Central somatosensory changes associated with improved dynamic balance in subjects with anterior cruciate ligament deficiency

To examine the mechanisms underlying return to pre-injury function in individuals with anterior cruciate ligament deficiency (ACL-D), we grouped 15 individuals (18–50 years of age) with ACL-D by functional status and strength (i.e. copers, non-copers and adapters) and compared measures of proprioception, somatosensory evoked potentials and neuromuscular responses to dynamic testing between groups. Seven subjects without ACL-D provided a comparative sample for dynamic balance testing (DBT). DBT consisted of bilateral EMG recordings of anterior tibialis, medial gastrocnemius, medial hamstrings and quadriceps during toes-down platform rotation. Relative latencies and relative amplitudes were calculated. Somatosensory evoked potential (SEPs) testing was based on identifying the presence or absence of the P27 potential. Proprioception was tested using threshold to detection of passive movement (TDPM). Those with the highest level of function, the copers, had a proprioceptive deficit, loss of P27 and altered postural synergies consisting of earlier and larger hamstring activation. Conversely, those with the lowest functional status, the non-copers, had strength and proprioception deficits, intact SEPs and inconsistent postural synergies. These results suggest that changes in central sensory representation may facilitate altered postural synergies that enable return to pre-injury functional status.