Anterior cruciate ligament femoral tunnel drilling through anteromedial portal: axial plane drill angle affects tunnel length

Abstract

Purpose: The purpose of this study was to correlate femoral tunnel length with axial drilling angle through the anteromedial portal.

Methods: Ten anatomically correct Sawbones knee models (Pacific Research Laboratories, Vashon, WA) were used for this study. With the knee flexed to 120°, tunnels were drilled through a simulated anterior medial portal with a custom outrigger guide. The guide provided consistently reproducible drilling angles of 20°, 40°, and 60° in the axial plane. Femoral tunnel lengths were recorded for each knee at each drilling angle. A 1-way analysis of variance (α = .05) was conducted to compare tunnel length in the 3 groups. Multiple comparisons were conducted by use of a Tukey post hoc test.

Results: The mean femoral tunnel lengths at 20°, 40°, and 60° were 37.0 mm, 36.9 mm, and 32.3 mm, respectively. The tunnels drilled at 20° and 40° were significantly longer than the 60° group (P < .001).

Conclusions: Our findings suggest that drilling femoral tunnels through an anteromedial portal at an axial angle of 20° or 40° produces longer femoral tunnels than with an axial drilling angle of 60°.

Clinical relevance: On the basis of this study, we recommend a 40° angle when approaching the lateral wall during femoral tunnel drilling through the anteromedial portal to optimize tunnel length while avoiding the acute angle and oblique entry of a 20° angle.