CORRECTION OF DEFORMITY: WHEN THE IMPLANT IS NOT ENOUGH

Limb deformity is common in patients presenting for knee arthroplasty, either related to asymmetrical wear patterns from the underlying arthritic process (intra-articular malalignment) or less often major extra-articular deformity due to prior fracture malunion, childhood physical injury, old osteotomy, or developmental or metabolic disorders such as Blount9s disease or hypophosphatemic rickets. Angular deformity that is above the epicondyles or below the fibular neck may not be easily correctable by adjusted bone cuts as the amount of bone resection may make soft tissue balancing impossible or may disrupt completely the collateral ligament attachments. Development of a treatment plan begins with careful assessment of the malalignment which may be mainly coronal, sagittal, rotational or some combination. Translation can also complicate the reconstruction as this has effects directly on location of the mechanical axis. Most intra-articular deformities are due to the arthritic process alone, but may occasionally be the result of intra-articular fracture, periarticular osteotomy or from prior revision surgery effects. While intra-articular deformity can almost always be managed with adjusted bone cuts it is important to have available revision type implants to enhance fixation (stems) or increase constraint when ligament balancing or ligament laxity is a problem. Extra-articular deformities may be correctable with adjusted bone cuts and altered implant positioning when the deformity is smaller, or located a longer distance from the joint. The effect of a deformity is proportional to its distance from the joint. The closer the deformity is to the joint, the greater the impact the same degree angular deformity will have. In general deformities in the plane of knee are better tolerated than sagittal plane (varus/valgus) deformity. Careful pre-operative planning is required for cases with significant extra-articular deformity with a focus on location and plane of the apex of the deformity, identification of the mechanical axis location relative to the deformed limb, distance of the deformity from the joint, and determination of the intra-articular effect on bone cuts and implant position absent osteotomy. In the course of pre-operative planning, osteotomy is suggested when there is inability to correct the mechanical axis to neutral without excessive bone cuts which compromise ligament or patellar tendon attachment sites, or alternatively when adequate adjustment of cuts will likely lead to excessive joint line obliquity which can compromise ability to balance the soft tissues. When chosen, adjunctive osteotomy can be done in one-stage at the time of TKA or the procedures can be done separately in two stages. When simultaneous with TKA, osteotomy fixation options include long stems added to the femoral (or tibial) component for intramedullary fixation, adjunctive plate and screw fixation, and antegrade (usually locked) nailing for some femoral osteotomies. Choice of fixation method is often influenced by specific deformity size location, bone quality and amount, and surgeon preference. Surgical navigation, or intra-operative x-ray imaging methods (or both) have both been used to facilitate accurate correction of deformity in these complex cases. When faced with major deformity of the femur or tibia, with careful planning combined osteotomy and TKA can result in excellent outcomes and durable implant fixation with less constraint, less bone loss, and better joint kinematics than is possible with modified TKA alone.