Surgical neck of humerus/ Surgical neck
The surgical neck of the humerus or collum chirurgicum in latin (‘collum’ meaning neck, and ‘chirurgicum’ meaning surgical) is the narrow region between the proximal end of the humerus and the superior half of the shaft.
There are two structures that lay directly posterior to the surgical neck: the axillary nerve (C5,C6) and the posterior circumflex humeral artery (arising from the axillary artery). Together they medially traverse the quadrangular space from the axilla and into the deltoid muscle region.
Most injuries of the proximal end of the humerus are fractures of the surgical neck, which gives it clinical importance. Unlike the expanded proximal region, this site is narrow and thus weaker. This is especially true with elderly people suffering from osteoporosis, who have brittle bones. The associated nerve (axillary) and artery (posterior circumflex humeral) can be prone to damage by fractures in this area. Despite it being a common fracture site, the damage of the associated structures is actually rare. However, nerve assessment should be done either way to rule out any possible neurological deficits.
In case of axillary nerve damage, paralysis of both teres minor and deltoid muscle can result. This causes loss of normal abduction and limits the flexion, extension, and rotation of the shoulder. Paralysis of the deltoid and teres minor muscles leads to a flat deformed shoulder appearance, depending on the severity of the nerve injury. This is due to muscle atrophy. Moreover, loss of sensation may occur over the upper lateral side of the arm, an area supplied by the superior lateral cutaneous branch of the axillary nerve.
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