The role of constraint in total knee arthoplasty.

One of the keys to long-term success in total knee arthroplasty is knee joint stability. In most deformities, soft tissue asymmetry is present and can be corrected by soft tissue balancing techniques that allow the implant to tension the joint in flexion and extension symmetrically with resultant knee joint stability. Once this stability has been established, standard implants (PCL retaining or posterior stabilized types) may be used. If persistent laxity occurs despite soft tissue balancing, implants with greater constraint must be used. The constrained condylar types will improve stability and are useful particularly in the severe valgus knee with marked medial laxity or in revision procedures. If femoral bone is well preserved, constrained condylar knees may be used without stems. When there is marked bone loss and absent ligament support, a rotating-type hinge knee may be needed to restore bone deficits through augmentation and stabilization of the knee by the fixed axis nature of these designs.