Experimental study on donor nerves for brachial plexus injury: comparison between the spinal accessory nerve and the intercostal nerve.

The spinal accessory nerve and intercostal nerves are widely used as donor nerves for neurotization in patients with brachial plexus injuries. However, the characteristic differences in reinnervation by the spinal accessory and intercostal nerves have not been investigated. The purpose of this study is to compare the resulting contractile properties of the biceps muscles following nerve-crossing procedures of spinal accessory nerve and intercostal nerves to the musculocutaneous nerves. In 10 beagle dogs, the spinal accessory nerve was used to reinnervate the left biceps muscle, and the second and third intercostal nerves were used to reinnervate the right biceps muscle. After 10 months, the reinnervated muscles were studied by measuring their force of contraction as well as by histochemical methods. Biceps muscles reinnervated by spinal accessory nerves (A transfers) acquired the properties of fast, fatigable muscles, whereas those reinnervated by intercostal nerves (IC transfers) acquired the properties of slow, fatigue-resistant muscles. Furthermore, histochemical studies showed that type II fibers were predominant in A transfers, whereas type I fibers were predominant in IC transfers. This study clearly demonstrates the differences between the spinal accessory nerve and intercostal nerves as donor nerves. This may lead us to select appropriate donor nerves for nerve-crossing procedures and free-muscle transfer depending on the desired functions to be reconstructed.