The lower extremity may be lengthened or shortened at the knee joint as the result of correcting deformity during arthroplasty. This tendency is probably greater with revision surgery.Fixed-flexion, varus, and valgus deformities may all be corrected with well-described surgical techniques. These techniques are based on specific beliefs about the pathology of soft tissues in the deformed knee. These techniques do not necessarily include maintaining normal limb length as a primary goal. With revision surgery, soft-tissue stability may eventually be lost, and prostheses with increased constraint will he necessary to stabilize the knee.