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.

Purpose: The purpose of this study was to establish patient mortality following salvage treatment (debridement, retention of prosthesis and antibiotic therapy) for infection of primary joint replacement, performed at the unit.

Method: A series of 89 patients underwent salvage treatment for infected primary total joint replacement (47 hips and 42 knees) between 1998 and 2003. The average age of the patients was 70.3 years (range 31.8 to 89.1). A survival analysis was performed using death as the sole endpoint and there were no patients lost to follow-up.

Results: There were a total of 26 deaths with a mean time to death of 3.3 years (range 0.8 to 7.2). The 7-year cumulative patient survival of was 66% (CI 5, number at risk 21).

Conclusions: The morbidity associated with infected total arthroplasty has been well documented. This study highlights that patients undergoing salvage treatment for this condition have significant mortality, with up to a third of patients potentially dying by 7 years.

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.

Aim: The aim of this study was to investigate whether viable chondrocytes can be isolated and subsequently expanded in culture, from cryopreserved intact human articular cartilage.

Method: Human articular cartilage samples, retrieved from patient undergoing total knee replacement, were cored as 5 mm diameter discs then minced to approximately 0.1 mm³ size pieces. Samples were cryopreserved at the following stages; intact cartilage discs, minced cartilage and chondrocytes immediately after enzymatic isolation. After completing of isolation, cell viability was examined using LIVE/DEAD fluorescent staining. Isolated chondrocytes were then cultured and a cell proliferation assay was performed at day 4, 7, 14, 21 and 28 days.

Results: The results showed that the viability of isolated chondrocytes from control, cryopreserved intact AC discs, minced AC and isolated then frozen samples were 71.84 ± 2.63%, 25.61 ± 2.41%, 31.32 ± 2.47 % and 42.53 ± 4.66% respectively. Isolated chondrocytes from all groups were expanded by following degrees after 28 days of culture; Group A: 10 times, Group B: 18 times, Group C: 106 times, and Group D: 154 times.

Conclusion: We conclude that viable chondrocytes can be isolated from cryopreserved intact human AC and then cultured to expand their number. This method could be employed to patients benefit undergoing autologous chondrocyte implantation.

Objective: To investigate the effect of lab based simulator training, on the ability of basic surgical trainees to perform diagnostic knee arthroscopy.

Method: 20 orthopaedic SHO’s with minimal arthroscopic experience were randomised to 2 groups. 10 received a fixed protocol of simulator based arthroscopic skills training. This consisted of 3 sessions of 6 simulated arthroscopies using a Sawbones bench-top knee model. Their learning curve was assessed objectively using motion analysis. Time taken, path length and number of movements were recorded. All 20 then spent an operating list with a blinded consultant trainer. They received instruction and demonstration of diagnostic knee arthroscopy before performing the procedure independently. Their performance was assessed using the intra- operative section of the Orthopaedic Competence Assessment Project (OCAP) procedure based assessment (PBA) protocol for diagnostic arthros-copy and further quantified with a global rating assessment scale.

Results: In theatre, simulator-trained SHO’s outscored all but one untrained SHO. The simulator trained group were scored as competent on more than 70% of occasions compared to less than 15% for the un-trained group (p< 0.05). The mean global rating score of the trained group was 24.4 out of 45 compared with 12.4 for the untrained group (p< 0.05). Motion analysis demonstrated objective and significant improvement in performance during simulator training.

Conclusion: The use of lab based arthroscopic skills training leads to subsequent significant improvement in operating theatre performance. This may suggest that formalised lab based training should be a standardised part of future surgical curricula. OCAP PBA’s appear to provide a useful framework for assessment however potential questions are raised about the ability of OCAP to truly distinguish levels of surgical competence.

Anteromedial osteoarthritis is a distinct phenotype of osteoarthritis. The arthritic lesion on the tibia is localised to the anteromedial quadrant with an intact ACL. Deficiency of the ACL leads to a progression to tricompartmental disease. Within the spectrum of intact ACL a varying degree of ligament damage is seen. Our aim was to correlate the progression of ACL damage to the geographical extent of disease and the degree of cartilage loss on the tibial plateau.

