Opening the medial tibiofemoral compartment by pie-crusting the superficial medial collateral ligament at its tibial insertion: a cadaver study.

BACKGROUND Arthroscopic treatment of tears in the middle and posterior parts of the medial meniscus can be difficult when the medial tibiofemoral compartment is tight. Passage of the instruments may damage the cartilage. The primary objective of this cadaver study was to perform an arthroscopic evaluation of medial tibiofemoral compartment opening after pie-crusting release (PCR) of the superficial medial collateral ligament (sMCL) at its distal insertion on the tibia. The secondary objective was to describe the anatomic relationships at the site of PCR (saphenous nerve, medial saphenous vein). MATERIAL AND METHOD We studied 10 cadaver knees with no history of invasive procedures. The femur was held in a vise with the knee flexed at 45°, and the medial aspect of the knee was dissected. PCR of the sMCL was performed under arthroscopic vision, in the anteroposterior direction, at the distal tibial insertion of the sMCL, along the lower edge of the tibial insertion of the semi-tendinosus tendon. Continuous 300-N valgus stress was applied to the ankle. Opening of the medial tibiofemoral compartment was measured arthroscopically using graduated palpation hooks after sequential PCR of the sMCL. RESULTS The compartment opened by 1mm after release of the anterior third, 2.3mm after release of the anterior two-thirds, and 3.9mm after subtotal release. A femoral fracture occurred in 1 case, after completion of all measurements. Both the saphenous nerve and the medial saphenous vein were located at a distance from the PCR site in all 10 knees. DISCUSSION PCR of the sMCL is chiefly described as a ligament-balancing method during total knee arthroplasty. This procedure is usually performed at the joint line, where it opens the compartment by 4-6mm at the most, with some degree of unpredictability. PCR of the sMCL at its distal tibial insertion provides gradual opening of the compartment, to a maximum value similar to that obtained with PCR at the joint space. The lower edge of the semi-tendinosus tendon is a valuable landmark for PCR of the distal sMCL.