Michael A. Kuhn
Hervey L. Kimball
Glen Ross
Pathogenesis
Etiology
Once poorly defined, the mechanism of elbow dislocation is now better understood. Traditional teaching stated that the mechanism of injury was hyperextension. A fall on the outstretched hand is the most common cause. The elbow experiences an axial compressive force during flexion as the body approaches the ground. The body rotates internally, with the forearm rotating externally to the trunk. This results in a supination moment at the elbow. At that point, the mechanical axis of the extremity is medial to the elbow, resulting in a valgus moment. O'Driscoll and Morrey suggest that an extension varus stress disrupts the lateral ligament complex first. If this dissipates the force, then a perched dislocation is the result. Continued force causes forearm rotation tearing the capsule, resulting in a complete dislocation. This has been described as the “ring of instability” progressing from disruption of the lateral ulnar collateral ligament (LUCL) to the capsule, and finally injury to the medial ulnar collateral ligament (MUCL). With a slightly flexed elbow, a tear in the medial collateral ligament complex occurs and the elbow dislocates.
While the tensile forces around the elbow result in ligamentous disruption, substantial compressive and shear forces occur on the articular surface. This can cause fractures of the proximal radius. Dislocations treated by open procedures have documented chondral injuries to the capitellum and trochlear surfaces at higher rates than previously believed. Understanding the mechanism of injury is important for appreciating classification, interpreting radiographs, formulating a treatment plan, anticipating complications, and guiding follow-up care.
Epidemiology
The elbow is the most commonly dislocated major joint in the pediatric age group and the second most common in the adult population. It is estimated that 6 of every 100,000 individuals will sustain an elbow dislocation during their lifetime. Elbow dislocations constitute 10% to 25% of all injuries to the elbow. More than one half of dislocations involve the nondominant extremity. It has been suggested that there is a protective instinct using the dominant side to protect from a fall. The mean age of an individual sustaining this injury is 30 years. There is a male predominance with 2 to 2.5 that of females with similar ratios in children.
Approximately 40% of elbow dislocations occur during sports. Gymnastics, wrestling, basketball, and football are commonly involved. Approximately 40% of dislocations have a poorly defined causes.
Pathophysiology
The injury progresses as a circle of tissue disruption from lateral to medial and can be broken into three stages. Stage 1 involves disruption of the ulnar component of the lateral collateral ligament. This results in posterolateral rotatory subluxation of the elbow, which reduces spontaneously. With continued force, disruption occurs anteriorly and posteriorly allowing for an incomplete posterolateral dislocation. This is a perched dislocation. Stage 3 has two parts. In stage 3A, all soft tissues are disrupted including the posterior part of the medial collateral ligament. The anterior band of the medial collateral ligament remains intact. This allows for posterior dislocation by the previously described posterolateral rotatory mechanism. In stage 3B, the entire medial collateral complex is disrupted. Varus, valgus, and rotatory instability are present. Surgical experience suggests that the medial collateral complex is disrupted in nearly 100% of elbow dislocations. Violation of the anterior bundle of the medial collateral ligament is considered the essential lesion. Disruption proximally from the humerus is most common. Dislocation is the final of three sequential stages of elbow instability, resulting from posterolateral ulnohumeral
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rotatory subluxation, with soft tissue disruption occurring from lateral to medial.
Classification
Traditional classification divides elbow dislocations into posterior, anterior, and divergent. Anterior dislocations are uncommon, occurring in only 1% to 2% of incidents. Anterior dislocations are usually seen in younger individuals. Posterior dislocations are divided based on the final relationship between the humerus and olecranon into posterior, posterolateral, posteromedial, and pure lateral dislocations. Posterolateral is most common, followed by lateral, and least commonly, posteromedial. A divergent dislocation is a rare injury associated with high-energy trauma. Displacement of the radius from the ulna occurs, resulting in disruption of the interosseous membrane, annular ligament, and distal radioulnar joint capsule.
Morrey proposed a simple classification distinguishing between a perched and complete dislocation. A medial or lateral resting position of the complete dislocation makes little difference with regard to treatment or prognosis. A perched dislocation is one in which the elbow is actually subluxated but the coronoid appears to impinge on the trochlea. In this type, the ligaments are less severely injured, and rehabilitation can be more rapid and recovery more complete.
