Influence of a secondary downsizing of the femoral component on the extension gap: a cadaveric study.

The purpose of this study was to evaluate the effect of a secondary reduction of the femoral component size on flexion and extension gaps intraoperatively in posterior-stabilized total knee arthroplasty (PS-TKA) monitored by computer-assisted surgery. The authors hypothesized that cutting additional bone on the posterior femoral condyle may increase the extension gap due to the posterior capsule and soft tissue loosening. Reduction of the femoral component size was performed by additional 4-in-1 cuts after the PS-TKA on 15 cadaveric knees using a ligamentous tension device with the aid of computer-assisted surgery. Measurements of the medial and lateral flexion gaps, as well as the medial and lateral extension gaps, were recorded before and after reducing the femoral component size. Trial components were used from a mobile-bearing total knee system.After reducing the femoral component size, the medial and lateral flexion and extension gaps measured larger than their initial size. The mean increases of the medial extension and flexion gaps and the lateral extension and flexion gaps were 1.3 ± 0.9, 1.0 ± 1.2, 1.1 ± 1.2, and 1.3 ± 1.3 mm, respectively; all 4 differences were significant (P ≤ .05). Surgeons should be aware of the effect of downsizing components intraoperatively because it might lead to an extension laxity. Thus, a downsizing of the femoral component may compromise the postoperative stability of TKA.