We systematically digitally mapped 50 tibial plateau resection specimens from clinical photographs of patients undergoing unicompartmental arthroplasty, additionally the damage to their ACL was graded (0: normal, 1:synovium loss, 2:longitudinal splits)

These images were imported into image analysis software. Accurate measurements were made of the dimensions of the specimen. Measurements included the AP distance to the anterior and posterior aspect of the lesion, and the distance to the start of the macroscopically non damaged cartilage. The areas of cartilage damage and full thickness loss were also recorded. The results were represented as a % of total area to account for variation in size of the resection specimens. We compared % of full thickness loss in patients with normal to those with damaged, but functionally intact ligaments.

All specimens had a similar macroscopic appearance. A significant difference was seen with the progression of ACL damage and area of eburnation of bone. Using an unpaired t test, a significant difference in area of % full thickness cartilage loss (P=0.047) was seen between patients with a normal and longitudinal splits within their ACL. No correlation between the clinical status of the ACL and start or finish point of cartilage loss on the tibial plateau

We surmise that the progression from anteromedial to tricompartmental osteoarthritis of the knee may be related to the graduated damage of the ACL.

A sibling risk study that shows a statistically significant increase in risk for anteromedial osteoarthritis of the knee.

Anteromedial osteoarthritis is a distinct phenotype of osteoarthritis. Previous studies have shown a genetic aetiology to both hip and knee osteoarthritis. The aim of this study was to determine the sibling risk of antero-medial osteoarthritis of the knee.

We conducted a retrospective cohort study of 132 probands with primary anteromedial osteoarthritis, who had undergone unicompartmental arthroplasty. Sibling were identified as having symptomatic knee problems by postal Oxford Knee Score (OKS). A positive OKS was defined as an OKS+/− 2SD of the mean of the proband group. Sibling spouses were used as controls. Those siblings & spouses that were symptomatic from the OKS were invited to undergo Knee X-rays, to look for radiological signs of osteoarthritis. Osteoarthritis was diagnosed as greater than Grade II on the Kell-gren Lawrence classification. The pattern of disease was noted and it was considered if the sibling were suitable for a unicompartmental knee arthroplasty. The prevalence and sibling risk of anteromedial osteoarthritis was determined using a randomly selected single sibling per proband family. The prevalence was determined in the 103 single proband sibling pairs.

There was a statistically significant risk within the sibling group P= 0.024 using the Chi square test. The relative risk of anteromedial osteoarthritis was. 3.21(95% CI 1.08 to 9.17)

Genetic factors play a major role in the development of anteromedial osteoarthritis.

Aim: This paper presents the 20-year survival and 10-year clinical follow-up results from the entire series of all medial Oxford meniscal bearing unicompartmental knee arthroplasties performed in a single centre in Sweden, between 1985 and 2004.

Method: Patients were contacted and information about the state of the knee collected. Revision surgery was used in the life-table survival analysis performed. For the entire cohort clinical follow up at 10-years is routinely performed, using the HSS knee score.

Results: The entire group comprised of 683 knees in 572 patients. The mean age at implantation was 69.7 (range 48–94). There had been 30 revision procedures: 8 for lateral arthrosis, 7 for component loosening, 3 for infection, 6 for bearing dislocation, 1 for bearing fracture and 5 for unexplained pain. The 10-year, 15-year and 20-year survival (all cause revision) were 94.1 % (CI 2.9, 237 at risk), 93.5% (CI 4.6, 101 at risk) and 92.3% (CI 15.1, 11 at risk) respectively. From the patients reviewed clinically the mean pre-operative HSS knee score was 57 (95% CI 1), compared to 87 (95% CI 1) at 10-years. Using HSS criteria the results were: 68% excellent, 23% good, 6% moderate and 2% poor.

Conclusion: The results show that this mobile bearing unicompartmental prosthesis offers patients excellent clinical results during the first decade and is durable during the second decade after implantation.

