Musculocutaneous Nerve: Anatomy, Function, Injury, and Management скачать в хорошем качестве

Musculocutaneous Nerve: Anatomy, Function, Injury, and Management

The musculocutaneous nerve originates from the lateral cord of the brachial plexus, with contributions from C5 to C7. It innervates the anterior compartment muscles of the arm, including the biceps brachii, brachialis, and coracobrachialis. Additionally, it provides cutaneous sensation to the lateral portion of the forearm. This nerve plays a crucial role in elbow flexion and forearm supination, particularly when the elbow is flexed. Anatomical Course In the axilla, the musculocutaneous nerve travels distally and laterally, piercing the coracobrachialis muscle approximately 3-8 cm distal to the tip of the coracoid process. Upon passing through the coracobrachialis, it continues distally, running superficial to the brachialis muscle and deep to the biceps brachii, branching along its path to provide motor innervation. Notably, the brachialis muscle receives dual innervation from both the musculocutaneous nerve and the radial nerve. At the elbow, the musculocutaneous nerve pierces the superficial fascia lateral to the distal biceps tendon and terminates as the lateral antebrachial cutaneous nerve, which supplies sensation to the lateral half of the forearm. Clinical Significance: Musculocutaneous Nerve Injury Pure musculocutaneous nerve injuries are uncommon. When affected, patients experience weakness in elbow flexion, weak forearm supination, and numbness in the anterolateral forearm, stopping at the wrist. Common causes of injury include: Trauma Surgical complications Compression from cast placement Sports-related injuries (notably in baseball pitchers) Due to the course of the lateral antebrachial cutaneous nerve in the cubital fossa, it is vulnerable to venipuncture-related injuries. Additionally, anterior shoulder dislocations can lead to musculocutaneous nerve injuries, which should be considered during patient evaluation. Compression at the Coracobrachialis Muscle: Proximal compression at the level of the coracobrachialis results in pain, weakness of the biceps brachii, and sensory deficits in the lateral antebrachial cutaneous nerve distribution. Symptoms may be aggravated by forceful, repetitive elbow flexion or full extension. Differential Diagnosis of Musculocutaneous Nerve Injury C6 Radiculopathy: Presents with neck pain, radicular symptoms extending distal to the wrist, and numbness in the thumb and index finger. Additional muscles supplied by C6 may also be affected. Distal Biceps Tendon Rupture: Causes elbow flexion weakness. Diagnosed clinically using the hook test or confirmed via MRI. Presents with the "Popeye" sign (biceps retraction). Lateral Antebrachial Cutaneous Nerve Injury: Frequently injured due to venipuncture or distal biceps tendon repair. During surgical repair of the distal biceps tendon, the nerve must be identified and protected to avoid damage. Diagnosis and Imaging When the diagnosis is unclear, an MRI is helpful in evaluating musculocutaneous neuropathy and ruling out other causes. Electrodiagnostic studies (EMG/NCS) may also assist in confirming the diagnosis. Management of Musculocutaneous Neuropathy Conservative Treatment (First-line): Rest and activity modification Nonsteroidal anti-inflammatory drugs (NSAIDs) Physical therapy Corticosteroid injections (in select cases) Surgical Intervention: Reserved for severe cases or failure of conservative management. Nerve decompression may provide symptom relief in selected patients. .Quizzes 1. The musculocutaneous nerve arises from which cord of the brachial plexus? ✔️ A. Lateral cord B. Medial cord C. Posterior cord D. Anterior cord Explanation: The musculocutaneous nerve originates from the lateral cord of the brachial plexus, primarily deriving fibers from C5-C7. 2. What is the primary motor function of the musculocutaneous nerve? ✔️ A. Elbow flexion and forearm supination B. Shoulder abduction C. Wrist extension D. Finger flexion Explanation: The musculocutaneous nerve controls elbow flexion and supination of the forearm, particularly when the elbow is flexed. 3. The musculocutaneous nerve pierces which muscle in the upper arm? ✔️ A. Coracobrachialis B. Brachialis C. Biceps brachii D. Triceps brachii Explanation: The musculocutaneous nerve pierces the coracobrachialis muscle before continuing distally. 4. The musculocutaneous nerve provides sensory innervation to which area? ✔️ A. Lateral forearm B. Medial forearm C. Posterior arm D. Palmar hand Explanation: The musculocutaneous nerve terminates as the lateral antebrachial cutaneous nerve, providing sensation to the lateral forearm. 5. A patient with musculocutaneous nerve injury will have the greatest weakness in which motion? ✔️ A. Elbow flexion B. Shoulder abduction C. Wrist extension D. Finger flexion Explanation: The musculocutaneous nerve primarily controls elbow flexion via the biceps brachii and brachialis muscles.