Gap balancing through small incisions: competing goals

Significant controversy exists in the literature regarding the pitfalls and benefits of minimally invasive total knee arthroplasty (TKA). Regardless, most surgeons today use smaller exposures than in previous years. Although more difficult, rigid adherence to classical gap balancing techniques can allow a surgeon to achieve ideal ligament and flexion/extension gap balance in TKA through a minimally invasive approach. There are certain groups of patients (obesity/medical comorbidities/vascular insufficiency) in whom small incision approaches should not be attempted due to increased risks of wound complications. Additionally, achievement of gap balance requires sequential and safe removal of bone starting with the patellar cut, followed by the distal femoral cut, then by the tibial cut, and concluding with completion of the femoral component cuts. Use of special instruments such as protective metal patellar buttons, medial to lateral distal femoral cutting blocks, and low profile spacer blocks can facilitate the surgical process. Accurate femoral component rotation is more difficult in minimally invasive approaches and must be carefully checked. A tight extensor mechanism in flexion can mislead the surgeon to place the femoral component in an internally rotated position. Furthermore, with limited visualization, surgeons must avoid overaggressive ligament releases early in the procedure prior to completion of bone cuts. However, with appropriate patient selection and a systematic approach to minimally invasive total knee arthroplasty, surgeons can continue to achieve ideal ligament balance with a more soft tissue friendly operation.