Quantification of anterior cortical bone removal and intermeniscal ligament damage at the tibial nail entry zone using parapatellar and retropatellar approaches.

OBJECTIVES: Anterior cortical bone removal at the tibial nail entry zone has been shown to alter biomechanical properties of the proximal tibia. However, no study has quantified the amount of bone removed. The purpose of this study was to quantify the amount of anterior bone removed at the nail entry zone and assess damage to adjacent intra-articular structures using both parapatellar and retropatellar techniques.
METHODS: The study was performed using 36 cadaveric knees (18 medial parapatellar and 18 retropatellar approaches). A guide pin was placed in the anatomic safe zone using fluoroscopic guidance and a 12.5-mm entry reamer used to open medullary canal. Soft tissues were removed, damage to intra-articular structures recorded, and size of osseous defect created in proximal tibia measured.
RESULTS: The surface area of bone removed with portal creation was not significantly larger with retropatellar (228.4 ± 38.1 mm) versus parapatellar technique (207.9 ± 33.4 mm(2); P = 0.108). This was substantially different than if the entry hole was perfectly round (122.7 mm(2)). No knee went without some damage to intra-articular structures using the parapatellar technique, as opposed to 33% knees with retropatellar technique (P = 0.019). Intermeniscal (IM) ligament was damaged in 83% parapatellar and 56% retropatellar knees (P = 0.146).
CONCLUSIONS: A substantial amount of anterior bone is removed during nail entry portal creation using both parapatellar and retropatellar techniques. Intra-articular structure damage, most commonly IM ligament disruption, was also found to occur at a lower rate with retropatellar technique. Avoidance of both anterior bone removal and IM ligament damage may not be possible because of size and geometrical constraints.