The Anatomy of the Thoracodorsal Nerve

The thoracodorsal nerve, also known as the middle subscapular nerve or the long subscapular nerve, provides motor function to a large triangular muscle in your back called the latissimus dorsi muscle. The thoracodorsal nerve branches out from a part of the brachial plexus. It’s a purely motor nerve.

Anatomy

The nerves of the brachial plexus supply most of the sensory function (feeling) and movement (motor function) of your arms and hands. As with other nerves and nerve structures, you have one on each side.

Your nerves are structured much like trees. Roots emerge from the spinal cord, exiting between vertebrae, then joining to form larger structures (like a tree trunk), then sending out branches, which also give way to more branches.

The brachial plexus is a network of nerves that originate from the spinal cord in your neck. Its five roots come from the spaces between the fifth through eighth cervical vertebrae (C5-C8) and the first thoracic vertebra (T1). From there, they form a big trunk, then divide, re-combine, and divide again to form many smaller nerves and nerve structures as they travel down toward your armpit.

Along its course through your neck and chest, nerves of the plexus eventually join together and form three cords, the:

• Lateral cord
• Medial cord
• Posterior cord

The posterior cord gives rise to several branches, some major and some minor. The major branches are:

• Axillary nerve
• Radial nerve

Its minor branches include:

• Superior subscapular nerve
• Inferior subscapular nerve
• Thoracodorsal nerve

Structure and Location

The thoracodorsal nerve splits off from the posterior cord in your armpit and travels downward, following the subscapular artery, to reach the latissimus dorsi muscle.

The latissimus dorsi, which is often referred to as "the lats,” is the largest muscle in the upper body. It connects to your upper arm, stretches across the back of your armpit forming what’s called the axillary arch, then broadens out into a large triangle that wraps around your ribs and much of your back.

The lats are easy to see on the body, especially when they’re well developed. They’re what gives bodybuilders that distinctive angle between the shoulders and waist.

The thoracodorsal nerve burrows deep within the latissimus dorsi and typically reaches all the way down to its lower edge, which is near your waist.

Anatomical Variations

Nerves, and other parts of our anatomy, aren’t exactly the same in everyone. While there’s typically a “standard” location and course of the thoracodorsal nerve, different subtypes have been identified.

It’s essential for doctors to understand the non-standard physiology surround nerves, muscles, and other structures so they can properly diagnose and treat problems. Knowing about variants of anatomy is of utmost importance for surgeons so they don’t inadvertently damage a nerve during a procedure.

The thoracodorsal nerve is known to branch off from the posterior cord of the brachial plexus from three different points. Additionally, the thoracodorsal nerve supplies the teres major muscle in about 13% of people.

The lats have a rare but important anatomical variation called Langer’s arch, which is an extra part that connects to muscles or connective tissue of the upper arm beneath its typical connection point. In people with this abnormality, the thoracodorsal nerve supplies function (innervation) to the arch. Surgeons working in this area, such as while performing axillary lymph node dissection, must be careful to avoid damaging the muscle or its nerve.

Function

The thoracodorsal nerve is a pure motor nerve, meaning that it doesn’t supply sensory function (sensation) but only deals with movement.

The latissimus dorsi is an important muscle, and without the thoracodorsal nerve, it doesn’t function. This muscle and its nerve:

• Stabilize your back
• Pull your body weight up, such as when doing pull-ups, climbing, or swimming
• Assist with breathing by expanding your rib cage when you inhale and contracting it when you exhale
• Rotate your arm in
• Pull your arm in toward the center of your body
• Extend your shoulders (stick them out behind you), by working with the teres major, teres minor, and posterior deltoid muscles
• Bring down your shoulder girdle by arching your spine
• Help you bend to the side by arching your spine
• Tilting your pelvis forward

Associated Conditions

The thoracodorsal nerve may be injured anywhere along its course by trauma or disease.

Symptoms of nerve damage can include:

• Pain that may be shooting, stabbing, or like electrical “zaps”
• Numbness or abnormal nerve sensations (i.e., tingling, “pins and needles”)
• Weakness and loss of function in the associated muscles and body parts, including wristdrop and fingerdrop

Because of its path through the armpit (axilla), the thoracodorsal nerve is of concern during breast-cancer procedures, including axillary dissection. That procedure is performed to examine or remove lymph nodes and it’s used both in staging breast cancer and in treating it.

According to a 2015 study, 11.3% of people with axillary lymph node dissection had damage to the nerve.

Breast Reconstruction

In breast reconstruction surgery, the lats are often used as a “flap” over the breast implant. Sometimes, the thoracodorsal nerve is left intact in these procedures, but sometimes it’s severed.

The medical community hasn’t yet reached a consensus on which method has the best outcomes for the patient, but there’s some evidence that leaving it intact can cause the muscle to contract and dislocate the implant.

An intact thoracodorsal nerve may also cause atrophy of the muscle, which can lead to shoulder and arm weakness that hampers numerous common movements, including standing up from a chair.

Rehabilitation

If the thoracodorsal nerve is damaged, treatments may include:

• Braces or splints
• Physical therapy to improve muscle strength
• If the nerve is compressed, surgery to remove the pressure