Which nerve is primarily affected by improper positioning of the lower arm?

The ulnar nerve is primarily affected by improper positioning of the lower arm due to its anatomical pathway and susceptibility to compression or traction injuries. The ulnar nerve runs along the inner side of the arm and passes behind the medial epicondyle of the humerus at the elbow, where it is particularly vulnerable. If the arm is positioned in a way that places stress or pressure on this area—such as excessive flexion, extension, or being compressed against a hard surface during a surgical procedure or inappropriately positioned during recovery—this can lead to ulnar nerve palsy. This condition can result in symptoms such as loss of sensation in the ring and little fingers, weakness in finger abduction, and difficulties with grip strength.

In contrast, while the median, radial, and axillary nerves can also be affected by arm positioning, their anatomical locations and the common types of positioning injuries suggest that they are less susceptible to damage compared to the ulnar nerve in this context. The median nerve, for instance, runs down the middle of the arm and could be affected by more generalized compression. The radial nerve is typically associated with wrist drop when injured, which usually occurs from compression in the upper arm region or a humeral fracture. The