In some cases, the SAN exits as a double branch, one passes to the SCM muscle and the other end towards the Trapezius muscle.
Article Anatomic relationship between the spinal accessory nerve and...
• The accessory nerve (XI) exits JF and located medial to digastric & stylohyoid muscles
• The XI n. cross, lateral and immediately posterior to IJV(70%). Can be medial to IJV (30%) and may split the vein in 3-5%.
• It lies lateral to the transverse process of the atlas, and the 0ccipital artery crosses the nerve
• Descends obliquely in level II (forms Level IIa and IIb )
• Penetrates the deep surface of the SCM & exits posterior surface of SCM 2 cm above the Erb’s point(were the great auricular nerve turns around the posterior border of SCM)
• Travels for 3 - 4 cm on levator scapulae
• Joined by branches of C3 & C4 (The contribution of these branches to the motor function of the trapezius is controversial)
• Enters the trapezius approx. 5 cm above the clavicle at approximately the junction of the lower and middle thirds of the muscle
It's not clear to me what your question is. If you have found a new pattern of division of the nerve then I would suggest you are in the best position to suggest a new classification, but as a jobbing surgeon I tend to just work on a descriptive classification (anterior to, posterior to or throught the IJV) and i would now just add an extra classification of a high division of the nerve. Can you post the full text of the article, ? It sounds interesting.
Thankyou; thats a very interesting article. I seem to spend a lot of time looking at the posterior border of the sternomastoid for the nerve as it emerges again from the muscle. This may help to explain why it can be difficult to find at times. When there appears to be a lot of disagreement between published articles it can be hard to know who to believe.
If you were involved in the original pub;lication, can I ask a couple of questions?
1. Was there any correlation between the two sides of a cadaver? i.e. If the nerve was unbranched on one side was it more likely to be unbranched on the other, or if it was connected to the CP one side was it more likely to be on the other side etc. etc?
2. I wonder if any of the morphological differences described by different authors may be because of their different location. The majority of early studies appear to have been conducted on caucasians. It is just about possible that there may be a subtle difference in the percentages of each distribution between different ethnic groups.I suspect this is probably not true, but your findings do seem significantly different from the established literature and I wonder why. What do you think?
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