We studied the bone mineral density (BMD) and the bone mineral content (BMC) of the proximal tibia in patients with a well-functioning uncemented Oxford medial compartment arthroplasty using the Lunar iDXA bone densitometer. Our hypothesis was that there would be decreased BMD and BMC adjacent to the tibial base plate and increased BMD and BMC at the tip of the keel.

There were 79 consecutive patients (33 men, 46 women) with a mean age of 65 years (44 to 84) with a minimum two-year follow-up (mean 2.6 years (2.0 to 5.0)) after unilateral arthroplasty, who were scanned using a validated standard protocol where seven regions of interest (ROI) were examined and compared with the contralateral normal knee. All had well-functioning knees with a mean Oxford knee score of 43 (14 to 48) and mean Knee Society function score of 90 (20 to 100), showing a correlation with the increasing scores and higher BMC and BMD values in ROI 2 in the non-implanted knee relative to the implanted knee (p = 0.013 and p = 0.015, respectively).

The absolute and percentage changes in BMD and BMC were decreased in all ROIs in the implanted knee compared with the non-implanted knee, but this did not reach statistical significance. Bone loss was markedly less than reported losses with total knee replacement.

There was no significant association with side, although there was a tendency for the BMC to decrease with age in men. The BMC was less in the implanted side relative to the non-implanted side in men compared with women in ROI 2 (p = 0.027), ROI 3 (p = 0.049) and ROI 4 (p = 0.029).

The uncemented Oxford medial compartment arthroplasty appears to allow relative preservation of the BMC and BMD of the proximal tibia, suggesting that the implant acts more physiologically than total knee replacement. Peri-prosthetic bone loss is an important factor in assessing long-term implant stability and survival, and the results of this study are encouraging for the long-term outcome of this arthroplasty.

Cite this article: Bone Joint J 2013;95-B:1480–3.

Introduction. Obesity has been considered a relative contra-indication in unicompartmental knee arthroplasty (UKA) due to fear of high wear rates, loosening and tibial collapse. The aim of this study was to investigate the impact of high body mass index (BMI) on ten-year survivorship and five-year functional outcome after Oxford UKA, a fully congruous mobile bearing design with large contact area and low wear rate. Methods. This prospective study examines a consecutive series of 595 knees (mean age 66 years, range: 33-88) undergoing Oxford UKA with a minimum 5-year follow-up. Patients were divided into three groups; Group I (Normal body weight), BMI <25 (n=171), Group II (overweight), BMI 25- 30 (n=264), and Group III (Obese), BMI ≥30 (n=160). The survivorship and functional outcome (as assessed by change in Oxford Knee Score [DeltaOKS]) and Knee Society Score (KSS) for all three groups were compared. Results. The mean follow-up was 6.3 years. There was no significant difference in the 10-year survivorship between groups (96% for all groups). Although numbers were small there was no significant difference in revision rates for patients with BMI ≥35 (n=1/38). Group III patients had a lower pre-operative OKS and lower post-operative OKS compared to groups I and II, although DeltaOKS was similar (p= .977). At last follow-up the Functional KSS was lower in group III (p=.11), although Objective KSS was not significantly different between groups (p=.954). Conclusion. Oxford UKA can be safely used in obese and morbidly-obese patients. Design features of congruous bearing and large contact area ensure low wear rates. Summary. No significant difference in revision rates noted between groups of increasing body mass index in this prospective study of outcome in patients undergoing medial Oxford unicondylar knee replacement

Objective. To investigate the reasons for revision of Oxford Unicondylar Knee Replacement (UKR). Does insert size used relate to requirement for revision?. Methods. We retrospectively reviewed the cases needing revision from a single surgeon consecutive series of 209 ‘Oxford’ UKRs. 10 cases required early (within 2 years) revision. The reasons for revision were investigated. A comparison of cases requiring revision by insert size implanted was made. Results. 10 cases required revision. 2 patients suffered from Sjorgens Syndrome which was undiagnosed at the time of primary surgery and underwent revision for ongoing pain, 2 cases fractured the tibia beneath the implant, 2 were revised for sepsis, and 3 cases were revised for ongoing pain without obvious cause. 1 case was revised for tibial component loosening. A significantly greater proportion of cases in which a size 6 insert was used required revision (4 of 11), compared with size 4 (1 of 44)(p=0.001) or size 5 (0 of 28)(p=0.002), and also compared with size 3 (3 of 31)(p=0.005). In cases where a size 3 insert is measured with this prosthesis, one option is to take a further tibial cut to rather use a size 6 insert. Given the five-fold increase in likelihood for requiring revision found in our series, we would recommend against this step. Conclusion. In conclusion we report a successful series of Oxford unicondylar knees taking early revision surgery as the endpoint. We recommend caution when considering a further cut when initial measurement suggests a size 3 insert, as in our series size 6 inserts showed a 5 fold increase in revision rate when compared to size 3

