Oxford medial unicompartmental knee arthroplasty. A survival analysis of an independent series.

We describe the outcome of a series of 124 Oxford meniscal-bearing unicompartmental arthroplasties carried out for osteoarthritis of the medial compartment. They had been undertaken more than ten years ago in a non-teaching hospital in Sweden by three surgeons. All the knees had an intact anterior cruciate ligament, a correctable varus deformity and full-thickness cartilage in the lateral compartment. Thirty-seven patients had died; the mean time since operation for the remainder was 12.5 years (10.1 to 15.6). Using the endpoint of revision for any cause, the outcome for every knee was established. Six had been revised (4.8%). At ten years there were 94 knees still at risk and the cumulative survival rate was 95.0% (95% confidence interval 90.8 to 99.3). This figure is similar to that reported by the designers of the prosthesis and to the best published results for independent series of total knee replacement. If patients are selected appropriately, this implant is a reliable treatment for anteromedial osteoarthritis of the knee

Medial unicompartmental arthroplasty after failed high tibial osteotomy.

Satisfactory selection criteria are essential for the successful outcome of unicompartmental knee arthroplasty (UCA). We report the frequency of revision of the Oxford medial unicompartmental arthroplasty in knees previously treated for anteromedial osteoarthritis by high tibial osteotomy (HTO). The combined results from three sources were used to allow statistical analysis of this uncommon subgroup. In the combined series of 631 knees (507 patients) which had medial unicompartmental replacement, 613 were primary procedures and 18 were for a failed HTO. The mean follow-up times of the two groups were similar (5.8 years and 5.4 years, respectively). At review, 19 (3.1%) of the primary procedures and five (27.8%) of those undertaken for a failed HTO had been revised to total knee replacement. Survival analysis revealed the ten-year cumulative survivals to be 96% and 66%, respectively. The log-rank comparison of these survivals revealed a highly significant difference (p < 0.0001). We recommend that the Oxford UCA should not be used in knees which have previously undergone an HTO

Oxford medial unicompartmental arthroplasty for focal spontaneous osteonecrosis of the knee.

BACKGROUND: Spontaneous osteonecrosis of the knee (SONK) is a distinct clinical condition occurring in patients without any associated risk factors. There is controversy as to the best method of treatment, and the available literature would suggest that patients with SONK have a worse outcome than those with primary osteoarthrosis when arthroplasty is performed. We assessed the outcome of medial unicompartmental knee arthroplasty (UKA) using the Oxford prosthesis for end-stage focal spontaneous osteonecrosis of the knee (SONK; Ahlbäck grades III and IV). PATIENTS AND METHODS: We assessed 29 knees (27 patients) with spontaneous osteonecrosis of the knee using the Oxford Knee Score. 26 knees had osteonecrosis of the medial femoral condyle and 3 had osteonecrosis of the medial tibial plateau. All had been operated on using the Oxford Medial Unicompartmental Knee Arthroplasty (UKA). This group was compared to a similar group (28 knees, 26 patients) who had undergone the same arthroplasty, but because of primary osteoarthrosis. Patients were matched for age, sex and time since operation. The mean length of follow-up was 5 (1-13) years. RESULTS: There were no implant failures in either group, but there was 1 death (from unrelated causes) 9 months after arthroplasty in the group with osteonecrosis. The mean Oxford Knee Score in the group with osteonecrosis was 38, and it was 40 in the group with osteoarthrosis. INTERPRETATION: Use of the Oxford Medial UKA for spontaneous focal osteonecrosis of the knee is reliable in the short to medium term, and gives results similar to those obtained when it is used for patients with primary osteoarthrosis

Proximal tibial strain in medial unicompartmental knee replacements

As many as 25% to 40% of unicompartmental knee replacement (UKR) revisions are performed for pain, a possible cause of which is proximal tibial strain. The aim of this study was to examine the effect of UKR implant design and material on cortical and cancellous proximal tibial strain in a synthetic bone model. Composite Sawbone tibiae were implanted with cemented UKR components of different designs, either all-polyethylene or metal-backed. The tibiae were subsequently loaded in 500 N increments to 2500 N, unloading between increments. Cortical surface strain was measured using a digital image correlation technique. Cancellous damage was measured using acoustic emission, an engineering technique that detects sonic waves (‘hits’) produced when damage occurs in material

Long-term clinical results of the Oxford medial unicompartmental knee arthroplasty

The purposes of this study were to investigate the mode of failure and survivorship of an independently performed series of medial Oxford unicompartmental knee arthroplasties. The study included 43 knees in 40 patients with a mean follow-up of 14.88 years: 13 knees (11 patients) had revision surgery (30%), and ten patients required conversion to total knee prosthesis. The mean International Knee Society (IKS) scores at the time of the revision were 145.52 [standard deviation (SD): 39.90, range: 167–200]. The overall alignment of the knee was restored to neutral, with a hip-knee-ankle (HKA) angle average of 178° (SD: 3.21°, range: 170–186°). Survivorship, as defined by an endpoint of failure for any reason, showed that the survival rate at five years was 90%, at ten years 74.7% and at 15 years 70%. Excluding inappropriate patient selection and surgeon-associated failures, our survival analysis plot is much improved: survivorship at five years is 94.5%, at ten years 85.7% and at 15 years 80.4%. The Oxford meniscal bearing arthroplasty offers long-term pain relief with good knee function. Unfortunately, we demonstrated a high complication rate, with some of the failures encountered indicating that the surgical technique is very demanding