Foot control in incomplete SCI: distinction between paresis and dexterity

To complement the clinical assessment of motor impairment after incomplete spinal cord injury (iSCI) by introducing a test that reliably distinguishes between muscle weakness (paresis) and impairment of dexterity in a simple foot motor task.

Auditory-paced ankle dorsi- and plantarflexion, in a supine position, was studied in 30 controls (to establish control values and to test reliability) and in 16 iSCI patients (test validation). The subjects were instructed to initiate dorsi- and plantarflexion as accurately in timing and with the largest range of motion (ROM) possible. For each frequency, accuracy of timing, ROM, peak velocity of dorsi- and plantarflexion and a time quotient for changing from dorsi- to plantarflexion and vice versa were determined. In iSCI subjects, these parameters were related to clinical measures of paresis, spasticity and proprioception.

The test parameters showed good to very good reliability. The iSCI subjects were able to follow the target frequency with high accuracy, while ROM and peak velocity for dorsi- and plantarflexion were significantly reduced. Furthermore, there was a strong correlation between ROM/peak velocities and motor scores within the iSCI patients.

Repetitive foot dorsi- and plantarflexion enables a distinction to be made between muscle weakness and reduced dexterity as the underlying cause of affected foot control. This distinction between and quantification of these two movement components complements the existing clinical examination, and in follow-up works, the recovery of these components may provide further insight into the mechanisms underlying motor function improvement after iSCI.