We report on a group of 20 metal-on-metal resurfaced hips (17 patients) presenting with a soft tissue mass associated with various symptoms. We describe these masses as pseudotumours.

All patients underwent plain radiography and fuller investigation with CT, MRI and ultrasound. Where samples were available, histology was performed. All patients in this series were female. Presentation was variable; the most common symptom was pain or discomfort in the hip region. Other symptoms included spontaneous dislocation, nerve palsy, an enlarging mass or a rash. The common histological features were extensive necrosis and lymphocytic infiltration. Fourteen of the 20 cases (70%) have so far required revision to a conventional hip replacement and their symptoms have either settled completely or improved substantially since the revision surgery. Two of the three bilateral cases have asymptomatic pseudotumours on the opposite side.

We estimate that about 1% of patients develop a pseudotumour in the first five postoperative years after a hip resurfacing. The cause of these pseudotumours is unknown and is probably multi-factorial, further work is required to define this; they may be manifestations of a metal sensitivity response. We are concerned that with time the incidence of these pseudotumours will increase.

Introduction: Treatment options for the young active patient with isolated symptomatic medial compartment OA and pre-existing ACL deficiency are limited. Implant longevity and activity levels may preclude TKA, whilst HTO and unicompartmentasl knee arythroplasty (UKA) are unreliable due to ligamentous instability. UKAs tend to fail because of wear or tibial loosening resulting from eccentric loading. Combined UKA and ACL reconstruction may therefore be a solution.

Method: Fifteen patients with combined ACL reconstruction and Oxford UKA (ACLR group), were matched (age, gender and follow-up period) with 15 patients with Oxford UKA with intact ACL (ACLI group). Prospectively collected clinical and x-ray data from the last follow-up (minimum 3 years, range: 3 – 5) were compared. Ten patients from each group also underwent in-vivo kinematic assessment using a standardised protocol.

Results: At the last follow-up, the clinical outcome for the two groups were similar. One ACLR patient needed revision due to infection. Radiological assessment did not show any significant difference between relative component positions and none of the patients had pathological radiolucencies suggestive of component loosening. Kinematic assessment showed posterior placement of the femur on tibia in extension for the ACLR group, which corrected with further flexion.

Conclusions: The short-term clinical results of combined ACL reconstruction and UKA are excellent. Lack of pathological radiolucencies and near normal knee kinematics suggest that early tibial loosening due to eccentric loading is unlikely.

Aim: The aim of this study was to asses the accuracy of skyline radiographs in the assessment of the patellofemoral joint, when compared to open intraoperative assessment.

Methods: Eighty nine patients undergoing knee replacement surgery were included in the study. Skyline radiographs were obtained preoperatively. These radiographs were assessed and graded by an experienced musculoskeletal radiologist using the Altman and Ahlbäck classifications. The grades were calculated for both the medial and lateral facets of the PFJ. Intraoperative assessment of the Patellofemoral joint was undertaken at the time of surgery. The damage was graded using the modified Collins classification (0: Normal, 1: Superficial damage, 2: Partial thickness cartilage loss, 3: Focal Full thickness cartilage loss < 2cm2, 4: Extensive full thickness cartilage loss < 2cm2). Data was obtained for the Medial Facet, Lateral Facet and Trochlea.

Results: Spearman’s rank correlation coefficient between the radiographic and macroscopic changes within the lateral PFJ were poor with both the Altman 0.22 (p=0.0350) and Ahlbäck 0.24 (p=0.018). The correlation of the medial PFJ was slightly better with a coefficient for Altman 0.42 (P< 0.0001) and Ahlbäck 0.34 (P> 0.001).

Conclusion: In conclusion skyline radiographs provide a poor to moderate preoperative assessment of the degree of osteoarthritis within the patella-femoral joint. This has significant implications for establishing radiographic criteria for planning patella-femoral joint replacement.

Purpose: The aim of this study is to compare the long-term survival results of TKA in patients under the age of 60, using

revision surgery and

Method: From our knee database we identified a cohort of 60 total knee replacements that had been performed over 15 years previously. We identified those who had died, those who had been revised and established the Oxford Knee Score (OKS) for all those still surviving.

Results Using the following endpoint criteria the cumulative 15-year survival was (A) revision surgery alone = 78% (CI 12), (B) revision surgery or an OKS less than or equal to 24 (50% of total OKS) = 63% (CI 13), and (C) revision surgery or moderate pain = 48% (CI 14).

Conclusion The functional survival of TKA in patients under the age of 60 decreases in the second decade following implantation with a significant number of prostheses failing the patient due to knee pain

Introduction: The information in the literature about the relative merits of cemented and cementless unicompartmental knee replacement (UKR) is contradictory, with some favouring cementless fixation while others favouring cemented fixation. Cemented fixations give good survivorship but there is concern about the radiolucency which frequently develops around the tibial component. The exact cause of the occurrence of radiolucency is unknown but according to some, it may suggest suboptimal fixation.

Method: Sixty-two knees (31 in each group) were randomised to receive either cemented or cementless UKR components. The components were similar except that the cementless had a porous titanium and hydroxyappatite (HA) coating. Patients were prospectively assessed by an independent observer pre-operatively and annually thereafter. The clinical assessment included Oxford Knee Score, Knee Society Scores and Tegner activity score. Fluoroscopically aligned radiographs were assessed for thickness and extent of radiolucency under the tibial implant.

Results: At one year there were no differences in the clinical outcome between the groups and there were no loose components. No radiolucencies thicker than 1mm were seen. At one year none of the cementless tibias and 30% of the cemented tibias had complete radiolucencies. One out of 31 cementless (3%) and 12 out of 31 cemented (39%) had partial radiolucencies. This difference between these two groups was high significant (p< 0 0001).

Conclusions: This study clearly demonstrates that the incidence of radiolucency beneath the tibial component is influenced by component design and method of fixation. With identical designs of tibial component none of the cementless components developed complete radiolucences whereas 30% of the cemented components did. We conclude that HA achieves better bone integration than cement.

Introduction: We report on a group of 20 metal-on-metal resurfaced hips (17 patients) presenting with a soft tissue mass associated with various symptoms; these masses we termed pseudotumours. All patients underwent plane radiography; CT, MRI and ultrasound investigations were also performed for some patients. Where samples were available histology was performed.

Methods: All patients in this series were female. Presentation was variable; the most common symptom was pain or discomfort in the hip region. Other symptoms included spontaneous dislocation, nerve palsy, a noticeable mass or a rash. The common histological features were extensive necrosis and lymphocytic infiltration. Fourteen of the 20 cases (70%) have so far required revision to a conventional hip replacement and their symptoms have either settled completely or improved substantially since the revision surgery. Two of the three bilateral cases have asymptomatic pseudotumours on the opposite side.

Conclusions: We estimate that about 1% of patients develop a pseudotumour in the first five postoperative years after a hip resurfacing. The cause of these pseudotumours is unknown and is probably multi-factorial, further work is required to define this; they may be manifestations of a metal sensitivity response. We are concerned that with time the incidence of these pseudotumours will increase.

The aim of this study was to investigate the molecular features of progressive severities of cartilage damage, within the phenotype of Anteromedial Osteoarthritis of the Knee (AMOA).

Ten medial tibial plateau specimens were collected from patients undergoing unicompartmental knee replacements. The cartilage within the area of macroscopic damage was divided into equal thirds: T1(most damaged), to T3 (least damaged). The area of macroscopically undamaged cartilage was taken as a 4th sample, N. The specimens were prepared for histological (Safranin-O and H& E staining) and immunohistochemical analysis (Type I and II Collagen). Immunoassays were undertaken for Collagens I and II and GAG content. Real time PCR compared gene expression between areas T and N.

There was a decrease in OARSI grade across the four areas, with progressively less fibrillation between areas T1, T2 and T3. Area N had an OARSI grade of 0 (normal).

The GAG immunoassay showed decreased levels with increasing severity of cartilage damage (ANOVA P< 0.0001). There was no significant difference in the Collagen II content or gene expression between areas. The Collagen I immunohistochemistry showed increased staining within chondrocyte territorial areas in the undamaged region (N) and immunoassays showed that the Collagen I content of this macroscopically and histologically normal cartilage, was significantly higher than the damaged areas (ANOVA P< 0.0001). Furthermore, real time PCR showed that there was a significant increase in Collagen I expression in the macroscopically normal areas (p=0.04).

In AMOA there are distinct areas, demonstrating progressive cartilage loss. We conclude that in this phenotype the Collagen I increase, in areas of macroscopically and histologically normal cartilage, may represent very early changes of the cartilage matrix within the osteoarthritic disease process. This may be able to be used as an assay of early disease and as a therapeutic target for disease modification or treatment.

Introduction: Avascular necrosis of the femoral head after resurfacing hip replacement is an important complication which may lead to fracture or failure. We compared the changes in femoral head oxygenation resulting from the posterior approach to those resulting from the anterolateral approach and the trochanteric flip approach.

Methods: In 37 patients undergoing hip resurfacing surgery, a calibrated gas-sensitive electrode was inserted superolaterally in the femoral head via the femoral neck following division of the fascia lata. Inter-operative X-ray confirmed correct electrode placement. Baseline oxygen concentration levels were recorded immediately after electrode insertion. All results were expressed relative to this baseline, which was considered as 100% relative oxygen concentration. Oxygen levels were monitored continuously throughout the operation. 10 patients underwent surgery through the posterior approach, 12 patients through the anterolateral approach and 15 through the trochanteric flip approach.

Results: A similar pattern of intra-operative reduction in femoral oxygen concentration was observed for all reviewed approaches. The average change in oxygen concentration during surgery through the trochanteric flip approach was found to be significantly less than through posterior (p< 0.02) and anterolateral (p< 0.02) approaches. Oxygen concentration following joint relocation and soft tissue reconstruction recovered significantly in the anterolateral and trochanteric flip group only. The posterior approach resulted in significantly lower oxygen concentration at the end of the procedure (22%, SD 31) than the anterolateral approach (123%, SD 99; p< 0.05) and the trochanteric flip approach (89%, SD 62, p< 0.02).

