Gross anatomic evidence of partitioning in the human fibularis longus and brevis muscles.

Evidence from a variety of studies suggests that many mammalian muscles are partitioned with respect to their architecture and innervation. Each of these specific muscle subvolumes is innervated by an individual muscle nerve branch, contains motor unit territories with a unique array of physiological attributes and has been known as a neuromuscular compartment or segment. This gross anatomic study investigated for evidence of neuromuscular segmentation in human fibularis (peroneus) longus and brevis muscles. Forty-three legs (24 left, 19 right) from embalmed adult cadavers were dissected. Any architectural segment within these muscles were identified. The specific innervation patterns of these muscles were also described. The fibularis longus muscle was consistently found to have connective tissue partitions that separated it into four parts: anterior superficial, anterior deep, posterior superficial, and posterior deep. The innervation pattern of this muscle was consistent with the segments defined by the connective tissue partitions. There were consistently four primary motor branches, each supplying a specific portion of the fibularis longus muscle. While a typical branching pattern was recognized, there was some variability as to the order of these branches as they originated. The fibularis brevis muscle was consistently found to have a central connective tissue partition that separated it into two portions: anterior and posterior. In 91% of the fibularis brevis muscles, there were two primary motor branches, one for each of the two segments of the muscle. In the other 9%, only one primary motor branch supplying the muscle could be identified.