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The axillary nerve is a nerve in the human body that supplies the deltoid and teres minor muscles. It originates from the brachial plexus at the level of the axilla (armpit) and carries nerve fibres from C5 and C6. The axillary nerve is vulnerable to damage during shoulder operations and sports injuries, which can result in paralysis and loss of sensation in the affected muscles. It has both sensory and motor functions, with the motor branches innervating the deltoid and teres minor muscles, and the sensory component supplying the skin of the lateral arm overlaying the deltoid.
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What You'll Learn
- The axillary nerve supplies the deltoid muscle
- It also supplies the teres minor muscle
- The axillary nerve carries sensory information from the shoulder joint
- It innervates the skin, covering the inferior region of the deltoid muscle
- Injury to the axillary nerve can result in atrophy of the deltoid muscle
The axillary nerve supplies the deltoid muscle
The axillary nerve is a nerve in the human body that provides both sensory and motor innervation to the deltoid muscle. It originates from the brachial plexus, specifically the upper trunk, posterior division, and posterior cord, at the level of the axilla (armpit). This nerve plays a crucial role in the functioning of the deltoid muscle, which is located in the shoulder region.
The axillary nerve has two main branches: the anterior branch and the posterior branch. The anterior branch wraps around the surgical neck of the humerus bone and innervates the anterior portion of the deltoid muscle. This branch also gives rise to small cutaneous branches that pierce the muscle and supply the overlying skin. The posterior branch, also known as the lower branch, supplies the posterior or back part of the deltoid muscle. It pierces the deep fascia, a type of connective tissue, and continues as the superior lateral cutaneous nerve of the arm. This nerve sweeps around the posterior border of the deltoid, supplying the skin over the lower part of the muscle.
The axillary nerve is particularly important for the movement and stability of the shoulder joint. The deltoid muscle, innervated by the axillary nerve, acts as an abductor, flexor, and extensor at the shoulder joint. This means it facilitates movements such as lifting the arm to the side, forward, or backward. The axillary nerve also provides sensory information from the shoulder joint, allowing individuals to be aware of the position and movement of their shoulder.
Injuries to the axillary nerve can have significant consequences for the deltoid muscle. Damage to this nerve can result in atrophy or wasting of the deltoid muscle, leading to a loss of the normal rounded appearance of the shoulder and giving it a flattened look. This condition is often seen in athletes who participate in contact sports, as the axillary nerve is vulnerable to injury during shoulder dislocations or fractures of the humerus bone.
Additionally, irritation or compression of the axillary nerve can result in various symptoms such as paresthesia, numbness, tingling, or loss of sensation in the area. Prolonged injury or compression can lead to progressive muscle weakness and atrophy. In some cases, direct neurotization or nerve transfers may be considered for treatment when direct repair or grafting of the axillary nerve is not feasible.
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It also supplies the teres minor muscle
The axillary nerve supplies the teres minor muscle. The teres minor is a rotator cuff muscle that externally rotates and adducts the arm. It originates from the scapula and extends to the head of the humerus. It is innervated by the axillary nerve, specifically the posterior branch of the axillary nerve, where it forms a pseudoganglion. A pseudoganglion contains no nerve cells, but nerve fibres are present.
The axillary nerve travels through the quadrangular space with the posterior circumflex humeral artery and vein to innervate the teres minor. The nerve lies behind the axillary artery and in front of the subscapularis, passing downward to the lower border of the muscle. It then winds around the neck of the humerus, through the quadrangular space, and divides into anterior and posterior branches. The posterior branch supplies the teres minor and the posterior part of the deltoid muscle.
The axillary nerve is vulnerable to injury, particularly in contact sports, and damage to the nerve can result in paralysis of the teres minor muscle. This can lead to a loss of abduction of the arm, weak flexion, extension, and rotation of the shoulder. One specific injury that can affect the axillary nerve is quadrangular space syndrome, which occurs when the muscles of the quadrangular space hypertrophy and impinge on the axillary nerve. This can result in atrophy of the teres minor muscle.
The teres minor muscle can be assessed using ultrasonography and MR angiography. Ultrasonography can detect fatty degenerative atrophy of the muscle, while MR angiography provides a detailed assessment of the artery. Denervation injuries of the teres minor are relatively common, and MRI examinations can help identify muscle edema and fatty infiltration associated with denervation.
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The axillary nerve carries sensory information from the shoulder joint
The axillary nerve travels through the quadrangular space, a region bordered by the teres minor muscle superiorly, the teres major muscle inferiorly, the long head of the triceps brachii medially, and the surgical neck of the humerus laterally. It exits the axilla by passing through this quadrangular space, alongside the posterior circumflex humeral artery and vein. After exiting the quadrangular space, the axillary nerve divides into anterior and posterior branches.
