The olecranon is a bony prominence of the ulna that represents that bone’s most proximal posterior surface at the elbow. While the olecranon is an attachment site for several muscle groups including the flexor carpi ulnaris and anconeus, the major muscle attachment is that of the triceps. The olecranon can thus be fractured (avulsed) by a traction force from triceps contracture. The relatively superficial position of the olecranon renders it susceptible to direct trauma as well. Displaced fractures of the olecranon often disrupt the articular surface of the elbow joint; these have to be realigned with surgery. Further, because the triceps can displace fractures that were originally not displaced, and because the elbow is relatively intolerant of prolonged immobilization, surgical treatment rather than casting is often needed even for fractures with minimal displacement.
Figure: Radiograph of displaced fracture. (http://www.wikiradiography.com/page/Imaging+Olecranon+Fractures)
Structure and function
The olecranon is a strong process of the proximal and posterior ulna that, together with the coronoid process, forms the trochlear notch. This notch holds the trochlea of the distal humerus forming the ulnohumeral articulation, the hinge joint of the elbow.
The trochlear notch is covered with articular cartilage, therefore most olecranon fractures (except the ones occurring exclusively on the tip) are, by definition, intra-articular fractures.
Successful treatment of olecranon fractures requires not only re-establishment of the extensor mechanism (which would be disrupted if/when a fracture displaces) but also preservation of elbow stability.
The main side-to-side (valgus and varus) stabilizers of the elbow are the collateral ligaments and the ulnohumeral/radiohumeral articulation, which provide a buttress againstulnar or radial compressive forces laterally. The olecranon is an important secondary stabilizer too: it inhibits anterior translation of the ulna with respect to the distal humerus just as the coronoid process of the ulna resists posterior subluxation of the ulna.
The triceps muscle inserts into the proximal ulna and posterior third of the olecranon. Its fibers blend with the periostium of the olecranon, the lateral ligaments and the articular capsule, forming a strong fibrous covering. This fibrous covering prevents fractures from being dramatically displaced unless the force is so great that the soft tissues are ruptured along with fracture of the bone.
The lateral border of the olecranon is the attachment point for the anconeus muscle.
The ulnar nerve runs on the posterior aspect of the elbow, behind the medial epicondyle of the humerus; it then turns anteriorly joining the ulnar artery. The proximity if the ulnar nerve to the olecranon makes it vulnerable to injury when fractures occur.
The flexor carpi ulnaris originates (in part) from the medial border of the olecranon.
Patients with fractures of the olecranon present with elbow pain after direct elbow trauma or fall. The primary determination to be made on exam is whether the extensor mechanism is intact. (Varus/valgus instability is rarely encountered and pain may impede its detection anyway.)
The mechanism of injury often determines the fracture pattern. If there is a fall on a semi-flexed arm, when the hand strikes the ground, the triceps muscle forcefully contracts, resisting further flexion of the elbow. This “breaking the fall” reaction leads to breaking the bone: an avulsion fracture of the tip of the olecranon, pulled off by the triceps. This mechanism is more commonly seen in elderly patients.
Less frequently, the cause is direct trauma to the tip of the elbow, which usually leads to comminuted fractures. This is the most common mechanism in younger patients.
In elderly patients, the bone fracture is often an isolated finding. The diagnostic attention is paid to determine why the patient fell. In younger patients, the mechanism of injury is often of higher energy and diagnostic attention is paid to make sure that there are no associated injuries elsewhere.
Other less common mechanisms are hyperextension injuries, such as those resulting in elbow dislocation in adults or supracondylar fractures in children. These can fracture the olecranon when it is impacted against the olecranon fossa of the distal humerus. Repetitive loading due to muscle forces such as throwing is a rare cause of olecranon injuries in adults, however in young pitchers such stress fractures are relatively common.
Because most fractures of the olecranon involve the joint surface, there is generally hemorrhaging into the joint with a resultant effusion. This produces pain and swelling.
Given the subcutaneous location of the ulna, open fractures are possible and must be excluded on exam.
Ulnar nerve neurapraxia may develop in 2-5% of cases.
A standard lateral radiograph of the elbow is sufficient for evaluation of isolated olecranon fractures. A true lateral X-ray is of paramount importance because it helps to determine the extent of the fracture, degree of displacement, comminution, radial head subluxation, and the degree of articular surface involvement.
A non-displaced, transverse or slightly oblique intra-articular break near the base of the olecranon is the most commonly seen olecranon fracture.
If there is no obvious radiographic evidence of a fracture, detection of a "fat pad sign" on the lateral view may be used to establish the presence of a bony injury. The fat pad sign is caused by bleeding within the joint: the distension of the joint capsule elevates the fat pads on top of it. Note that there are both anterior and posterior fat pads, and it is the posterior that is more commonly involved with an olecranon fracture; an anterior fad pad sign suggests an injury to the radial head or neck.
Figure: A radiograph showing both anterior and posterior fat pad signs. The yellow line outlines the joint capsule lifting the fat pads off the shaft of the humerus. (Modified from http://upload.wikimedia.org/wikipedia/commons/8/89/Fettpolsterzeichen_pathologisch_Ellenbogen.png)
It is important to assess for fracture displacement potential on radiographs. That is, most olecranon fractures exhibit little or no displacement, but some may displace with elbow motion. Thus, a fracture is considered non-displaced only when the fracture gap is less than 2mm, even when the elbow is flexed at 90°.
