Acute anterior cruciate ligament reconstruction with an augmented remnant repair: a comparative macroscopic and biomechanical study in an animal model

Purpose: Our purpose was (1) to compare the structural integrity and healing capacity of the acutely repaired anterior cruciate ligament (ACL) remnants and (2) to determine whether the short-term postoperative biomechanical results of the acute remnant-repairing anterior cruciate ligament reconstruction (ACLR) were superior to the conventional ACLR.

Methods: An acute complete ACL femoral detachment model was created in 50 rabbits. The rabbits were immediately randomly allocated into the remnant-repairing ACLR group (group 1, n = 25) and the conventional ACLR group (group 2, n = 25). Each animal in both groups was subjected to unilateral ACLR with semitendinosus tendon autografts. During ACLR, the ACL remnants were acutely repaired with the femoral-tensioning technique in group 1, whereas the ACL remnants were debrided in group 2. The outcomes of the remnant were macroscopically evaluated in group 1. The remnant's structural integrity and remnant-to-graft healing capacity were divided into 3 categories (grade A, good; grade B, fair; or grade C, poor) according to 2 distinct criteria. Biomechanical tests including the anterior tibial translation test at 30° and 90° of knee flexion and tensile tests were compared between groups. All the macroscopic evaluations and biomechanical tests were performed postoperatively at week 12.

Results: The macroscopic evaluations of the ACL remnants in group 1 (n = 25) showed that the remnants' structural integrity was grade A (well-maintained continuity with an adequate amount of tissue and tension on probing) in 10 specimens (40%), grade B (fairly maintained continuity with thin and slack fibers detected) in 5 (20%), and grade C (resorption with no remnant left in situ) in 10 (40%). The remnant-to-graft healing capacities among the specimens with surviving remnants (grades A and B for structural integrity, n = 15) were all classified as grade C (an obvious remnant-to-graft interval through the entire length of the graft). For the biomechanical tests, there were no significant differences between the groups (25 in each group) with respect to the anterior tibial translation test at 30° (P = .15) and 90° (P = .91) of knee flexion and stiffness (P = .66), ultimate failure load (P = .11), and elongation at failure (P = .92).

Conclusions: In our rabbit model of ACL femoral detachment, the acutely repaired ACL remnants showed a high resorption rate, low healing capacity, and poor biomechanical properties. The acute remnant-repairing ACLR had no evident superiority over the conventional ACLR in rabbits.

Clinical relevance: The findings did not support the contention that the remnant-repairing ACLR, even performed in the acute setting, could produce better postoperative knee joint stability outcomes than the conventional ACLR.