*2.5.1.2 Thoracic outlet syndrome (TOS)*

**Anatomy:** The thoracic outlet formed by the clavicle and the first rib is an anatomical region in the lower part of the neck through which important neurovascular structures. The thoracic outlet contains 3 spaces, called the interscalene triangle, costoclavicular space, and subcoracoid space, where neurovascular structures can

## *Upper Extremity Entrapment Neuropathy DOI: http://dx.doi.org/10.5772/intechopen.98279*

be compressed. The first anatomical stenosis encountered while the neurovascular bundle moves from the lower part of the neck towards the axillary region and the proximal part of the arm is an interscalene triangle. This triangle is bordered anteriorly by the anterior scalene muscle, posteriorly by the middle scalene muscle and inferiorly by the medial surface of the first rib. Brachial plexus and subclavian artery are located in this triangle. The 2nd and 3rd anatomical stenosis regions are the costoclavicular space, and the subcoracoid space. The middle third of the clavicle from the anterior, the first rib from the posteromedial and the upper order of the scapula from the posterolateral form the borders of costoclavicular triangle. The third space is the subcoracoid space under the coracoid process. The brachial plexus or its branches can be compressed in one of these spaces (**Figure 3**) [21, 22].

**Description:** Thoracic outlet sydrome is a condition that compression of the neurovascular bundle (brachial plexus and subclavian vessels) exiting the thoracic outlet [1, 21].

**Causes:** The compression that causes the syndrome can occur due to various anomalies of the bone and soft tissues. Bony abnormalities include the abnormal protrusion of the first rib or clavicle, the presence of a cervical rib, improper union or nonunion of the bone after fracture, or bone healing with excess callus

#### **Figure 3.**

*The schematic drawing of entrapment sites (interscalene triangle, costoclavicular space, subcoracoid space) of the brachial plexus in the thoracic outlet syndrome.*

#### *Demyelination Disorders*

tissue and retrosternal dislocation of the clavicle. Soft tissue anomalies include such as the presence of a fibrous band in the interscalene triangle, the presence of accessory neck muscles (minimus scalene muscle), anterior scalene hypertrophy, variations in scalene muscles and soft tissue tumors such as a Pancoast's tumor [1, 21]. It has been reported that congenital or post-traumatic malformations can cause compression, as well as due to occupational disease or due to excessive use in athletes who frequently perform overhead and throwing activities [23, 24]. Repeated overhead use by athletes engaged in this sport leads to loss of stability of the shoulder girdle and hypertrophy of the scalene muscles and pectoralis minor muscle. As a result, compression may occur in neurovascular structures in the region [25].

**Clinical features:** Neurogenic TOS involve include paresthesia, numbness,, and weakness radiating from the neck region and shoulder and extending into the arm and hand. TOS can cause paresthesia in a wide area. Symptoms can be seen unilateral or bilateral. Pain is felt especially over the trapezius muscle [1, 9, 24].

## *2.5.2 Impingement syndromes around the shoulder*
