Neuromuscular response to competing ACL surgeries - ABSTRACT The overall project objective is to leverage patients enrolled in the BEAR-MOON Trial to evaluate a neuromuscular mechanism that may explain differences in functional outcomes between the novel bridge-enhanced anterior cruciate ligament restoration (BEAR) and the standard of care, anterior cruciate ligament reconstruction surgery (ACLR). Whereas ACLR requires removal of the injured ligament and the bony insertion sites to implant a tendon graft, BEAR uses a scaffold to promote healing of the injured ACL. Therefore, the ACL neural structures and bony insertions remain intact with BEAR, while they are severed and removed during ACLR. Early clinical studies have shown that muscle strength is restored following BEAR, but not after ACLR at 2-year follow-up. We have data to show that joint motion abnormalities similarly persist over a decade after ACLR, which are thought to be a risk factor for posttraumatic osteoarthritis. Therefore, we postulate that differences in muscle recovery and joint motion are due to the preservation of neuromuscular function with BEAR. The BEAR-MOON Trial (the parent study) is a multicenter, randomized control trial comparing 2-year outcomes of BEAR to those of ACLR. While the parent study will establish whether differences exist between procedures, it was not designed to determine the mechanism behind those differences. Therefore, the overarching ancillary study hypothesis is that BEAR preserves the neuromuscular activation patterns about the knee that, in turn, promote normal hop landing joint motion compared to ACLR at 2 years post-surgery. The ancillary study addresses three aims: 1) to apply our innovative machine learning approach to classify neuromuscular activity patterns as belonging to ACLR, BEAR or healthy control subjects (Controls); 2) to compare knee position between ACLR, BEAR, and Controls at ground contact when landing from a 1-leg hop; and 3) to determine the relationship between neuromuscular activity patterns and joint motion abnormalities. Twenty-six subjects enrolled in the BEAR-MOON Trial at Rhode Island Hospital will be recruited into the ancillary study at their 2-year parent study follow-up visit. An age- and sex-matched control group will be recruited from the community. All 39 subjects will perform a 1-leg hop-for-distance activity while surface electromyography is recorded to assess neuromuscular function (Aim 1), and biplane videoradiography will be performed to evaluate precise tibiofemoral motion (Aim 2). Regression analysis will be used to relate neuromuscular activation patterns with tibiofemoral position (Aim 3). The ancillary study dovetails well with the parent study, which is now in its final year of recruitment. If the hypotheses of the ancillary study are supported, the results will demonstrate that ACL mechanoreceptor continuity is the mechanism governing neuromuscular function, and that its loss with ACLR is a driver of joint motion dysfunction and possible downstream joint arthrosis that can be explored in future longitudinal studies.
