Thoracic Outlet Syndrome
The thoracic outlet is the space between the anterior scalene muscles in the side of the neck and the rib cage. Nerves and blood vessels (neurovascular bundle), which originate in the cervical spine run, down the neck through the thoracic outlet, under the clavicle (collarbone), through the axilla (armpit) and extend further into the arm. These nerves and blood vessels allow for normal sensory and vascular supply.
Thoracic outlet syndrome (TOS) is a compression or irritation to the nerves and blood vessels passing through the thoracic outlet. Once these structures are compressed there will be sensation differences to the arm or forearm such as: pins and needles, pain, paraesthesia, loss of muscle strength and coldness.
There are several types of thoracic outlet syndrome. First, the neurovascular bundle can be compressed in or by the anterior scalene muscles at the side of the neck. Second, the presence of a cervical rib, which is an extra rib arising from the seventh cervical vertebra, can cause compression to the neurovascular bundle. Third, the thoracic outlet space can be reduced thereby restricting the neurovascular bundle. Lastly, the pectoralis minor muscle, which is located in the upper chest, can spasm, depress the scapula and cause a compression to the neurovascular bundle.
To define the various TOS, read below:
i) Anterior Scalene Syndrome
Anterior Scalene Syndrome - A Thoracic Outlet Syndrome where the neurovascular bundle is compressed by the scaleni anticus and medius muscles (anterior scalene muscles). These muscles can spasm due to some trauma or may become hypertonic due to unusual posture.
ii) Cervical Rib Syndrome
Cervical Rib Syndrome - A Thoracic Outlet Syndrome in which a rudimentary cervical rib located at the C7 vertebrae compresses the neurovascular bundle. The presence of rudimentary or extra cervical rib is very small, about 1% of the population will have a cervical rib.
iii) Costoclavicular Syndrome
Costoclavicular Syndrome - A Thoracic Outlet Syndrome where there is narrowing of the space between the clavicle and first rib. This results in compression of the brachial plexus (nerve bundle) and subclavian artery.
iv) Pectoralis Minor Syndrome
Pectoralis Minor Syndrome or Hyperabduction Syndrome is a Thoracic Outlet Syndrome where the pectoralis minor muscle spasms, compressing the brachial plexus (nerve bundle). Occupations with a high rate of repetitive movements will produce sustained muscle tension and result in symptoms.