Abstract
Introduction
Historically, the outcomes of knee replacement were evaluated based on implant longevity, major complications and range of motion. Over the last recent years however, there has been an intensively growth of interest in the patient's perception of functional outcome. However, the currently used patient related outcome (PRO) scores are limited by ceiling effects which limit the possibility to distinguish between good and excellent results post knee arthroplasty. The Forgotten Joint Score (FJS) is a new PRO score which is not influenced by ceiling effects, therefore making it the ideal instrument to compare functional outcome between various types of implants. It is based on the thought that the ultimate goal in joint arthroplasty is the ability of a patient to forget their artificial joint in everyday life.
The aim of this study is to compare the FJS between patients who undergo TKA and patients who undergo medial UKA at least 12 months post-operatively. We hypothesized that the UKA which is less extensive surgical procedure will present better FJS than TKA, even 12 month postoperative.
Methods
All patients who underwent medial UKA or TKA were contacted 12 months post-operatively. They were asked to complete the FJS, the Western Ontario and McMasters Universities Osteoarthritis index (WOMAC) and the EuroQol-5D (EQ-5D). A priori power analysis was conducted using two-sample t-test. 64 patients in each group were needed to reach 80% power for detecting a 12 point (SD 24) significant difference on the FJS scale with a two-sided significant level of 0.05. A p-value <0.05 was considered as statistically significant.
Results
128 patients were included. 64 underwent medial UKA and 64 TKA. At an average of 1.5 years follow-up in the UKA group and 1.4 years in the TKA group, the FJS was significantly higher in the UKA group (73.0±23.3) than the TKA group (59.1±26.8). No significant differences were noted for all 3 WOMAC domains (figure 1) and 5 EQ-5D domains (figure 2).
Conclusion
Our data suggests that patients who undergo UKA are better capable of forgetting their artificial joint in daily life and therefore are more satisfied. Furthermore our data suggests that the FJS should be used in future studies since it has the ability to detect top-end differences where the conventional PRO scores are unable to distinguish between good and excellent results following knee replacement.
