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.

We report 17 patients (20 hips) in whom metal-on-metal resurfacing had been performed and who presented with various symptoms and a soft-tissue mass which we termed a pseudotumour. Each patient underwent plain radiography and in some, CT, MRI and ultrasonography were also performed. In addition, histological examination of available samples was undertaken.

All the patients were women and their presentation was variable. The most common symptom was discomfort in the region of the hip. Other symptoms included spontaneous dislocation, nerve palsy, a noticeable mass or a rash. The common histological features were extensive necrosis and lymphocytic infiltration. To date, 13 of the 20 hips have required revision to a conventional hip replacement. Two are awaiting revision.

We estimate that approximately 1% of patients who have a metal-on-metal resurfacing develop a pseudotumour within five years. The cause is unknown and is probably multifactorial. There may be a toxic reaction to an excess of particulate metal wear debris or a hypersensitivity reaction to a normal amount of metal debris. We are concerned that with time the incidence of these pseudotumours may increase. Further investigation is required to define their cause.

Purpose of study: We report the results of a prospective case series of 10 patients who developed tumour-like masses following resurfacing arthroplasty

Method: Ten subjects were referred to the tumour service at the Nuffield Orthopaedic Centre with symptomatic masses around the hip, all had previously received a resurfacing arthroplasty.

We report the clinical, radiographic and histologic features of these cases.

Results: MRI and ultrasound scanning was preformed, which demonstrated masses with solid and cystic components.

Biopsy was performed and subsequent histological examination revealed a profound plasma-cell lymphocytic response associated with metal wear debris.

There were no infections in this series.

Three subjects required revision surgery.

Conclusion: Over 50,000 resurfacing arthroplasties have been implanted worldwide over the past ten years. Although the early clinical results are encouraging little is known about the long term consequences of large head metal on metal bearing surfaces. Despite this, these devices are being widely marketed and are often implanted in younger patients. Resurfacing arthroplasties are associated with high serum and urine metal ion concentrations, metal particles have also been shown to migrate along the lymphatic system. In addition, there is now evidence that high local metal ion concentrations can induce haempoietic cancers.

This study suggests that resurfacing arthoplasty can also induce a local hypersensitivity reaction in response to metal wear debris. It therefore raises new concerns regarding the long-term safety of this procedure.

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 purpose of the study: to determine if Patient height-and gender could be used to predict component size With a minimally invasiveapproach for unicompartmental knee replacement.

Material and methods: One hundred x-rays of patients (44 men, 56 women), who had undergone Oxford UKR, were reviewed. The preoperative radiographs were assessed for component size using the standard template. The postoperative x-rays were reviewed to determine-whether the ideal component size had been used or if not what could be the most appropriate. Patient’s height was recorded. The proportion of patients for whom an appropriate size could be selected by either template or height measurements was calculated.

Current templating system accurately predicted the ideal size in 67%. In no case was the size incorrect by more than one size. The following size bands were set according to height. For men: size small in patients less than160 cm, medium less than 170 cm and large less than 180cm. For women: size small in patients less than 165 cm, medium less than 175cm and large less than 185 cm. Height accurately predicted the ideal size in75%. In no case was the assessment of component size incorrect by more than one size.

As the Oxford femoral component is spherical, its size is not critical and it is acceptable to use one size too large or too small. Both height and templating safely predicted an acceptable size in all cases and predicted the ideal size in about 70% > Conclusion: Gender specific height should be used to predict the component size in situations were templating is difficult as in digital x-rays orsuperimposition of the two femoral condyles, and non-standardised x-raymagnification.

The indications for unicompartmental knee arthroplasty (UKA) remain controversial; in particular the threshold of disease in the patellofemoral compartment is debated. Whilst some authorities ignore the condition of the patellofemoral joint, others consider pre-existing patellofemoral osteoarthritis (PFOA) a contra-indication to UKA. The aim of this study was to determine the influence of PFOA on the outcome of medial UKA.

This prospective study involved one hundred consecutive patients who had undergone cemented medial Oxford UKA (phase 3), via a minimally invasive approach, at least one year previously. Patients were divided into two groups according to the presence or absence of full thickness cartilage loss (FTCL) on the patella or trochlea at operation. A pre-operative skyline radiograph was graded using the Altman score, by an independent Musculoskeletal Radiologist. Outcome was evaluated with the Knee Society Score (AKSS) and the Oxford Knee Score (OKS, maximum 48). Groups were compared for differences in knee score and Altman grade using a one way ANOVA. Repeat analysis was performed using the presence of anterior knee pain (AKP) as the group defining variable.

