Medial rather than lateral knee instability correlates with inferior patient satisfaction and knee function after total knee arthroplasty
Introduction
Many pre- and postoperative factors can affect patient satisfaction and knee function after total knee arthroplasty (TKA) [1], [2], [3], [4]. Ligament balancing is one of the key surgical elements used to improve postoperative knee function [5], [6]. It is commonly thought that balanced medial and lateral gaps are essential, and that imbalanced gaps lead to malfunction and failure [7], [8].
In contrast, a magnetic resonance imaging (MRI) analysis showed that in normal knees at 90° of flexion the lateral joint gap was larger than the medial joint gap [9]. Another study also reported that the lateral extension gap was slightly more lax compared with the medial extension gap in a radiographic analysis [10]. In addition, recent studies showed that intraoperative lateral joint laxity at 90° knee flexion was an important factor affecting postoperative knee flexion angle after TKA [11], because lateral joint laxity from mid-to-deep knee flexion played an important role in determining internal tibial rotation against the femoral component [12]. Achieving good range of motion certainly has a great clinical impact on patient satisfaction after TKA [13], [14], but the question arises whether successful TKA is possible using unequal medial and lateral joint gaps. Few studies have evaluated in detail the effect on patient symptoms of medial–lateral knee stability during knee flexion, and achieving the relevant amount of soft tissue balancing in TKA is clinically beneficial for predicting postoperative patient satisfaction.
In this study, it was hypothesised that medial joint laxity would be associated with lower patient satisfaction, more severe symptoms, and reduced functional activities as measured with the 2011 Knee Society Knee Scoring System (2011 KS), though lateral joint laxity would be permissible to a certain degree in TKA.
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Participants
Three-hundred and forty-three primary TKAs were performed with the Bi-Surface knee system (Kyocera Medical, Osaka, Japan) at our institute between June 2003 and October 2011 [15]. This retrospective case series analysed 50 knees in 41 patients who made regular clinic visits from November 2012 to December 2013 and who agreed to participate in this study.
The exclusion criteria included knees with either valgus deformity or severe bony defects requiring bone grafting or augmentation. Of the 57
Results
Postoperative 2011 KS scores showed that the mean satisfaction score (out of 40) was 25.5 (SD 10.5; range six to 40), the symptoms score (25) was 18.0 (SD 6.9; range 0–25), the expectations score (15) was 9.0 (SD 2.8; range three to 15), the walking and standing score (30) was 20.8 (SD 7.9; range two to 30), the standard activities score (30) was 21.5 (SD 7.1; range 0–30), and the advanced activities score (25) was 11.7 (SD 6.6; range 0–25).
The mean postoperative knee extension and flexion
Discussion
The present findings demonstrate that medial joint laxity is related to inferior satisfaction and knee function as determined by 2011 KS scores after TKA. Medial stability is very important in TKA because the medial collateral ligament (MCL) is a secondary restraint to anterior instability [23]. Since almost all post-TKA knees lack an anterior cruciate ligament (ACL), medial joint laxity coupled with the absence of the ACL increases dynamic instability, reducing postoperative knee function. The
Conclusions
Knees with medial joint laxity in flexion resulted in an inferior postoperative outcome, and lateral joint laxity did not affect patient satisfaction or knee function. It is proposed that to improve patient satisfaction and knee function, care should be taken to maintain medial stability during TKA.
Conflict of interest
The authors declare that they have no conflicts of interest.
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These authors contributed equally to this article.