Humerus extension

The bony structures of the elbow are the distal end of the humerus and the proximal ends of the radius and ulna. The elbow joint complex allows two degrees of freedom in motion flexion/extension and pronation/supination. The elbow joint complex is three separate synovial articulations. The humeral-ulnar joint is the articulation between the trochlea of the distal radius and the trochlear fossa of the proximal ulna. The humero-radial joint is formed by the articulation between the capitulum of the distal humerus and the head of the radius. The proximal radioulnar joint is formed by the head of the radius and the radial notch of the proximal ulna. 

Fig. 8.12. Oblique fracture of the humerus 3 weeks post-injury. Extensive callus is visible and outlining the stripped periosteum...

To prevent impingement, the lower end of the humerus has two fossae, one at the front and one at the back. This gives the human elbow a range of 0 -142° of flexion extension with 5 of further passive flexion. About 9 of abduction and adduction exist in the ulno-humeral joint. This range of movement is essential to complete the full arc of pronation and supination. 

The motions observed in the elbow joint are flexion, extension, and rotation (supination and pronation). Flexion and extension are the only motions that involve the true elbow joint, the ulna with the humerus. The elbow joint has the composite motions of elbow flexion, with forearm supination, and elbow extension, with forearm pronation. Therefore, the superior radioulnar joint and its motions complicate, and are part of, elbow joint motion. 

Humeroradial articulation consists of the concave head of the radius articulating with the convexshaped capitellum of the humerus. Motion of this articulation must accompany humeroulnar flexion-extension. This angular motion is accompanied by ventral and dorsal translatory slide of the radius on the humerus dorsal radial slide with extension and ventral radial slide with flexion (Fig. 81-2). Extension stress is the major cause of posterior radial head somatic dysfunction. 

Range of motion should be checked actively and passively. Extension is minimal because of bony impingement. Flexion will be limited by the size of the biceps muscle. Besides the gross motions of flexion, extension, supination and pronation, the motion of the head of the radius must be evaluated as it glides on the lateral ulna. The motions of abduction and adduction of the ulna on the humerus should be evaluated. 

Fig. 2 Schematic of elbow joint in (a) flexion (b) extension in 0 ,30 and 90 position. Point O was considered as center of rotation ulna about humerus. G=16N is gravity force of forearm...

The bone structures about the elbow joint include the proximal ends of the ulna and radius and the distal end of the humerus (Fig. 8.1). The radial head articulates with the humeral capitellum in a pivotal mode and the ulna with the humeral trochlea in a hinge mode. The proximal radio-ulnar articulation is composed of the radial head which revolves within the sigmoid (radial) notch of the ulna allowing pronation-supination movements. These articulations cooperate during complex joint movements allowing a wide degree of flexion, extension and axial... 

Fig. 8.2a,h. Elbow joint. Articular anatomy, a Schematic drawing of a midsagittal view through an extended elbow with b CT scan correlation demonstrates the articular relationship between the trochlea of the humerus (H) and the trochlear groove of the ulna (U), leading to flexion and extension joint movements. The extrasynovial anterior (asterisk) and posterior (star) fat pads are closely applied to the distal end of the humerus and lie just superficial to the joint space (in black). Note the insertion of the brachialis (Br) and the triceps (tr) muscles, which are the main flexor and extensor muscles of the elbow respectively... 

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