There were 28 patients with FTCL, and both groups were well matched for age, gender and activity levels. Analysis showed no significant difference in post operative knee scores between groups with either the presence of FTCL or the presence of AKP pre-operatively as a factor. There was no significant difference in Altman grade between groups.

Intra-operative evidence of PFOA in patients with medial compartment osteoarthritis does not prejudice the outcome of UKA. Even the inclusion of patients with symptomatic AKP, without necessarily having PFOA, does not affect the outcome after UKA. These short results are encouraging, but longer follow up is required.

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

Oxford Unicompartmental knee arthroplasty (UKA) is now performed using a minimally invasive surgical (MIS) technique. Although early results are encouraging, the studies assessing outcome could be criticised for the restricted number of patients and limited follow-up. Aim of this study was to assess clinical outcome and prosthetic survival rate inpatients with minimally invasive Oxford medial UKA.

This prospective study assessed 500 consecutive patients, who underwent cemented Oxford UKA for medial OA using MIS technique. Patients were assessed using objective and functional Knee Society Score (KSS).

This study has confirmed preliminary findings that Oxford UKA using a minimally invasive approach is safe, reliable and effective.

Patellofemoral joint degeneration is often considered a contraindication to medial unicompartmental knee replacement. We examined the validity of this preconception using information gathered prospectively on the intra-operative status of the patellofemoral joint in 824 knees in 793 consecutive patients who underwent Oxford unicondylar knee replacement for anteromedial osteoarthritis. All operations were performed between January 1998 and September 2005. A five-point grading system classified degeneration of the patellofemoral joint from none to full-thickness cartilage loss. A subclassification of the presence or absence of any full-thickness cartilage loss was subsequently performed to test selected hypotheses. Outcome was evaluated independently by physiotherapists using the Oxford and the American Knee Society Scores with a minimum follow-up of one year.

Full-thickness cartilage loss on the trochlear surface was observed in 100 of 785 knees (13%), on the medial facet of the patella in 69 of 782 knees (9%) and on the lateral facet in 29 of 784 knees (4%). Full-thickness cartilage loss at any location was seen in 128 knees (16%) and did not produce a significantly worse outcome than those with a normal or near-normal joint surface. The severity of the degeneration at any of the intra-articular locations also had no influence on outcome.

We concluded that, provided there is not bone loss and grooving of the lateral facet, damage to the articular cartilage of the patellofemoral joint to the extent of full-thickness cartilage loss is not a contraindication to the Oxford mobile-bearing unicompartmental knee replacement.

Anterior knee pain and/or radiological evidence of degeneration of the patellofemoral joint are considered to be contraindications to unicompartmental knee replacement. The aim of this study was to determine whether this is the case.

Between January 2000 and September 2003, in 100 knees (91 patients) in which Oxford unicompartmental knee replacements were undertaken for anteromedial osteoarthritis, pre-operative anterior knee pain and the radiological status of the patellofemoral joint were defined using the Altman and Ahlback systems. Outcome was evaluated at two years with the Oxford knee score and the American Knee Society score.

Pre-operatively 54 knees (54%) had anterior knee pain. The clinical outcome was independent of the presence or absence of pre-operative anterior knee pain. Degenerative changes of the patellofemoral joint were seen in 54 patients (54%) on the skyline radiographs, including ten knees (10%) with joint space obliteration. Patients with medial patellofemoral degeneration had a similar outcome to those without. For some outcome measures patients with lateral patellofemoral degeneration had a worse score than those without, but these patients still had a good outcome, with a mean Oxford knee score of 37.6 (SD 9.5). These results show that neither anterior knee pain nor radiologically-demonstrated medial patellofemoral joint degeneration should be considered a contraindication to Oxford unicompartmental knee replacement. With lateral patellofemoral degeneration the situation is less well defined and caution should be observed.

The Oxford hip and knee scores have been extensively used since they were first described in 1996 and 1998. During this time, they have been modified and used for many different purposes. This paper describes how they should be used and seeks to clarify areas of confusion.

Aim: To investigate the functional and radiological outcome of shelf acetabuloplasty in adults with significantly symptomatic acetabular dysplasia, with a minimum of a 5 year follow-up.

