Medial and lateral soft-tissue releases to correct varus and valgus deformities in primary total knee arthroplasty are achieved by sequential release of contracted soft-tissue constraints or, occasionally, advancement of elongated ligaments1-3. In primary total knee arthroplasty, soft-tissue constraints are typically well-defined anatomical structures, whereas, in revision total knee arthroplasty, the soft-tissue constraints may be thickened and scarred, attenuated, or absent. Soft-tissue balance in revision total knee arthroplasty is achieved by a combination of soft-tissue releases and variation in the bone resection level, implant position, and implant size4.
Relationship Between Medial-Lateral and Flexion-Extension Balancing
Medial-lateral soft-tissue balance depends on the length of the collateral ligaments and musculotendinous constraints, which may be contracted or elongated as a result of prior surgery and/or deformity. Balance of the collateral ligaments implies that the soft-tissue tension on the medial and lateral sides of the knee, as determined with varus and valgus stress-testing with spacer blocks or trial components in place, is symmetric. This may require release of contracted soft tissues (Fig. 1). Medial-lateral soft-tissue balance may be different in flexion and extension because the posterior capsule and the hamstring tendons contribute to medial-lateral stability in full extension whereas they are lax during flexion (Fig. 2). Medial-lateral soft-tissue balance in flexion depends on the integrity of the collateral ligaments. Soft-tissue balance may be achieved in full extension but not in flexion if one of the collateral ligaments is lax.
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