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

PURPOSE

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.

METHODS

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.

RESULTS

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).

CONCLUSION

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.

Comparison Between Intra- and Extra-articular Tension of the Graft During Fixation in Anterior Cruciate Ligament Reconstruction

PURPOSE

To evaluate the tension deprivation through the tunnels with and without preconditioning at the time of fixation, and the influences of cyclic loading and pretensioning on graft tension in anatomic single bundle anterior cruciate ligament (ACL) reconstruction using a hamstring tendon.

METHODS

Nine fresh-frozen cadaveric knees underwent anatomic ACL reconstruction using hamstring grafts. Each specimen was examined to ensure that there was no severe osteoarthritic change, ligament insufficiency, or torn menisci by manual and arthroscopic evaluation. Applied graft tension was measured at the tibial tunnel outlet using a graft tensor with a load cell. Intra-articular graft tension was evaluated by using an originally developed microforce sensor, which was sutured into the graft. Both tensions were simultaneously measured just after initial tensioning under 3 different conditions: condition 1, just after initial tensioning of 20 N at 20° of knee flexion without preconditioning; condition 2, after the same initial tensioning following 5 rounds of passive cyclic flexion-extension movement; and condition 3, after the same initial tensioning following 5 minutes of static pretensioning of 20 N.

RESULTS

The intra-articular tension was 12.7 ± 5.3 N in condition 1, 12.0 ± 4.8 N in condition 2, and 13.5 ± 4.8 N in condition 3. In these 3 conditions, intra-articular graft tension was significantly lower than the applied tension of around 20 N (no pretension: P = .009, cyclic pretension: P = .004, static pretension: P = .008), with no difference among the 3 conditions (P = .82).

CONCLUSIONS

The intra-articular graft tension was significantly lower than the applied tension from the outside of the joint, even after cyclic loading and pretensioning.

CLINICAL RELEVANCE

It is difficult to evaluate the intra-articular graft tension precisely on the basis of the extra-articular tension at time zero in ACL reconstruction.