Discussion and Conclusion: The anterolateral and trochanteric flip approaches disrupt the femoral head blood supply significantly less than the posterior approach in patients undergoing resurfacing. The most consistent intra-operative oxygen levels were observed during surgery through the trochanteric flip approach. Oxygen concentration during the anterolateral approach was found to be highly dependent upon leg position. The incidence of complications related to avascular necrosis might be decreased by adopting blood supply conserving surgical approaches.

Aim: To investigate the capacity for retention of arthroscopic technical skills.

Methods: Six consultant lower limb surgeons were given standardized instruction on how to perform an arthroscopic Bankart suture on a lab-based ALEX shoulder model. Each surgeon then performed a suture repair three times and returned to repeat the process on four consecutive occasions, approximately two weeks apart. Six months later the same surgeons returned again to repeat the entire process. They received no further tuition or instruction. Their performance was objectively assessed throughout using validated motion analysis equipment to produce learning curves using time taken, number of movements and total path length.

Results: The initial learning curves and the learning curves at 6 months were the same.

Conclusions: Arthroscopic skills were not retained over a 6 month period. The same learning curves were identified suggesting the need for regular repetition of this simulated task if the level of learning is to be maintained. This has implications for technically difficult arthroscopic procedures suggesting a minimum level of frequency is needed to maintain optimum surgical performance.

Introduction: A major concern with cemented hip resurfacing arthroplasty (HRA) femoral components is the thermal damage to femoral head during cement curing; this maybe linked to fracture (reported incidence ~2%) and early failure. We investigated the effect of a modifid surgical technique using pulse lavage, lesser trochanter suction and early reduction on the maximum temperature recorded in the femoral head during HRA, compared to manual lavage and reduction after cement curing.

Methods: Patients undergoing total hip replacement (THR) were given a dummy HRA procedure, during which a temperature probe was inserted into the femoral head and the measuring tip placed close to the reamed surface; the position of the probe was confirmed by inter-operative xray. Four subjects received a dummy HRA femoral component using manual lavage and Simplex cement. The implanted femur was kept dislocated until the cement cured. The implanted heads were then removed and sectioned to locate the temperature probes, the THR surgery was then performed. Five patients receiving a definitive HRA were also measured; for these subjects suction on the lesser trochanter was used, pulse lavage given for 30 seconds prior to cementing with Simplex, and pulse lavage of the femoral head for 2 minutes, applied 1 minute after cementing the femoral component. The implanted joint was then immediately reduced and a further two minutes of pulse lavage applied to the reduced joint. Temperatures were recorded until the cement finally cured. In every case the cement was hand mixed for 1 minute and the component implanted at 2 minutes 30 seconds after mixing began.

Results: Sectioning showed that probe tips were < 0.5mm from cement mantle. The maximum temperature recorded in the femoral head was significantly (p=0.014) greater for the manual technique, median value of 47.2°C (37.0 to 67.9°C), than for the pulse lavage technique, median value of 32.7°C (31.7 to 35.6°C).

Discussion: The results show that excessive bone temperatures can occur during hip resurfacing. Temperatures above 45°C kill bone cells, the manual technique may lead to substantial thermal necrosis. Technique modification, with the use of suction on the lesser trochanter, generous use of pulse-lavage and joint reduction prior to cement curing, significantly reduced the temperatures recorded. With the modified technique, the maximum temperatures were well below the threshold of thermal damage. This modified technique is recommended as the potential for thermal bone necrosis is significantly reduced.

Introduction: Avascular necrosis of the femoral head after resurfacing hip replacement is an important complication which may lead to fracture or failure. We compared the changes in femoral head oxygenation resulting from the anterolateral approach to those resulting from the posterior approach.

Methods: In 22 patients undergoing hip resurfacing surgery, a calibrated gas-sensitive electrode was inserted supero-laterally in the femoral head via the femoral neck following division of the fascia lata. Inter-operative X-ray confirmed correct electrode placement. Baseline oxygen concentration levels were recorded immediately after electrode insertion. All results were expressed relative to this baseline, which was considered as 100% relative oxygen concentration. Oxygen levels were monitored continuously throughout the operation. 10 patients underwent surgery through the posterior approach, 12 patients through the antero-lateral approach.

Results: During the operation patterns were similar for both groups, except following joint relocation and soft tissue reconstruction; oxygen concentration recovered significantly in the anterolateral group only. The posterior approach resulted in significantly lower (p< 0.01) oxygen concentration at the end of the procedure (22%, SD 31) than the antero-lateral approach (123%, SD 99).

Discussion and Conclusion: The anterolateral approach disrupts the femoral head blood supply significantly less than the posterior approach in patients undergoing resurfacing. The incidence of complications related to avascular necrosis might be decreased by adopting blood supply conserving surgical approaches.

Aim: The diagnosis of partial biceps tears cannot be made reliably with existing physical exam tests. Diagnostic arthroscopy is recommended if this diagnosis is suspected.

The accuracy of the physical examination for biceps pathology remains controversial. The goal of this study was to investigate the validity and clinical usefulness of various physical tests used for diagnosing partial tears of the biceps tendon.

Materials & Methods: The study was a prospective blinded study of 847 consecutive patients who underwent arthroscopic procedures for a variety of shoulder conditions. Forty subjects were found at the time of arthroscopy to have partial biceps tears (24 men and 16 women) with an average age of 59 YO (range from 18 to 83 YO). A pre-operative physical examination using 9 different commonly used tests was performed for all the patients. Statistical analysis included sensitivity, specificity, negative predictive value (NPV), positive predictive value (PPV) and likelihood ratios (LR) for these tests.

Results: The prevalence rate of partial tears was 5 percent of all arthroscopic procedures. Associated conditions included rotator cuff tears (85 percent) and anterior instability (7.5 percent). The sensitivity, specificity, PPV, NPV and the LR for the Speed_s test were 50 percent, 67 percent, 8 percent and 96 percent and 1.51, respectively. None of the other tests was sensitive (less than 50 percent). The lift-off sign had a LR of 2.61 but had a sensitivity of only 28 percent.

Conclusion: The diagnosis of partial biceps tears cannot be made reliably with existing physical exam tests. Diagnostic arthroscopy is recommended if this diagnosis is suspected.

Aim: Distal clavicle excision (DCE) is the treatment of choice for A–C joint arthritis.The overall complication rate for open, isolated DCE is higher than previously reported.

Distal clavicle excision (DCE) is the treatment of choice for A–C joint arthritis. Isolated DCE., as an open procedure has been considered to be a safe procedure, and it is the gold standard for comparison for arthroscopic distal clavicle excision. This study attempts to define the incidence of complications after isolated, open DCE.

Materials & Methods: This prospective, non-randomized study included 702 patients who underwent arthroscopic surgery of the shoulder. 580 patients were included in the control group. All patients underwent a thorough preoperative evaluation and final diagnosis was given after arthroscopic evaluation. There were 42 patients with isolated A–C joint arthritis, which underwent an open D.C.E. Mean follow up was 16.7 months. There were 30 men and 12 women with a mean age of 42,6 (± 12,5) years. The dominant arm was involved in 30 patients. 16 patients participated in sports while 9 of them were competitive athletes. 38 (90%) patients had symptomatic arthritis, 2(5%) cases were of osteolysis and separation arthritis each.

Results: 22 (52%) of the 42 patients developed complications. There were 2 deep infections and 2 stitches abscesses. 4 (9.5%) patients developed a stiff shoulder and 1(2.4%) patient developed heterotopic ossification. 16 (38%) patients had tenderness in A–C joint for a period over 3 months while 6 (14%) patients had local tenderness at the last follow up. Painful scar was present in 2 (5%) patients over 3 months.

Conclusions: The overall complication rate for open, isolated DCE is higher than previously reported. Patients should be advised of these possibilities and this study serves as a baseline for comparison for future study.

Introduction: Treatment options for the young active patient with isolated symptomatic medial compartment osteoarthritis and pre-existing anterior cruciate ligament (ACL) deficiency are limited. Implant longevity and activity levels may preclude total knee arthroplasty (TKA), whilst high tibial osteotomy HTO and unicompartmental arthroplasty (UKA) are unreliable due to ligamentous instability. UKA’s tend to fail because of wear or tibial loosening resulting from eccentric loading. Combined UKA and ACL reconstruction may therefore be a solution.

Method: Fifteen patients with combined ACL reconstruction and Oxford UKA (ACLR group), were matched (age, gender and follow-up period) with 15 patients with Oxford UKA with intact ACL (ACLI group). Prospectively collected clinical and x-ray data from the last follow-up (minimum 3 years, range: 3–5) were compared. Ten patients from each group also underwent in-vivo kinematic assessment using a standardised protocol.

Results: At the last follow-up, the clinical outcome for the two groups were similar (ACLR: OKS 46, KSS (objective): 99, ACLI: OKS 43, KSS (objective): 94). One ACLR patient needed revision due to infection. Radiological assessment did not show any significant difference between relative component positions and none of the patients had pathological radiolucencies suggestive of component loosening. Kinematic assessment showed posterior placement of the femur on tibia in extension for the ACLR group, which corrected with further flexion.

Conclusions: The short-term clinical results of combined ACL reconstruction and UKA are excellent. Lack of pathological radiolucencies and near normal knee kinematics suggest that early tibial loosening due to eccentric loading is unlikely. Similarly, wear is unlikely to be a problem because of the wear resistance of mobile bearing devices.

Introduction: The Oxford unicompartmental knee replacement (UKR) use in the lateral compartment has been associated with a reduced flexion range and increased medial compartment pain than seen with its medial counterpart due to, in part, the inadequacy of a flat tibial tray replacing the domed anatomy of the lateral tibia. A new design incorporating a domed tibial component and a biconcave meniscal bearing has been developed to overcome these problems.

This study reports a clinical comparison of new and old establishing whether this modified implant has maintained the established normal kinematic profile of the Oxford UKR.

Method: Patients undergoing lateral UKR for OA were recruited for the study. Fifty one patients who underwent UKR with the domed design were compared to 60 patients who had lateral UKR with a flat inferior bearing surface. Kinematic evaluation was performed on 3 equal subgroups (n = 20); Group 1-Normal volunteer knees, Group 2-Flat Oxford Lateral UKR’s and Group 3-Domed Oxford Lateral UKR’s. The sagittal plane kinematics of each knee was assessed using videofluoroscopic analysis whilst performing a step up and deep knee bend activity. The fluoroscopic images were recorded digitally, corrected for distortion using a global correction method and analysed using specially developed software to identify the anatomical landmarks needed to determine the Patella Tendon Angle (PTA) (the angle the patella tendon and the tibial axis).