Antero-medial osteoarthritis of the knee displays a well recognised pattern of cartilage damage on the medial tibial plateau. Anteriorly there is a full thickness cartilage defect, with transition to a partial thickness defect, becoming full thickness in the posterior third of the plateau. The retained posterior cartilage is macroscopically normal, but no previous study has assessed its histo-logical features. This study characterises the histological changes, to examine if antero-medial OA of the knee represents a model of progressive osteoarthritic cartilage damage.

Five unicompartmental resection specimens of patients with idiopathic single compartment antero-medial osteoarthritis were assessed. The samples were stained with H& E and Saffinin-O stains and reviewed using the Mankin system, an established method for scoring osteoarthritic changes in cartilage (range 0 [normal] to 14 [grossly osteoarthritic]) Digital images of the histology were reviewed by two observers to exclude inter and intra observer error. Each specimen was assessed at 4 interval points (A,B,C,D) along the A-P axis starting from the most posterior aspect of the exposed bone to the area of macroscopically normal cartilage. Three repeat measurements were taken from the macroscopically normal region (D1,D2,D3). The scores were compared to historical age matched controls of non-osteoarthritic cartilage, where a Mankin grade of < 3 suggests normal cartilage.

From anterior to posterior the H& E staining showed a consistent decrease in structural integrity and cellularity of the cartilage, matched by a qualitative decrease in GAG content (Saffinin-O staining). Mean Mankin scores showed a progressive decrease in score; A = 14.0 (95% CI 0), B = 5.8 (95%CI 2.4), C = 4.4 (95%CI 2.5), D = 1.0 (95%CI 0.9) {p=0.04 ANOVA}. Repeated measurements at the macroscopically normal area showed the Mankin grade was maintained; D1= 1.0 (95%CI 0.9), D2 = 0.6 (95%CI 0.5), D3 = 0.6 (95%CI 0.6).

The results show that the retained posterior cartilage in antero-medial arthritis has a consistently normal Mankin grade. We suggest the defect represents a model of progressive cartilage damage from near normal (posterior) to the grossly osteoarthritic state (anterior).

Introduction This study assesses the outcome of medial unicompartmental knee arthroplasty (UKA) using the Oxford prosthesis for end-stage focal spontaneous osteonecrosis of the knee (SONK, Ahlback grades III & IV).

Methods A total of 29 knees (27 patients) with SONK were assessed using the Oxford Knee Score. Twenty-six had osteonecrosis of the medial femoral condyle; 3 had osteonecrosis of the medial tibial plateau. This group was compared to a similar group who had undergone Oxford Medial UKA for primary osteoarthritis. Patients were matched for age, sex and time since operation.

Results Mean length of follow-up was 5.2 years (range 1–13 years). There were no implant failures in either group, but there was one death 9 months post-arthroplasty from unrelated causes in the group with osteonecrosis. The mean Oxford Knee Score (SD) in the group with osteonecrosis was 37.8 (7.6) and 40.0 (6.6) in the group with osteoarthritis. There was no significant difference between the two groups using Student’s t-test (p=0.29).

Interpretation Use of the Oxford Medial UKA for focal spontaneous osteonecrosis of the knee is reliable in the short to medium term, and gives similar results to when used for patients with primary osteoarthritis.

Introduction and Aims: Single compartmental replacement procedures are increasingly preferred over total knee replacement (TKR) for single compartment osteoarthritis of the knee joint. Theoretically, reduced disruption of the native joint should produce more normal kinematics. This study aimed to describe and compare the sagittal plane kinematics of four different, commonly used devices.

Method: Four groups of patients who had undergone successful single compartment replacement at least two years previously were recruited. Fifteen following Oxford medial UKA, 12 following medial St Georg Sled UKA, five following Oxford lateral UKA, and 12 following Avon PFJ replacement. Patients performed flexion/extension against gravity, and a step-up during video fluoroscopy. The Patellar Tendon Angle (PTA), the angle between the long axis of the tibia and the patella tendon, was obtained as a function of knee flexion. This relationship provides indication of sagittal movement between femur and tibia through range and has been validated as a reliable measure of joint kinematics.

