Abstract
Unicompartmental knee replacements (UKR) have many advantages over total replacements (TKR), including better function and less morbidity. However, in general, they have a higher failure rate. To minimise the UKR failure rate it is essential that the implant should not wear out, and that the appropriate indications and surgical techniques are used. The Oxford UKR has a fully congruent mobile bearing and has been shown in a retrieval study to have minimal wear.
The indications for the use of Oxford UKR are clearly defined. It is recommended for medial compartment osteoarthritis, with a functionally intact Anterior Cruciate Ligament. The Varus deformity should be correctable and there should be full thickness cartilage in the lateral compartment, which is best demonstrated on a valgus stress radiograph. It is appropriate for about one in four osteoarthritic knees needing replacement.
The designer, Mr Goodfellow, achieved a 98% (CI 93% to 100%) survival at 10 years, using the appropriate indications. However, data from the designer is open to bias. An independent series of 420 Oxford UKR from Dr Svard achieved a 94% (CI 86% to 100%) survival at 15 years, with no loss to follow-up. In the Swedish Knee Arthroplasty Register, in centres implanting at least 2 UKR per month, the survival rate of the Oxford UKR was 93% at 8 years. In centres doing very few UKR the failure rate was higher. These poor results were probably because of inappropriate indications or technique. To address the problem of inconsistent results new simplified instrumentation (Phase 3) has recently been introduced. This instrumentation has been specifically designed for a minimally invasive approach.
Patients recover three times quicker after minimally invasive UKR than after TKR. A Radiographic comparison demonstrated the Oxford UKR can be implanted as precisely through a short incision as through a standard incision. A fluoroscopic study demonstrated that knee kinematics after minimally invasive UKR are virtually normal and are substantially better than after TKR. At one year the first 58 minimally invasive Oxford (Phase 3) UKR implanted by a single surgeon had an average flexion of 135°, Knee Society knee score of 97 and function score of 92.
We conclude that UKR is the treatment of choice for medial compartment osteoarthritis provided appropriate implants, indications and surgical techniques are used.
The abstracts were prepared by Professor Jegan Krishnan. Correspondence should be addressed to him at the Flinders Medical Centre, Bedford Park 5047, Australia.