Knee kinematics were assessed by analysing the movement of the femur relative to the tibia using the PTA.

Results: PTA/KFA values, for both devices, from extension to flexion did not show any significant difference in PTA values in comparison to the normals as measured by a 3-way ANOVA. The Domed implant achieved higher maximal active flexion during the lunge exercise than those with a flat implant. Only 33% of the flat UKR’s achieved KFA of 130° or more under load whilst performing a lunge, compared with 75% of domed UKR’s and 90% of normal knees. No flat UKR achieved a KFA of 140° or more, yet 50% of all domed UKR’s did, as did 60% of all normal knees.

Conclusions: There was no significant difference in sagittal plane kinematics of the domed and flat Oxford UKR’s. Both designs had favorable kinematic profiles closely resembling that of the normal knee, suggesting normal function of the cruciate mechanism. The domed knees had a greater range of motion under load compared to the flats, approaching levels seen with the normal knee, suggesting that limited flexion for the flat plateau results from over tightening in high flexion and that this is corrected with the domed plateau. Problems with the second generation of lateral Oxford UKA have been rectified by a new bi-concave bearing without losing bearing stability and normal kinematics.

Introduction: Interest in hip resurfacing has recently been renewed by the introduction of metal-on-metal designs; it is being increasingly used for young patients, with over 30,000 implanted worldwide. The 5 year clinical results appear promising, but there are no long term data available. Radiostereometry (RSA) measures of implant migration have been able to predict implant failure; specifically large and continuous migration predicts aseptic loosening. We present the results of a five year RSA study examining the migration of the Birmingham Hip Resurfacing (BHR).

Methods: Twenty-four subjects with primary OA were implanted with the BHR device and with bone markers for RSA. RSA measurements were taken at 3, 6, 12, 24 and 60 months. The migration of the head and the tip of femoral component were measured in 3D.

Results: Preliminary analysis showed that the total 3D migration of the head and tip over five years was 0.32mm and 0.23mm respectively.

Discussion: A distal migration of more than 0.4mm over 2 years increases the likelihood of failure in conventional stems. The total migration of the BHR was approximately 0.3mm over a five year period, significantly less than cemented THR devices. The device is stable and this is promising for long-term survival.

Finite element (FE) analysis is widely used to calculate stresses and strains within human bone in order to improve implant designs. Although validated FE models of the human femur have been created (Lengsfeld et al., 1998), no equivalent yet exists for the tibia. The aim of this study was to create such an FE model, both with and without the tibial component of a knee replacement, and to validate it against experimental Results: A set of reference axes was marked on a cleaned, fresh frozen cadaveric human tibia. Seventeen triaxial stacked strain rosettes were attached along the bone, which was then subjected to nine axial loading conditions, two four-point bending loading conditions, and a torsional loading condition using a materials testing machine (MTS 858). Deflections and strain readings were recorded. Axial loading was repeated after implantation of a knee replacement (medial tibial component, Biomet Oxford Unicompartmental Phase 3). The intact tibia was CT scanned (GE HiSpeed CT/i) and the images used to create a 3D FE mesh. The CT data was also used to map 600 transversely isotropic material properties (Rho, 1996) to individual elements. All experiments were simulated on the FE model. Measured principal strains and displacements were compared to their corresponding FE values using regression analysis.

Experimental results were repeatable (mean coefficients of variation for intact and implanted tibia, 5.3% and 3.9%). They correlated well with those of the FE analysis (R squared = 0.98, 0.97, 0.97, and 0.99 for axial (intact), axial (implanted), bending, torsional loading). For each of the load cases the intersects of the regression lines were small in comparison to the maximum measured strains (< 1.5%). While the model was more rigid than the bone under torsional loading (slope =0.92), the opposite was true for axial (slope = 1.14 (intact) 1.24 (implanted)) and bending (slope = 1.06) loads. This is probably due to a discrepancy in the material properties of the model.

Background: The Oxford unicompartmental knee replacement (UKR) use in the lateral compartment has been associated with a reduced flexion range, increased medial compartment pain and a higher dislocation rate than seen with its medial counterpart due to the inadequacy of a flat tibial tray replacing the domed anatomy of the lateral tibia. A new design incorporating a domed tibial component and a biconcave meniscal bearing has been developed to overcome these problems. This current study was designed to establish whether this modi-fied ‘domed’ implant has maintained the established normal kinematic profile of the Oxford UKR.

Methods: The study population consisted of 60 participants from three equal groups; Group 1- Normal volunteer knees (n = 20), Group 2 – Flat Oxford Lateral UKR’s (n = 20) and Group 3 – Domed Oxford Lateral UKR’s (n = 20). The sagittal plane kinematics of each involved knee was assessed continuously using videofluoroscopic analysis. A standardised protocol of step-up and deep lunge was used to assess loadbearing range of motion during which the patella tendon angle (PTA) was measured as a function of the knee flexion angle (KFA).

Results: PTA/KFA values compared at 10 degree KFA increments from maximal extension to maximal flexion for all 3 groups did not demonstrate any statistically significant difference in PTA values between any group as measured by a 3-way ANOVA. The Domed implant achieved higher maximal active flexion during the lunge exercise than those with a Flat implant. Only 33% of the Flat UKR’s achieved KFA of 130 degrees or more under load whilst performing a lunge, compared with 75% of domed UKR’s and 90% of normal knees. No Flat UKR achieved a KFA of 140 degrees or more, yet 50% of all domed UKR’s did, as also did 60% of all normal knees.

Conclusions: There is no significant difference in the sagittal plane kinematics of the domed and flat Oxford UKR’s. Both implant designs have a favourable kinematic profile closely resembling the normal knee. The domed knees though do have a greater range of motion under load as compared to the flats, approaching levels seen with the normal knee.

Introduction: Restoration of predictable and normal knee kinematics after a TKR can improve the patient’s function. Traditional designs exhibit grossly abnormal kinematics with the femur subluxing posteriorly in extension and a paradoxical forward slide in flexion. In addition, the kinematics are very variable. Newer designs were intended to overcome these problems, owing to their ability to provide ‘guided motion’ of the components. The medial pivot knee uses a specifically designed articulating surface constraining the femoral component to externally rotate about an axis through the medial compartment.

This study assesses the functional in vivo kinematics of Advanced Medial Pivot (AMP) TKR and compares it to kinematics of the normal knee.

Methods: Thirteen patients with pre-operative diagnosis of primary osteoarthritis, who had undergone a knee replacement with the AMP knee at least one-year prior were recruited in this study. All had an excellent clinical outcome (as assessed by AKSS) and underwent fluoro-scopic analysis whilst performing a step up activity. Knee kinematics were assessed by analysing the movement of the femur relative to the tibia using the Patella Tendon Angle (PTA) through the range of knee flexion. This data was compared to that of thirteen normal knees.

Results: The PTA for the normal knee has a linear relationship with knee flexion. The PTA is 14 degrees in full extension and decreases to -10 degrees at 100 degrees knee flexion during a step-up exercise. Between extension and 60 degrees of knee flexion, no significant difference was found between the PTA for the normal knee and for the AMP. The PTA for AMP is significantly higher for values of knee flexion exceeding 60 degrees. The standard deviation for different values of knee flex-ion is similar to that seen in the normal knee.

Conclusions: In extension, the PTA is near normal but in flexion PTA is higher than normal suggesting that the femur is too anterior. The variability of the kinematics for AMP TKR is similar to that of the normal knee and is better than that of most other knee designs that we have studied in the past, indicating that it is a stable TKR.

Introduction: The cam-post mechanism of Posterior Stabilized Total Knee Arthroplasty (PS-TKA) should provide a constraint that limits anterior translation of the femur on the tibia in flexion and thereby ensure femoral roll-back with progressive knee flexion. In a previous fluoroscopic study we showed that the sagittal plane kinematics of a PCL substituting TKA (Scorpio PS) was abnormal in flexion, suggesting inefficiency of the cam-post mechanism. We also assessed the movement of the femur relative to the tibia using the Patella Tendon Angle (PTA) through the range of knee flexion (0 to 90 degrees). The aim of the current study was to investigate in greater detail why the cam-post mechanism was ineffective by assessing the contact point movement and the distance between the cam and post.

Method: Twelve patients with Scorpio PS TKA underwent fluoroscopic assessment of the knee during a step up exercise and a weight bearing deep knee bend. The image distortion was corrected using a global correction method and the data was analysed using a 3D model fitting technique. Having determined the component position, the minimum distance between cam and post were determined. The femoro-tibial contact positions of the medial and lateral condyles were determined relative to the mid-coronal plane of the tibial component. The PTA was calculated by measuring the angle subtended by patella tendon with the tibial axis and was plotted against knee flexion angle (KFA).

Results: The relationship between PTA and KFA was abnormal relative to the normal knee. Between extension and 60 degrees flexion there was forward movement of both medial (11 mm) and lateral (5 mm) femoral condyles. Thereafter, both condyles moved back (10 mm). The cam-post mechanism failed to engage in one case while in others it engaged between 70 to 100 degrees.

Conclusions: The 3D analysis has confirmed the preliminary findings of the previous study using the PTA and KFA relationship. Despite the cam engaging in flexion normal knee kinematics were not restored. The femoral roll-back is inadequate and starts to occur at least 20 degrees before the cam and post engage.

The aim of this study was to use motion analysis to study a surgeon’s learning curve for an arthroscopic Bankart repair on a training model in a skills laboratory. Six fellowship trained lower limb surgeons unfamiliar with advanced shoulder arthroscopy performed an arthroscopic Bankart repair on an ALEX shoulder model. Standardised training was given and then an electromagnetic tracking system used to objectively assess hand movements, distance travelled by hands and time taken while the surgeons performed the technique. The arthroscopic repair was repeated three times on four consecutive occasions by each surgeon giving a total of 72 repair episodes. Analysis revealed improvement of all outcome parameters with less hand movements, less distance travelled and less time to complete the task. This study objectively demonstrates a learning curve for arthroscopic Bankart suture in a skills laboratory. It indicates the potential benefits of practicing aspects of arthroscopic techniques in a skills centre on appropriately selected models.

