Coronal malposition effects in total knee arthroplasty: a finite element analysis

Prosthetic component malposition is not infrequent, because of technical flaws, especially without a computed navigation system. We assumed that an inclined interline of a prosthetic knee with components parallel in the coronal plane provides a better load distribution and lower contact pressure towards a varus malalignment. For that we studied, using finite element analysis, load intensity and distribution for three situations: ideal alignment of prosthetic components, tibial varus malposition of 3° and 8° leading to tibio-femoral varus malalignment (i.e. an unbalanced knee) and the same tibial varus malpositions, but with the femoral component also malpositioned in the coronal plane, so that they are parallel, and with equally tightened collateral ligaments (i.e. a balanced knee). We found that maximum contact pressure and underlying bone compression forces are higher for a balanced knee with an inclined interline than in ideal alignment, but lower than in an unbalanced knee. According to our results, 2- and 4-mm additional medial plateau resection on a proper balanced knee does not significantly affect the load distribution towards ideal alignment. Balancing is a key factor for prosthetic survival in cases when a certain degree of coronal malposition cannot be avoided.