Functional compensative mechanism of upper limb with root avulsion of C5-C6 of brachial plexus after ipsilateral C7 transfer

ObjectiveTo investigate the compensative mechanism of no further impairment of the upper limb after ipsilateral C7 transfer for treatment of root avulsion of C5-C6 of the brachial plexus.MethodsSixty Sprague Dawley (SD) rats were randomly divided into a C7-transection group and a control group, 30 rats each. In the C7-transection group, the left forelimbs of the animals underwent transection of ipsilateral C7 nerve root while C5 and C6 nerve roots were avulsed. In the control group, the left forelimbs only underwent C5 and C6 root avulsion. The representative muscles of C7 (innervated mainly by C7) including latissimus dorsi, triceps, extensor carpi radialis brevis and extensor digitorum communis were evaluated with neurophysiological investigation, muscular histology and motor end plate histomorphometry 3, 6 and 12 weeks after operation. The right forelimbs of all rats were taken as the control sides.ResultsThree weeks after operation, the recovery rates of amplitudes of compound muscle action potential (CMAP) and CMAP latency, muscular wet weight and cross-sectional area of muscle fibers, and area of postsynaptic membranes of those four representative muscles in the C7-transection group were significantly lower than those of the control group (P <0.05 or P <0.01). Six weeks postoperatively, the recovery rates of CMAP amplitude and latency of the triceps showed no significant difference between the C7-transection group and the control group (P>0.05). For the extensor carpi radialis brevis and the extensor digitorum communis, the recovery rates of the cross-sectional area of muscle fibers, the amplitude and latency of CMAP and the area of postsynaptic membranes showed no significant difference between the two groups (P>0.05), while the rest parameters were still significantly different between the two gr o up (P <0.05 o r P <0.01). As far as the ultramic rostructure was concerned in the C7-transection group, more motor end plates of four representative muscles were observed and their ultramicrostructure also had a tendency to mature as compared with those of 3 weeks postoperatively. Twelve weeks after operation, all parameters of the C7-transection group were not significantly different from those of the control group (P >0.05). In the C7-transection group, the motor end plates were densely distributed and their ultramicrostructure in four representative muscles appeared to be mature as compared with those of the control group.ConclusionsAfter ipsilateral C7 transfer for treatment of root avulsion of C5-C6 of the brachial plexus, the nerve fibers of the lower trunk can compensatively innervate fibers of C7-representative muscles by means of motor end plate regeneration, so there is no further impairment on the injured upper limb.