Background: The Oxford unicompartmental knee replacement (UKR) use in the lateral compartment has been associated with a reduced flexion range and diminished femoral rollback. It is postulated that this may be due to a flat tibial tray replacing the domed anatomy of the lateral tibia, tightening the posterolateral flex-ion gap. A new design incorporating a domed tibial component and a biconcave meniscal bearing has been developed to increase; (i) the posterolateral flexion gap in deep knee flexion (ii) meniscal bearing movement and (iii) lateral femoral condyle (LFC) rollback. A cadaveric study was designed to test these three outcomes.

Methods: The sagittal plane kinematics of seven thawed fresh frozen cadaver specimens within an upright Oxford testing rig were assessed under three different conditions; (i) intact normal cadaver knee (ii) flat lateral Oxford UKR (iii) domed lateral Oxford UKR. Each condition was tested during three ranges of motion (ROM) and data recorded during a flexion or extension half cycle. Knee flexion angle (KFA) and displacement measures of the lateral collateral ligament (LCL), LFC rollback and anteroposterior meniscal bearing movement were performed throughout knee ROM using four [3 linear, 1 rotary] potentiometer devices. Potentiometer data was recorded as a voltage reading and subsequently converted to either a millimetre displacement or degree measure using a calibration formula. All data points were compared at 10 degree interpolations of KFA.

Results: The flexion half cycles demonstrated the flat Oxford lateral UKR achieved 80.7% of normal cadaveric LFC rollback. The domed Oxford lateral UKR achieved 108.8% of normal cadaveric LFC rollback. The ratio of LFC rollback in the domed to flat UKR’s was 1.35 times (134.9%). Meniscal bearing movement in flexion demonstrated a domed to flat UKR ratio of 1.3 times (129.7%). Similar values were obtained for extension half cycles in favour of the domed Oxford lateral UKR. No significant differences were identified in LCL measures.

Conclusions: The domed Oxford lateral UKR implant allows for improved bearing movement and femoral rollback when compared to the flat Oxford lateral UKR. The sagittal plane kinematics of the domed Oxford lateral UKR as represented by femoral rollback values approximate those of the normal cadaver knee.

Finite element (FE) analysis is widely used to calculate stresses and strains within human bone in order to improve implant designs. Although validated FE models of the human femur have been created (Lengsfeld et al., 1998), no equivalent yet exists for the tibia. The aim of this study was to create such an FE model, both with and without the tibial component of a knee replacement, and to validate it against experimental results.

A set of reference axes was marked on a cleaned, fresh frozen cadaveric human tibia. Seventeen triaxial stacked strain rosettes were attached along the bone, which was then subjected to nine axial loading conditions, two four-point bending loading conditions, and a torsional loading condition using a materials testing machine (MTS 858). Deflections and strain readings were recorded. Axial loading was repeated after implantation of a knee replacement (medial tibial component, Biomet Oxford Unicompartmental Phase 3). The intact tibia was CT scanned (GE HiSpeed CT/i) and the images used to create a 3D FE mesh. The CT data was also used to map 600 transversely isotropic material properties (Rho, 1996) to individual elements. All experiments were simulated on the FE model. Measured principal strains and displacements were compared to their corresponding FE values using regression analysis.

Experimental results were repeatable (mean coeffi-cients of variation for intact and implanted tibia, 5.3% and 3.9%). They correlated well with those of the FE analysis (R squared = 0.98, 0.97, 0.97, and 0.99 for axial (intact), axial (implanted), bending, torsional loading). For each of the load cases the intersects of the regression lines were small in comparison to the maximum measured strains (< 1.5%). While the model was more rigid than the bone under torsional loading (slope =0.92), the opposite was true for axial (slope = 1.14 (intact) 1.24 (implanted)) and bending (slope = 1.06) loads. This is probably due to a discrepancy in the material properties of the model.

Hip resurfacing arthroplasty (HRA) is increasingly carried out as an alternative to total hip arthroplasty (THA) in young patients. During the procedure, a metal stem on the retrosurface of the HRA is inserted into the femoral head to ensure the implant is located centrally with respect to the femoral neck. It has been suggested that the stem may interfere with bone loading. In light of this, the current study employed finite element (FE) models to investigate the change in the HRA-implanted bone mechanics as a result of removing the stem. FE models of a cadaveric femur pre- and post-HRA surgery were analysed to determine changes in bone stress/ strain.

The implanted models simulated geometry for a cemented HRA with and without a non-cemented stem (HRA-Stem and HRA-NoStem, respectively) and included more accurate multiple material parameters to simulate the non-homogeneous material distribution in the femoral bone. The models included loading conditions simulating an instant at 10% of the gait cycle. Bone stresses/strains in the femoral head and neck of the implanted models were compared with the intact condition to assess the change in bone mechanics. Changes in cement mantle stresses between the HRA-Stem and HRA-NoStem models were also compared.

When comparing similar volumes of bone in the femoral neck, both HRA models showed a similar variation in stress from the intact condition and bone stresses were low in comparison to the ultimate strength of cortical bone. There was less change in peak strain energy in the femoral head of the HRA-NoStem model than the HRA-Stem model. Cement mantle stresses in the HRA-NoStem model were slightly higher than for the HRA-Stem model and the peak compressive stress was close to the fatigue limit for bone cement.

These preliminary results suggest that the bone loading is more normal without the stem. However, there are increased cement mantle stresses.

Lisfranc injury is named after Jacques Lisfranc, a field surgeon in Napoleon’s army.

Based on Columnar classification of Lisfranc fracture dislocation, study of injury to medial column was carried out as they have the potential to be a severe cause of residual disability in the foot if not properly treated at the initial stage. Importance of Medial column is that it forms the highest point of longitudinal arch and may be injured in isolation or in association with lateral and middle column. Complex deforming forces may cause unusual pattern of medial column injuries at more than one level. There is renewed interest in this injury over past decade as modalities of treatment have changed over a period of time from conservative to fixation with K-wires to rigid fixation with screws to fixation with absorbable screws or combination of above.

We present 21 cases of medial column injuries in Lis-franc fracture-dislocation. Age ranged from 18 to 65 yrs. All were male. Four fixed with compression screws,12 fixed with K-wires, 2 managed conservatively, 3 were neglected cases. Post-operatively POP back splint was given, K-wire removal at 8 weeks, screw removal after 12 weeks and partial weight bearing started at 8-12 weeks. Follow-up ranged from 3 months to 3 years.

They were graded on basis of residual pain, foot shape, and movements. Best results were seen in cases where rigid intertarsal / intercolumnar stability was achieved by screw fixation. There was residual inter-cuneiform subluxation in 4 cases, which were fixed with K-wires, and this led to residual pain. Conservative/neglected cases had poor results.

Intercolumnar / intertarsal instabilities should be primarily recognized and stabilized under compression. Stabilization should not only be within the 3 columns but also intercolumnar, thus maintaining the relative length of 3 columns and hence reconstitution of medial longitudinal arch.

Patellofemoral Pain Syndrome is characterized by anterior knee pain during activities such as squatting that is thought to be caused by abnormal patellar motion. However, the causative role has yet to be verified since it is difficult to measure the three-dimensional kinematics of the patellofemoral joint (PFJ) in vivo. We developed a fluoroscopy-based method to measure patellar motion as it moves under load through a cycle of flexion and compared the results with those obtained using Roentgen Stereophotogrammetric Analysis (RSA). Our data suggest that the fluoroscopy-based method has sufficient accuracy to detect clinically significant differences in patterns of patellar motion.

The purpose of our study was to determine how accurately a fluoroscopy-based method measures patellar tracking.

Our method measures three-dimensional PFJ kinematics with sufficient accuracy to be of clinical value in assessing dynamic motion.

Patellar tracking can be assessed during aggravating activities to identify specific tracking abnormalities related to anterior knee pain.

Four cadaver knees were imaged using computed tomography (CT). Surface models were generated and the coordinates of implanted tantalum beads (in the femur, patella, and tibia) were determined. A series of fluoroscopic images were taken with the knees loaded in a rig at various flexion angles. Each calibrated fluoroscopic image was registered to the CT model using a point-based method such that the high-resolution CT model was matched to the position of knee flexion associated with each fluoroscopic image. The patellar orientation and position relative to the femur was then reconstructed and described using a gyroscopic joint coordinate system. Measurements were made under the same test conditions using the established uniplanar RSA technique. Fluoroscopy-based and RSA-based measures of patellar orientation and position were compared.

The mean measurement error (SD) for patellar flexion, spin, and tilt was 1.86 (1.55), 1.16 (1.14), and 1.15 (1.10) degrees, respectively. For proximal, lateral and anterior patellar translation, the mean measurement error (SD) was 2.11 (2.16), 0.59 (0.47), and 1.24 (1.18) mm, respectively.

The accuracy of the fluoroscopy-based method of measuring PFJ kinematics was poorer than the reported accuracy of RSA but appears to be sufficiently low to be of clinical value.

Funding: Supported by an operating grant from the Canadian Institutes for Health Research and a Strategic Grant from the Natural Sciences and Engineering Research Council. NJM is supported by TAS/CIHR Partnership Fund.

The design philosophy of polished tapered total hip replacements (THR), such as the Exeter, intends for them to migrate distally within the cement mantle. As well as migration, dynamically induced micromotion (DIMM) occurs as a result of functional activity between the implant and the cement. The aim of the current study was to develop and validate a finite element (FE) model of the Exeter/cement/bone system which can be used to predict DIMM and investigate the stresses induced in the cement mantle during functional activity.

In the context of the current study, DIMM is defined as the displacement of the implant component relative to the bone when moving from double leg stance to single leg stance on the operated limb. Using Roentgen Stereo-photogrammetric Analysis (RSA), DIMM was measured in 21 patients implanted with Exeter stems 3 months post-operatively. A previous study, using a reduced FE model of the Exeter stem and the surrounding cement mantle focused on the solution of the contact problem at the stem-cement interface. It was demonstrated that sliding contact combined with Coulomb friction and an appropriate parameter setting could be used to predict DIMM of a polished tapered stem. For the purposes of the current study, the previous simple model was incorporated into the FE model of the Muscle Standardised Femur and validated against the RSA measurements for DIMM. For the current extended model, loading included muscle forces representing all active muscles acting on the femur. The effect of initial cement stresses and interdigitation was also considered.

