I just had rather lengthy discussion with doctors at the James and from Vanderbilt about this issue. Everyone here is correct, to an extent. The radiation fibrosis causes stiffness and thickening of the tissues, which can a) provide a superficial tightening, and b) exert pressure on adjacent nerves. The nerve damage from the neck dissection is an independent comorbidity, particularly if Level V nodes were removed. Both the Spinal Accessory Nerve and branches from the brachial plexus can be involved, as they travel through the SCM, scalene and trapezius muscles.

I have all of the above, and just started an exercise regimen to improve range of motion and hopefully reduce stiffness.