A rare case of tendinous clavicular insertion of the trapezius muscle: Could it be a cause for supraclavicular nerve entrapment syndrome?

Supraclavicular nerve entrapment syndrome is a rare cause for anterior shoulder girdle pain. This syndrome is usually related to anatomic variants involving the bones, fibrous bands, muscles, and tendons. Here, we report a case of an unusual tendinous insertion of trapezius muscle with the possible entrapment of the supraclavicular nerves. The tendon appeared from the muscle fibers and inserted into the clavicle along the posterior boundary posterior triangle and ran forward above the clavicle and inserted into the clavicle, apart from the insertion of the sternocleidomastoid muscle, along with the few additional slips of the sternocleidomastoid muscle. The supraclavicular nerve coursed downward deep into this variant tendon and its lateral division and then passed through the gap formed between the tendon and the clavicle. In addition to this, the external jugular vein (EJV) passed through the same thin gap. Clinicians should be aware of such rare variations, which might be a possible cause for the supraclavicular nerve entrapment syndrome.