The spinal accessory nerve (cranial nerve XI) supplies sternocleidomastoid and the upper traps. Check out the image below from Mumenthaler and Schliack (1991). If injured, it can lead to a droopy and painful shoulder and difficulty with overhead activities. Anyone trained in physical examination should pick the problem quickly. It is also worth pondering some aspects of the anatomy of the nerve. It is quite superficial in the posterior cervical triangle, even palpable sometimes and it is also quite mobile -shoulder shrugging, protraction and retraction all give the spinal accessory a good physical workout.
Most of the literature points to injury post-surgery such as lymph node resection, with some reports of injury from trauma including whiplash and forced shoulder girdle retraction. Minor injury may well be missed and even inadvertently treated via muscle rehabilitation. Shoulder girdle depression manoeuvres especially in retraction surely mobilise the spinal accessory nerve and help provide a mechanically permissible environment.
The catchy headline comes from a case study in Finland. No aggression, it was all lovely stuff! But it is a reminder of the vulnerability of this cranial nerve and even though this is the only report of an injury post bite, I am sure it is not the only case of nerve injury from a misplaced hickey delivered by an enthusiastic teenager. Maybe we should provide education on safe and non-safe places for love bites.
Readers could also reflect – if cranial nerve XI is a motor nerve, how can it be painful? Obviously the nerve can’t hurt by itself but it can set up a sources of nociception from either or all:
- the denervated muscle
- the innervated connective tissue of the nerve
- a local immune response
- and motor nerves, including the accessory nerve probably have sensory fibres as well.
Happy but safe nibbling!
– David Butler
It could be that the droopy position of the shoulder sensitize the upper trunk of the plexus. The sternocleidomastoid and trapezius muscles receive fiber contributions from the second, third and fourth cervical nerves. This may also affect the shoulder girdle alignment so the levator scapulae muscles gets tensed and may cause shoulder pain. We know also that the nerve has visceral connections. It could be a referral pain.
These are my thoughts….