Introduction
Medial-lateral and flexion-extension soft-tissue balance are important components of a successful revision total knee arthroplasty. Symmetric medial and lateral collateral ligament tension in both flexion and extension as well as equal sizes of the flexion and extension gaps should be achieved prior to implantation of the final components. Medial-lateral soft-tissue tension and flexion-extension gap sizes are related but not identical issues. Medial-lateral soft-tissue balancing requires release of contracted medial or lateral ligaments and tendons or, alternatively, advancement and reconstruction of lax ligaments. Flexion-extension balancing may involve release of contracted posterior soft tissue but also is affected by variation in the size and position of the implants. If adequate medial-lateral and flexion-extension stability cannot be achieved, use of a constrained implant is appropriate.

Medial-Lateral Soft-Tissue Balancing
Assessment of the ligamentous status of the knee prior to primary or revision total knee arthroplasty should include a clinical evaluation of the patient’s gait and standing alignment. Signs of a valgus thrust may indicate medial laxity. Examination of knee stability should be performed at full extension, at 15° to 30° of flexion, and at 90° of flexion. Both varus-valgus and anteroposterior stability should be assessed. Radiographic assessment for bone loss, malalignment, and deformity is important. Varus and valgus stress anteroposterior radiographs may be helpful for distinguishing laxity due to component loosening from ligament laxity. The use of ligament reconstruction to balance soft tissues in knees with severe fixed deformities was popularized by Krackow1 . While the technique has been described for varus, valgus, and recurvatum deformities of the knee, currently it is used primarily to treat severe fixed valgus deformity. Krackow1 classified valgus deformities into three types. Type-1 deformities are mild to moderate with intact medial capsular ligaments. Type-2 deformities include more severe angular malalignment with attenuation of the medial collateral ligament (Fig. 1). Type-3 deformities are caused by a tibial plateau fracture or by overcorrection following a valgus proximal tibial osteotomy.