National Board of Chiropractic Examiners (NBCE) Practice Test

In a patient diagnosed with TOS (Thoracic Outlet Syndrome), which muscle is commonly affected due to compression?

1. Serratus Anterior

2. Scalenes

3. Pectoralis Major

4. Latissimus Dorsi

The correct answer is: Scalenes

In the context of Thoracic Outlet Syndrome (TOS), the scalene muscles, particularly the anterior and middle scalenes, are often implicated due to their anatomical location and function. These muscles are situated between the cervical spine and the first rib, which is a critical area where the brachial plexus and subclavian vessels pass. When TOS occurs, it is frequently due to compression or entrapment of these neurovascular structures as they traverse the thoracic outlet. The scalenes are involved in causing such compression because they can become tight or hypertrophied, leading to a reduction in the available space for the surrounding neurovascular structures. This can result in symptoms such as neuropathy, pain, and vascular claudication in the affected arm. While other muscles like the serratus anterior, pectoralis major, and latissimus dorsi play important roles in shoulder movement and stability, they are not typically the primary muscles associated with the compression phenomena seen in TOS. Understanding the role of the scalenes helps clarify why they are a central focus in discussions of Thoracic Outlet Syndrome.