Musculocutaneous nerve: Histotopographic study and clinical implications

Abstract

Surgical reconstruction of severe brachial plexus injuries includes nerve grafting and neurotization techniques of the musculocutaneous nerve (MCN) to recover elbow flexion. In treating recurrent anterior shoulder instability, knowledge of the topography of the MCN is important for the margin of safety available during dissection. The present study evaluates the origin and course of the MCN and its branches, and their relationships to bone landmarks. Twelve unembalmed cadavers (50-82 years old) were dissected. A histological study of the MCN and the coracobrachialis muscle (CB) was also carried out. The mean distance (+/-SD) of the MCN from the coracoid process to the origin, points of entry to, and exit from the CB were 2.9 +/- 0.5 cm, 7.7 +/- 2.5 cm, and 11.6 +/- 0.8 cm, respectively. The first two findings were also validated during surgical approaches to the shoulder in 59 subjects. The mean distance of the MCN from the acromion to the origin, points of entry to, and exit from the CB were 6.4 +/- 0.3 cm, 7.7 +/- 0.8 cm, and 10.4 +/- 1.9 cm, respectively. The mean length of the MCN from its origin to the points of entry to and exit from the CB were 6.7 +/- 1.6 cm and 11.0 +/- 1.0 cm, respectively. The mean length of the MCN inside the muscle was 4.4 +/- 1.9 cm. The distance from the coracoid process to the point of entry to the CB and the length of the MCN inside the muscle were inversely related (P < 0.05). The distance from the coracoid process to the point of exit of the MCN was positively correlated with the length of the nerve within the CB (P < 0.05). Histology showed that, during the intramuscular course of the MCN, the epineurium is composed of 4-5 concentrically arranged lamina of connective tissue which shows different dispositions along the circumference of the nerve trunk. On the ventral and dorsal aspects of the nerve the lamina are closely packed, but on the medial and lateral sides they are separated by thin layers of adipose tissue. This uneven disposition of the adipose tissue gives the epineurium an oval profile in transverse section (mean circular factor 0.8). The arrangement of the fibroadipose tissue sheaths may be compared to a "telescope" and may allow compliance between variations of length of CB and the constant course of the MCN. Clinically, a decrease in this "sliding system" may expose the nerve to mechanical effects of muscle contraction, with the possibility of a compression syndrome.

The course and variations of the branches of the musculocutaneous nerve in human fetuses

“…Helfet (1958) recognized the clinical significance of a high entry of the MCN into coracobrachialis. Subsequently, several investigators have suggested that the entry point of the MCN into coracobrachialis is clinically important, with a correlation between high entry points and frequency of nerve injuries being reported (Flatow et al, 1989;Ozturk et al, 2005;Macchi et al, 2007). Some studies have reported cases in which the MCN does not pierce cor-acobrachialis, in which case a direct branch from lateral cord of the brachial plexus was observed to supply the muscle (Eglseder and Goldman, 1997;Venieratos and Anagnostopoulou, 1998).…”

Histotopographic Study of the Fibroadipose Connective Cheek System

“…Retroperitoneal pelvic connective tissue may act as a shock absorber, particularly efficient in response to sudden increases in abdominal pressure [De Caro et al, 1998]. The arrangement of the fibroadipose tissue sheaths of the epineurium of the musculocutaneous nerve may be compared to a 'telescope', which allows harmonic compliance between variations in the length of the coracobrachialis muscle with respect to the constant course of the musculocutaneous nerve [Macchi et al, 2007]. The deep fibroadipose connective layer of the SMAS may represent a buffer device with respect to deep muscle activity, since it can modulate excessive involvement of facial physiognomy due to the direct transmission of collateral contraction effects during the activity of the masseter and buccinator muscles (masticatory and phoniatric functions) to the overlying cutaneous facial plane.…”

“…For each region of the subcutaneous tissue, the following parameters were recorded: mean thickness of the subcutaneous tissue, superficial and deep fibroadipose connective tissue, superficial fascia and septa. The mean area and circularity factor of adipose lobules in the superficial and deep fibroadipose connective tissue were also recorded [Macchi et al, 2007]. Each region was subdivided into five equal parts and the thickness measured in each part.…”

Body parts removed during surgery: A useful training source

“…Within surgical departments, the need for professionals in human gross anatomy is uncontested (Fasel et al, 2005). In our experience, anatomic and clinical research examines anatomical structures from new perspectives (Macchi et al, 2007b(Macchi et al, ,c, 2008 and can lead to improved surgical practice (Tiengo et al, 2004(Tiengo et al, , 2007Macchi et al, 2005). In our project, the continuity of the diagnostic and therapeutic phases was achieved by the active involvement of residents in the steps involved in donation of body parts.…”