Material and Methods: 77 consecutive shelf procedures (68 patients) with an average follow-up of 10.9 years (range: 6–14) were reviewed. The Oxford hip score (OHS) was used for clinical assessment. Centre-edge angle (CEA) and acetabular angle (AA) were measured as indicators of joint containment. The severity of osteoarthiritis was based primarily on the extent of joint space narrowing. Survivorship analyses using conversion to THR as an endpoint were performed. Logrank tests were used to compare the survivorship of the shelf procedure against the variables of age, preoperative osteoarthiritis, pre and postoperative AA, CEA angles.

Results: The average age at time of surgery was 33 years (range: 17–60). At the time of the last follow-up, the mean OHS was 34.6 (maximum score: 48). Mean postoperative CEA was 55 (Pre-operatively: 13 degrees) while mean postoperative AA was 31 (Pre-operatively: 48 degrees). Thirty percent of hips needed THR at an average duration of 7.3 years. The survival in the 45 patients with only slight or no joint space narrowing was 97% (CI, 93%–100%) at 5 years and 80% (CI, 56%–100%) at 10 years. This was significantly higher (p= 0.0007) than the survival in the 32 patients with moderate or severe osteoarthiritis, which was 72% (CI, 55%–89%) at 5 years and 29% (CI, 13%–45%) at 10 years. There was no significant relationship between survival and age, pre and postoperative AA, CEA angles (p> 0.05).

Conclusion: Shelf-acetabuloplasty offers symptomatic relief to adults with acetabular dysplasia but overall deteriorates with time. About 50% of the patients do not need THR for over 10 years. Best results with shelf-acetabuloplasty were achieved in patients with slight or no joint narrowing.

We sought to determine whether smoking affected the outcome of reconstruction of the anterior cruciate ligament. We analysed the results of 66 smokers (group 1 with a mean follow-up of 5.67 years (1.1 to 12.7)) and 238 non-smokers (group 2 with a mean follow-up of 6.61 years (1.2 to 11.5)), who were statistically similar in age, gender, graft type, fixation and associated meniscal and chondral pathology. The assessment was performed using the International Knee Documentation Committee form and serial cruciometer readings.

Poor outcomes were reported in group 1 for the mean subjective International Knee Documentation Committee score (p < 0.001), the frequency (p = 0.005) and intensity (p = 0.005) of pain, a side-to-side difference in knee laxity (p = 0.001) and the use of a four-strand hamstring graft (p = 0.015). Patients in group 1 were also less likely to return to their original level of pre-injury sport (p = 0.003) and had an overall worse final 7 International Knee Documentation Committee grade score (p = 0.007).

Despite the well-known negative effects of smoking on tissue healing, the association with an inferior outcome after reconstruction of the anterior cruciate ligament has not previously been described and should be included in the pre-operative counselling of patients undergoing the procedure.

The options for treatment of the young active patient with isolated symptomatic osteoarthritis of the medial compartment and pre-existing deficiency of the anterior cruciate ligament are limited. The potential longevity of the implant and levels of activity of the patient may preclude total knee replacement, and tibial osteotomy and unicompartmental knee arthroplasty are unreliable because of the ligamentous instability. Unicompartmental knee arthroplasties tend to fail because of wear or tibial loosening resulting from eccentric loading. Therefore, we combined reconstruction of the anterior cruciate ligament with unicompartmental arthroplasty of the knee in 15 patients (ACLR group), and matched them with 15 patients who had undergone Oxford unicompartmental knee arthroplasty with an intact anterior cruciate ligament (ACLI group). The clinical and radiological data at a minimum of 2.5 years were compared for both groups.

The groups were well matched for age, gender and length of follow-up and had no significant differences in their pre-operative scores. At the last follow-up, the mean outcome scores for both the ACLR and ACLI groups were high (Oxford knee scores of 46 (37 to 48) and 43 (38 to 46), respectively, objective Knee Society scores of 99 (95 to 100) and 94 (82 to 100), and functional Knee Society scores of 96 and 96 (both 85 to 100). One patient in the ACLR group needed revision to a total knee replacement because of infection. No patient in either group had radiological evidence of component loosening. The radiological study showed no difference in the pattern of tibial loading between the groups.

The short-term clinical results of combined anterior cruciate ligament reconstruction and unicompartmental knee arthroplasty are excellent. The previous shortcomings of unicompartmental knee arthroplasty in the presence of deficiency of the anterior cruciate ligament appear to have been addressed with the combined procedure. This operation seems to be a viable treatment option for young active patients with symptomatic arthritis of the medial compartment, in whom the anterior cruciate ligament has been ruptured.

