Olecranon Fossa

The blood supply to the capitellum is via end arterioles from the inferior ulnar collateral artery crossing the olecranon fossa posteriorly into the lateral condyle to the ossific nucleus of the capitellum. This predisposes to avascular necrosis following displaced capitellar fractures. 

The teardrop or hourglass sign is formed by the anterior margin of the olecranon fossa and the posterior margin of the coronoid fossa with the capitellum forming the inferior portion. The capi-tellum and trochlea (if ossified) should be super-... 

The articular surfaces of the elbow are contained within the joint capsule, which also encloses non-articular surfaces, including the coronoid, radial fossa and olecranon fossae. It attaches just distal to the coronoid and olecranon processes. The whole of the radial head is within the capsule. 

Three fat pads lie over the capsule, the anterior over the coronoid fossa, the posterior over the olecranon fossa and a third over the supinator as it wraps over the radius. Fracture, haematoma and effusion into an intact capsule may cause capsular distension, which can distort these fat pads, improving their visibility and identifying occult fractures (Fig. 18.4). In the setting of acute trauma, a visible... 

Some fractures may be reduced by closed manipulation and stabilisedby percutaneous K-wires. Evaluation of fracture reduction may be aided by intraoperative arthrogram. The most stable and therefore ideal configuration of K-wires is for a common entry point on the lateral edge of the condyle, with one wire running transversely to the medial condyle, and the second at about 60 aiming at the medial cortex above the olecranon fossa. 

Metaphyseal fractures can be classified according to mechanism of injury. The majority of injuries occur with the elbow in extension, the olecranon locked in the olecranon fossa and the maximum stress developed in the proximal metaphyseal region leading to fracture. When a valgus stress is applied, there may be asso ciated compression fractures of the radial neck and avulsion of the medial epicondyle. Varus stress is associated with radial head subluxation. 

The olecranon fossa appears as a wide and deep concavity of the posterior aspect of the humeral shaft filled with the hyperechoic posterior fat pad (Fig. 8.21a) (Miles and Lamont 1989). At both sides of this fossa, the posterior aspect of the medial and lateral epicondyles can be seen on transverse images. While examining the joint at 45 flexion, intra-articular fluid tends to move from the anterior synovial space to the olecranon recess, thus making the identification of small intra-articular effusions easier. Gentle rocking motion of the patient s elbow during scanning maybe helpful to shift elbow joint fluid into the olecranon recess. More distally, the... 

Fig. 8.71a,b. Synovitis of the elbow joint pitfall. a,b Transverse 12-5 MHz US images over the posterior olecranon recess a in a normal subject and b in a patient with rheumatoid arthritis and an olecranon recess (arrows) appears markedly distended by fluid. In a, the normal hypoechoic fat contained. In b the olecranon fossa, between the lateral (LE) and medial (ME) epicondyles, should not be confused with the synovitis process shown in b. In doubtful cases, careful dynamic examination with elbow flexion and extension movements may be helpful for the diagnosis. Note the erosion (arrowhead) on the posteromedial aspect of the lateral epicondyle. T, distal triceps tendon... 

Figure 28. Cross section of the arm through the proximal end of the olecranon fossa.

Extension of the elbow from the anatomic position is limited (5 to 10 degrees) by contact of the olecranon process with the fossa, tension in the anterior ligament, and resistance of anterior muscles. The triceps brachii is the only significant elbow muscle that functions in extension. There is some minor contribution by the anconeus. Because most elbow extension is accomplished by gravity, the triceps functions primarily against resistance. 

The elbow is one of the most stable joints of the body. In normal states, elbow joint motion ranges approximately from 0° to 150° of flexion and from 75° in pronation to 85° in supination. Elbow extension is limited by contact of the olecranon in the posterior humeral fossa, and tightening of the anterior band of the medial collateral ligament, of the joint capsule and of flexor muscles. On the other hand, the bulk of anterior muscles of the arm, the tension of the triceps and the contact of the coronoid process in the anterior humeral fossa limit elbow flexion. Pronation and supination movements are primarily limited by passive muscle constraints rather than ligaments. 

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