Ultrasonographic evaluation of functioning free muscle transfer: comparison between spinal accessory and intercostal nerve reinnervation.

This study focuses on the application of ultrasonography as a means of measuring the cross-sectional area (CSA) of the transferred muscle and evaluating its force recovery following functioning free muscle transfer. The objective of the study was to compare the CSA of a transferred muscle that is either reinnervated by the spinal accessory nerve (SAN) or the intercostal nerve (ICN), and to evaluate the difference in their force recovery. Ten patients with complete avulsion of the brachial plexus who underwent a double free muscle technique for restoring prehensile function were evaluated. All patients were followed up for at least 1.5 years after the operation. The CSAs of 20 transferred gracilis muscles in 10 patients, reinnervated either by SAN or ICN, were measured by ultrasonography. The CSA was measured at relaxation and at maximal isometric contraction. The force recovery of each muscle was expressed as the contraction rate (CR), calculated by dividing the CSA of the muscle in maximum isometric contraction by the CSA of the muscle in relaxation. The mean CSA of the transferred muscles reinnervated by the SAN was 2.98 +/- 0.723 cm (2) in relaxation and 3.95 +/- 1.296 cm (2) in maximum isometric contraction; thereby a CR of 1.32 +/- 0.174 was obtained. The mean CSA of the transferred muscles reinnervated by the ICN was 2.32 +/- 0.520 cm (2) and 2.69 +/- 0.566 cm (2) in relaxation and maximal isometric contraction, respectively; thus a CR of 1.16 +/- 0.068 was obtained. Results showed that the CR was significantly higher among the transferred muscles reinnervated by the SAN than those by the ICN. This study demonstrated that muscles that are reinnervated by the SAN resulted in stronger recovery than those reinnervated by the ICN, and that ultrasonography has the capacity to evaluate force recovery of each muscle by measuring the CSA during the two phases of muscle activity.