The thoracodorsal nerve originates from the posterior cord of the brachial plexus. This nerve receives contributions from spinal nerves C6, C7 and C8. Due to its length and the fact that it arises between the superior and inferior subscapular nerves, the thoracodorsal nerve is also known as the middle subscapular or long subscapular nerve.
The thoracodorsal nerve is a pure motor nerve. Its main function is to provide motor innervation for the latissimus dorsi muscle, a broad, flat muscle that occupies the majority of the lower posterior thorax.
This article will discuss the anatomy and function of the thoracodorsal nerve.
|Posterior cord of brachial plexus (C6, C7, C8)
|Small terminal muscular branches
|Latissimus dorsi muscle
Origin and course
The thoracodorsal nerve is a motor nerve that arises from the posterior cord of the brachial plexus. It receives contributions from nerve roots C6-C8, but the predominant contribution is from C7. It originates near the apex of the axilla, between the superior and inferior subscapular nerves and posterior to the subscapular artery. Upon originating, it descends down the posterior axillary wall where it joins the neurovascular bundle of the latissimus dorsi muscle (thoracodorsal artery, vein and nerve).
As it courses inferiorly, the nerve initially lies posterior to the subscapular artery, but soon after crosses it and passes onto the anterior side of this artery, now named the thoracodorsal artery. The thoracodorsal artery and nerve then together across the inferior margin of the teres major muscle to pierce the latissimus dorsi muscle. In the muscle, the nerve gives off smaller motor branches that extend across the whole muscle and innervate it. The anatomical location of the thoracodorsal nerve is important in surgery, as this nerve is often used as a nerve graft.
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Branches and innervation
The thoracodorsal nerve carries solely motor fibers. Its main function is to innervate the latissimus dorsi muscle. When it reaches the muscle, the thoracodorsal nerve gives off several small terminal branches that reach the margins of the muscle and supply the whole muscle.
The latissimus dorsi is a flat and broad muscle that contributes to both thoracic and brachial (i.e. arm) motion.
Find out more about thoracodorsal nerve and other branches of the brachial plexus with the resources below!
Thoracodorsal nerve injury
Thoracodorsal nerve injuries are common complications of surgical procedures performed in the axillary region (e.g. surgical interventions for breast cancer patients). Due to this fact, it is very important to identify the thoracodorsal nerve and its anatomical relations in axillary clearance procedures.
The injury of this nerve is characterized by paresis or paralysis of the latissimus dorsi muscle. In other words, patients are unable to perform full extension, rotation, and adduction of the arm. In addition, the thoracodorsal nerve is often used as a nerve graft when the long thoracic nerve (C5-C7) is injured.
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