The Exeter stem demonstrated significant DIMM (p< 0.017). The FE model, accounting for sliding contact at the cement–implant interface was able to predict similar distal migration of the head and the tip. The results of both the calculations and the measurements showed that the femoral head moves medially, distally and posteriorly relative to the bone. In the cement mantle, maximum principal stresses were oriented circumferentially, minimum principal stresses were oriented radially. When the taper got engaged, submicroscopic movements which did not recover following unloading still took place and accumulated.

The results of the present study showed that it is possible to measure DIMM in the Exeter stem and combine this with FE modelling of the contact mechanism. Future studies will include various activities, such as walking or stair climbing. Based on accumulated submicroscopic movements, short-, mid- or long-term migration patterns will be predicted.

Skin and soft tissue loss is very common in modern high velocity trauma. Such wounds pose problem of coverage. We present a good alternative to skin grafting & flaps i.e. SINGH’S skin traction device for wound closure in these patients.

The technique is based on the principle of tissue expansion and makes use of viscoelastic properties of the skin i.e. creep and stress relaxation. 100 cases with 116 wounds with skin and soft tissue loss were treated. Two parallel kirshner wires (1.5mm) were passed through the dermis on either side of the wound margins and interconnected by compression device consisting of threaded rod having two blocks and compression knob. Gradual compression approximated the wound margins. Patients ranged in age from 15 to 65 years with average age of 30.5 years. Main modes of injury were roadside accidents and machinery accidents. Average operating time was about 20 minutes. 50 amputation stump wounds were also treated.

Excellent results were observed in 48 (41.4%), good in 42 (36.2%), fair in 14 (12%) and poor in 12 (10.4%) wounds. Main complication was cutting through of wires.

We found that this technique is simple, economical and effective. No special training and instruments are needed and can be done by junior surgeon at small centres. It provides full thickness cover to the wound which matches the surrounding normal skin in quality, sensations and colour. Above all this technique can be successfully used in infected wounds and wounds with exposed bone and tendons. Careful gradual compression judged by pain and blanching gives better results and fewer complications.

The long-term survival of total knee arthroplasty (TKA) has been well established; however, functional outcome remains inconsistent. More normal postoperative TKA kinematics have been shown to produce better knee function. Improved kinematics can be obtained by using implants with optimised surface geometry. Hence a TKA with an appropriate surface geometryis likely to provide superior long-term functional outcome. The Advance-Medial Pivot TKA (Wright Medical) is a fixed bearing prosthesis with a conforming medial compartment and a non-conforming (flat on flat) lateral compartment. This surface geometry is designed with the intention of replicating the normal knee motion of sliding or pivoting medially and rolling back laterally.

Aim: To investigate the sagittal plane kinematics of Advanced Medial Pivot Knee and compare with those of “flat on flat” fixed bearing TKA and normal knees

18 patients who had undergone primary TKA for osteoarthritis were recruited at an average of 18 months post operation. These patients performed flexion and extension exercises against gravity and a step up exercise. Video fluoroscopy of these activities was used to obtain the patellar tendon angle (PTA). This is a previously validated method for assessing sagittal plane kinematics of a knee joint. The kinematic profile of the Advance Medial Pivot Knee was compared to the profile of 14 normal knees and 30 flat on flat, fixed bearing TKA’s.

The sagittal plane kinematics of the Advance TKA differed from the normal knees. However, similarly to normal knees, a linear relationship was observed between PTA and knee flexion angle throughout knee flexion range. The kinematics of the Medial Pivot Knee were similar to normal when the knee was in a highly flexed position.

Functional plane kinematics of the Advance Medial Pivot TKA appear to meet the design criteria in that a linear relationship between PTA and flexion angle is maintained. Further work is required to establish if these improved sagittal plane kinematics translate into improved functional outcome.

We evaluated the accuracy of a Magnetic Resonance Imaging (MRI)-based method to measure three-dimensional patellar tracking during loaded knee flexion. This method determines the relative positions of the knee bones by shape matching high-resolution three-dimensional geometric models of these bones to fast low-resolution scans taken during loaded flexion.

The accuracy of the method’s assessment of patellar position and orientation was determined by comparing test measurements in four cadaver specimens to measurements made in the same specimens using Roentgen Stereophotogrammetric Analysis (RSA). This MRI-based method is more accurate than current two-dimensional imaging methods.

The purpose of this study was to determine the accuracy of a MRI-based technique for measuring patellar tracking in loaded flexion.

This novel, noninvasive, MRI-based method measures three-dimensional patellar tracking during loaded knee flexion with sufficient accuracy to detect clinically significant changes.

Although abnormal patellar tracking is widely believed to be associated with pain and cartilage degeneration at the patella, these relationships have not been clearly established because most current methods assess only the two-dimensional alignment of the patella at one position. Measurements possible with this method should be sufficiently accurate to yield new insights into these relationships.

Four cadaver knee specimens were flexed through seventy-five degrees of flexion in an MRI-compatible knee loading rig. A high-resolution image was acquired with each knee in extension and then a series of low-resolution scans (in two slice directions: axial and sagittal) were acquired through a flexion cycle. Segmenting bone outlines from high-resolution scans generated models of the femur, tibia and patella. These models were shape matched to the segmented bone outlines in the low resolution scans. Patellar attitude and position were determined and compared to measurements made using RSA.

The mean measurement error in every kinematic parameter was lower for “fast” sagittal plane slices than for “fast” axial plane slices. In general, the mean measurement error was increased by decreasing the number of low-resolution slices.

This method is more accurate than many two-dimensional methods, exposes participants to no ionizing radiation, and can be used through a large range of loaded knee flexion.

Funding: Supported by an operating grant from the Canadian Institutes for Health Research and a Strategic Grant from the Natural Sciences and Engineering Research Council. NJM is supported by the Arthritis Society/CIHR Partnership Fund.

Please contact author for figures and/or tables.

Medial unicompartmental replacement (UKR) has been shown to have superior functional results to total knee replacement (TKR) in appropriately selected patients, and this has been associated with a resurgence of interest in the procedure. This may relate to evidence showing that the kinematic profile of UKR is similar to the normal knee, in comparison to TKR, which has abnormal kinematics. Concerns remain over the survivorship of UKR and work has suggested the anterior cruciate ligament (ACL) may become dysfunctional over time. Cruciate mechanism dysfunction would produce poor kinematics and instability providing a potential mechanism of failure for the UKR.

Aim: To test the hypothesis that the sagittal plane kinematics (and cruciate mechanism) of a fixed bearing medial UKR deteriorate over time (short to long term).

A cross sectional study was designed in which 24 patients who had undergone successful UKR were recruited and divided into early (2–5 years) and late (> 9 years) groups according to time since surgery. Patients performed flexion/extension against gravity, and a step up. Video fluoroscopy of these activities was used to obtain the Patellar Tendon Angle (PTA), the angle between the long axis of the tibia and the patella tendon, as a function of knee flexion. This is a previously validated method of assessing sagittal plane kinematics of a knee joint.

This work suggests the sagittal plane kinematics of a fixed bearing UKR is maintained in the long term. There is no evidence that the cruciate mechanism has failed at ten years. However, increased tibial bearing conformity from ‘dishing’, and adequate muscle control, cannot be ruled out as possible mechanisms for the satisfactory kinematics observed in the long term for this UKA.

Objectives : To determine the change in passive knee kinematics after Oxford Unicompartment Arthoplasty (UKA) (Biomet, Uk); and to compare the change in kinematics post-operatively between image guided and the normal surgical procedure.

Background: In anteromedial osteoarthritis, only the medial compartment of the knee is affected and the collateral ligaments as well as the cruciate mechanism are intact. These preconditions make the knee suitable for UKA. The operative technique of the Oxford UKA theoretically allows the surge on to replicate the natural kinematics of the knee, due to accurate ligament balancing and fully congruent meniscal bearing design of the prosthesis. Our hypothesis was that no difference in tibiofemoral kinematics is observed after UKA. In addition we also hypothesised that the results of the image guided surgery would be the same as the normal surgical procedure.

Design/Methods: To test this hypothesis, we conducted a study using 13 normal human cadaveric knees. For kinematic analysis, the Surgetics TM surgical navigation system (Praxim, France), equipped with custom written tracking software, was used. Reference markers were mounted to the proximal tibia and the distal femur. In a standardized set-up, the knee was positioned in a leg holder and preoperative kinematics of the normal knee was recorded after a para-patellar mini-incision (70–90 mm). Joint kinematics were recorded during passive knee flexion and plotted against flexion angle. Oxford UKA was performed; the standard Phase III instrumentation was used for six knees and the image guided procedure was used for seven knees. The main difference between the standard and image guided procedures was that the inter-medullary rod was not used for the image guided surgery. After the operation postoperative kinematics were recorded using the same measurement protocol. All data were processed using Matlab 6.1 analysis software (The Math Works Inc., MA, USA). Preoperative and postoperative tibiofemoral kinematics were determined and compared. The mechanical axes of the tibia and femur were determined and kinematics represented as functions of knee flexion range. Over both the flexing and extending cycles of the knee the changes in tibiofemoral rotation (& #916;ROT), tibiofemoral ab/adduction (& #916;ABD), and distances between the origins of the mechanical axes (& #916;X, & #916;Y, & #916;Z) were calculated between pre and post-operative states.

Design/Methods: To test this hypothesis, we conducted a study using 13 normal human cadaveric knees. For kinematic analysis, the Surgetics TM surgical navigation system (Praxim, France), equipped with custom written tracking software, was used. Reference markers were mounted to the proximal tibia and the distal femur. In a standardized set-up, the knee was positioned in a leg holder and preoperative kinematics of the normal knee was recorded after a para-patellar mini-incision (70–90 mm). Joint kinematics were recorded during passive knee flexion and plotted against flexion angle. Oxford UKA was performed; the standard Phase III instrumentation was used for six knees and the image guided procedure was used for seven knees. The main difference between the standard and image guided procedures was that the inter-medullary rod was not used for the image guided surgery. After the operation postoperative kinematics were recorded using the same measurement protocol. All data were processed using Matlab 6.1 analysis software (The Math Works Inc., MA, USA). Preoperative and postoperative tibiofemoral kinematics were determined and compared. The mechanical axes of the tibia and femur were determined and kinematics represented as functions of knee flexion range. Over both the flexing and extending cycles of the knee the changes in tibiofemoral rotation (& #916;ROT), tibiofemoral ab/adduction (& #916;ABD), and distances between the origins of the mechanical axes (& #916;X, & #916;Y, & #916;Z) were calculated between pre and post-operative states.

