Introduction
Incorrect restoration of the joint line during total knee arthroplasty (TKA) can result in joint instability, anterior knee pain, limited range of motion, and joint stiffness. Although restoration of the correct joint line (i.e., creating an optimal gap in extension and flexion) should be considered in all TKA procedures, no surgical techniques have been established for restoring it. We performed the femoral posterior condylar precut technique (Kaneyama R. Bone Joint Res. 2014; 3) in 91 TKA cases and evaluated the joint line by measuring the thickness of the surgically removed femoral bone and femoral components.
Methods
A total of 91 knees in 73 patients who underwent primary TKA between June and December 2013 were reviewed retrospectively. The posterior cruciate ligament was preserved in all patients. First, in the femoral posterior condylar precut technique, the extension gap was created by the measured resection technique. Then we created a temporary gap in flexion 4 mm smaller than that created by the measured resection technique and remove posterior osteophytes and soft tissue for good ligament balance. Once the component gap was determined, final femoral posterior condyle cutting was performed to create an optimal gap and rotation. We evaluated the joint line from the differences in thickness between the surgically removed femoral bone and femoral components, and revised the thickness of the bone saw accordingly. The value was positive when the joint line had been raised and negative when it had been lowered.
Results
Subjects were 17 men (20 knees) and 56 women (71 knees) with a mean age of 72.6 years. The amount of distal femoral bone surgically removed was 8.5±1.8 mm (medial) and 8.3±2.0 mm (lateral) and that of posterior bone was 9.8±1.2 mm (medial) and 7.2±0.8 mm (lateral). The difference in the joint line was –0.4±2.2 mm (medial) and 0.5±3.9 mm (lateral) in extension and 1.1±2.7 mm (medial) and –0.6±1.9 mm (lateral) in flexion.
Discussion
There are no established surgical techniques for restoring the joint line. Typically, surgical procedures are decided preoperatively by considering the amount of femoral bone to be surgically removed and rotation and cannot be changed during the operation if the gap is found to be incorrect. In our femoral posterior condylar precut technique, however, is possible to fine-tune it at the final step in surgery, making it possible to control the surgical removal of femoral bone, thereby reducing differences in the joint line.