Description
The elbow is an inherently stable joint requiring a significant force to dislocate. Elbow dislocations require prompt identification and treatment and are most often associated with osteochondral injuries and post-traumatic stiffness
Structure and function
The elbow joint is composed of the distal end of the humerus and the proximal ends of the radius and the ulna, and consists of three articulations: the highly congruent ulnohumeral joint that allows for the hinge-like movement of flexion and extension and the radiohumeral and proximal radioulnar joints that allow for the forearm rotation movements of pronation and supination.
A synovial membrane surrounds the elbow joint, which is lined with a joint capsule. The capsule thickens on the medial and lateral sides into distinct ligaments. The medial side contains the strong medial collateral ligament (MCL) that consists of three bands (anterior, posterior, transverse) and primarily resists a valgus stress (Figure 1). The lateral ligaments include the lateral (radial) collateral ligament (LCL) and the lateral ulnar collateral ligament (LUCL) that provide rotatory stability (Figure 2). The annular ligament encircles the radial head and stabilizes the proximal radioulnar joint.
Figure 1. The medial elbow ligaments. The anterior band of the MCL extends from the medial epicondyle of the distal humerus to the coronoid process of the ulna. The posterior band of the MCL extends from the olecranon inserting onto the coronoid process.
Figure 2. The lateral elbow ligaments. The LCL extends from the lateral epicondyle of the distal humerus to the radial head. The lateral ulnar collateral ligament spans the lateral epicondyle to the proximal ulna and the annular ligament encircles the radial head with an ulnar attachment.
The ulnohumeral articulation is the primary osseous stabilizer of the elbow joint. The trochlear notch of the proximal ulna forms a “C” shape with the anterior inferior portion called the coronoid process. The coronoid acts as an anterior buttress to posterior dislocations.
In order to dislocate the elbow, there must be a complete or near complete disruption of the capsuloligamentous stabilizers. The progression of injury is from lateral to medial, first with failure of the LCL then the MCL, depending on the degree of energy involved.
Epidemiology
Elbow dislocations constitute 10-25% of all injuries to the elbow and are second only to dislocations of the shoulder among injuries to the upper extremity
. Elbow dislocations occur more often in males and adults with a mean age of 30, as same force in children more often results in a supracondylar fracture of the distal humerus
Clinical presentation
Patients present after an acute injury with soft tissue swelling and deformity about the elbow. The mechanism of injury for a posterior dislocation is a fall onto an extended abducted arm and is rarely associated with any neurovascular injury. Anterior dislocations occur as a result of a strong blow to the posterior aspect of a flexed elbow. Although rare, anterior dislocations are more commonly associated with injury to the brachial artery or the median nerve. A thorough neurovascular exam is required before and after reduction of the elbow as well as an exam of the wrist and shoulder.
Elbow dislocations are described based on the anatomic location of the olecranon relative to the distal humerus with posteriolateral being most common (80%). The injuries can be further classified into simple- no associated fracture, or complex- a fracture is present.
Red flags
Examine any evidence of bleeding around the elbow to exclude an open injury. Examination should also include the forearm to exclude compartment syndrome, and the wrist and shoulder since a concomitant injury may be present in 10-15% of cases
Differential diagnosis
Suspect an elbow dislocation in an adult presenting with a painful, deformed elbow after sustaining a high-energy trauma. Pediatric patients more commonly present with fractures about the elbow especially supracondylar fractures of the distal humerus. A nursemaid elbow, a dislocated radial head, should also be considered in children ages 1-4 with a painful, flexed elbow that they are unwilling to move.
Radiographs can exclude fractures of the olecranon, radial head, distal humerus and forearm. An elbow dislocation with spontaneous reduction should also be considered in a patient with a swollen painful elbow after a traumatic event with normal radiographs.
Damage to the articular cartilage of the distal humerus or radial head may not be evident on plain radiographs unless a large displaced fragment is present.
Soft tissue injury to the LCL, MCL or the interosseous membrane of the forearm should also be excluded in the presence of normal radiographs.
Objective evidence
AP, lateral and oblique radiographs of the elbow are necessary to evaluate a traumatic elbow injury. Oblique views can be helpful in identifying periarticular fractures. The position of the olecranon relative to the distal humerus and an associated radial head or coronoid fracture should be described (Figure 3).
Figure 3. Lateral radiograph of the elbow showing an anterior dislocation.
Post reduction AP, lateral and oblique films should always be obtained immediately following reduction. These are required to document a congruent reduction and to rule out any previously unidentified fracture or entrapped bony fragments within the joint space.
