Table 10.2 shows the published 10, 15 and 20-year results of the Phase 1 and Phase 2 OUKA. The 10 year survival rate ranges from 82% to 98%. The series with the second lowest survival rate, by Vorlat et al. (2000), had broad indications and included patients who had undergone previous HTO or had inflammatory arthritis. Similarly, in the series by Kumar et al. (1999) four of the seven revisions were attributed to loosening, two were for disease progresion and one was for tibial fracture. Seven of a cohort of 100 cases were subsequently found to have inflammatory arthritis. There were no revisions for wear. In the designer series, which should be indicative of the best results that can be achieved, the survival was 98% (Murray et al, 1998).
Table 10.3 includes all the published and presented series with 10-year survival rates of the Phase 3 medial OUKA. The authors were contacted to determine what percentage of their knee replacements were OUKA. The nine papers include over 6000 patients with an estimated average survival rate at 10 years of about 95% (range 91 – 97%). Although most series were performed by one or two surgeons, in two a large number of surgeons were involved. In one series from Oxford (Bottomley et al., 201555), which did not include designer surgeons, there were 56 surgeons. In the series from Basingstoke (Briant-Evans et al., 2013), there were 35. Despite the high numbers of surgeons, many of whom were trainees, the 10-year results were good, suggesting the indications for the operation are very important. In these institutions, it is likely that there was a standard set of indications, whereas the surgical skill among the trainees is probably somewhat variable. Further evidence that the indications are important relates to the usage of the device. In the nine series, somewhere between 20% and 60% of the surgeons’ knee replacements were OUKA. This fits well with the registry data because it shows that, to obtain good results with the OUKA, usage between 20% and 50% should be aimed for. To achieve this, the recommended indications should be used.
In addition to these series including 10-year results, there are other shorter series reporting the results of the OUKA. Hamilton et al. are conducting a meta-analysis of published phase 3 OUKA results. The authors identified 47 studies and contacted the authors to determine what percentage of their knee replacement practice was UKA (Hamilton et al, 2016). There were marked differences between those who use the UKA in a small proportion of their knee replacement practice compared with those who use it in a high proportion. For <10% usage, UKA revision rate per 100 observed component years was 2.13 (SD 1.36). For >10% and <30%, it was 1.47 (SD 0.92). For ≥ 30%, it was 0.67 (SD 0.52). A Kruscal-Wallis test revealed statistically significant differences between the three groups (p = 0.021).
Table 10.2 Survival Rates for Oxford Medial Arthroplasties Phase 1 & 2 at 10, 15 & 20 years. Only the most recent report of a series is included.
Table 10.3 Reported 10-year survival of Oxford Phase 3.
