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Thoracodorsal Nerve

Key Points:
• Innervates the latissimus dorsi muscle.
• Originates from roots C6, C7, C8.
Physical examination of the thoracodorsal nerve includes the motor examination of the latissimus dorsi muscle.
Detailed Examination Links:
Latissimus dorsi
Summarized Examination:
• To assess the muscle and ensure substitutions are not made, both sides should be examined simultaneously as the patient coughs.  The muscle can be felt between the examiner’s thumb and fingers bilaterally (examiner stands behind patient) as the patient coughs.  The examiner will feel the normal latissimus dorsi contract, and can compare the test side with the contralateral, normal side using this double simultaneous exam technique.
Pathological Findings:
• Because the latissiums dorsi muscle has many possible substitutions (including the following: lateral abdominal muscles, posterior deltoid, teres major, quadratus lumborum, and biceps powered elbow flexion if resistance is given distally) clinical deficits are difficult to detect.  There are some specific activities such as weight lifting (latissiumus pull-down exercises), butterfly stroke in swimming and upside-down pushups where patients may perceive weakness on the pathologic versus normal side.  However, the relatively expendable nature of this muscle for flap surgery speaks to the minimal pathologic findings that are clinically perceived.
Clinical Relevance:
• Important nerve to examine because its function is often maintained in even very severe brachial plexus injuries, where it can act as a donor nerve for nerve transfer procedures.
Relevant Anatomy:
• Roots: C6, C7, C8.
• Nerve: Thoracodorsal nerve.
• Muscles Innervated: Latissimus dorsi.
• Innervation Route: C6, C7, C8 → posterior cord → thoracodorsal nerve → latissimus dorsi.