Re-visiting the brachialis muscle: morphology, morphometry, gender diversity, and innervation

A bilateral four-headed brachialis muscle with a variant innervation: a cadaveric report with possible clinical implications

PURPOSE

Anterior compartment muscles of the arm present high morphological variability, with possible clinical significance. The current cadaveric report aims to describe a bilateral four-headed brachialis muscle (BM) with aberrant innervation. Emphasis on the embryological background and possible clinical significance are also provided.

METHODS

Classical upper limb dissection was performed on an 84-year-old donated male cadaver. The cadaver was donated to the Anatomy Department of the National and Kapodistrian University of Athens.

RESULTS

On the left upper limb, the four-headed BM was supplied by the musculocutaneous and the median nerves after their interconnection. On the right upper limb, the four-headed BM received its innervation from the median nerve due to the musculocutaneous nerve absence. A bilateral muscular tunnel for the radial nerve passage was identified, between the BM accessory heads and the brachioradialis muscle.

CONCLUSION

BM has clinical significance, due to its proximity to important neurovascular structures and frequent surgeries at the humerus. Hence, knowledge of these variants should keep orthopedic surgeons alert when intervening in this area. Further dissection studies with a standardized protocol are needed to elucidate the prevalence of BM aberrations and concomitant variants.

Anatomical Variations of the Musculocutaneous Nerve in the Human Fetus

OBJECTIVES

Knowing the motor branches and variations of the musculocutaneous nerve to the muscles along its course will facilitate the treatment of flexor spasticity and supracondylar fractures of the humerus in order to minimize nerve lesion. In fetal cadavers, the purpose of our study was to determine the number and course of the formation variations and motor branches of the musculocutaneous nerve. The significance of studying fetal nerve variations is due to injury to the brachial plexus roots during birth.

METHODS

Our study was conducted using the anatomical dissection technique on 102 upper limbs from 51 fetuses ages ranged from 17 to 40 weeks. Throughout its course, the variations and motor branches of the musculocutaneous nerve were analyzed.

RESULTS

In 13.7% of cases, the musculocutaneous nerve did not pierce the coracobrachialis. The musculocutaneous nerve gave the muscles 1-3 motor branches. Additionally, motor branches terminated with 1-7 fringes. The biceps brachii motor branches of the musculocutaneous nerve were typed. Accordingly, 15.6% were type 1A, 3.9% were type 1B, 35.4% were type 1C, and 19.6% were type 1D. It was determined that 23.5% of the extremities were type 2 and that 1.9% were type 3. The distance between the musculocutaneous nerve's motor branches and the acromion was proportional to the arm's length. There were no statistically significant differences between the sides and genders for any measurement.

CONCLUSIONS

Our study's findings will aid in the diagnosis and treatment of pediatrics, orthopedics, surgical sciences, and radiology conditions. It reduces the risk of iatrogenic injury and postoperative complications. We also believe that our research will serve as a resource for anatomists and other scientists.

Nerve transfer in the spastic upper limb: anatomical feasibility study

PURPOSE

Nerve transfers represent an innovative tool in the surgical treatment of upper limb paralysis. Well-documented for brachial plexus sequalae and under evaluation for tetraplegic patients, they have not yet been described for spastic upper limbs. The typical spastic deformity involves active and spastic flexor, adductor and pronator muscles, associated with paralysed extensor and supinator muscles. Experience with selective neurectomy has shown an effective decrease in spasticity together with preservation of muscle strength. We conceptualized a combination of neurectomy and nerve transfer, by performing a partial nerve transfer from a spastic elbow flexor muscle to a paralyzed wrist extensor muscle, hypothesizing that this would reduce the spasticity of the former and simultaneously activate the latter.

METHODS

Ten cadaveric dissections were performed in order to establish the anatomic feasibility of transferring a motor branch of the brachioradialis (BR) onto the branch of the extensor carpi radialis longus (ECRL) or brevis (ECRB). We measured the emergence, length, muscle entry point and diameter of each branch, and attempted the transfer.

RESULTS

We found 1-4 motor nerve for the BR muscle and 1-2 for the ECRL muscle. In all cases, the nerve transfer was achievable, allowing a satisfactory coaptation. The ECRB branch emerged too distally to be anastomosed to one of the BR branches.

CONCLUSION

This study shows that nerve transfers from the BR to the ECRL are anatomically feasible. It may open the way to an additional therapeutic approach for spastic upper limbs.