Functional improvement after unicompartmental knee replacement: a follow-up study with a performance based knee test

In literature no reports appear on functional recovery of unicompartmental knee replacement using both subjective and objective methods. Functional aspects are especially of importance, since prosthetic replacement is considered more often in younger patients, who require an optimal knee function for activities such as sports. In a prospective study on 38 patients with a mean age of 62.2 years functional improvement was measured. Using Knee Society Score (KSS) as a clinician based score and the Dynaport (R) Knee Test as a functional test measurements were performed at preoperative, 3 and 6 months, 1 and 2 years, after surgery. The Dynaport (R) Knee Test is an accelerometer-based system that objectively measures functional aspects of gait during various tasks of daily life. It consists of four sub scores. The KSS assesses pain and function. Both scores range from 0 to 100. The mean KSS preoperative was 44.0 and improved significantly to 81.7 at 3 months (P < 0.001) and to 87.4 (P = 0.025) at 6 months. No significant differences were noted after 6 months. The mean preoperative Dynaport (R) Knee Test score was 35.8 and at 3 months 43.6 (P < 0.001), 48.6 at 6 months (P < 0.001). No significant differences were noted after 6 months follow-up. Of the Dynaport sub scores, the low demanding tasks Lift and Move and Locomotion, cease to improve beyond 6 months. The high demanding task Transfers only improved up to 3 months. However, the other high demanding tasks Rise and Descend showed improvement beyond 1 year after surgery, since the improvement from 6 months to 2 years was significant (P = 0.023). This study has found that functional recovery continues beyond 6 months and even up to 2 years. It seems only more challenging tests can discriminate on improvement beyond a point where questionnaires cease to improve. The use of objective measurement methods is advocated next to the clinician based scores and self reported questionnaires.