Diagnosis
Evaluation
Prior to any reduction, assessment of neurovascular status is mandatory. Anteroposterior and lateral radiographs should be obtained if possible. Evaluation of associated injuries should be reserved until reduction has been obtained. Computerized tomography and magnetic resonance imaging are often of limited value. These are reserved if adequate radiographs cannot be obtained, and can be used for later reconstructive planning.
Associated Injuries
Associated injuries with elbow dislocation are common. Radial head and neck fractures occur in 5% to 10% of elbow dislocations. Avulsion fractures of the medial or the lateral epicondyles occur in approximately 12% of the cases, and coronoid fractures occur in 10% of dislocations. The incidence of associated fractures in children is high, approaching 50%. With open physes, a medial epicondyle avulsion is the most common associated injury. Incarceration of the fragment can occur. Although prereduction and postreduction radiographs reveal periarticular fractures in 12% to 60% of dislocations, operative findings have revealed unrecognized osteochondral injuries in nearly 100% of acute elbow dislocations. The vast majority of these injuries are small fractures not requiring operative intervention.
Neurovascular injuries are rare, but can be potentially devastating. There are multiple case reports of brachial artery injuries with posterior dislocation. Although it may not be necessary to explore the brachial artery routinely if a radial pulse is present, it is accepted that disruption of the brachial artery should be treated with ligation and vein grafting. Median nerve entrapment has been reported with relocation of a dislocated elbow. The median nerve may be displaced posteriorly through a space created by avulsion of the medial epicondyle or the common flexor origin. This can result in a tension of the median nerve across the margin of the epicondylar flare and may “notch” the bone, producing a late radiographic sign known as the Matev sign.
With a dislocated elbow, extensive soft tissue swelling commonly occurs. Intact structures including the forearm fascia, the biceps tendon, and the lacertus fibrosis may exert a constricting effect resulting in increased compartment pressures. Compartment syndrome is possible and should be considered. Careful observation is required, and differentiation from neurologic stretch injuries is necessary.
Treatment
Nonsurgical Treatment
An expeditious atraumatic reduction is the goal. This is often best accomplished with conscious sedation or general anesthesia with adequate muscle relaxation. Muscle relaxation is the key to joint reduction. Care is taken to avoid multiple reduction attempts. A prone traction and countertraction maneuver is often successful (Fig. 51-1). Reduction is usually achieved by extending the elbow with countertraction on the arm and a thumb used to manipulate the coronoid clearing the trochlea. Perched dislocation can be treated with intra-articular analgesia and sedation whereas
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a complete dislocation may require general anesthesia and a muscle relaxant. Uncommonly, a dislocation occurs that is irreducible by closed reduction. This is most frequently associated with fractures. When a dislocation is irreducible, the radial head has been shown to be trapped in the soft tissues of the forearm or can buttonhole through the forearm fascia. These require surgical intervention. Surgical repair of ligaments without associated fractures in the acute dislocation has not been shown to improve return to activity or function.
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Figure 51-1 Prone position for traction/countertraction elbow relocation. |
Following reduction, instability is best assessed with the patient under anesthesia or an anesthetized elbow. The quality of joint reduction provides a clue to postreduction stability. Palpating a reduction “clunk” is a favorable sign of joint stability. The elbow is examined for valgus, varus, and posterolateral rotatory instability. Both varus and valgus instability are performed with the elbow in full extension and flexion up to 30 degrees. Most dislocated elbows are unstable to a valgus stress. This is best tested with the forearm in pronation to lock the lateral side. It is important to evaluate the tendency for redislocation occurring in extension, which can signify a potentially unstable joint. Posterolateral rotatory instability is diagnosed by the lateral pivot shift test. A positive test is manifested by a clunk that is heard and felt when the ulna and radius reduce on the humerus.
Postreduction radiographs should be obtained to confirm a concentric reduction. Anteroposterior and lateral views should be obtained. Widening of the joint space may indicate entrapped osteochondral fragments, which must be removed surgically. Posterolateral rotatory instability may also present as a nonconcentric reduction.
The wrist and shoulder should be examined to rule out concomitant injuries, which occur in 10% to 15% of cases. The distal radioulnar joint and interosseous membrane should be evaluated for tenderness and instability to rule out injury.
