Intramuscular innervations of muscle flaps that are commonly used in clinical settings

Abductor hallucis, latissimus dorsi, gracilis, rectus abdominis, sartorius and pectoralis minor are muscle flaps that are commonly used in clinic, but their intramuscular innervation has seldom been systematically investigated.

Five Chinese fresh human cadavers were included in the study and abductor hallucis, latissimus dorsi, gracilis, rectus abdominis, sartorius and pectoralis muscles were dissected. After gross anatomy measurement, the specimens were then stained by Sihler's staining technique. Intramuscular innervation was observed and the number as well as distribution was recorded.

Intramuscular nerves were clearly visualized by Sihler's staining technique. Based on the shape and muscle-tendon morphology, Lim et al. in Muscle Nerve 29:523-530, 2004 grouped the muscles into trapezoidal-shaped (type I), spindle-shaped (type II), and combination-shaped (type III). According to Lim's study the abductor hallucis was a type IIb muscle and was divided into two compartments by the distal tendon. Latissimus dorsi was a type I muscle, divided into 3-4 compartments by intramuscular nerve branches. Gracilis was a type IIa muscle and the distal part was divided into two compartments by intramuscular nerve branches. Rectus abdominis was a type III muscle and the four bellies comprised four compartments, each of which could be designated as a subunit. Sartorius was a type II muscle and it could be divided into 2-3 compartments along the long axis. Pectoralis minor was a type I muscle that was divided into two compartments by extramuscular terminal nerves.

The six muscles are divided into several compartments by the tendon or nerve branches, and all of them make good donor tissue for muscle compartment transfer in reconstructive surgery.