Abstract
Background
In this study, we investigated the long-term clinical results and survivorship of minimally invasive unicompartmental knee arthroplasty (UKA) by collecting cases that have been implanted for >10 years ago.
Methods
Medial UKA on 180 cases in 142 patients was performed over a period of 1 year after the first introduction of minimally invasive UKA from January 2002 to December 2002. Among these, 166 cases in 128 patients who underwent Oxford phase 3 medial UKA using the minimally invasive surgery, with the exclusion of 14 cases including 10 cases of follow-up loss and 4 cases of death, were selected as the subject. The mean age of the patients at the time of surgery was 61 years, and the duration of the follow-up was minimum 10 years. All the preoperative diagnosis was osteoarthritis of the knee joint. Clinical and radiographic assessments were measured by the Knee Society clinical rating system, and the survival analysis was confirmed by the Kaplan–Meier method with 95% confidence interval (CI).
Results
The mean Knee Society knee and function scores improved significantly from 53.8 points (25 to 70) and 56.1 points (35 to 80) preoperatively to 85.4 points (58 to100) and 80.5 points (50 to 100) at 10-year follow-up, respectively(P<0.001). The mean range of the motion of the knee joint recovered from 128.6° (110° to 135°) to 132.5o (105o to 135o) (P<0.001), and the tibiofemoral angle changed from the mean 0.2° of varus (7o of varus to 7o of valgus) to 4.6° of valgus (2° of varus to 11° of valgus) under the weight-bearing X-ray (P<0.001). Failures following the UKA occurred in 16 cases in 14 patients out of a total of 166 cases (9.6%), and the mean time of the occurrence of the failure was 6.2 years after the surgery. The causes of the failure included 7 cases of simple dislocation of mobile bearing, 4 cases of loosening of implant, 1 case of dislocation of mobile bearing accompanied by loosening of implant, and 1 case of dislocation of mobile bearing accompanied by the rupture of the medial collateral ligament (MCL). Moreover, there was 1 case of fracture of polyethylene bearing, 1 case of deep infection and 1 case of failure because of medial tibial condylar fracture. Of the total of 16 cases of failures, 11 cases (69%) were treated with revision total knee arthroplasty (TKA), whereas 5 cases (31%) were treated with a simple change of mobile bearing. The 10-year survival rate was 90.5% (95% CI, 85.9 to 95.0) when failure was defined as all the reoperations, whereas the 10-year survival rate was 93.4% (95% CI, 89.6 to 97.1) when the cases in which only revision TKA was defined as failure.
Conclusions
The results of this study show outstanding functions of the knee joint and satisfactory 10-year survival rate after minimally invasive UKA. Therefore, minimally invasive UKA could be a useful method in the treatment of osteoarthritis in one compartment of knee joint.
