On the Fatigue Life of the Human Anterior Cruciate Ligament: Experimental Studies of the Effects of Limited Internal Femoral Rotation and Microscopic Entheseal Anatomy.

Abstract

Anterior cruciate ligament (ACL) injuries pose significant health and financial burdens, such as the early development of knee osteoarthritis. It is imperative to better prevent these injuries, but several knowledge gaps exist, including: (1) why athletes with a restricted range of hip internal rotation are more prone to ACL injuries; (2) whether this restriction can increase the ACL’s susceptibility to a fatigue failure; and (3) why the ACL ruptures more frequently near its femoral enthesis, especially the posterolateral fibers during pivot landings. This dissertation addresses these gaps. I hypothesized that limiting range of internal femoral rotation would increase peak ACL strain and risk of ACL fatigue failure during in vitro single-leg pivot landings. A custom-built testing apparatus applied an impulsive load, which induced knee compression, flexion moment, and internal tibial torque to human male and female knee specimens. A novel femoral rotation device controlled internal femoral rotation. As the range of internal femoral rotation was decreased, peak ACL strain increased 1.3% per 10° decrease and ACL fatigue failure risk increased 17-fold, when accounting for sex of specimen donor. These results suggest that screening for a limited range of hip internal rotation should become a component of ACL injury prevention programs and evaluation protocols for those with ACL injuries and/or reconstructions. I also hypothesized that micro-anatomical differences would exist between ACL entheses, as well as regionally within the femoral enthesis. The microscopic appearance of the ACL entheses was quantified in unembalmed human knee specimens using standard histological methods. The femoral enthesis had more fibrocartilage and a more acute ligament entheseal attachment angle than the tibial enthesis. The profiles of the femoral entheseal tidemarks varied within an enthesis and between donors, with six profiles predominating, but bilateral similarities existed. Within the femoral enthesis, there was more fibrocartilage in the inferior region of the origin of the anteromedial fibers. These fibers originated from the femur at a more acute angle than the posterolateral fibers. Perhaps these differences can induce a strain concentration at the inferior margin of the posterolateral fibers femoral enthesis, thus making this region susceptible to damage accumulation, during pivot landings.PhDKinesiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111583/1/mbeaulie_1.pd