Abstract
Objective: When the extension gap is smaller than the flexion gap during total knee arthroplasty (TKA), an additional osteotomy of the distal femur is needed, which results in joint line elevation. We hypothesized that the chief cause of a decrease in the extension gap is excessive tension of both the medial collateral ligament and posteromedial capsule during knee extension. Therefore, we introduced a new technique called the “posteromedial-longitudinal capsulotomy” (PMLC) in May 2013 that allowed the separation of the medial collateral ligament from the posteromedial capsule, making it possible to expand the extension gap selectively. Our objective in this study was to assess the relationship between PMLC and the joint line in total knee arthroplasty.
Methods: We compared two groups: Group A (70 patients, 85 knees) who underwent TKA before May 2013 prior to the introduction of PMLC, and Group B (77 patients, 91 knees) who underwent TKA after its introduction after May 2013. The posterior cruciate ligament was preserved in all patients. We evaluated the joint line based on differences in thickness between the surgically removed femoral bone and femoral components. We adjusted the thickness of the bone saw accordingly.
Results: Expansion of the extension gap was needed in 66 of the 85 Group A knees (78%) and in 75 of the 91 Group B knees (82%), respectively. The technique for expansion in Group A was additional distal femoral osteotomy in 20 cases and other soft tissue release in 46 cases. In Group B there was additional distal femoral osteotomy in 14 cases and PMLC in 61 cases. The amount of distal osteotomy was 2.9 mm in Group A and 1.1 mm in Group B, which was significantly smaller. The amount of differences in the joint line was 0.9±3.2 mm (medial) and 1.6±2.6 mm (lateral) in Group A and −0.4±2.2 mm (medial) and 0.6±1.9 mm (lateral) in Group B, respectively.
Conclusion: PMLC significantly reduces the amount of osteotomy required in TKA, and makes it possible to control elevation of the joint line.
