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.