Conclusions: The image guidance system used in our study is a valuable tool for assessing pre- and postoperative knee kinematics. Oxford Unicompartmental Knee Arthroplasty with the Phase III instrumentation in the presence of the cruciate mechanism reproduces the normal kinematics of the knee very accurately. The image guided procedure, performed without the inter-medullary rod, produced similar results to the standard surgery. Image guidance has a great potential for the assessment of pre- and post-replacement kinematics of the knee joint during surgery.

Functional outcome after patellofemoral joint replacement (PFA) for osteoarthritis remains inconsistent. It is believed that functional outcome for joint replacement is dependent upon postoperative joint kinematics. Minimal disruption of the native joint, as in PFA, should produce more normal kinematics and improved outcome. No previous studies have examined joint kinematics after isolated PFA.

Aim: To investigate the sagittal plane kinematics of patellofemoral replacement and compare with the normal knee.

Twelve patients who had undergone successful PFA at least two years previously were recruited. Patients performed flexion/extension against gravity, and a step up. Video fluoroscopy of these activities was used to obtain the Patellar Tendon Angle (PTA), the angle between the long axis of the tibia and the patella tendon, as a function of knee flexion. This is a previously validated method of assessing sagittal plane kinematics of a knee joint. The kinematic profile of the PFA joints was compared to the profiles for fourteen normal knees.

Overall, the kinematic plot obtained for PFA reflected similar trends to that for normal knees; but the PTA was slightly but significantly increased throughout the entire range of flexion (two degrees). This is equivalent to an average displacement of the lower pole of the patella of 1.5mm.

Sagittal plane knee kinematics after PFA are much more normal than after TKR and this should give improved functional outcome. The observed increase in PTA through range may result from increased patella thickness or a shallow trochlear groove and may influence patellofemoral contact forces.

Patellofemoral pain is a significant problem for patients with Total Knee Replacements (TKRs). It is hypothesized that pain is related to high patellofemoral forces (PFF). The aim of this study is to validate a model to estimate PFF after TKR, using a combination of non-invasive measurement and theoretical modeling.

Experiments were performed on four cadaver knee specimens to compare the PFF and the quadriceps force (QF) estimated by a model, with those measured using force transducers. Each knee was tested in its initial state and after implantation of three Scorpio designs: Cruciate Retaining (CR), Posterior Stabilised (PS), and the Posterior Stabilised Mobile Bearing (PS+). Each knee was extended/flexed under a simulated quadriceps load with 3 kg hung from the distal tibia. Relative movement of the bones was measured using a Vicon 612 motion analysis system. A 6DOF force transducer was used to measure PFFs and a uni-axial transducer was used to measure QFs. A fluoroscope simultaneously captured images of the leg extension activity. Parameters measured from the images were used as inputs to the model.

The measured and estimated PFF and QF matched closely between 20o and 80o of knee flexion for the TKRs. At higher flexion angles, the model overestimated the PFF by a maximum of 23N (7.6% max) for the PFF and by 31N for the QF (10.3% max). The estimated and measured Patellar Flexion Angles (PFA) were within 3.5o throughout the flexion range.

The model accurately predicts sagittal plane patellar kinematics and kinetics, using only fluoroscopy and externally measured forces as inputs. However, the model has a limitation in assuming that the extending moment is only due to the quadriceps.

Award for the best student biomaterials paper (US$ 2,000); a proper certificate

Roentgen stereophotogrammetric analysis (RSA) is a tool that can provide quantitative information for objective evaluation and comparison of implant migration. The purpose of this study was to develop and validate a new method to determine the position and orientation of an implant with RSA that does not require the implant modification or acquisition of accurate 3D implant models. This method utilizes information from certain common features of implant geometry. This method has demonstrated in-vitro precision and accuracy of 0.005 !0.059 mm in position and 0.09 ! 0.166° in orientation which is equivalent to both marker and model based RSA methods

Roentgen stereophotogrammetric analysis (RSA) is a tool that can provide quantitative information for objective evaluation and comparison of implant migration. RSA measures have demonstrated the ability to both predict premature implant failure before clinical or standard radiological signs appear, and to elucidate implant wear which is considered a major causal factor in failure. To provide this functionality, RSA requires either the modification of each implant by the addition of spherical markers or the acquisition of accurate 3D models of each implant. These approaches can significantly limit the application of the RSA method. The purpose of this study was to develop and validate a new method to determine the position and orientation of an implant with RSA that does not require the modifying or acquiring accurate 3D models of each implant. This method is based on the geometric inter-relationship between the pair of RSA images and geometric information from the projected outlines of certain paired (visible in both views) features of implant geometry. Evaluations were performed on a metallic acetabular cup modified with spherical markers. The implant features used in this case where the hemispherical shell and the planar circle at the base of the acetabular cup. This method has demonstrated an average in-vitro precision and accuracy of 0.005 !0.059 mm in position and 0.09 ! 0.166° in orientation which was equivalent to that achieved with the marker based method and equivalent to published model based RSA results.

Funding: NSERC, GEOIDE, University of Calgary.

Proprioception protects joints against injurious movements and is critical for joint stability maintenance under dynamic conditions. Knee replacement effect on proprioception in general remains elusive. This study aimed to evaluate the changes in proprioceptive performance after knee replacement; comparing Total (TKA) to Unicompartmental Knee Arthroplasty (UKA).

Thirty-four patients with osteoarthritis were recruited; 15 patients underwent TKA using the AGC prosthesis and 19patients underwent UKA using the Oxford prosthesis. Both cruciate ligaments were preserved in the UKA group, while only the PCL was preserved in TKA patients. Patients’ age was similar in both groups.> Joint Position Sense (JPS) and postural sway were used as measures of proprioception. Both groups were assessed pre- and 6 months post-operatively in both limbs. JPS was measured as the error in actively and passively reproducing five randomly ordered knee flexion angles between 30 and 70°using an isokinetic dynamometer. Postural sway (area and path) was measured during single leg stance using a Balance Performance Monitor. Functional outcome was assessed using the Oxford Knee Score (OKS).

Pre-operatively, no differences in JPS or sway were found between limbs in either group. No differences existed between the two groups. Post-operatively, both groups had significant improvement of JPS in the operated limb (UKA mean4.64°, SD1.44° and TKA mean5.18°, SD1.35°). No changes in JPS were seen in the control side. A significant improvement (P< 0.0001) in sway area and path was found in the UKA group only in both limbs. No significant changes in sway occurred in either limb of TKA patients. The OKS improved from 21.4 to 35.5 for TKA patients and from 23.9 to 38for UKA patients.

Both UKA and TKA improve proprioception as assessed by JPS. However, UKA alone improves postural sway in both limbs. This may impart explain why UKA patients function better than TKA patients

The Charnley Elite femoral component was first introduced in 1992 as a new design variant of the original Charnley femoral component (De Puy, Leeds, UK) with modified neck and stem geometry. The original component had undergone few changes in nearly forty years and has excellent long-term results. Early migration of the new stem design was determined by Roentgen Stereophotogrammetric Analysis (RSA)1. Rapid early migration of a component relative to the bone, measured by RSA, is predictive of subsequent aseptic loosening for a number of femoral stems. As there was rapid early migration and rotation of the Charnley Elite stem, we predicted that the long-term results would be poor. An outcome assessment is indicated as stems of this type are still being implanted.

One hundred Charnley Elite stems, implanted in our centre between 1994 and 1997 were included in a prospective, cross-sectional follow-up study. Outcome measures include validated clinical scores (Charnley hip score, Harris hip score and Oxford hip score) and radiological scores (Gruen classification) as well as revision rates over the past 10 years.

The clinical follow-up supports the RSA predictions of early failure of the Charnley Elite femoral stem.

Hypothesis Stem surface finish & cement mantle conformity influences pressure at the stem/cement interface, under physiological load.

Method We developed a scaled mechanical analogue of a cemented Exeter femoral stem with a temperature and pressure controlled fluid environment. The stem was subjected to physiological torsional & axial loads using a material testing machine with two perpendicularly mounted actuators. Rough (Ra=2.2μm), matt (Ra=1.16μm) & polished (Ra=0.02μm) stems were tested in both conforming & artificially created, asymmetrically worn, cement mantles. Pressure was recorded at five sites along the interface.

Results Pressure was generated in both conforming and worn mantles. Peak pressures recorded in worn mantles were nearly four times greater than in conforming; peak stem tip pressures, worn: 12000Pa, versus conforming: 4680Pa. The axial load was the main determinant of pressure generation in the conforming mantle. Torsional loads generated a rise in interface pressure in both mantle types but the resultant stem toggle seen in the worn mantle had a significant positive effect on pressure. Pressure fluctuations generated in the conforming mantle had the greatest range at the tip. Peak pressures within the worn mantle were more uniform, but marginally greater on the posterior wall. Surface finish influenced pressure; surface roughness had a positive association with pressure within conforming mantles & the reverse effect in worn mantles.

Conclusion Asymmetrical wear leads to increased pressure generation at the stem/cement interface under physiological loads, with the torsional load playing a key part in pressure generation. Well fixed, debonded stems also generate limited pressure fluctuations at their mantle interface. This is principally due to axial load. Mantle shape dictates the influence of surface finish on pressure; surface roughness increases pressure within conforming mantles, but reduces pressure when the mantle is worn. This may be a confounding effect of worn mantle shape, restricting non-polished stem movement.

Introduction: The design philosophy of polished tapered THR stems, such as the Exeter, intend for them to migrate distally within the cement mantle. In addition it is likely that micromotion occurs as a result of functional activity. The pattern of induced stresses will be a function of stem geometry & surface finish, as well as applied loading. Aim: To investigate the stresses induced in the cement mantle of a polished tapered THR stem during functional activity.

