The effect of extraarticular varus and valgus deformity on total knee arthroplasty.

Because of trauma, metabolic bone disease, congenital deformity, or prior osteotomy, an extraarticular deformity may be present in patients requiring total knee arthroplasty. If the extraarticular deformity is not corrected extraarticularly, it must be corrected by compensatory distal femoral or proximal tibial wedge resection to produce overall limb alignment. Because such a wedge resection between the proximal and distal attachments of the collateral ligaments will produce asymmetrical ligament length, complex instabilities may result. This article, through overlay templates and trigonometric analysis, evaluates all the issues confronting the surgeon deciding whether to pursue intraarticular or extraarticular correction. The conclusions are as follows: (1) the closer a deformity is to the knee, the greater its importance, (2) femoral deformities are more difficult to correct intraarticularly than tibial deformities because femoral compensatory wedge resection produces instability only in extension, and (3) intraarticular correction of varus deformities produces lateral instability that is usually better tolerated than medial instability, and some extraarticular deformities are best treated by extraarticular correct, independent, or total knee arthroplasty.

A mathematical analysis of the effect of flexion and rotation on apparent varus/valgus alignment at the knee.

The quantitative effect of flexion and rotation on apparent varus/valgus deformity was analyzed, and the expected amount of deformity as a function of flexion rotational artifact determined, as shown by use of formulae and tabulated computational results. These results were calculated first when no deformity was present initially, and also for varying amounts of initial deformity.