The clinical outcome of the Phase 3 OUKA was reported in 2006 (Pandit et al, 2015). The mean objective Knee Society Score improved from 33 to 92, the mean function score improved from 46 to 80, with 85% considered Excellent (Fig. 10.12). The mean flexion deformity decreased from 6° to 2° and the mean flexion limit increased from 115° to 133° (Fig. 10.13). The Knee Society Score is not a good tool for assessing the outcome of UKA. For example it does not give credit for flexion beyond 125°. A study by Choy et al. (2011) from Korea of 188 knees in 166 patients, with a mean follow up of 6.5 years, found that the mean flexion limit increased from 135° preoperatively to 150° (140° to 165°) postoperatively; 81% of the patients could squat and 91% could sit cross-legged, both activities that require full flexion in Korea. The very high preoperative range of motion reflects the social practices of that country.
Figure 10.12 Change in Knee Society Score (Objective) for 101 knees, pre-op in red, mean five-year follow-up in green.
Figure 10.13 Maximum flexion in 101 knees (pre-op in red, mean follow-up of five years in green).
Another problem with the Knee Society Score is that points are deducted for malalignment. Although this is appropriate for TKA where the aim is usually to restore neutral alignment, it is not appropriate for the OUKA where the aim is to restore pre-disease alignment. Gulati et al. (2009) found that 18% of patients had mild varus postoperatively (about 5° from neutral) and 8% had marked varus (about 10° from neutral). As the OKS was no worse in those with varus than those with neutral alignment, the deductions are unjustified. Removing the deduction increased the postoperative KSS-objective) from 77 (SD 15) to 89 (SD 14) in the mild varus group and from 70 (SD 13) to 94 (SD 8) in the marked varus group. We favour the OKS for assessing outcome and find that, on average, the preoperative score is about 25 (SD 9) and the postoperative score at 10 years is about 40 (SD 9)
Price et al. (2001) compared the rate of recovery (measured by the time taken to achieve straight-leg raising, 70° of flexion, and independent stair climbing) in 40 OUKAs performed through a short incision medial to the patellar tendon, without dislocation of the patella, using Phase 3 instrumentation, with 20 OUKAs implanted through an open approach with dislocation of the patella. Both groups were compared with 40 AGC (Biomet, Swindon, UK) TKAs performed for osteoarthritis during the same time period. The average rate of recovery after the short-incision UKA was twice as fast as after open UKA and three times as fast as after TKA.
