Unicompartmental knee replacement (UKR) is an established treatment for single compartment end-stage knee arthrosis with good recorded survivorship. Although often used in more active, younger patients, patient selection remains controversial. To identify risk factors for early failure we compared patients with UKR failure requiring revision to total knee replacement (TKR) with a control group. Between September 2002 and 2008, 812 Oxford Mobile Bearing Medial UKRs were implanted. 21 implants (20 patients) required revision to TKR within 5 years. The leading cause for revision was lateral compartment disease progression (11 patients). In the revision group, 17 patients were female (81%), average age at index surgery was 64.1 (range 48–81) and average BMI 31.8 (range 24.4–41.5). Our UKR patients with early failure requiring revision were more likely to be female (p=0.0012) whilst age and BMI were similar between groups. Although the change in tibio-femoral valgus angle was similar, control group patients started in varus becoming valgus post-operatively, whereas revision group patients started in valgus and became more valgus post-operatively. This might explain lateral compartment disease progression as our leading cause of early failure. We believe females with medial compartment disease but valgus alignment are at greater risk of early failure and it is particularly important not to overstuff the medial compartment.
Orthopaedic practice is increasingly guided by conclusions drawn from analysis of Joint Registry Data. Analysis of the England and Wales National Joint Registry (NJR) led Sibanda et al to conclude that UKR should be reserved for more elderly patients due to higher revision rates in younger patients. To determine our UKR revision rates at the Great Western Hospital we requested knee arthroplasty data from the NJR, Hospital Episode Statistics (HES) data submitted by our centre to the Primary Care Trust, and interrogated our internal theatre implant database. This revealed significant discrepancies between different data sources. We collected data from each source for 2005, 2006, and 2007. Operations were classified as TKR, UKR, Other or Unspecified. Results are illustrated in the attached table: Key findings: Our theatre implant database appears most accurate and includes a greater number of joint replacement operations than NJR or HES data and fewer ‘unspecified’ procedures. On average 15% NJR, 0% HES and 0.3% theatre data procedures were ‘unspecified’. NJR data comprises an average 17 fewer, and HES data an average 36 fewer procedures each year compared with our theatre data. Up to 80% UKRs performed are recorded as TKR in HES data. In summary there is significant inaccuracy in our NJR data which may affect the validity of conclusions drawn from NJR data analysis. HES data is even less accurate with implications for hospital funding. We strongly advise other centres to continue to maintain accurate implant data and to perform a similar audit to calculate error rates for NJR and HES data. Further analysis is required to identify at which stage of data collection inaccuracies occur so that solutions can be devised. We are currently analysing data from 2008 and 2009.
Unicompartmental knee replacement (UKR) is an established treatment for single compartment end-stage arthrosis with good recorded survivorship. UKRs are often implanted into more active younger patients, but patient selection remains controversial. A recent study, led by the Royal College of Surgeons Clinical Effectiveness Unit, demonstrated that prosthesis revision rates decrease strongly with age (Van Der Meulen et al 2008). It has therefore been suggested that UKR should only be considered in elderly patients. This contrasts our observed experience of early revision cases leading us to compare these patients with a control group. Between September 2002 and 2008, 812 Oxford Mobile Bearing Medial UKRs were implanted. We compared all patients who underwent UKR revision to Total Knee Replacement (TKR) against a control group of 50 consecutive UKR patients. 20 implants have required revision to TKR in 19 patients since 2002. Median age at index surgery was 68 (range 48-81), median BMI was 31 (range 25-41.5), 17 patients were female (85%), and median implant survival was 25 months (range 6-57). Control group median age at index surgery was 66 (range 46-81), median BMI was 30 (range 22-51), and 27 patients were female (54%). Median Oxford Knee Score recorded in September 2009 was 36 (range 14-54) for revision patients and 21 (range 14-39) for the control group (p=0.021). Our UKR patients with early failure requiring revision are far more likely to be female (p=0.015), as well as older and with a higher BMI than the control group. We feel this is a subset of patients at high risk of failure, despite meeting all criteria for UKR. The underlying causes are likely to be multifactorial, but a key factor may be that this group has varus tricompartment osteoarthritis rather than classical anteromedial osteoarthritis. Our data counters recent advice based on National Joint Registry data.
