 | This article includes a list ofgeneral references, butit lacks sufficient correspondinginline citations. Please help toimprove this article byintroducing more precise citations.(May 2015) (Learn how and when to remove this message) |
 | This articlemay be too technical for most readers to understand. Pleasehelp improve it tomake it understandable to non-experts, without removing the technical details.(June 2022) (Learn how and when to remove this message) |
| Musculocutaneous nerve | |
|---|---|
 Nerves of the left upper extremity. (Musculocutaneous labeled at upper right.) | |
| Details | |
| From | Lateral cord (C5-C7) |
| To | Lateral cutaneous nerve of forearm |
| Innervates | Anterior compartment of the arm |
| Identifiers | |
| Latin | nervus musculocutaneus |
| MeSH | D009138 |
| TA98 | A14.2.03.024 |
| TA2 | 6421 |
| FMA | 37064 |
| Anatomical terms of neuroanatomy | |
Themusculocutaneous nerve is amixed branch of thelateral cord of thebrachial plexus derived from cervical spinal nerves C5-C7. It arises opposite the lower border of thepectoralis minor.[1] It provides motor innervation to the muscles of theanterior compartment of the arm: thecoracobrachialis,biceps brachii, andbrachialis.[2] It provides sensory innervation to the lateral forearm (via itsterminal branch).[3] It courses through the anterior part of the arm, terminating 2 cm above elbow;[citation needed] after passing the lateral edge of the tendon ofbiceps brachii it is becomes known as thelateral cutaneous nerve of the forearm.[3]
Musculocutaneous nerve arises from the lateral cord of the brachialplexus with root value of C5 to C7 of the spinal cord. It follows the course of the third part of theaxillary artery (part of the axillary artery distal to thepectoralis minor) laterally and enters the frontal aspect of the arm where it penetrates thecoracobrachialis muscle. It then passes downwards and laterally between thebiceps brachii (above) and thebrachialis muscles (below), to the lateral side of the arm; at 2 cm above the elbow it pierces thedeep fascia lateral to the tendon of the biceps brachii and is continued into the forearm as thelateral cutaneous nerve of the forearm.[4]
In its course through the arm it innervates the coracobrachialis, biceps brachii, and the greater part of the brachialis.[4]
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.[4]
The musculocutaneous nerve also gives articular branches to the elbow joint and to the humerus.[4]
The musculocutaneous nerve presents frequent variations and communications with themedian nerve.[5][6]
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 thecoracoid process (positiveTinel'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 thebicipital 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 theErb's point.[8]
In indirect trauma, violentabduction and retroposition of the shoulder can stretch the nerve and result tension of thecoracobrachialis with musculocutaneous nerve lesion. Those with this type of lesion is presented with pain, reduced sensation, and tingling of the lateral part of forearm (lateral antebrachial cutaneous nerve - terminal sensory only branch of musculocutaneous nerve) 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. Rupture of the SHORT HEAD of the biceps can decrease elbow flexion strength, where the brachialis muscle is intact. Rupture of the LONG HEAD of the biceps results in mild weakening of forearm supination as long as the supinator muscle is intact.Electromyography test is negative.[8]
In direct trauma, fracture of the humerus, gun shot, glass pieces injuries and more, can cause the musculocutaneous nerve lesion.[8]
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.[9]
To diagnose traumatic nerve injury, operative exploration should be performed without delay. If reconstruction of the motor function of the musculocutaneous nerve (elbow flexion) is needed then there are several options, depending on the injury pattern and timeframes. If the nerve is in-continuity and the fascicles appear healthy under the operating microscope thenNeurolysis may be sufficient. When there is a division or segment of non-viable nerve then interpositional autografting is preferred. If reinnervation is likely to take months (e.g. if the injured segment is long and long grafts are needed, or in the case of proximal injuries such as root avulsion or upper trunk injury) then nerve transfer is preferred as this will reinnervate the muscle faster; in the case of upper trunk injuries, the ideal neurotisation appears to be the double Oberlin transfer[10]., although data on this topic are sparse and heterogeneous.
This article incorporates text in thepublic domain frompage 935 of the 20th edition ofGray's Anatomy(1918)