Following reduction, a CT scan may be performed to further identify osseous injury when there is a high suspicion of periarticular fracture or an incongruent reduction. Arteriography may be required to investigate a devascularized limb if a vascular injury is suspected.
The fat pad sign is sometimes seen on lateral radiographs of the elbow following trauma (Figure 4). Elevation of the anterior and posterior fat pads suggests a hemarthrosis and the presence of an occult intracapsular fracture
. Although the presence of an anterior fat pad sign if often normal in an elbow radiograph, a posterior fat pad sign is always abnormal and suggests underlying pathology.
Figure 4. Lateral radiograph of the elbow demonstrating an anterior and posterior fat pad sign.
Risk factors and prevention
There are no specific preventative measures beyond avoiding incidental trauma to the upper extremity. Motor vehicle accidents, sports injuries, and other high-energy mechanisms account for most elbow dislocations in young individuals
.
Treatment options
The goals of treatment include a concentric reduction of the elbow, immobilizing the elbow within a stable construct and early range-of-motion and rehabilitation.
After completing a detailed history and physical exam, a closed reduction should always be attempted in the emergency department. Adequate muscle relaxation and analgesia are essential in facilitating reduction, which is most often achieved with conscious sedation.
The reduction manoeuvre for a posterior dislocation first begins with inline traction to correct medial and lateral displacement of the elbow. The forearm should be supinated and pressure is applied to the tip of the olecranon while flexing the elbow. A palpable “clunk” is a favorable sign of joint reduction.
After reduction, the stability of the elbow must be examined. In posterior dislocations, the elbow is typically less stable in extension and therefore is splinted in at least 90 degrees of flexion. If the LCL is disrupted and the MCL intact, the elbow will be more stable in forearm pronation. If the LCL is intact and the MCL disrupted, the elbow will be more stable in supination.
Post-reduction radiographs are obtained to confirm a concentric reduction and exclude associated fractures. A posterior splint is applied with the appropriate forearm rotation for 5 to 7 days. Depending on stability, the splint can be removed for early range-of-motion exercises using a brace with or without an extension block.
Indications for surgical intervention include a failure to obtain stability of the elbow with reduction and immobilization, osteochondral fragment of soft tissue entrapment that prevents concentric reduction and complex dislocations with associated fractures.
Outcomes
Post-traumatic stiffness is much more common than instability after elbow dislocation. Most often, patients will lose the terminal 10-15 degrees of elbow extension. Early active mobilization in the first 2-3 weeks is helpful in preventing arthrofibrosis (pathologic thickening of the joint capsule).
Calcification of the soft tissues, aka heterotopic ossification, may occur in up to 75% of patients after an elbow dislocation but rarely limits motion
Post-traumatic rotatory instability as a result of lateral elbow ligament insufficiency is rare and a hinged elbow orthosis may be required during the rehabilitation period.
Miscellany
A “Terrible Triad of the Elbow” is characterized by an elbow dislocation with a lateral ulnar collateral ligament tear (LUCL), a radial head fracture and a coronoid fracture.
Key terms
Elbow dislocation, reduction, elbow instability, post-traumatic arthrofibrosis
Skills
Performing and documenting a detailed neurovascular exam of the upper extremity; identifying and describing abnormal pathology on an elbow radiograph; recognizing the urgency of reducing a dislocated elbow and the importance of post-reduction radiographs and physical exam; describing the emergency room management and splinting of an acute elbow dislocation.
References
Durig M, Muller W, Ruedi TP, Gauer EF: The operative treatment of elbow dislocation in the adult. J Bone Joint Surg Am 1979;61:239-244.
Mehlhoff TL, Noble PC, Bennett JB, Tullos HS: Simple dislocation of the elbow in the adult: Results after closed treatment. J Bone Joint Surg Am 1988;70:244-249.
Josefsson PO, Nilsson BE: Incidence of elbow dislocation. Acta Orthop Scand 1986;57:537-538.
Skaggs DL, Mirzayan R. The posterior fat pad sign in association with occult fracture of the elbow in children. J Bone Joint Surg Am. 1999 Oct;81(10):1429-33.
Cohen MS, Hastings H 2nd. Acute elbow dislocation: evaluation and management. J Am Acad Orthop Surg. 1998 Jan-Feb;6(1):15-23
Josefsson PO, Johnell O, Gentz CF: Long-term sequelae of simple dislocation of the elbow. J Bone Joint Surg Am 1984;66:927-930.