Method: Using Roentgen Stereophotogrammetric Analysis (RSA) dynamically induced micro-motion (DIMM) was measured in 21 patients implanted with Exeter stems. DIMM was measured as the difference in stem position in going from double to single leg stance on the operated limb. All subjects were measured 3 months post-operatively. A finite element (FE) model of the femur, including all muscles was used to investigate the stress distribution within the cement; contact was modelled with sliding elements allowing separation. The model was validated by comparison to the DIMM measurements.

Results: The Exeter stem demonstrated significant DIMM(p < 0.017), the average motions are given in the table below. The FE model, with sliding contacts was able to predict similar distal migration of the head. The peak minimum principal stress in the mantle was approx 33MPa and occurred in the proximal medial region. Movements occurred at the stem/cement interface.

Discussion and Conclusion: It is possible to measure DIMM in the Exeter stem and combining this with FE modelling the mechanism of stress transfer between the stem and mantle can be investigated in a manner that can be validated.

Introduction: Minimally invasive surgery (MIS) presents challenges in achieving alignment for unicompartmental knee arthroplasty (UKA). Aim: Development and assessment of an image guidance system for MIS implanted Oxford UKA.

Methods: The Surgetics platform which uses intra-operative data acquisition was chosen as the base system. Software was developed to determine height of tibial cut, image guidance of saws, alignment of components and assessment of ligament tension. The accuracy of component placement was assessed in vitro using matched pairs of knees randomised into navigated (NAV n=10) and standard manual (MAN n=10) procedures; standardised postoperative A-P and lateral radiographs were used. Pre and post-operative kinematics were assessed (NAV n=6, MAN n=7). The changes postoperatively over knee flexion and extension were calculated for tibiofemoral rotation (ΔROT) and ab/adduction (ΔABD).

Results: Accurate component placement was achieved with both methods without significant differences. Tibial cut height was more accurately in the NAV group (re-cut rate: NAV 33%, MAN 50%). NAV femoral component placement was as accurate as MAN with intramedullary rod. For the flexing cycle mean ΔROT was −0.06° (range 6.08° to −3.93°) and mean ΔABD was −0.04° (range 3.39° to −5.72°). There were no observable differences between the NAV and MAN kinematics. Overall, no observable differences were found between pre and post-operative kinematics.

Conclusions: Image guidance produces accurate placement through MIS approach and reduces the amount of tibial bone resection.

Introduction: Numerous studies in the orthopaedic literature have reported changes in knee kinematics following rupture of the Anterior Cruciate Ligament (ACL). Gait analysis is currently the preferred method for studying these in vivo kinematics. The accuracy of this method of analysis remains limited due to errors related to skin movement artefact. Most studies have therefore been limited to analysing subjects performing simple tasks such as straight-line walking, since results become increasingly inaccurate as the subject moves faster. Standard skin marker formats allow measurements of knee flexion angle and varus/valgus angles to be recorded relatively accurately during such tasks. Accurate measurements of rotations and translations at the knee joint, however, are not possible with these set-ups.

Aim: To produce a new method for interpretation of kinematic data from gait analysis, to allow accurate measurement of 3-D displacements at the knee joint during dynamic activity.

Method: We employed two different sets of skin markers in an attempt to increase the accuracy of our data, by diminishing the effects of skin movement. The Kabada¹ marker set was used with retroreflective spheres of 14.5mm diameter. This marker set was used to establish 3-D femoral and tibial co-ordinate systems. We then established a femoral and tibial co-ordinate centre within the distal femur and proximal tibia respectively. A second set of markers was used similar to the “point-cluster” method described by Andriacchi et al². This involved groups of eight smaller spheres (9.5mm diameter) placed in a non-uniform distribution on each of the thigh and shank segments. The positions of all these remaining markers, relative to the co-ordinate centres were then established. 15 subjects were then recorded while performing a series of running and cutting tasks. For each trial that was then analysed, we used all visible markers to optimize the recorded position of the tibial and femoral co-ordinate centres, using a method similar to that described by Soderkvist³. The displacements of these co-ordinate centres were then used to calculate the 3-D tibio-femoral kinematics. Reliability and repeatability tests suggest that this method produces results accurate to 3–4mm.

Conclusion: We believe we have developed a practical and accurate method to analyse 3-D joint kinematics from gait laboratory data.

Purpose This study aims to investigate blood flow in the femoral head during Metal-on-Metal Hip Resurfacing (MMHR) through the posterior approach by monitoring oxygen concentration during the operative procedure.

Methods Following division of fascia lata, a calibrated gas-measuring electrode was inserted into the femoral neck, aiming for the anterolateral quadrant of the head. Baseline oxygen concentration levels were detected after electrode insertion 2–3cm below the femoral head surface and all intra-operative measures were referenced against these. Oxygen levels were continuously monitored throughout the operation. Results of measurements from ten patients are presented.

Results Oxygen concentration was reduced during the surgical approach and average oxygen concentration following dislocation and circumferential capsulotomy dropped to 43% of baseline (Std.dev +/−37%), this was a highly significant reduction (p< 0.005). Insertion of implants resulted in a further significant drop in oxygen concentration (p< 0.02) to 16% of baseline (Std. dev +/−27%). Oxygen concentration rose slightly after relocation of the resurfaced joint and reconstruction of posterior soft tissues, reaching 22% (Std.dev +/−31%) of initial baseline oxygen levels. Considerable variation between subjects was observed. Three subjects had no remaining oxygen concentration at the end of surgery.

Conclusion Intra-operative measurement of oxygen concentration in blood perfusing the femoral head is feasible. During MMHR there is a dramatic decrease in femoral oxygenation during surgical approach and implant fixation. This may increase the risk of avascular necrosis and subsequent femoral neck fracture. Future experiments will determine if less invasive procedures or a different approach can protect the blood supply to femoral neck and head.

Introduction: Knee joint arthroplasty (total or unicompartmental) is the standard operative treatment for osteoarthritis (OA). Survival rate is good for both types but functional outcome is different. The function of unicompartmental knee arthroplasty (UKA) is substantially better than that of total knee arthroplasty (TKA). As function can be strongly influenced by proprioceptive ability, it is possible that improved outcome seen in patients with UKA results from retaining proprioceptive function associated with the cruciate ligaments. This prospective longitudinal study aimed to evaluate the change in proprioceptive performance after knee replacement; comparing TKA to UKA.

Methods and Materials: Two groups of patients with OA as diagnosed clinically and by X-ray were recruited. Group 1 consisted of 15 patients (mean age 65.8 years range 57–72 years, 10 females and 5 males) listed for TKA with the AGC prosthesis (Biomet, UK). Group 2 consisted of 19 patients (mean age 65.5 years range 52–75 years; 9 females and 10 males) listed for UKA with the Oxford UKA (Biomet, UK) for medial compartment OA. The ACL and PCL were present and preserved in all patients in Group 2, while only the PCL was preserved in Group 1 patients. Joint Position Sense (JPS) and postural sway were used as measures of proprioception performance. Both groups were assessed pre-and 6 months post-operatively in both limbs. JPS was measured using a dynamometer (KinCom, Chatanooga Ltd) as the error in actively and passively reproducing five randomly ordered knee flexion angles (30°, 40°, 50°, 60° and 70°). Postural sway (area, path and velocity) was measured during single leg stance using a Balance Performance Monitor (SMS Medical) for 30 seconds interval. Functional outcome was assessed using the Oxford Knee Score (OKS).

Results: Pre-operatively, no differences in JPS or sway were found between limbs in either group. No differences existed between the two groups. Post-operatively, both groups had significant improvement of JPS in the operated limb only (Mean ± standard deviation for UKA 4.64±1.44° and for TKA 5.18±1.35°). No changes in JPS were seen in the control side. An improvement in sway was found in the UKA group only. UKA patients showed significant improvement in both sway area and path (p< .0001) for both limbs post-operatively. No significant post-operative changes in sway occurred in either limb of TKA patients. The OKS improved postoperatively in both groups, rising from 21.4 to 35.5 for TKA patients and from 23.9 to 38 for UKA patients.

Conclusion: Interestingly, joint position sense improved for both groups but did not seem to show any difference between UKA and TKA. Postural sway was influenced by joint replacement type. Ligament retention may contribute to improved global postural control seen after unicompartmental knee arthroplasty and may explain the higher level of function seen in these patients.

Introduction: The incidence of femoral neck fracture is approximately 2% after resurfacing hip replacement. Avascular necrosis is thought to be a contributory factor. The aim of this study was to investigate oxygen concentration in the femoral head during metal-on-metal hip resurfacing (MMHR).

Materials and Methods: In ten patients, following division of the fascia lata, a calibrated gas-measuring electrode was inserted into the supero-lateral quadrant of the femoral head via the femoral neck. Xsrays confirmed placement of the electrode 2-3 cms below the femoral head surface. Baseline oxygen concentration levels were recorded immediately upon electrode insertion and used as a reference for all intra-operative measures. Oxygen levels were monitored continuously throughout the operation.

Results: Oxygen concentration was reduced during the surgical approach and average oxygen concentration following dislocation and circumferential capsulotomy dropped significantly (p< 0.005) to 38% of baseline (SD=26%). Insertion of implants resulted in a further significant drop in oxygen concentration (p< 0.04) to 21% of baseline (SD=28%). Oxygen concentration rose slightly, but not significantly after relocation of the resurfaced joint and reconstruction of posterior soft tissues, reaching 22% of initial baseline oxygen levels. Considerable variation between subjects was observed.

Discussion: Intra-operative measurement of oxygen concentration in blood perfusing the femoral head is possible. During MMHR there is a dramatic decrease in femoral head oxygenation during surgical approach and implant fixation. This may increase the risk of avascular necrosis and subsequent femoral neck fracture. Future experiments will determine if a different surgical approach can protect the blood supply to the femoral head and neck. Measurements of femoral head oxygenation during metal-on-metal hip resurfacing demonstrated a significant concentration decrease during surgical approach and implant fixation.

