Knee: Axial instability

The results of TKA are among the best outcomes following any orthopedic procedure. Failures do occur, however, and tend to fall into recognizable patterns. Varus-valgus instability and anterior-posterior instability in flexion are common modes of failure. Failure to achieve symmetric medial-lateral soft tissue balance and symmetric flexion and extension spaces intraoperatively likely account for most of these cases. In primary TKA, the use of well-designed, posterior-stabilized prostheses that are implanted in strict accordance with the principles reviewed in this article should help prevent instability from occurring, particularly in the anterior-posterior plane in flexion. If instability occurs, revision surgery using the same basic principles to correct the imbalances is successful in most cases.