Constraint in total knee arthroplasty: when and what?

Tibiofemoral instability is increasingly recognized as a common mode of failure in total knee arthroplasty. Despite this, there are few published guidelines concerning treatment options, component selection, and expected results. In the treatment of the unstable total knee arthroplasty, cruciate-retaining designs can be considered only in the presence of well-balanced ligaments, including the posterior cruciate ligament. More predictable results are obtained with the use of cruciate-substituting components, but they provide no varus-valgus stability and cannot compensate for severe flexion laxity. Varus-valgus constrained designs cannot provide long-term stability in cases of varus-valgus instability or severe flexion laxity. Such cases are most reliably treated with a linked implant. Copyright 2003 Elsevier Inc. All rights reserved.