Background: In anteromedial osteoarthritis, only the medial compartment of the knee is affected and the collateral ligaments as well as the cruciate mechanism are intact. These preconditions make the knee suitable for UKA. Our hypothesis was that no difference in tibiofemoral kinematics is observed after UKA. In addition we also hypothesised that the results of the image guided surgery would be the same as the normal surgical procedure.

Design/Methods: To test this hypothesis, we conducted a study using 13 normal human cadaveric knees. For kinematic analysis, the SurgeticsTM surgical navigation system (Praxim, France), equipped with custom written tracking software, was used. Reference markers were mounted to the proximal tibia and the distal femur. In a standardised set-up, the knee was positioned in a leg holder and preoperative kinematics of the normal knee was recorded after a para-patellar mini-incision . Joint kinematics were recorded during passive knee flexion and plotted against flexion angle. Oxford UKA was performed; the standard Phase III instrumentation was used for six knees and the image guided procedure was used for seven knees. After the operation postoperative kinematics were recorded using the same measurement protocol. All data were processed using Matlab 6.1 analysis software (The MathWorks Inc., MA, USA). Preoperative and postoperative tibiofemoral kinematics were determined and compared. The mechanical axes of the tibia and femur were determined and kinematics represented as functions of knee flexion range. Over both the flexing and extending cycles of the knee the changes in tibiofemoral rotation (ΔROT), tibiofemoral ab/adduction (ΔABD), and distances between the origins of the mechanical axes (ΔX, ΔY, ΔZ) were calculated between pre and post-operative states.

Results: The mean differences between pre- and postoperative kinematics for all cases are given as the mean and range in parentheses. For the flexing cycle was ΔROT −0.06 (6.08 to −3.93) degrees, ΔABD was −0.04 (3.39 to −5.72) degrees, ΔX was 0.69 (2.69 to −1.84) mm, ΔY was −0.22 (4.13 to −3.41) mm and was ΔZ 0.27 (4.09 to −1.47) mm. For the extending cycle was ΔROT 0.1 (5.87 to −3.61) degrees, ΔABD was −0.06 (5.72 to −5.95) degrees, ΔX was 0.35 (2.73 to −2.39) mm, ΔY was −0.39 (5.58 to −3.08) mm and was ΔZ 0.21 (3.77 to −1.12) mm. There were no observable differences between the standard and image guided changes in kinematics. Overall, no observable differences were found between pre and post-operative kinematics.

Conclusions: The image guidance system used in our study is a valuable tool for assessing pre- and postoperative knee kinematics. Oxford Unicompartmental Knee Arthroplasty with the Phase III instrumentation in the presence of the cruciate mechanism reproduces the normal kinematics of the knee very accurately.

Introduction Metal-on-Metal Hip Resurfacing (MMHR) has been established as a successful alternative to Total Hip Replacement (THR). However, several series report a 2 % incidence of early femoral neck fractures. Avascular necrosis (AVN) was considered to be responsible for the majority of observed fractures, raising concerns about the femoral head blood supply during MMHR. This study aims to further understand the mechanisms of femoral blood flow restriction by monitoring gas levels (O2) during the operative procedure.

Methods Patients undergoing MMHR using the posterior approach were evaluated. Following division of fascia lata, a guide wire was introduced up the femoral neck, aiming for the anterosuperior quadrant of the head. It was then removed. A calibrated gas-measuring electrode was inserted in the created bone channel. X-ray confirmation was obtained to ensure that the active measurement area of the electrode was 2–3cm below the femoral surface. O2 and N2O levels were then continuously monitored throughout the operation.

Results A preliminary analysis of four patients is presented: Stable N2O- measurements throughout the procedure confirmed valid electrode measurements. Baseline oxygen concentration levels of 40%– 60% were detected before division of short rotators. After hip dislocation oxygen concentration dropped in all patients to levels ranging between 0% and 5%. Oxygen concentration was found to remain depressed at these levels throughout the entire operation in three patients. Recovery of O2 concentration to baseline levels was observed in one patient 15 minutes after dislocation.

Discussion In three patients the extended posterior approach and joint dislocation had a dramatic effect on the perfusion in the femoral head. These patients have a high risk for development of AVN and potential femoral neck fracture. Whilst the results require further verification, subsequent experiments will determine if less invasive procedures or specific positioning of the limb can protect the femoral blood supply.

Introduction: The Charnley Elite femoral component was first introduced in 1992 as a new design variant of the original Charnley femoral component (De Puy, Leeds, UK) with modified neck and stem geometry. The original component had undergone few changes in nearly forty years and has excellent long-term results.

Early migration of the new stem design was determined by Roentgen Stereophotogrammetric Analysis (RSA). Rapid early migration of a component relative to the bone, measured by RSA, is predictive of subsequent aseptic loosening for a number of femoral stems. As there was rapid early migration and rotation of the Charnley Elite stem, we predicted that the long-term results would be poor. An outcome assessment is required as stems of this type are still being implanted.

Materials and method: One hundred Charnley Elite stems, implanted in our centre between 1994 and 1997 were included in a prospective, cross-sectional follow-up study. Outcome measures include validated clinical scores (Charnley hip score, Harris hip score and Oxford hip score) and radiological scores (Gruen classification) as well as revision rates over the past 10 years.

Results: The preliminary analysis results are given. The mean time to follow-up was 8.28 years. 20 patients have died due to causes unrelated to their operations. 10 patients had stem revisions: 9 for aseptic loosening and 1 for a peri-prosthetic fracture. This indicates a significant 10% failure rate of the prosthesis in less than 10 years.

Preliminary clinical scores in the patients who had not undergone any subsequent surgery were adequate (Oxford Hip Score mean average of 23.9).

Thirteen percent of radiographs analysed had evidence of loosening, giving an overall loosening rate of 14% at 8 years.

Discussion and conclusion: The clinical follow-up supports the RSA predictions of early failure of the Charnley Elite femoral stem.

Polyethylene particulate wear debris continues to be implicated in the aetiology of aseptic loosening following knee arthroplasty. The Oxford unicompartmental knee arthroplasty employs a spherical femoral component and a fully congruous meniscal bearing to increase contact area and theoretically reduce the potential for polyethylene wear. This study measures the in vivo ten-year linear wear of the device, using a roentgenstereophotogrammetric technique.

In this in vivo study, seven medial Oxford unicompartmental prostheses, which had been implanted ten years previously were studied. Stereo pairs of radiographs were acquired for each patient and the films were analysed using a roentgen stereophotogrammetric analysis calibration and a computer-aided design model silhouette-fitting technique. Penetration of the femoral component into the original volume of the bearing was our estimate of linear wear. In addition, eight control patients were examined less than three weeks post-insertion of an Oxford prosthesis, where no wear would be expected. The control group showed no measured wear and suggested a system accuracy of 0.1 mm. At ten years, the mean linear wear rate was 0.02 mm/year.

The results from this in vivo study confirm that the device has low ten-year linear wear in clinical practice. This may offer the device a survival advantage in the long term.

Introduction: Total knee replacement (TKR) is a common treatment for end stage osteoarthritis of knee. The best knee replacement is one in which the kinematics of the normal knee are reproduced. Amongst several factors affecting kinematics, variation in surface geometry and the retention/ sacrifice of the PCL are considered especially important. It is not known which of these two factors is most influential for establishing optimum joint kinematics after TKR.

Method: Four groups of patients who had undergone TKR at least one year previously were recruited. Two groups of patients had undergone replacement with a single axis design (Scorpio, Stryker Howmedica) in both PCL retaining (Scorpio CR, n=15) and PCL sacrificing (Scorpio CS, n=15) variants. The other two groups had undergone replacement with the traditional polyradial design prosthesis (Sigma, Depuy, Johnson & Johnson), again with both PCL retaining (Sigma CR, n=14) and PCL sacrificing (Sigma CS, n=13) variants. An in-vivo fluoroscopic analysis was carried out on all patients. Patients were asked to perform closed chain step up and open chain extension and flexion against gravity. The kinematic profile of each knee was obtained by measuring patella tendon angle (PTA) at specific angles of knee flexion (KFA) using an established fluoroscopic method. The data was also compared with the kinematic profile of normal knees. American Knee Society, Oxford and Patella Scores were recorded for all patients.

Results: All groups were comparable in terms of age and gender. In addition, no significant difference was found between groups in clinical outcome. PTA results for a step-up exercise are shown in the figure. A one way ANOVA between groups revealed that knee kinematics after total knee replacement is different to that for normal knees. No differences were found between groups when the data was analysed using CR/CS as the independent variable. The only differences between groups were found when surface geometry was used as the independent variable. It was shown that the kinematic profile of the single axis Scorpio design (in both CR & CS ) was closer to normal, especially near extension, than the traditional polyradial design (Sigma CR & CS).

Conclusions: Kinematics after a total knee replacement differ from that for a normal knee. Differences in surface design between knee replacements appear to have greater influence on kinematics than the presence or absence of the PCL.

Introduction and Aims: Since existing data relating to the kinematics of ACL-deficient knee joints relates mainly to walking, the kinematics during more dynamic activities remains unknown; therefore, the aim of this unique study was to describe in vivo ACL-deficient knee kinematics and muscle activity during running and cutting.

Method: Fifteen subjects with proven unilateral ACL rupture were measured performing running and cutting tasks prior to surgical reconstruction. Gait analysis was used to determine inter-limb differences in displacements at the knee joint during stance phase. Simultaneous EMG analysis was performed to give temporal measures of lower limb muscle activity.

Results: No significant inter-limb difference was seen for tibio-femoral translation in the sagittal or coronal planes during any part of stance phase. The ACLD limb showed a significantly reduced maximum knee flexion angle (40.4 vs. 44.0 degrees) compared to the ACL-intact (ACLI) limb (p=0.04). Internal tibial rotation was significantly greater (7.3 vs. 0.7 degrees) in the ACLD limb at toe-off (p=0.03). The quadriceps muscle group was found to be active for a significantly greater percentage of stance phase in the ACLD limb compared to the ACLI limb (p=0.001).

Conclusion: The ACL-deficient gait involves consistently greater knee extensor activity than ACL-intact gait during running, and as a consequence maximum knee flexion angle is reduced. These findings contrast with the description of ‘quadriceps-avoidance’ gait often described for ACL-deficient subjects. ACL-deficient gait also demonstrates increased rotational instability during terminal stance phase.