Thoracic Outlet Syndrome

• Publication year: 2020
• Author: Peter Abaci, MD Los Gatos, California

Thoracic Outlet Syndrome

Peter Abaci, MD Los Gatos, California

Patients routinely present to occupational health clinics with complaints of upper-extremity pain, numbness, and weakness. While there are a number of well-established conditions and diagnoses that can present with these symptoms, thoracic outlet syndrome (TOS) is a less common and sometimes controversial diagnosis that also gets considered. But what is thoracic outlet syndrome, and where does it fit in the diagnosis and treatment of upper-extremity injuries?

Thoracic outlet syndrome comprises a varied and diffuse set of disorders that cause compression of what is termed the neurovascular bundle, comprising the brachial plexus, subclavian vein, and subclavian artery, as it exits through the thoracic outlet. The thoracic outlet is the area at the base of the neck between the clavicle and the first rib. It is marked off by the anterior scalene muscle in the front, the middle scalene muscle in the back, and inferiorly by the first rib. The brachial plexus is a network of nerves that carry input from the spinal cord to the arm and hands and that intertwine like the Los Angeles freeway system. Compression of any three of these components can lead to a diagnosis of TOS, but over 90 percent of the cases involve the nerves of the brachial plexus.

Causes

Trauma, repetitive motions, or anatomic variations can cause TOS. Traumatic causes are usually high-velocity or high-impact events like motor vehicle accidents. Whiplash injuries are a known source of TOS symptoms. In other cases, fractures or bruising can directly cause compression of nerves or vascular structures. Scar tissue formation can later put added tension on the neurovascular bundle.

Overuse or repetitive motion activities can lead to TOS. One way this can occur is by hypertrophy, or buildup, of certain key muscles that border the thoracic outlet, exerting pressure on the brachial plexus. Overuse can also lead to a buildup of inflammation, swelling, and scar tissue, and lots of physical exertion can lead to something known as strenuous thrombosis, where clotting can accumulate in the subclavian vein.

Many types of anatomic variations have been described as factors causing TOS, but the most common is probably the presence of a cervical rib. A cervical rib is an extra rib that forms at the base of the neck and can be seen in up to one percent of the population. While its presence can compress the thoracic outlet, not everyone with a cervical rib...