Upper and lower motor neuron lesions in the upper extremity muscles of tetraplegics

Paralysed upper extremity muscles of 24 tetraplegic patients were examined to determine whether their lower motor neuron was intact. Primary emphasis was placed on the forearm finger flexor muscles (Flexor Digitorum Superficialis and Flexor Digitorum Profundus) and finger extensor muscles (Extensor Digitorum Communis and Extensor Indicis). It was found that the vast majority of these muscles in C4, C5 and C6 subjects retained some or all of their lower motor neurons intact. In C5 subjects, examination was performed on additional muscles that were potentially most useful in an orthosis utilising functional stimulation. Similar to the results of the finger flexor and extensor muscles, the muscles of the wrist and thumb generally had the lower motor neuron at least partially intact. A muscle that often was an exception was M. Flexor Carpi Radialis. These studies indicate that most of the forearm muscles of the upper extremity in high level spinal cord injury patients which are paralysed have the lower motor neuron totally or partially intact. With electrically induced exercise, such muscles are strengthened to functional levels of contraction. Subsequent electrical activation enables the quadriplegic patients to use the muscle functionally.