Serratus anterior in vivo contractile force study

Background: A major limitation of functional muscle transfer for facial and intrinsic hand reanimation is the inability to predict the force that will be generated by the transplanted muscle. Methods: The authors studied the contractile force of the slips of the serratus anterior in situ in 10 patients and tested the gracilis muscle in four subjects as a control. Results: Mean contractile force generated by each serratus slip was 0.178 pound (range, 0.019 to 0.797 pound). This compares favorably with the maximum force generated by smiling (0.307 pound). Muscle strength correlated strongly with age (r = -0.805, p = 0.005). The lowest slip generated less force than those above it (0.133 pound versus 0.191 pound); this difference did not reach statistical significance. When the strength of the lowest slip is compared with the more superior slips as a percentage of total force generated by the slips (to compensate for the effect of age on muscle strength), the lowest slip was significantly weaker (18.6 percent of total force versus 25.5 percent of total force, p = 0.013). Mean contractile force generated by the gracilis was 0.963 pound, significantly different from that generated by a serratus anterior slip (p = 0.009). Conclusions: Each serratus slip could potentially be used to generate a separate force vector for facial reanimation. Further separation of the flap along preexisting fascial planes may allow generation of up to 10 independent force vectors, making the serratus anterior muscle flap an attractive option for facial reanimation and possibly intrinsic hand muscle reconstruction.