Residual innervation of the pelvic floor muscles in people with motor-complete spinal cord injury

Individuals classified clinically as having a motor-complete spinal cord injury (mcSCI) should lack voluntary motor function below their injury level. However, neurophysiological assessments using electromyography (EMG) and transcranial magnetic stimulation (TMS) have demonstrated that people with mcSCI retain limited cortical descending innervation and voluntary activation of muscles below their level of injury, including muscles of the trunk and lower limb. Here we explored the possibility of whether there is also preserved innervation of the pelvic floor muscles (PFM) in people with mcSCI. The PFM are controlled by widespread cortical and sub-cortical areas and typically co-activated with trunk and gluteal muscles to maintain continence and regulate intra-abdominal pressure. Nine mcSCI and eight control subjects participated in this cross-sectional study. Surface EMG was used to record activity in the PFM. Data were recorded while participants attempted various maneuvers of the trunk and pelvis. We also applied transcranial magnetic stimulation at incrementing levels of intensity over the primary motor cortex area to record motor evoked potentials (MEPs) in the PFM. When performing the maneuvers, activation of the PFM was possible in all controls and the majority of SCI participants. However, the PFM were only activated in the SCI participants during maneuvers that engaged other trunk muscles. MEP responses in the PFM were also elicited in all controls and SCI participants, but MEP response characteristics were significantly altered in the SCI group. Our results suggest that people with mcSCI retain some residual innervation of the PFM after injury, possibly via indirect cortical descending pathways.