The anterior branch of the axillary nerve wraps around the surgical neck of the humerus and innervates the deltoid muscle, a muscle of the shoulder. It also gives off small cutaneous branches that supply the skin overlaying the muscle. The posterior branch supplies the teres minor, one of the rotator cuff muscles, and the posterior portion of the deltoid. This branch pierces the deep fascia and continues as the superior lateral cutaneous nerve of the arm, supplying the skin over the lower part of the deltoid and the upper part of the long head of the triceps brachii.
The axillary nerve is vulnerable to injury, especially during shoulder operations or in athletes who participate in contact sports. Injury to the axillary nerve can result in paralysis and atrophy of the teres minor and deltoid muscles, causing a loss of abduction, flexion, extension, and rotation of the arm at the shoulder joint. It can also lead to sensory deficits, including numbness, tingling, and loss of sensation in the skin over the regimental badge area, which is innervated by the superior lateral cutaneous nerve branch of the axillary nerve.
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It innervates the skin, covering the inferior region of the deltoid muscle
The anterior interosseous nerve (AIN) is a branch of the median nerve that supplies the deep muscles on the anterior of the forearm. The median nerve itself is formed from the roots of the fifth, sixth, seventh, and eighth cervical nerves, as well as the first thoracic nerve. These nerve roots form the brachial plexus, which divides to form the medial and lateral cords, which then converge to form the median nerve.
The AIN classically innervates 2.5 muscles. It provides motor innervation to the deep forearm muscles, including the flexor digitorum profundus (FDP) muscle to the index (and sometimes the middle) finger, the flexor pollicis longus (FPL) muscle to the thumb, and the pronator quadratus of the distal forearm. The AIN also has a large sensory nerve to the volar wrist bones. Compression of the AIN branch of the median nerve at the elbow can cause referred pain in the volar wrist/distal volar forearm.
The AIN passes deep to the pronator quadratus muscle, terminating close to the wrist joint. It runs along the volar surface of the FDP, coursing along the interosseous membrane between the ulna and radius, FDP, and FPL, branching to innervate these muscles. It ends in the pronator quadratus near the wrist joint.
The AIN does not provide cutaneous innervation. However, it does provide some sensation to the distal radioulnar and carpal joints and joint capsule. The terminal branch of the AIN travels through the posterior surface of the pronator quadratus, where it also provides sensory branches to the carpal bones of the wrist.
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Injury to the axillary nerve can result in atrophy of the deltoid muscle
The axillary nerve is a nerve in the human body that provides motor and sensory innervation to the upper limb. It originates from the brachial plexus and travels through the quadrangular space to innervate the deltoid and teres minor muscles. The axillary nerve is responsible for the abduction, flexion, and extension of the arm at the shoulder joint.
Injury to the axillary nerve can occur due to various reasons, including anterior-inferior dislocations of the shoulder joint, compression of the axilla with a crutch, or fracture of the surgical neck of the humerus. This nerve is particularly vulnerable to damage during shoulder operations, making it the most common peripheral nerve injury in athletes who participate in contact sports.
When the axillary nerve is injured, it can result in paralysis or atrophy of the muscles it innervates, including the deltoid muscle. Atrophy of the deltoid muscle leads to a loss of the normal rounded appearance of the shoulder, giving it a flattened look. The arm will also hang to the side in an adducted position due to the failure of the deltoid muscle to counter the adductor muscles in the arm and chest.
Additionally, injury to the axillary nerve can cause sensory deficits, such as numbness, tingling, and loss of sensation in the skin over the regimental badge area. Prolonged injury can lead to progressive muscle weakness and atrophy, further exacerbating the condition.
Treatment options for axillary nerve injuries include direct neurotization with donor nerves or nerve transfers using other nerves, such as the spinal accessory nerve or upper intercostal nerves. However, patients seen longer than 15 to 18 months after trauma may not benefit from surgical repair due to the potential poor condition of the deltoid muscle.
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Frequently asked questions
The axillary nerve innervates the deltoid and teres minor muscles. It also carries sensory information from the shoulder joint and innervates the skin covering the inferior region of the deltoid muscle, known as the regimental badge area.
Injury to the axillary nerve can result in paralysis of the teres minor and deltoid muscles, leading to a loss of arm abduction, weak flexion, extension, and rotation of the shoulder. It can also cause loss of sensation in the skin over the regimental badge area. In newborn deliveries, failure of the Moro reflex can be a sign of axillary nerve injury.
The axillary nerve has one named branch, the superior lateral brachial cutaneous nerve, and two unnamed muscular branches that serve the deltoid and teres minor muscles.
