PubMed1984
It is known that cross-reinnervation occurs when regenerating nerve fibers recombine in brachial plexus injury, especially in obstetrical paralysis. This cross-reinnervation causes abnormal contraction in many muscles simultaneously during voluntary movement. To date, however, little has been reported on its pathophysiology, severity and prognosis. In order to clarify these problems, 362 cases of obstetrical paralysis were studied clinically and electromyographically, and abnormal muscle contractions during voluntary movement were analyzed. The results are as follows; Cross-reinnervation is seen in most cases which have suffered from transection or severe injury near the transection of the nerve fibers (including that in the neural tube), and which have got recovery better than manual muscle testing grade (2) "poor". Cross-reinnervation is caused by cross-reinnervation of nerve fibers which regenerate in the wrong muscles. Muscle contraction occurring in many muscles simultaneously is different from co-ordinate movement. Other paradoxical muscle action is found besides that of contraction. Cross-reinnervation can be classified into the following types by the muscle groups showing the contraction. Deltoid m., biceps brachii m. type, Deltoid m., biceps brachii m., triceps brachii m. type, Biceps brachii m., triceps brachii m. type, Deltoid m., biceps brachii m., triceps brachii m., forearm mm. type, Deltoid m., biceps brachii m., forearm mm. type, Biceps brachii m., triceps brachii m., forearm mm. type, Triceps brachii m., forearm mm. type. Abnormal muscle activity caused by cross-reinnervation is found from 4-6 months after nerve recovery from Wallerian degeneration, and it does not improve, but physical therapy or operative treatment can bring improvement in daily activities. Clinical severity of cross-reinnervation is correlated to the severity of paralysis and in proportion to the ratio of normally recovered nerve fibers and cross-reinnervated nerve fibers. It suggests that cross-reinnervation is caused by the discordant recovery from injury of nerve fibers in the brachial plexus. The site of cross-reinnervation depends on the severity of paralysis. Usually it spreads from the 5th and 6th cervical nerve roots to the upper trunk, medial trunk, posterior cord and lastly to the lower trunk and medial cord, determined by the severity of paralysis. This agrees with the way of spreading of obstetrical paralysis.
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