Surgical Treatment
All complete elbow dislocations without large periarticular fractures result in medial and lateral ligament ruptures. Rarely is surgical treatment necessary in the acute setting. Josefsson et al. evaluated 31 acute elbow dislocations without concomitant fractures. Under anesthesia nine were unstable with full extension. They surgically explored all 31 elbows, finding ruptures of the medial and lateral ligaments. The tendency of elbows to dislocate correlated with the degree of muscular injury to the flexor-pronator and extensor origins on the humerus. They concluded that muscular flexor and extensor origins represent secondary stabilizers of the elbow. If they are intact, they provide adequate stability to allow ligamentous healing after elbow dislocation. Prospective studies have failed to show improvement of early collateral ligament repair over early motion after a simple elbow dislocation.
Acute surgical intervention is indicated in few incidents. An open elbow dislocation and acute compartment syndrome require urgent intervention. Postreduction instability requiring 50 to 60 degrees of flexion to remain stable may require intervention. Elbow dislocations with unstable fractures require surgical stabilization. The unstable elbow will redislocate even with a well-fitting cast or splint (Fig. 51-2). If this occurs, rigid external fixation with pins in the humerus and ulna are required to maintain a stable concentric reduction. Dynamic external fixation may be used allowing motion in the stable range of motion.
Rehabilitation
The results of treatment of a simple closed elbow dislocation are not universally successful. Most authors recommend a period of immobilization lasting from 3 to 10 days. Restoration of full range of motion, especially extension, is not reliably achieved. Nonimmobilization and early rapid motion under supervision has been shown to achieve range of motion within 5 degrees of extension of the contralateral elbow with an excellent functional outcome.
Patients with persistent loss of motion by 6 to 8 weeks postinjury require additional intervention. If by 6 to 8 weeks full motion has not been obtained, patient-adjusted static flexion and extension splints are used to facilitate regaining motion. Rehabilitation should be closely supervised.
Results
Melhoff et al. reviewed the long-term sequelae of simple dislocations. Sixty-five percent reported loss of motion especially in extension. They found a direct correlation with the period of immobilization. Immobilization >3 weeks resulted in a high incidence of contractures. Uncomplicated dislocations generally have very satisfactory results. Excellent results with full range of motion, normal strength, absent pain, and good stability may be expected in 50% of patients. Good results, defined as <15 degrees of motion loss, minimal discomfort, and normal stability, may be expected in one third of patients. Fair or poor results are generally associated with complications and severe injuries and occur in 15% of cases.
Most patients note continued improvement up to 6 months and rarely up to 18 months. Limitations in extension are the most common problem. Recurrent instability has not been commonly reported, but symptoms have been noted in ≤35 percent of cases. Even long after healing, approximately 50% of patients followed up long term complain of discomfort or residual symptoms attributed to their elbow after a dislocation. This is predominately reported during heavy loading of the affected extremity. Approximately 60% of patients reported that their elbow did not feel as “good” as the contralateral elbow. Mechanical testing reveals a 15% average loss of elbow strength.
Complications
Neurologic problems occur in ≤20% of dislocations. Symptoms range from transient paresthesia to a rare permanent ulnar palsy. Median nerve involvement is less common. Stretching and distortion of the anterior structures may result in spasm, intimal damage, thrombosis, or rupture of the brachial artery. Because dislocation involves disruption of collateral circulation, the forearm can be placed at risk.
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Ischemic myositis, myonecrosis, impaired vascularity, or claudication may result.
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Figure 51-2 Patient with recurrent instability and dislocated 2 weeks after closed reduction. A: The redislocation was not initially recognized with only a lateral radiograph. The joint is not congruent. B: Orthogonal anteroposterior (AP) view shows the clear dislocation. C: Lateral radiograph obtained after open repair of medial and lateral ligaments with a congruent, stable joint. |
Compartment syndrome can result from intramuscular bleeding and edema formation within the flexor compartment of the forearm. Pain with passive finger and wrist extension out of proportion to the injury raises clinical suspicion. Compartment pressures are obtained when the diagnosis is in doubt, and arteriography is obtained if arterial injury is suspected.
Posttraumatic stiffness is much more common than instability after elbow dislocation. Limitation of extension is common with frequent loss of 10 to 15 degrees of terminal extension. Bracing and therapy are not generally useful after 1 year. If there is sufficient limitation of 30 degrees or more, capsulolysis may be considered. The anterior capsule can be released via an open or arthroscopic approach.
