The influence of patellar position on soft tissue balance in minimal incision total knee arthroplasty.

Purpose: This study aims to clarify the influence of surgical exposure on intra-operative soft tissue balance measurements using a new tensor in minimal incision total knee arthroplasty (TKA).

Methods: Sixty patients with osteoarthritis of the knee received minimal incision TKAs. Twenty patients received a posterior-stabilized TKA using a quadriceps sparing approach, and the other forty patients, using a limited medial parapatellar (mini) approach. After femoral trial placement, soft tissue balance was measured using an offset type tensor at full extension and 90° of knee flexion, with the patella both laterally retracted and reduced. The joint component gap and varus imbalance were used to assess the difference in patellar position and surgical exposure.

Results: At extension, the joint component gap and varus imbalance showed no statistical difference regardless of patellar position in either TKA. However, the joint component gaps decreased at 90° of flexion when the patella was laterally retracted in both TKAs. Additionally, a significantly smaller joint gap was observed in the quadriceps sparing TKA than the mini-TKA with a retracted patella at 90° of flexion. Varus ligament imbalances decreased with the patella laterally retracted at 90° of flexion in the quadriceps sparing TKA, not in the mini-TKA.

Conclusion: Surgeons should be aware of the influence in surgical exposure of the joint gap and ligament balance during patella shift in minimal incision TKA.

Level Of Evidence: III.