WOMAC)), physical function (SF-36; Physical Component Score (PCS)), emotional health (SF-36; Mental Component Score (MCS)), and musculoskeletal burden of illness (Hip and Knee Disability and Osteoarthritis Outcome Scores; Oswestry Disability Index). Using descriptive statistics, we compared the baseline demographic characteristics and symptom profiles of patients undergoing TKR (n = 1362) and those undergoing THR (n = 1013).Introduction:
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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:
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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:
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There is an increasing trend within the US for utilization of total knee replacement for patients who are still of working-age. Numerous causes have been suggested, ranging from greater participation in demanding sporting activities to the epidemic of obesity. A universal concern is that increased arthritis burden will lead to increased disabilty and unsustainable health-care costs both now and in the future with increasing rates of revision surgery in the years ahead. This raises the critical question: Are younger patients receiving knee replacement prematurely? To address this issue, we compared the severity of operative knee pain and functional status in younger versus older TKR patients, drawing upon a national research registry. A cohort of 3314 primary TKR patients was identified from the FORCE national research consortium from all surgeries performed between July 1st 2011 and March 30th 2012. This set of patients was derived from 120 contributing surgeons in 23 US states. Data characterizing each patient undergoing surgery was derived from patients, surgeons and hospitals, and included the SF 36 Physical Component Score (PCS), the Knee injury and Osteoarthritis Outcome Score (KOOS) and the Oswestry Low Back Pain Disability Questionnaire. WOMAC scores were also calculated from the KOOS data and transformed to a 0-to-100 scale with lower scores representing worse impairment. Using descriptive statistics, we compared the demographic and baseline characteristics of patients younger than 65 years of age (n = 1326) vs. those 65 years of age and older (n = 1988).Introduction:
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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:
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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
Recent retrieval studies and registry reports have demonstrated an alarming incidence of early failure of metal-on-metal THR. This appears to be due to fretting and corrosion at the taper junction (trunnion) between the neck and large diameter heads in metal-on-metal hip implants. It has been proposed that designs with lower bearing clearances and greater cup flexibility deform during implantation leading to increased frictional torque and micromotion at the head-neck taper junction. Small movements at the trunnion may suggest elastic deformation, but large movements may suggest slippage at the friction interface. This study was conducted using retrieved metal-on-metal components to test the hypotheses that: 1. Cup deformation through localized compression leads to increased bearing torque, and 2. Increased torques generated in large head metal-on-metal bearings cause motion of the head-neck taper junction. Nine metal-on-metal hip implants were received from a national joint retrieval service and tested in a mechanical testing machine. The components were of three different designs (ASR, BHR, and Durom) and ranged in diameter from 42–54 mm. A custom jig was constructed to generate controlled radial compression at opposite points on the rim of an acetabular component. The jig was positioned inverted to the normal anatomical position and was angled to simulate the anatomical orientation of the cup (35° inclination, 10° anteversion). With the exception of an initial compression load of 100N, the cups were compressed at 200N intervals to a maximum of 2000N. Three trials at each cup compression load were performed. The torque developed about the trunnion axis was measured as the head articulated through a motion arc of 60° and the friction factor was calculated. Head–neck micromotion was continuously monitored using a non-displacement inductive transducer. Changes in micromotion from the 100N compression load were calculated.Introduction
Materials and Methods
The Rejuvenate modular neck stem (Stryker, Mahwah, NJ) was recently recalled due to corrosion at the neck-stem junction. The purpose of this study was to investigate the rate of corrosion related failures and survivorship of this implant, and analyze the correlation between the implant and patient factors with serum metal ion levels. Between June 2009 and July 2012, 123 Rejuvenate stems (97 modular and 26 non-modular) THAs were implanted in 104 patients by a single surgeon via a modified anterolateral approach. Serum Cobalt (Co) and Chromium (Cr) levels (microgram per liter [μg/L]) were obtained in all patients. In cases of elevated serum metal ion levels or symptomatic hip, patients underwent magnetic resonance imaging (MRI) for assessment of osteolysis or adverse local tissue reactions (ALTR). Correlation between implant factors (implant size, head size, head length, offset), patient factors (age, gender, BMI) with serum metal ion levels and revisions were analyzed using logistic regression models.Background:
Material and Methods:
Angular mismatch of the modular junction between the head and the trunion has been recognized as a contributing factor to fretting and corrosion of hip prostheses. Excessive angular-mismatch can lead to relative motion at the taper interface, and tribo-corrosion of the head-neck junction secondary to disruption of the passive oxide layer. Although manufacturing standards have been adopted to define acceptable tolerances for taper angles of mating components, recent investigations of failed components have suggested that stricter tolerances or changes in taper design may be necessary to avoid clinical failures secondary to excessive taper wear and corrosion. In this study we examine the effect of angular-mismatch on relative motion between the taper and bore subjected to normal gait load using finite element methods. Computer simulations were executed using a verified finite element model (FEM), the results from which were determined to be consistent with literature. A stable, converging hexahedral mesh was defined for the trunnion (33648 elements) and a tetrahedral mesh for the femoral head (51182 elements). A friction-based sliding contact was defined at the taper-bore interface. A gait load of 1638N (2.34 × BW, BW = 700N) was applied at an angle of 30° to the trunnion axis (Figure 1) on an assembled FEM. A linear static solution was set up using Siemens NX-Nastran solver. Angular-mismatch was simulated by incrementing the conical half-angle of the bore to examine these cases: 0°, 0.005°, 0.010°, 0.015°, 0.030°, 0.050°, 0.075°, 0.100°, 0.200°and 0.300°.Introduction:
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Femoro-acetabular impingement reduces the range of motion of the hip joint and is thought to contribute to hip osteoarthritis. Surgical treatments attempt to restore hip motion through resection of bone at the head-neck junction. Due to the broad range of morphologies of FAI, the methodology of osteochondroplasty has been difficult to standardize and often results in unexpected outcomes, ranging from minimal improvement in ROM to excessive head resection with loss of cartilage and even neck fracture. In this study we test whether a standardized surgical plan based on a pre-determined resection path can restore normal anatomy and ROM to the CAM-impinging hip. Computer models of twelve femora with classic signs of cam-type FAI were reconstructed from CT scans. The femoral shaft and neck were defined with longitudinal axes and the femoral head by a sphere of best fit. Boundaries defining the maximum extent of anterior resection were constructed: (i) superiorly and inferiorly along the anterior femoral neck at 12:30 and 5:30 on the clock face, approximating the locations of the vascularized synovial folds; (ii) around the head-neck junction along the edge of the articular cartilage; and (iii) at the base of the neck, perpendicular to the neck axis, 20–30 mm lateral to the articular edge. All four boundaries were used to form 3 alternative resection surfaces that provided resection depths of 2 mm (small), 4 mm (medium), and 6 mm (large) at the location of the cam lesion. Solid models of each femur after virtual osteochondroplasty were created by Boolean subtraction of each of the resection surfaces from the original femoral model. For each depth of neck resection, we measured the following: (i) alpha angle, (ii) anterior offset of the head-neck junction, and (iii) volume of bone removed. Before and after each resection, we also measured the maximum internal rotation of the hip in 90° flexion and 0° abduction.Introduction:
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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:
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