MECHANISM OF INJURY AFFECTS NEUROMUSCULAR PATTERNING OF HAMSTRINGS AND QUADRICEPS FOLLOWING ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION

MECHANISM OF INJURY AFFECTS NEUROMUSCULAR PATTERNING OF HAMSTRINGS AND QUADRICEPS FOLLOWING ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION A.R.C. Elias, R.L. Mizner University of Montana, Missoula, MT At least 70% of the 200,000+ anterior cruciate ligament (ACL) injuries in the United States each year are non-contact injuries with most occurring during jump landing. The muscular components of joint stability influence the strain on the ACL during sports. As such, intrinsic neuromuscular faults during jump landing are thought to increase the risk of non-contact ACL injury. We therefore would expect differences in athletes’ muscle recruitment patterns depending on their ACL mechanism of injury (MoI). Co-contraction between the hamstring and quadriceps muscles can influence the knee’s dynamic joint stability. Injured athletes who are unable to return to sports without surgery (i.e., non-copers) exhibit increased co-contraction during hop landing compared to ACL-deficient athletes who return to sport without knee instability (copers). PURPOSE: To determine whether co-contraction of the hamstrings with the quadriceps is increased in athletes with a non-contact MoI. METHODS: Thirty-two athletes with unilateral ACLR (24 non-contact, 8 contact) participated a one-time session analyzing single leg landing of both limbs off a 20 cm platform using a 3-D motion analysis system. Peak knee flexion and vertical ground reaction force (VGRF) served as measures of performance. Vastus lateralis and biceps femoris recruitment were analyzed using surface EMG and normalized to maximal voluntary isometric contraction. Instantaneous hamstring/quadriceps co-contraction was integrated over the weight acceptance phase of landing to generate a co-contraction index (CoI). The mean CoI was compared between groups (contact v. non-contact) using a one-sided independent t-test. Due to the discrepancy in already low sample sizes, we verified the results using a bootstrapped 95% confidence interval (CI) of the difference in means with 10000 iterations. RESULTS: There was no significant difference in peak knee flexion or VGRF between groups. However, athletes with a non-contact MoI utilized significantly greater co-contraction in landing than those with a contact MoI in both the involved limb (non-contact: 34.58±19.56; contact: 22.46±7.47; p=0.008, 3.67-21.72 CI) and uninvolved limb (non-contact: 24.71±13.22; contact: 18.39±4.60; p=0.027, 1.06-13.25 CI). CONCLUSIONS: Though similar in knee joint motion and limb loading during landing, athletes who sustain non-contact injuries utilize very different neuromuscular patterns than those injured by contact. These data demonstrate that neuromuscular faults persist despite resolution of knee laxity with surgery. The bilateral nature of the differences in CoI suggests a common central source of the motor patterning