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 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=0.31).

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.

Aims: The purpose of this study is to determine the causes of failed medial Oxford unicompartmental knee arthroplasty (UKA) and assess the outcome after revision surgery.

Materials And Methods: From 1993 to 2003, sixty-nine Oxford UKA (58 patients) were revised to a total knee replacements (TKR) at this centre. The type of implant used at revision surgery, pre- and post-revision American Knee Society (AKS) and Tegner scores were analyzed retrospectively.

Results: The patient’s mean age at the time of UKA was 64.5 years (range: 50–79). The average pre-revision scores were as follows: AKS-Objective score was 41.2 (± 10.4), the AKS-functional score was 56.8 (±10.0) and the average Tegner score was 1.5 (±0.6). The mean follow-up period was 38.3 (range: 12–107) months. The common causes of failure were: lateral compartment osteoarthritis (34.0%), component loosening (30.4%) and early or late infection requiring two-stage revision surgery (14.3%). The majority were revised using a standard primary TKR implant and only six (9%) requiring augmentation stems. Patellar resurfacing was performed in 25% of cases. The mean polyethylene liner width of the revision TKR was 13.4mm (±3.7). The average post-revision scores were: AKS-Objective score 77.4 (±13.1), the AKS-functional AKS score 70 (±21.1) and the average Tegner score of 2.2 (±0.8). Three knees needed rerevision for infection of the revised implant.

Conclusions: Lateral compartment osteoarthritis was the commonest indication for revision surgery for a failed medial Oxford UKA. Revision of a UKA is technically easier and the results are superior to the published results of revision of a primary TKR. In more than 90% cases, no augmentation or stemmed implants were necessary.

Introduction: The indications for medial unicompartmental knee arthroplasty (UKA) remain controversial; in particular, those relating to the state of the patello-femoral joint (PFJ). Some authorities consider the presence of anterior knee pain (AKP) and/or full thickness cartilage loss (FTCL) to be a contraindication. The aim of this study was to determine the influence of patello-femoral problems on the outcome of medial UKA.

Materials and Methods: This prospective study involved one hundred knees with cemented medial Oxford UKA (phase 3), via a minimally invasive approach. Pre-operatively presence or absence of AKP was noted. The cartilage status of medial and lateral patello-femoral joint was grade and recorded intra-operatively. Outcome was evaluated at one-year with the Knee Society Score and the Oxford Knee Score (OKS).

Results: 54% of patients had pre-operative AKP. The clinical outcome at one year was not dependent on the presence or absence of pre-operative AKP [OKS: 40.2 (± 8.2) for patients without pre-op. AKP and OKS: 40.8 ((± 6.8) for patients with pre-operative AKP]. 35% of patients had FTCL seen at operation in the PFJ. The outcome at one year was independent of the state of the medial and/or lateral PFJ [OKS = 40.7 (± 7) with normal or partial thickness cartilage loss and OKS = 39.8 (± 7) with full thickness cartilage loss in PFJ]

Conclusions: These short-term results suggest that for the Oxford UKA the presence of anterior knee pain or full thickness cartilage damage in patello-femoral joint should not be considered to be a contraindication.

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: With a minimally invasive approach for unicompartmental knee replacement (UKA), it is difficult to determine the femoral component size intra-operatively. It can be difficult to template pre-operative radiographs due to superimposition of the two femoral condyles, and non-standardised x-ray magnification.

Aim: The purpose of the study was to find an easy, reliable, alternative method for this assessment such as height and gender.

Material and methods: One hundred x-rays of patients (44 men, 56 women), who had undergone Oxford UKR, were reviewed. Preoperative radiographs were templated, and postoperative x-rays were reviewed to determine the ideal component size. Patient’s height was recorded. The proportion of patients for whom an appropriate size could be selected by either template or height measurements was calculated.

Results: Current templating system accurately predicted the ideal size in 67 patients. The following size bands were set according to height. For men: size small in patients less than160 cm, medium less than 170 cm and large less than 180 cm. For women: size small in patients less than 164 cm, medium less than 174 cm and large less than 184 cm. Height accurately predicted the ideal size in 75 patients. In no case was the assessment of component size incorrect by more than one size.

Conclusion: Gender specific height safely predicted the ideal component size in 75 percent of patients undergoing UKA. Component size can be determined satisfactorily from patient height and gender and can be used as adjunct to existing templating method.