What Effect Does Anterior Cruciate Ligament Tibial Guide Orientation Have on Tibial Tunnel Length?

PurposeTo evaluate the effects of alteration in tibial guide pin insertion angle and external starting point on tibial tunnel length for anterior cruciate ligament (ACL) reconstruction.MethodsTen cadaveric tibial specimens were used. One pin was placed at each of variable insertion angles (55°, 50°, and 45°) of the tibial targeting device aimed at the center of the tibial ACL footprint. These 3 pins started externally along the anterior border of the superficial medial collateral ligament. A fourth pin at 50° was placed at a different external tibial starting point 1.5 cm anterior to the anterior border of the superficial medial collateral ligament. The intraosseous length of each pin was measured. Statistic analyses were performed with the Kruskal-Wallis test, with significance set at P < .05.ResultsThe mean length for the 55° tibial tunnel was 50.3 mm (range, 42 to 56 mm); for the 50° tunnel, it was 48.9 mm (range, 44 to 55 mm); for the 50° anterior tunnel, it was 47.6 mm (range, 39 to 55 mm); and for the 45° tunnel, it was 47.3 mm (range, 41 to 52 mm). Changing the angle of the tibial guide did not significantly affect the length of the tibial tunnel (P = .18). Changing the external tibial starting point did not affect the length of the tibial tunnel (P = .39).ConclusionsChanging the tibial guide angle between 45°, 50°, and 55° does not appreciably change tibial tunnel length. Moving the starting point anterior 1.5 cm toward the tibial tubercle also has no effect on the tibial tunnel length. The lack of significant changes in tunnel length with these interventions may reflect the associated changes that occur in proximal tibial morphometry with change in external tibial starting position.Clinical RelevanceChanging tibial tunnel length in ACL reconstruction likely requires more distalization of the external tibial starting point than is achieved simply by altering the tibial aiming guide angle by 10° or less.