Results: The kinematic profile for each group was compared to that of the profile for 12 normal and 30 TKR (AGC) knees. All three tibiofemoral devices produced knee kinematics similar to the normal knee. The PTA was found to have a linear relationship to flexion angle, decreasing with increasing knee flexion angle. No such linear relationship exists for the TKR joint, which display abnormal kinematics. The PF device also reflected similar trends to that for normal knees except that the PTA was moderately increased throughout the entire range of flexion (three degrees).

Conclusion: In contrast to TKR, all single compartmental knee replacements provided kinematics similar to the normal joint. The kinematic pattern of the PFJ replacement may be of most interest as the observed increase in PTA through range could influence patello-femoral contact forces

Introduction and Aims A randomised controlled trial (RCT) and a multi-centre unilateral cohort study were performed as part of the stepwise introduction of a new mobile bearing knee. The aim was to ensure that outcome for the new device was at least as good as that for an established fixed bearing device. This paper presents three year follow up of the published one year results. Instability and prevalence of “clicking” from the joint were examined in detail.

Method 1. A multi-centre RCT of patients undergoing bilateral knee replacement compared functional outcome between two different prostheses, the new mobile bearing device (TMK) and an established fixed bearing device (AGC). 2. A separate multi-centre cohort of 166 patients who had undergone a unilateral mobile bearing procedure at least six months previously was used to assess complication rate and corroborate any findings from the bilateral trial. Outcome measures included Oxford Knee Scores, American Knee Society ratings and complication rate.

Results The bilateral trial revealed no significant differences in outcome between the two devices. Revision rate for all (199) mobile bearing knees was less than 2%. The mean Oxford Knee Score for outcome for all mobile bearing knees was 37.1 ± 10.1. About 7% of patients reported instability. Clicking was more common in the TMK (48%) than in the AGC (30%) and was reported as a problem in 16% of TMK’s in the cohort study. However, clicking was unrelated to outcome score in both studies.

Conclusion At three years, the mobile bearing device was as good as the fixed bearing device. There was a relatively high prevalence of “clicking” in the TMK but the cause remains unclear. Furthermore, the symptom was not associated with poor functional outcome. The bilateral RCT and cohort study allows assessment of function and potential problems. It provides rigourous scientific justification for the introduction and early assessment of new implants.

Polyethylene wear remains an important cause of failure in knee replacements. Retrieval studies, simulators and simple X-ray methods produce wear data that may be inaccurate or unrealistic. We have developed an accurate RSA system for measuring wear in-vivo. Using this system we have found wear rate in a fixed bearing TKR to be about 0.1mm/yr[1]. In this abstract we extend the study to fully congruent mobile bearings.

Four Oxford uni-compartmental knee replacements, with excellent clinical results were studied ten years after implantation. RSA X-rays were taken in double leg stance with the knee in full extension and 15 and 30 degrees flexion. Following RSA calibration, silhouettes of the components on the stereo X-rays were extracted using a Canny edge detector and were matched to silhouettes projected using CAD models to determine the 3D component position. The average minimum thickness of the bearing was determined and was compared with the measured minimum thickness of 14 unused bearings to calculate linear penetration.

The average linear penetration after average 10 years implantation (range 8.5 to 10.25 years) was 0.16 mm (SD 0.13 mm). The average penetration rate was 0.017 mm/year (SD 0.011 mm/year). The maximum linear penetration rate was 0.027 mm/year.

The penetration rate is similar to that obtained in a retrieval study [2]. Compression of the bearing is minimal due to 6sqcm of contact area. This study therefore demonstrates that polyethylene wear on the upper and lower surfaces is minimal in fully congruous mobile bearing knee replacements.

