Flexible instruments outperform rigid instruments to place anatomic anterior cruciate ligament femoral tunnels without hyperflexion

Purpose: This study evaluated the ability of flexible instruments compared with rigid instruments to place anatomic femoral tunnels in anterior cruciate ligament reconstructions by use of both transtibial drilling and anteromedial drilling without hyperflexion.

Methods: Rigid and flexible pins were placed in 12 matched pairs of cadaveric knees with transtibial drilling (6 pairs) and anteromedial drilling (6 pairs) at 110° of flexion. Intraosseous pin lengths, femoral exit locations, and tunnel alignment were measured.

Results: Transtibial drilling with rigid pins placed relatively vertical femoral tunnels 5.8 ± 1.0 mm superior to the central anterior cruciate ligament insertion. Transtibial drilling with flexible pins placed tunnels in the center of the femoral attachment, but the tunnels were relatively close to the posterior femoral cortex, with a mean distance of 8.0 ± 5.9 mm (P < .05), compared with transtibial drilling with rigid pins. Anteromedial drilling resulted in central anatomic pin placements with rigid and flexible instruments. Tunnel lengths with flexible pins were longer (42.0 ± 7.2 mm) compared with tunnel lengths with rigid pins (32.5 ± 7.1 mm) (P < .01). Flexible pins exited farther from the posterior cortex compared with rigid pins (P < .01). In 3 of 6 knees with rigid pins, the exit point was at the posterior border of the femoral cortex. All flexible pins exited a safe distance from the posterior femoral cortex.

Conclusions: Transtibial drilling with rigid instruments did not produce anatomic femoral tunnels. Transtibial drilling with flexible pins produced anatomic tunnels, but the tunnels were close to the posterior femoral cortex. Anteromedial drilling without hyperflexion produced anatomic tunnels by use of rigid and flexible instruments, but with flexible instruments, the tunnels were longer and were farther from the posterior femoral cortex. Anteromedial drilling with flexible pins produced tunnels with good length and the best position.

Clinical relevance: Flexible instruments compared with rigid instruments can facilitate the creation of anatomic femoral tunnels by use of anteromedial drilling without hyperflexion.