Relationship of the Musculocutaneous Nerve and Its Twigs to the Coracoid Process: An Operative Exposure

Abstract

Background: A musculocutaneous nerve (MCN) injury is a rare complication of the Latarjet procedure. Most of these injuries are neurapraxias and resolve with time; however, permanent injuries can occur. Understanding the anatomy and relationship of the MCN to the coracoid process is essential to prevent injuries. Purpose: To provide realistic, in situ–referenced measurements for the Latarjet procedure. Study Design: Descriptive laboratory study. Methods: A total of 12 matched-pair cadaveric specimens (24 fresh-frozen shoulders) were dissected. Coracoid osteotomy was performed, and the MCN and its respective twigs were identified. Measurements were made from the coracoid process to the entry site of the nerve twigs and trunk into the coracobrachialis muscle. Results: Overall, 70.8% of specimens had twigs; however, there was a discrepancy in the presence (41.7%) and number (75.0%) of twigs in the paired specimens. The most proximal twigs were, on average, 33.5 ± 8.1 mm (range, 21.9-47.6 mm) from the coracoid process. The main trunk was, on average, 51.1 ± 14.4 mm (range, 16.7-71.9 mm) from the coracoid process. In 33.3% of specimens, the nerve entered the coracobrachialis at a distance shorter than 5 cm below the coracoid process, and this increased to 91.7% when the twigs were accounted for. Conclusion: The previously described safe zone of 5 cm below the coracoid process may not be reliable to protect the MCN or its twigs. Using 3 cm would decrease the chances of damaging a twig or the main trunk. In 33.3% of the specimens, the nerve entered the coracobrachialis at a distance shorter than 5 cm below the coracoid process, and this increased to 91.7% when twigs were accounted for. Clinical Relevance: As the Latarjet procedure is an emerging technique, it is essential to be aware of the anatomic structures and the relation between different neural structures to anatomic points of reference. Therefore, the results of this study add significant information for a safe surgical procedure for the majority of patients suffering from shoulder instability.

A Review of the Typical Course of the Musculocutaneous Nerve into the Coracobrachialis Muscle: Its Variability and Possible Clinical Implications

“…Α total of 126 studies were identified, 28 of which were assessed as full-text articles (Figure 1). Out of these, 23 manuscripts (1,2,15,(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38) were used for estimation of the MCN's typical course, 10 (6, 12, 15, 17, 27, 34, 36, 39-41) for calculation of the distance between the CP and the entrance point of the MCN into the CB, and 7 (2,6,12,15,17,36,40), for computation of the distance between the CP and the point of origin of the proximal branches.…”

“…of CP-MCN penetration into the CB is frequently recorded as between 5-8 cm (1,3,12,13). In addition, MCNs with higher penetration into the CB have also been reported (14)(15)(16)(17). The current study reviews the data literature and estimates the prevalence of the MCN's typical course through the CB.…”

“…Small motor branches to the CB appear in 76.12% of cases, with an average distance of 3.8 cm (median 3.7 cm). Some studies recorded the presence of those accessory branches originating at a high-level position from the MCN's main trunk (12,17,36). Although this point needs further investigation, surgeons need to know this correlation when operating in this area, as MCN lesions result in reduced elbow flexion strength and sensory impairment of the forearm's radial aspect.…”

Coracobrachialis muscle morphology and coexisted neural variants. A cadaveric case series

“…In addition, the lateral root duplication was observed in 3 upper limbs unilaterally (11.1%, 3/27) by the current case series, while Pandey and Shukla [22] recorded a lower prevalence of 4.65% (8/172 cadavers). Some studies recorded the presence of accessory branches originating at a high-level position from the MCN main trunk [10,17,25]. Although this research point needs further investigation from larger clinical studies, surgeons need to know this correlation when operating, as the MCN lesions result in reduced elbow exion strength and sensory impairment of the forearm radial aspect.…”