Observation of the relationship between the shape of skeletal muscles and their nerve distribution patterns: a transparent and microanatomic study

Abstract

Background: There are many gaps in the understanding of the neuroanatomy of skeletal muscles with regards to the nerve distribution pattern and shape of the muscles. This study was designed to examine the entire intramuscular nerve-distribution patterns of various human skeletal muscles.

Methods: The relationships among nine skeletal muscles with various architecture (rhomboid major, biceps brachii, flexor pollicis longus, rectus femoris, sternohyoid, trapezius, masseter, digastric muscles) and their nerve-distribution patterns were investigated in four fetal cadavers using the Sihler staining method. The diameter and number of extramuscular (main) and major nerve branches, the number of minor nerve branches, and anastomoses were examined and evaluated statistically.

Results: With regards to the number of extramuscular (main) nerve branches, the rhomboid major muscle resembled the flexor pollicis longus, trapezius, masseter, and sternohyoid muscles, and the anterior belly of the digastricus muscle (p > 0.05), whereas it was significantly different from the rectus femoris, the posterior belly of digastricus, and the long and short heads of the biceps brachii (p < 0.05). Trapezius and masseter muscles were different from all of the skeletal muscles that were studied with regards to the diameter of main branches (p < 0.05). The masseter muscle had the largest diameter (p < 0.05). With regards to the number of minor nerve branches, the sternohyoid muscle was significantly different from all the skeletal muscles that were studied (p < 0.05) except the short head of the biceps brachii, rectus femoris, and the posterior belly of digastricus (p > 0.05). As for the number of neural anastomoses, the sternohyoid muscle was statistically different from all skeletal muscles that were studied (p < 0.05) except the masseter and trapezius muscles (p > 0.005).

Conclusions: A surgeon's thorough knowledge of the relationship between the shape and nerve distribution pattern of skeletal muscles is important in successful reinnervation and regeneration of these muscles. It might also be useful in the field of muscle transplantation.