Stress distribution is deviated around the aperture of the femoral tunnel in the anatomic anterior cruciate ligament reconstruction

Final tunnel location in the anterior cruciate ligament (ACL) reconstruction is unpredictable due to tunnel widening and/or transposition. The mechanical stress around the tunnel aperture seems to be a major factor but is not fully investigated. The purpose of this study was to measure the stress from the ACL graft around the tunnel aperture when the ACL graft tension reaches its peak.

Six cadaveric knees were used. Single-bundle ACL reconstruction was performed using a hamstrings graft. Both femoral and tibial tunnels were created at the centre of the original ACL footprint. A 7-mm-internal-diameter aluminium cylinder with pressure sensors was placed in the femoral tunnel. Hamstrings graft with a microtension sensor was inserted. After fixation, passive extension-flexion was performed while monitoring the tunnel aperture pressure and the graft tension simultaneously. The pressure on the femoral tunnel aperture when the ACL graft tension reach its peak was compared between four directions.

The ACL graft tension peaked (67 ± 49 N) at full extension (−5.8 ± 4.1°). Pressure at the femoral tunnel aperture was different between different directions (p < 0.01). Distal part had significantly larger pressure (1.7 ± 1.3 MPa) than the other directions (p < 0.01). Second largest pressure was carried in the anterior part (0.6 ± 0.5 MPa), followed by proximal and posterior parts (0.4 ± 0.3, 0.2 ± 0.2 MPa respectively).

The stress distribution at the femoral tunnel aperture is not equal in different directions, while the distal part dominantly bears the stress from the ACL graft. Surgeons should pay close attention to the distal edge of the femoral tunnel which should be inside the anatomic ACL footprint eventually.