bubble_chart Overview

The anterior scalene muscle is located deep in the lateral part of the cervical spine, originating from the anterior tubercles of the transverse processes of the third to sixth cervical vertebrae and inserting at the scalene tubercle on the inner edge of the first rib. The middle scalene muscle, the largest and longest of the three scalene muscles, arises from the posterior tubercles of the transverse processes of the lower six cervical vertebrae and attaches to the upper surface of the first rib, between the scalene tubercle and the subclavian groove. Between the anterior and middle scalene muscles lies a triangular space, with the first rib forming its base, through which the brachial plexus and subclavian artery pass.

bubble_chart Etiology

This disease is related to the triangular space formed by the neurovascular bundle passing through the scalene muscles.

1. Congenital malformation: The anterior and middle scalene muscles fuse into one, so the brachial plexus must split the fibers of the anterior and middle scalene muscles to pass through.
2. Hypertrophy of the anterior scalene muscle, which can be primary or secondary to spasms of the anterior scalene muscle caused by irritation of the brachial plexus.
3. The attachment point of the anterior scalene muscle is more lateral, resulting in narrowing of the triangular space.

All three of the above conditions can compress the neurovascular bundle, leading to scalene syndrome.

bubble_chart Clinical Manifestations

The anterior scalene syndrome occurs in middle-aged individuals, more frequently in women than in men, and more commonly on the right side than the left. Patients typically exhibit drooping shoulders and underdeveloped shoulder girdle muscles. Symptoms vary depending on the compressed tissue:

1. Compression of the subclavian stirred pulse: The pain is ischemic and throbbing, with a sudden onset accompanied by soreness and discomfort. It begins in the neck and radiates to the hand and fingers, with pronounced numbness and tingling. The pain lacks clear boundaries. Cervical movement exacerbates the pain, as neck extension narrows the scalene interval, intensifying the pain, while neck flexion widens the interval, providing relief. Traction on the affected limb, lowering the shoulder, worsens the symptoms.
2. Compression of the brachial plexus: This occurs in chronic cases where the lower trunk of the brachial plexus is compressed, causing sharp pain that radiates to the medial forearm and the 4th and 5th fingers.
3. Simultaneous compression of the subclavian stirred pulse and brachial plexus: Symptoms resemble those of a cervical rib.

Patients often support their head with their hand, tilting it toward the affected side to relieve tension in the anterior scalene muscle. The tense and tender anterior scalene muscle can be palpated in the supraclavicular fossa. Pressure on the muscle elicits severe tenderness and radiating pain, which worsens with neck extension. Sometimes, hypersensitivity, coldness, motor impairment, and loss of reflexes may occur in the hand. Local anesthetic injection can relieve anterior scalene muscle spasms and alleviate symptoms.

bubble_chart Auxiliary Examination

X-rays can be used to rule out deformities of the cervical and thoracic spine, such as cervical ribs or abnormalities of the first rib. Angiography is valuable for diagnosing this condition and can also locate the compression of the subclavian stirred pulse.

bubble_chart Treatment Measures

The results of conservative treatment are satisfactory. Injecting local anesthetics directly into the anterior scalene muscle immediately relieves symptoms, and sometimes even achieves a permanent cure. Tuina has certain therapeutic effects. If conservative treatment is ineffective and the symptoms become intolerable, surgical intervention should be considered. The surgical approach can be referenced to that for cervical rib surgery. During the operation, careful exploration should be conducted to identify the cause and location of compression on the brachial plexus and subclavian artery. The anterior scalene muscle should be severed, and the compressed nerves and blood vessels should be separated and decompressed.