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Nerves of the left upper extremity. (Musculocutaneous labeled at upper right.)
|From||lateral cord (C5-C7)|
|To||lateral cutaneous nerve of forearm|
|Innervates||anterior compartment of the arm|
|Anatomical terms of neuroanatomy|
The musculocutaneous nerve arises from the lateral cord of the brachial plexus, courses through the anterior part of the arm, and terminates at 2 cm above elbow as lateral cutaneous nerve of the forearm.
Musculocutaneous nerve arises from the lateral cord of the brachial plexus with root value of C5 to C7 of the spinal cord. It follows the course of the third part of the axillary artery (part of the axillary artery distal to the pectoralis minor) laterally and enters the frontal aspect of the arm where it penetrates the coracobrachialis muscle. It then passes downwards and laterally between the biceps brachii (above) and the brachialis muscles(below), to the lateral side of the arm; at 2 cm above the elbow it pierces the deep fascia lateral to the tendon of the biceps brachii and is continued into the forearm as the lateral cutaneous nerve of the forearm.
In its course through the arm it innervates the coracobrachialis, biceps brachii, and the greater part of the brachialis. Its terminal branch, the lateral cutaneous nerve of the forearm, supplies the sensation of the lateral side of the forearm from the elbow to the wrist. Besides, the musculocutaneous nerve also gives articular branches to the elbow joint and to the humerus.
- It may adhere for some distance to the median and then pass outward, beneath the biceps brachii, instead of through the coracobrachialis.
- Some of the fibers of the median may run for some distance in the musculocutaneous and then leave it to join their proper trunk; less frequently the reverse is the case, and the median sends a branch to join the musculocutaneous.
- The nerve may pass under the coracobrachialis or through the biceps brachii.
- Occasionally it gives a filament to the pronator teres, and it supplies the dorsal surface of the thumb when the superficial branch of the radial nerve is absent.
Injury to the musculocutaneous nerve can be caused by three mechanisms: repeated microtrauma, indirect trauma or direct trauma on the nerve. Overuse of coracobrachialis, biceps, and brachialis muscles can cause the stretching or compression of musculocutaneous nerve. Those who have it can complain of pain, tingling or reduced sensation over the lateral side of the forearm. This symptom can be reproduced by pressing over the region below the coracoid process (positive Tinel's sign). Pain can also be reproduced by flexing the arm against resistance. Other differential diagnoses that can mimick the symptoms of musculocutaneous palsy are: C6 radiculopathy (pain can be produced by movement of the neck), long head of biceps tendinopathy (no motor or sensory deficits), pain of the bicipital groove (relieved by shoulder joint injection). Electromyography test shows slight neural damage at the biceps and the brachialis muscles with slower motor and sensory conduction over the Erb's point.
In indirect trauma, violent abduction and retroposition of the shoulder can stretch and the musculocutaneous nerve lesion. Those with this type of lesion is presented with pain, reduced sensation, and tingling at the antero-lateral part of the arm and lateral part of forearm with reduced strength of elbow flexion. Tinel's sign can be positive. Differential diagnosis includes C5 and C6 nerve root lesions of the brachial plexus where the abduction, external rotation, and elbow flexion is lost. On the other hand, rupture of the biceps can cause the loss of flexion of the elbow without sensory deficits. Electromyography test is negative.
In direct trauma, fracture of the humerus, gun shot, glass pieces injuries and more, can cause the musculocutaneous nerve lesion. Iatrogenic nerve injuries (for example during orthopedic surgery involving an internal fixation of the humerus) are relatively common and in a certain percentage of cases probably inevitable, though an adequate knowledge of the surgical anatomy can help to reduce its frequency.
- Krishna, Garg (2010). "8 - Arm". BD Chaurasia's Human Anatomy (Regional and Applied Dissection and Clinical) Volume 1 - Upper limb and thorax (Fifth ed.). India: CBS Publishers and Distributors Pvt Ltd. p. 88. ISBN 978-81-239-1863-1.
- Choi D, Rodríguez-Niedenführ M, Vázquez T, Parkin I, Sañudo JR (January 2002). "Patterns of connections between the musculocutaneous and median nerves in the axilla and arm". Clin Anat. 15 (1): 11–7. doi:10.1002/ca.1085. PMID 11835538.
- Guerri-Guttenberg RA, Ingolotti M (September 2009). "Classifying musculocutaneous nerve variations". Clin Anat. 22 (6): 671–83. doi:10.1002/ca.20828. PMID 19637305.
- Guerri-Guttenberg, Roberto A.; Ingolotti, Mariana (2009). "Classifying musculocutaneous nerve variations". Clinical Anatomy. 22 (6): 671. doi:10.1002/ca.20828. PMID 19637305.
- Celli, Andrea; Celli, Luigi; F Morrey, Bernard (25 January 2008). "28 - Traumatic isolated lesions of musculocutaneous nerve". Treatment of Elbow Lesions: New Aspects in Diagnosis and Surgical Techniques. Springer. pp. 299–302. ISBN 9788847005914. Retrieved 26 January 2018.
- Zhang J, Moore AE, Stringer MD (April 2011). "Iatrogenic upper limb nerve injuries: a systematic review". ANZ J Surg. 81 (4): 227–36. doi:10.1111/j.1445-2197.2010.05597.x. PMID 21418465.
- Musculocutaneous_nerve at the Duke University Health System's Orthopedics program
- Hand kinesiology at the University of Kansas Medical Center