Quadriceps Function in ACL Reconstructed Patients With and Without Knee Osteoarthritis

Post-traumatic quadriceps dysfunction is well-documented following anterior cruciate ligament reconstruction (ACL-R), and is associated with impairments detrimental to joint-specific and global health, including decreased physical activity, accelerated onset of knee joint osteoarthritis, and decreased quality of life. Since articular cartilage degeneration is irreversible, the hallmark for prevention is early detection with thorough evaluation of quadriceps neuromuscular function. Neuromuscular adaptations are theorized to arise from alterations in spinal-mediated and corticospinal pathways, and if unaddressed, may present a limiting factor in recovery from ACL-R. The specific origins of impairment have been theorized as a way to address subtle underlying factors impeding the recovery of quadriceps function following ACL-R. By understanding the temporal nature of neuromuscular adaptations, clinicians and researchers can improve patient care. The focus of manuscript 1 was to compare quadriceps neuromuscular function at clinically relevant time points following ACL-R, including patients who experienced post-traumatic knee osteoarthritis. We found that patients early (< 1 year), late (> 2 years), and with osteoarthritis after ACL-R exhibited quadriceps weakness and decreased corticospinal input to the quadriceps compared to healthy individuals. The focus of manuscript 2 was to identify the relationship between objective measures of quadriceps function and patient-reported outcomes at clinically relevant time points following ACL-R, including patients who experienced post-traumatic knee osteoarthritis. We found that perceived knee function and global health status were best explained by objective measures of quadriceps function in patients early and with osteoarthritis after ACL-R. Both limb symmetry and unilateral limb performance were meaningful to patients early, and unilateral limb performance was meaningful to patients with osteoarthritis after ACL-R. Measures of isokinetic quadriceps strength (torque, work, power) consistently demonstrated the strongest relationships with patient-reported outcomes. The focus of manuscript 3 was to investigate the underlying constructs of lower extremity muscle function that uniquely describe aspects of quadriceps neuromuscular function in patients after ACL-R. We found that unique constructs of peripheral, central, and combined peripheral and central muscle function are likely to exist in ACL-R patients. Quadriceps function (total work at 90°/sec, active motor threshold, and central activation) of the involved limb was able to discriminate best between ACL-R patients and healthy individuals compared to the uninvolved limb or limb symmetry. It is unclear if early changes in strength, endurance, voluntary activation, and corticospinal excitability perpetuate long-term muscle dysfunction; however, the temporal relationships of these measures may be a contributing factor to long-term outcomes. If left unaddressed, the progressive nature of contributing factors may result in irreversible joint injury.