Introduction: Anterior cruciate ligament (ACL) injury is the first cause of knee instability. There is not enough evidence for the best therapeutic option, as operative and non-operative treatments of anterior cruciate ligament (ACL) injuries are often associated with a lack of proprioception and a persistent muscle weakness of unclear origin.
Material and methods: This study in the cat experimentally compares in the long-term both neural and muscular activity in the knee articular nerves (PAN and MAN), quadriceps and hamstrings, in the chronic unstable knee and the reconstructed knee. Experimental section of ACL in twenty four cat’s knees was followed by stable reconstruction in six knees and unstable reconstruction in eight knees, leaving the other ten knees unstable without reconstruction. Electrical activity from muscles and nerves was registered with Ni-Cr electrodes. Mean firing activity and peristimulus time histograms (PSTH) for each structure were obtained. Secondly, it evaluates the neuromuscular response changes due to the graft’s mechanical competence, comparing stable and unstable reconstructed knees. Two different grafts were evaluated in the reconstructed knee, pediculated extensor digitorum longus and free bone-tendon-bone from patellar tendon. Statitiscal analysis consisted in Mann-Whitney’s test with Bonferroni adjustment between groups, and a two-way ANOVA to evaluate the separate effect of graft type and graft competence.
Results: We found an increased periarticular muscle activity during anterior tibial translation in chronically unstable knees. Both reconstructed and non-reconstructed unstable knees lose the fast reactive activity in the articular nerves. When stability was recovered after reconstruction, knees showed a more adjusted, although incomplete, muscular reaction. No differences were observed among grafts, but their mechanic competence was determinant in the neuromuscular firing activity.
Discussion: ACL injured knees in the cat, with or without reconstruction, display confirmed abnormalities in neuromuscular reaction in the long-term, while to regain stability with a competent graft in the reconstructed knee is crucial to lessen this anomalous reaction.
