Axillary (C5-6) injuries are caused by a fractured surgical neck of the humerus or an anterior dislocation of the humerus. It causes a

• flattened deltoid
• loss of arm abduction at the shoulder from 15º-100º (recall that 0º to 15º is done by the supraspinatus via the suprascapular nerve)
• loss of sensation over the deltoid and lateral arm

Musculocutaneous (C5-7) injuries are caused by upper trunk compressions and result in

• reduced biceps (C5-6) reflex
• weakness of forearm flexion and supination
• loss of sensation over the lateral forearm