Effects of Posteromedial Vertical Capsulotomy on the Medial Extension Gap in Cruciate-retaining Total Knee Arthroplasty

Introduction: Equality between the extension gap (EG) and the flexion gap (FG) is one of the most important factors for good clinical results in total knee arthroplasty (TKA). The gap situation during surgery has a wide variation. The EG needs to be widened in patients with varus knees that have a small EG. For this purpose, posterior soft tissue release is necessary to avoid additional resection of the distal femur, which would cause undesirable joint line elevation. However, the detail methodology and efficacy of the posterior release is unknown. The usual method for widening the EG is by posterior capsular release from the femur or tibia or by posterior transverse capsulotomy. However, the effect of these procedures on the EG is not always sufficient because the EG is influenced by the posterior capsule and by the medial collateral ligament (MCL). Based on our experiences, we believe the MCL and posterior capsule complex would have some influence on the EG and we hypothesize that contracture of the posterior capsule pulls the MCL backward and prevents full extension of the knee because full elongation of the MCL is limited. We believe that it is necessary to separate the MCL from the contractured posterior capsule to widen the EG sufficiently. We also performed posteromedial vertical capsulotomy to divide the connection between the MCL and the posterior capsule in TKA.