Introduction: Radiolucencies are frequently observed around joint replacements. Their signiþcance & etiology remain unclear. Aim: 1. To study radiolucency under tibial tray of Oxford UKA and correlate it to the clinical outcome. 2. To study implant migration using RSA and study the correlation between migration and radiolucency. Materials and Methods: Fifty consecutive patients cemented Oxford UKA with a minimum follow up of two years were studied. At 2 years precisely aligned radiographs were obtained and evaluated for presence and extent of radiolucency under the tibial tray. The patients were divided into two groups Ð those with (Group I) and those without presence of radiolucency under the tibial tray (Group II). All the patients were assessed using KSS. Patients had RSA marker balls inserted around the prosthesis at the time of index procedure. Using RSA, the degree and direction of implant movement was measured at 1 & 2 yrs post surgery. Results: A) There were 26 patients in group I and 24 in group II. Both the groups were well matched for age and sex distribution. There was no signiþcant difference between the two groups when various clinical scores were compared. Maximum width of radiolucency was 1.1 mm and the average width was 0.57 mm. B) RSA study: By 12 months, the tibial component had migrated signiþcantly distally (mean: 0.42 mm, S.D.: 0.15 mm) and anteriorly (mean: 0.47 mm, S.D. 0.27mm). No signiþcant migration occurred after 12 mths. There was no correlation between presence or extent of radiolucency and migration of the tibial component. Conclusion: There is no relationship at 2 years between radiolucency and clinical results. There is also no relationship between radiolucency and migration. Therefore radiolucencies of 1mm or less can be ignored

Radiolucencies are generally thought to be a manifestation of loosening. They are commonly seen under the tibial component of the Oxford Unicompartmental knee replacement. However, they are not associated with long term failure [1]. The aim of this study was to investigate any relationship between radiolucencies and component migration.

Eight medial Oxford Unicompartmental knee prostheses were examined post-operatively, at 12 months and at 24 months using Roentgen Stereophotogrammetric Analysis (RSA). The serial radiographs were calibrated and three dimensional CAD models were matched to the extracted component shapes. Implanted bone marker balls were then selected on all radiographs. The components were superimposed. Migration calculation was achieved by comparing relative positions of components to bone marker balls in the serial radiographs. Fluoroscopically screened X-rays were taken to determine whether there were any radiolu-cencies under the tibial component.

By 12 months, the femoral component had migrated significantly anteriorly (0.35 mm) and proximally (0.61 mm). The tibial component had migrated significantly distally (0.42 mm) and anteriorly (0.47 mm). Although on average there appeared to be a small further migration between 12 and 24 months, this was not statistically significant in any direction.

Six of the eight patients had radiolucencies at 24 months. None of the radiolucencies were was complete. The maximum radiolucency was 1 mm thick and the average was 0.57 mm. There was no correlation between radiolucency and migration.

The proximal femoral migration and distal tibial migration can be explained by the load across the knee. We cannot yet explain the anterior tibial migration. Radiolucencies almost always occur and are not related to migration.This confirms they are not associated with loosening.

When the Oxford unicompartmental meniscal bearing arthroplasty (UCA) is used in the lateral compartment of the knee 10% of the bearings dislocate. An in-vitro cadaveric study was performed to investigate if the anatomy and joint geometry of the lateral compartment was a contributory factor in bearing dislocation. More specifically, the study investigated if the soft tissue tension of the lateral compartment, as determined by the length of the lateral collateral ligament (LCL), was related to bearing dislocation. A change in length of greater than 2 mm is sufficient to allow the bearing to dislocate.

The Vicon Motion Analysis System (Oxford Metrics, Oxford, UK) was used to assess length changes in the LCL of seven cadaveric knees. Measurements were made of the LCL length through knee flexion and of the change in LCL length when a varus force was applied at a fixed flexion angle. Measurements were made in the normal knee and with the knee implanted with the Oxford prosthesis.

In the intact knee the mean LCL change was 5.5mm (8%) over the flexion range. After implantation with the Oxford UCA the mean change in length was only 1 mm (1%). There was a significant difference in the LCL length at 90° (p=0.03) and 135° (p=0.01) of knee flexion compared to the intact knee. When a varus force was applied the LCL length change of the intact knee (5.4 mm) was significantly different (p=0.02) to that of the knee with the prosthesis implanted (2.7 mm)

This study used a new method to dynamically measure LCL length. It found that after implantation of the Oxford lateral UCA the LCL remains isometric over the flexion range and does not slacken in flexion as it in the normal knee. This would suggest that the soft tissue tension was adequate to contain the bearing within the joint.

