Spinal cord implantation of avulsed ventral roots in primates; correlation between restored motor function and morphology.

Functional restitution following spinal cord implantation of avulsed ventral roots was assessed electromyographically and correlated with the morphology of the regenerated neural structures in primates. The C5-C8 ventral roots were avulsed from the spinal cord in seven Macaca fascicularis monkeys. In three animals the roots were immediately reimplanted into the ventrolateral part of the spinal cord. In two monkeys the avulsed roots were reimplanted with a delay of 2 months and in two control animals the roots were not reimplanted. There was substantial recovery of function after both immediate and delayed spinal cord implantation of the avulsed ventral roots. The population of neurons that had regenerated was larger than on the control side, indicating a rescue of cells after an immediate root implantation. Different functional types of neurons had been attracted to regrow axons to the implanted root as judged by their position in the ventral horn. Thus, neurons normally supplying antagonistic muscles, such as the triceps muscle, participated in the innervation of the biceps muscle. Functionally this deficient directional specificity was correlated to both spasticity and co-contractions among agonistic and antagonistic muscles. Occasional electromyographic signs of function occurred also in control animals where the avulsed roots had not been implanted. This recovery was found to depend on regrowth from the site of avulsion, within the pia mater among the leptomeningeal cells and to the avulsed roots. The acceptable functional dexterity regained due to corrective surgery is discussed in terms of neurotrophism and plasticity.