The joints and muscles of the elbow complex are designed to serve the hand. They provide mobility for the hand in space by shortening and lengthening the upper extremity. This allows the hand to be brought close to the face for eating and grooming or to be placed at a distance from the body equal to the length of the entire upper extremity. Rotation at the elbow complex provides additional mobility for the hand. In conjunction with providing mobility for the hand, the elbow complex structures also provide stability for skilled or forceful movements of the hand when performing activities with tools or implements. Many of the 15 muscles that cross the elbow complex1 also act at either the wrist or shoulder, and therefore the wrist and shoulder are linked with the elbow in enhancing the function of the hand.
The elbow complex includes the elbow joint (humeroulnar and humeroradial joints) and the proximal and distal radioulnar joints. The elbow joint is considered to be a compound joint that functions as a modified or loose hinge joint. One degree of freedom is possible at the elbow, permitting the motions of flexion and extension, which occur in the sagittal plane around a coronal axis. A slight bit of axial rotation and side-to-side motion of the ulna occurs during flexion and extension, and that is why the elbow is considered to be a modified or loose hinge joint rather than a pure hinge joint.2 Two major ligaments and five muscles are directly associated with the elbow joint. Three of the muscles are flexors that cross the anterior aspect of the joint. The other two muscles are extensors that cross the posterior aspect of the joint.
The proximal and distal radioulnar joints are linked and function as one joint. The two joints acting together produce rotation of the forearm and have 1 degree of freedom of motion. The radioulnar joints are diarthrodial uniaxial joints of the pivot (trochoid) type and permit rotation (supination and pronation), which occurs in the transverse plane around a longitudinal axis. Six ligaments and four muscles are associated with these joints. Two muscles are for supination, and two are for pronation. The elbow joint and the proximal radioulnar joint are enclosed in a single joint capsule but constitute distinct articulations.
Case 8-1: Patient Case
James Daly, a 40-year-old carpenter, has come into the clinic complaining of pain in his right lateral forearm. He says that he has experienced numerous episodes of pain in the same area over the past few years. Usually the pain lessens, but does not entirely disappear, after a short rest period of 1 or 2 days. The current episode of pain is more severe than those he has experienced in the past; it has continued for a much longer period of time and has not been relieved by a short period of rest. He reports that ...