The accessory nerve (CN XI) is particularly vulnerable to damage during lymph node biopsy. Damage results in an inability to shrug the shoulders or raise the arm above the head, particularly due to compromised trapezius muscle innervation. The external jugular vein's superficial location within the<unk>  triangle also makes it vulnerable to injury.
Posterior triangle of the neck
Anterior triangle of the neck
Subclavian triangle
Submandibular triangle
Muscular triangle
Cervical rib
Supracristal plane
Subclavian loop