New method for acquiring the expected extension gap in total knee arthroplasty.

purposeAdjusting the soft-tissue balance during surgery is crucial in total knee arthroplasty (TKA). However, even using the gap technique, the expected tibial gap is sometimes not achievable. We developed a new method of proximal tibial cutting to acquire the expected tibial gap and insert a tibial liner of appropriate thickness.

methodsThis study included 128 patients who underwent medial pivot-type TKA for varus knee osteoarthrosis. After completion of the femoral cut using and removal of the bony spur at the medial tibia according to the preoperative plan, we inserted a trial femoral component to the distal femur. Applying valgus manual stress on the knee in extension, we measured the medial gap between the femoral trial and tibial plateau using calipers, defining this medial gap as "pre-gap". A proximal tibial cut was made referring to the pre-gap in the pre-gap group (n = 64). We defined Δgap as the difference between the expected tibial liner thickness and the final tibial liner thickness during surgery. We compared Δgap between the pre-gap group and a control group with conventional tibial cutting without pre-gap measurement (n = 64).

resultsThe frequency of an ideal tibial cut (Δgap = 0) was 82% in the pre-gap group and 61% in the control group. The frequency of outliers (Δgap ≥ 2 mm) was 4% and 18%, respectively. The expected tibial liner was selected more frequently in the pre-gap group than in the control group.

conclusionsOur method was beneficial for acquiring the expected gap in extension to avoid an inadequate gap. LEVEL OF EVIDENCE III: Case-control study.