Joint stability can also be inferred from radiographs. If the fracture involves more than 50% of the ulnohumeral articulation, the elbow can be assumed to be unstable. Associated lesions such as coronoid fractures, radial head fractures or torn collateral ligaments may also produce instability.
Olecranon fractures account for 10% of elbow fractures in adults but are much rarer in children. In the growing bone, the olecranon is comparatively short and thick; excessive forces on the elbow therefore typically break the distal humeral shaft, sparing the olecranon. Consequently, the presence of an olecranon fracture in a child suggests a primary bone disease such as osteogenesis imperfecta.
Anterior elbow dislocations often occur with associated olecranon fractures, especially when a direct blow posteriorly is suffered. Lateral radiographs confirm this association. Similarly, Monteggia fractures (ie a fracture of the proximal third of the ulna with dislocation of the head of the radius) can be produced by the same mechanism as an olecranon fracture; this would be detected with anteroposterior, lateral, and oblique radiographs of the elbow that includes the shaft of the ulna.
Supracondylar fractures of the humerus should also be considered, especially in children who fall on semiflexed arms and/or suffer direct blows on the elbow. Radial head fractures and fractures of the coronoid process may produce elbow instability and complicate olecranon fractures.
An abnormality in the relationship between the osseous landmarks (i.e., line and triangle formed by epicondyles and olecranon) may be used to distinguish between intra-articular fractures, dislocations and supracondylar fractures.
- Comminution of an olecranon fracture suggests higher energy and implies other associated injuries (which must be diligently excluded).
- Blood on the skin may signify an open fracture, perhaps sustained by the bone poking out when the fracture is maximally displaced, then retracting back into the skin when the bone straightens out somewhat.
- Inadequate imaging. Even if the presentation is classic for an isolated elbow injury, films of the wrist are also required.
Treatment options and outcomes
The treatment goals are to maintain a stable and anatomic reduction, achieve stability of the joint and enable early active motion .
Fractures with up to 2mm of displacement and an intact extensor mechanism may be treated with immobilization in a long arm cast for three weeks. The elbow should be placed between 45° and 90° of flexion. After one month (before radiographic union is expected), supervised gentle passive motion is started to limit joint stiffness. When radiographic evidence of union is achieved, active movement is encouraged.
Fractures with significant displacement (>2mm) or comminution may require surgical intervention because of compromised extending power. Approximately 70% of the extending power is estimated to be lost when the fracture is displaced more than 1.5 cm.
Tension band wiring or plating are the most common techniques for fixation. The rationale behind the tension band technique is that it transforms the tension forces (from the pull of the triceps) that would tend to displace the fracture into compression forces across the fracture line
Figure: A lateral x-ray showing tension band wiring of an olecranon fracture. (modified from http://www.wikiradiography.com/photo/9545649/tension+band+wiring+olecranon+fracture)
Figure: Drawing of tension band fixation. Without fixation, the pull of the triceps would tend to displace the fracture. (The lines of force are shown in green arrows). A tension band is constructed by passing a flexible metal wire (shown in blue) through a drill hole in the bone. It is then wrapped across the dorsal surface of the ulna and held in place by two rigid pins placed within the shaft of the bone (shown here in red). Thus, a fulcrum is created around which compression forces (shown here in white arrows) are generated across the fracture line (shown in yellow).
Excision of the fracture fragment and reattachment of the triceps tendon may be indicated in elderly patients or debilitated patients, especially when the fragment is too small or comminuted for successful internal fixation .
Olecranon fractures that are amenable to non-operative treatment heal well in almost all instances: good function is achieved by more than 95% of patients. Stiffness after casting is the primary complication.
In patients treated operatively, symptomatic hardware requiring removal is a common complication. Injury to the ulnar artery, the median or anterior interosseus nerves (AIN) is possible with penetration of the K-wires through the anterior cortex of the ulna.
Postoperative infection rarely occurs. Heterotopic ossification (bone tissue forming at an abnormal anatomical site, usually in soft tissue) occurs in 10-15% of patients. Loss of motion is rarely significant (usually less than 15° of extension) and nonunion occurs in about 1% of patients and is treated by internal fixation and bone grafting.
Risk factors and prevention
Risk factors include any underlying medical pathology that could cause a fall (e.g., muscle weakness), especially in older patients, and any pathology that could weaken the bone such as osteogenesis imperfecta, osteoporosis, steroid use, or vitamin D deficiency. Young pitchers are prone to stress fractures from overuse.
Elbow pads for high contact sports and activities may be used to protect from direct blows that could cause fractures.
In mixed martial arts competitions, an elbow drop (a move in which a fighter drives his elbow into the opponent's body) take advantage of the strength of the olecranon. It is forbidden primarily because of the risk to the recipient of the blow, though of course the striker may sustain a fracture, too.
Olecranon is a word of Greek origin whose second root is “kranion”, meaning head. (The word “cranium” has the same root.) Still, the olecranon should not be thought of as the “ulnar head” as the first root is “olene,” meaning “elbow,” not "ulna."
olecranon, ulna, ulnar nerve neurapraxia, triceps advancement, tension band wiring
Recognize on examination failure of the extensor mechanism, fracture displacement, and joint instability.
Correctly interpret radiographs and describe the fracture pattern.
Identify fractures that would require operative treatment.
Apply elbow immobilization until definitive treatment is obtained.