Medial rather than lateral knee instability correlates with inferior patient satisfaction and knee function after total knee arthroplasty.

BACKGROUND: It is commonly thought that balanced medial and lateral tibiofemoral joint gaps are essential, but the effect of joint laxity on clinical outcome after total knee arthroplasty (TKA) is unclear. It was hypothesised that medial joint laxity correlates with inferior patient satisfaction and knee function, although lateral joint laxity is allowed to a certain degree in TKA.

METHODS: This study included 50 knees that underwent primary TKA. Knee laxity was measured with postoperative stress radiographs in flexion and extension, and patient satisfaction and knee function were evaluated by the 2011 Knee Society Knee Scoring System.

RESULTS: In a comparison of medially tight and medially loose knees in flexion, the scores for satisfaction, symptoms, standard activity, and advanced activity were significantly better in medially tight than in medially loose knees (satisfaction: 29.8, 22.2; symptoms: 20.3, 15.9; standard activities: 24.2, 19.1; and advanced activities: 15.3, 8.7, in the tight and loose knees, respectively). Neither lateral joint laxity during knee flexion nor medial joint laxity during knee extension was associated with a poor postoperative clinical outcome, whereas lateral joint laxity and the standard activity score in extension had a moderate positive correlation.

CONCLUSIONS: Knees with medial joint laxity during flexion resulted in an inferior postoperative outcome, and lateral joint laxity did not influence patient satisfaction or function. Care should be taken to maintain medial joint stability during the TKA procedure.