The humerus is the largest and longest bone of the upper extremity. The humerus articulates in its upper end with the scapula. This comprises the shoulder joint and, where it meets the bones of the forearm, the elbow joint as well. In between these joints, the humerus is a long tubular bone, or diaphysis.
One important structure closely associated with this long bone is the radial nerve. The nerve wraps around the bone in a spiral direction along its corresponding radial groove. The radial nerve gives innervation to the wrist and finger extensor muscles. Injury to it leads to significant motor dysfunction. There are multiple tendon insertions and muscular attachments along the bone that make its anatomy rather complex.
The radius and the ulna are the two long bones of the forearm.