Relating Corticomotor Structure And Function With Knee Function After ACL Injury

The role of the central nervous system in ACL injury has gained attention to understand the brain’s susceptibility to maladaptive plasticity and its implications for recovery. Persistent quadriceps weakness after ACL rupture (ACLR) is a common pathological deficit that may be related to structural and functional cortical changes. Thus, it is necessary to thoroughly assess the neural factors that underlie brain plasticity and functional deficits associated with ACLR. PURPOSE: To determine the relationship between cortical thickness, corticomotor size, and knee function after ACLR. METHODS: Nine women with a history of unilateral ACLR (23.2±2.5 yr) and 10 healthy controls (23.5±3.2 yr) participated in a laboratory visit and MRI visit. Participants performed unilateral maximal isometric knee extensions to compute limb symmetry index (LSI). Transcranial magnetic stimulation pulses were delivered to each vastus medialis oblique (VMO) hotspot with continuous monitoring of biceps femoris (BF) activity using a 96 mm curved double coil. A motor mapping procedure was performed that included 120 pulses in a 6x6cm grid to derive motor map surface area and volume of the VMO and BF. Structural MRIs were acquired to derive paracentral lobule (PCL) cortical thickness. Independent samples t-test compared LSI between groups. Mixed-model ANCOVAs (leg x group) with Sidak post-hoc tests were used to examine differences in maximal force, PCL thickness, map surface area, and map volume. Injury laterality and footedness score were covariates. RESULTS: ACLR’s previously injured leg was weaker than the healthy leg, with no between-leg differences in CON. ACLR had greater PCL thickness and VMO map volume in the hemisphere corresponding to the previously injured leg than the healthy leg. Similarly, BF surface area and map volume were greater in the previously injured leg’s corresponding hemisphere compared to the contralateral hemisphere. CON had symmetrical PCL thickness, but the dominant limb had a greater VMO map volume. CONCLUSION: Our results indicate that years after ACLR, plasticity in corticomotor structure is homotopic with apparent maximal strength imbalance between legs. The asymmetry in leg-specific brain structure between hemispheres may contribute to the skeletomotor deficits common after ACLR. Freddie H. Fu, MD Graduate Research Award, the CMU-Pitt Brain Imaging Data Generation & Education (BRIDGE) Center Seed Grant, and SHRS PhD Student Award