What is Thoracic Outlet Syndrome (TOS)?

• A. Compression of the neurovascular bundle in the thoracic outlet; due to postural defects such as forward head and rounded shoulders; with tight scalene/pectoralis and weak serratus anterior/lower trapezius.
• B. Compression of the brainstem.
• C. Disorder of the thoracic spine only with no neurovascular involvement.
• D. Peripheral nerve entrapment in the elbow.

Answer: (A)

Thoracic Outlet Syndrome involves compression of the neurovascular bundle as it passes through the thoracic outlet from the neck into the arm. Postural defects such as forward head posture and rounded shoulders crowd the space, and tight scalene muscles plus tight pectoralis minor can further narrow the outlet. Weakness in scapular stabilizers like the serratus anterior and lower trapezius reduces control of the shoulder blade, worsening the compression. This combination explains why symptoms appear in the upper limb—nerve, artery, or vein issues can arise depending on what part of the bundle is affected. The other options describe problems that don’t involve compression at the thoracic outlet or don’t affect the neurovascular structures in that region.