Achieving correct soft tissue balance and preparing equal and rectangular extension and flexion joint gaps are crucial goals of TKA. Intraoperative gap balances would change postoperatively; however, changes in joint gap balances between pre- and postoperation remain unclear. To explore these changes associated with TKA, we prospectively investigated 21 posterior cruciate ligament retaining TKAs for varus knees. Intraoperative extension gap balance (iEGB) was 2.6 ± 2.0° varus versus postoperative extension gap balance (pEGB) of 0.77 ± 1.8° valgus ( ), while no significant difference between intraoperative flexion gap balance (iFGB) and postoperative flexion gap balance (pFGB) was observed. We also explored correlations between intraoperative and postoperative gap balances but found no significant correlations. These observations indicate that (i) surgeons should avoid excessive release of the medial soft tissue during TKA for varus knees and (ii) intraoperative gap balance may not be necessarily reflected on postoperative gap balance. 1. Introduction Achieving correct soft tissue balance of the knee is fundamental to the success of TKA , and an equal joint gap during extension and flexion is a prerequisite for satisfactory soft tissue balance [2–4]. In addition, equalizing the distance from the femoral component to the tibial surface (i.e., the joint gap) throughout the full range of knee motion prevents lift-off of the tibial component and theoretically assists in achieving proper contact pressure and kinematics. Thus, preparing equal and rectangular extension and flexion joint gaps is the most important goal of TKA. Meanwhile, most surgeons agree that accurate ligament balancing of the knee with varus deformity is difficult especially during posterior cruciate ligament retaining (CR)-TKA. The standard procedure for ligament balancing of the medial side of the knees uses subperiosteal release of the medial collateral ligament (MCL) [5–7]. Despite performing such release of MCL, varus balance is likely to remain in most CR-TKAs because posterior cruciate ligament (PCL) is an important component of the medial supporting mechanism of the knee . Recently, Sekiya et al. reported that residual lateral ligamentous laxity immediately after surgery subsequently corrected itself spontaneously in some instances . This finding suggests that some degree of residual lateral laxity, namely, varus balance, may be tolerable for varus knees so long as proper valgus alignment is maintained. However, it has not been explored whether remaining varus balance is
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