However, when a varus force was applied the LCL did not sufficiently resist a displacing force producing an LCL length change greater than 2 mm.

The evidence provided by this study is contradictory. The “lack of change in LCL length through flexion” suggests that the ligament remains tight through range and is unlikely to allow dislocation. However, the amount of distraction possible when an adducting moment is applied is sufficient to allow bearing dislocation. The length tension properties of the lateral structures are therefore implicated in the mechanism of dislocation.

The aim of the study was to measure in-vivo the 10-year linear and volumetric polyethylene wear of a fully congruent mobile bearing unicompartmental knee arthroplasty (OUKA).

We studied six OUKA’s that had all been implanted 10 years previously. Each patient was examined in even double leg stance at a range of knee flexion angles, in a calibration cage. A stereo pair of X-ray films was acquired for each patient at 0°, 15° and 30° of flexion. The films were analysed using an RSA style calibration and a CAD model silhouette-fitting technique. The position and orientation of each femoral and tibial component was found relative to each other and the bearing position inferred. Penetration of the femoral component into the original volume of the bearing was our estimate of linear wear. The volumetric wear is calculated from the measured linear wear and the known surface area of the bearing. In addition eight control patients were examined less than 3 weeks post-operation where no wear would be expected.and 30We studied seven OUKA’s that had all been implanted at least 10 years previously. A stereo pair of X-ray films was acquired for each patient at 0 Results: The control group showed no measured wear. The seven OUKA’s had an average maximum depth of linear penetration of 0.40 mm at a mean follow-up of 10.9 years. The linear wear rate was 0.033 mm/year. The volumetric material loss was 79.8 mm3. If a steady gradual material loss is assumed, 8 mm3 of UHMWPE was lost per year.

Polyethylene particulate wear debris continues to be implicated in the aetiology of component loosening and implant failure knee following arthroplasty. The OUKA employs a spherical femoral component and a fully congruous meniscal bearing to increase contact area and theoretically reduce the potential for polyethylene wear. The results from this in-vivo study confirm that the device has low 10-year linear and volumetric wear in clinical practice. This may protect the device from component loosening in the long term.

The indications for unicompartmental knee arthroplasty (UKA) can be contentious. Concerns exist about implanting a UKA in younger individuals. It has been reported that it is contra-indicated in patients under the age of 60. The suggestion is that younger patients may compromise their outcome after surgery by their increased activity levels. However, the number of publications with data on UKA in young patients is minimal and the age/activity related criteria for UKA remains unknown.

The aim of the study was 1) to confirm that younger UKA patients have higher activity levels than older patients, and 2) to test the hypothesis that younger, more active patients have inferior outcome when compared to older less active patients.

Fifty consecutive patients undergoing UKA who were under 60 years (Group Y) and 50 patients over 60 years (Group O) were recruited. Indications were anteromedial arthritis with full thickness lateral compartment cartilage, a functioning ACL and a correctible varus. All patients underwent Oxford UKA using the minimally invasive technique. This device employs an unconstrained fully congruous meniscal bearing. Outcome was evaluated using Knee Society Scores. Activity level was documented using Tegner Activity Score.

Average age of patients for group Y and O was 55 and 68 years respectively. Minimum follw-up was 2 years. pre-op. knee scores were comparable for each group. (y: 38.8, O: 35.8) and patients in both groups siginificantly improved after surgery. A significant difference in Tegner score was found between the two groups after surgery (y:4.1, O:2.6). More than 50% of younger patients regularly participated in high demand activities like skiing, tennis and manual labour. No statistically significant differences in any other post op. knee scores or complication rate were found despite adequate study power.

Younger patients have increased activity levels after UKA when compared to an older age group. There is no evidence that the outcome of UKA in younger more active patients will be inferior to those who are older and more sedentary.