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Medial Antebrachial Cutaneous Nerve (MABC)

Key Points:
• Patient complaints of pain at the elbow/medial forearm area require examination of this nerve, especially after ulnar nerve decompression at the elbow or other medial elbow-related surgery/injury.
Sensory Innervation:
• Provides sensation to the medial cutaneous aspect of the arm.
• Originates from roots C8, T1 and branches from the medial cord.
Nerve Grafting: This nerve is expendable to use as a nerve graft and sensory examination of this nerve will confirm its utility. Specifically, the anterior branch of MABC can be harvested while sparing the posterior branch.
Sensory examination includes testing the medial forearm sensory territory innervated by the medial antebrachial cutaneous nerve.
Sensory Examination:
• Ask patients to draw area of diminished sensation/numbness on a body diagram.
• Testing the skin along the medial aspect of the forearm for reduced/absent sensation by use of light touch or other sensory examination modalities.
Clinical Relevance:
• Provides sensation to the medial forearm.
• The posterior division of MABC specifically provides sensation to the natural resting surface of the elbow and forearm.  As such, the posterior branch should be spared if the MABC is harvested for graft material.
• The anterior division of MABC is expendable and can be used as graft material. Harvest of this nerve generally is done with the tourniquet down as it is easily found in the proximal arm with a larger nerve diameter. Therefore, harvest of MABC requires the removal of the tourniquet unlike the lateral antebrachial cutaneous nerve which is harvested in the antecubital fossa distal to an arm-level tourniquet.
• This nerve can be injured during medial elbow surgical procedures and can lead to painful neuroma formation when injured. Patients will complain of neuropathic pain at the medial elbow and distal forearm. Procedures within the nerve course vicinity include ulnar nerve decompression/transposition.
Adjacent Sensory Distribution:
PROXIMAL – Medial brachial cutaneous nerve.
LATERAL/ANTERIOR – Lateral antebrachial cutaneous nerve.
LATERAL/POSTERIOR – Posterior antebrachial cutaneous nerve.
DISTAL/ANTERIOR – Palmar cutaneous branch of ulnar nerve.
DISTAL/POSTERIOR – Dorsal cutaneous branch of ulnar nerve.
Relevant Anatomy:
• Roots: C8, T1.
• Nerve: Medial antebrachial cutaneous nerve,
• Sensory Territory: Medial aspect of the forearm.
• Innervation Route: C8, T1 → medial cord → medial antebrachial cutaneous nerve.
Course: The medial antebrachial cutaneous (MABC) nerve branches from the medial cord or the brachial plexus at a point just distal to where the medial brachial cutaneous nerve branches off. They course through the arm in close proximity to each other as well as the basilica vein. The MABC nerve continues distally in the distal forearm and separates into two main branches (anterior branch and posterior branch) to innervate the elbow and the medial aspect of the forearm. The anterior branch continues distally through the elbow region to innervate the medial aspect of the forearm, while the posterior branch continues posterior to innervate the posterior cutaneous aspect of the elbow.
Nerve Grafting: The anterior branch of the medial antebrachial cutaneous (MABC) nerve is often used as grafting material due to the ease of harvesting this nerve within the arm and the expendability of the respective forearm sensory territory. The posterior branch of the MABC nerve is less expandable due to the sensory territory (resting surface of the elbow/forearm) that it innervates. Therefore, this specific nerve branch should be preserved to prevent future difficulties (pressure sores, etc.) due to loss of sensation.