Oxford medial uni compartmental knee replacement is a common and widely accepted procedure that relies on accurate positioning and alignment of the implants for optimal outcome and longevity. Posterior slope of the tibial base plate has been shown to be an important factor affecting long term survivorship. The aim of the study was to evaluate whether navigation increased the accuracy of Oxford knee replacements using the posterior slope of the tibial component as an index measure. The posterior slope of tibial trays from 58 sequential Oxford medial unicondylar knee replacements over a two year period was checked on standard lateral x-rays against the recommended range. There were 12 cases in the navigated and 46 in the conventional group across six Orthopaedic firms. The mean posterior slope for navigated and conventional implantations was 4.75 and 3.3 degrees respectively with the difference not being statistically significant. However, when considering the data for low volume surgeons, the mean posterior slope with and without navigation was 4.75 and 1.83 degrees respectively which was significant with a p value of 0.017. Navigation was also found to significantly decrease the chance of implanting the knee with the posterior slope outside the acceptable range (p=0.024). In both analyses the navigated cohort had a narrower data spread and fewer outliers compared to the conventional group. No other factors were found to significantly correlate with the posterior slope. The study suggests that navigation might help low volume surgeons in increasing the accuracy and decreasing the incidence of extreme variations from the desirable range of implant positioning for unicompartmental knee replacements

Narrow, well-defined radiolucent lines commonly observed at the bone-implant interface of unicompartmental knee replacement tibial components have been referred to as physiological radiolucencies. These should be distinguished from pathological radiolucencies, which are poorly defined, wide and progressive, and associated with loosening and infection. We studied the incidence and clinical significance of tibial radiolucent lines in 161 Oxford unicondylar knee replacements five years after surgery. All the radiographs were aligned with fluoroscopic control to obtain views parallel to the tibial tray to reveal the tibial bone-implant interface. We found that 49 knees (30%) had complete, 52 (32%) had partial and 60 (37%) had no radiolucent lines. There was no relationship between the incidence of radiolucent lines and patient factors such as gender, body mass index and activity, or operative factors including the status of the anterior cruciate ligament and residual varus deformity. Nor was any statistical relationship established between the presence of radiolucent lines and clinical outcome, particularly pain, assessed by the Oxford Knee score and the American Knee Society score. We conclude that radiolucent lines are common after Oxford unicompartmental knee replacement but that their aetiology remains unclear. Radiolucent lines were not a source of adverse symptoms or pain. Therefore, when attempting to identify a source of postoperative pain after Oxford unicompartmental knee replacement the presence of a physiological radiolucency should be ignored

Introduction: Debate continues regarding the optimal timing of surgery for patients requiring bilateral knee arthroplasty; we reviewed the costs, clinical and functional outcomes of 116 patients undergoing simultaneous or staged bilateral surgery using 3 different prostheses. Method: Data were retrospectively collected from 116 consecutive patients undergoing 232 knee replacements over 10 years, either simultaneously or over 2 hospital admissions (staged). Post-operative complication rate, total cost of treatment (calculated from pros-theses, theatre time, days in hospital and number of clinic attendances) and functional (HSS) score at 1 year were the outcome measures. Results: 54 patients underwent Oxford unicondylar knee replacements, 41 simultaneously, 13 staged; respective mean total costs were £9890 and £13,553 (p< 0.001). 42 patients were treated with AGC prostheses; 14 simultaneously, 28 staged, with respective total costs of £12,187 and £16,920 (p< 0.001). 10 TMK patients had simultaneous surgery (mean total cost £14,812), 10 were staged (£20,191); p< 0.001. For all 3 prostheses, there was no significant difference in complication rate or 1 year functional outcome between simultaneous and staged groups. Discussion: Some authors advocate replacing both knees simultaneously as safe and cost-effective; others report significant increases in medical and surgical morbidity. Our series shows significant cost savings with no increase in complication rate

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