Differential Pretensions of a Flexor Tendon Graft for Anterior Cruciate Ligament Reconstruction: A Biomechanical Comparison in a Porcine Knee Model

Purpose: The best way to apply the pretension force to the soft tissue graft during anterior cruciate ligament (ACL) reconstruction remains controversial. We compared manual, intra-, and extra-articular pretension techniques and determined the magnitude of displacement of the femur-graft-tibia complex in response to repetitive loading. Type of Study: A biomechanical-controlled study. Methods: Fresh porcine knees and profundus digital flexor tendons of hind limbs were used. Specimens were divided into 3 groups. Group A (manual pretension, n = 9) consisted of grafts that were pretensioned only by a maximal manual pull before final fixation on the tibial side. Group B (extra-articular pretension, n = 9) consisted of grafts that were pretensioned using a commercial tensiometer at 89 N for 15 minutes on the tendon preparation board, followed by pulling using maximal manual force before final fixation. Group C (intra-articular pretension, n = 9) consisted of grafts that were fastened on the femoral side first and then underwent application of a pretension force at 89 N for 5 minutes before final fixation on the tibial side. These femur-graft-tibia complexes from the 3 groups were loaded from 0 to 150 N at a frequency of 1 Hz for 1,000 cycles and then underwent a tensile load-to-failure test at a rate of 150 mm/min. Results: The displacement of the femur-graft-tibial complex in response to cyclic loading for group C (5.4 ± 0.3 mm) was significantly lower than those for groups A (12.5 ± 1.1 mm) and B (8.8 ± 0.8 mm) (P < .001). The fixation stiffness of group C (47.9 ± 17.6 N/mm) was significantly greater than that of group A (32.5 ± 9.7 N/mm) (P < .05) but not significantly different from that of group B (53.1 ± 9.1 N/mm). The ultimate failure load in each group was not significantly different. Conclusion: Intra-articular pretension of the graft before final fixation can significantly minimize graft elongation at time 0 compared with manual and extra-articular pretension. Clinical Relevance: Intra-articular or in vivo pretension of the graft using instruments may minimize the graft elongation in the early period of rehabilitation after ACL reconstruction.