Heterotopic bone formation occurs at three primary locations following dislocations. Ossification in the lateral and medial collateral ligaments occurs most frequently (reported in approximately 75% of cases) but seldom causes impairment. Ossification occurs in the anterior capsule above the coronoid process. True ectopic ossification that limits motion is rare, occurring in <5% of cases. Motion-limiting ossification excision is delayed until reactive bone has matured, generally at 1 year.
Elbow dislocations with radial head fractures can be associated with distal radioulnar instability. This is a variant of the Essex-Lopresti injury. The combined injury makes radial head reconstruction important for both elbow stability and axial stability of the forearm. If the radial head is not reconstructible, a metal prosthesis or allograft radial head will provide axial support to the radius and improve valgus stability of the elbow. Temporary pin fixation of the distal radioulnar joint in a neutral position may be added to resist the tendency of proximal radial migration.
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TABLE 51-1 Elbow Dislocation Protocol |
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Author's Preferred Treatment
Diagnosis of acute elbow dislocation is usually straightforward, and careful evaluation of radiographs should allow classification of a complex or simple dislocation. Most injuries will be simple, without significant associated fracture. A rapid but complete neurovascular assessment is documented.
Reduction is carried out expeditiously. On-field reduction may be performed under select conditions if indicated. This will involve an obvious dislocation and an experienced provider at the injury site. Most patients will require transportation to an acute care facility for radiographic evaluation.
Ease of reduction is generally inversely proportional to the degree of muscle spasm present. Analgesia may be provided with conscious monitored sedation, or regional or general anesthesia. The prone position with an assistant controlling the proximal humerus for traction/countertraction has been helpful. The forearm is supinated, and with pressure on the proximal olecranon, a successful reduction can usually be achieved. The stability of the reduction is assessed with range of motion, and the patient is temporarily placed in a sling for postreduction x-ray films.
Most reductions will be stable. We have found for this group, an aggressive early range of motion (ROM) protocol, emphasizing activemotion, has been helpful for maximizing final range of motion and minimizing extension loss (Table 51-1). Rarely, an elbow dislocation without fracture will be grossly unstable following reduction. In this circumstance, an early MRI, followed by exploration and repair of the medial collateral ligament, flexor-pronator tendon, and lateral ulnar collateral ligament can restore stability. Our experience has been that early range of motion is critical to ensuring a successful outcome.
Suggested Readings
Cohen MS, Hastings HH. Acute elbow dislocation: evaluation and management. J Am Acad Ortho Surg. 1998;6:15–23.
Josefsson PO, Gentz CF, Johnell O, et al. Surgical versus non-surgical treatment of ligamentous injuries following dislocation of the elbow joint. J Bone Joint Surg Am. 1987;69:605–608.
Matev I. A radiological sign of entrapment of the median nerve in the elbow joint after posterior dislocation: a report of two cases. J Bone Joint Surg. 1976;58B:353.
Melhoff T. The elbow dislocation revisited: pathoanatomy, stabilizing structures, and keys to rehabilitation. In: Current Concepts of Elbow Surgery, A Comprehensive Review. Rosemont, IL: American Academy of Orthopaedic Surgeons; 1992.
Melhoff TL, Noble PC, Bennett JB, et al. Simple dislocation of the elbow in the adult: results after closed treatment. J Bone Joint Surg Am. 1988;70:244–249.
Mezera K, Hotchkiss RN. Fractures and dislocations of the elbow. In: Rockwood CA Jr, Green DP, Bucholz RW, et al. Fractures in Adults. 5th ed. Philadelphia: Lippincott, Williams & Wilkins; 2001:921–934.
O' Driscoll SW, Morrey BF. Elbow dislocation and subluxation: a Spectrum of instability. Clin Orthop. 1992;280:186–197.
O'Driscoll SW. Elbow dislocations. In: Morey B, ed. The Elbow and Its Disorders. 3rd ed. Philadelphia: WB Saunders; 2000;409–420.
Ross G, McDevitt ER, Chronister R, et al. Treatment of simple elbow dislocation using an immediate motion protocol. Am J Sports Med. 1999;27:308–311.