Elbow Dislocation: Posterior vs. Anterior, Causes, Symptoms, and Treatment

What is the difference between a posterior and anterior elbow dislocation?

Elbow dislocations occur when the bones of the forearm (radius and ulna) lose their normal alignment with the upper arm bone (humerus). Posterior dislocations, where the forearm bones move backward, are by far the most common type, typically resulting from a fall onto an outstretched hand, while anterior dislocations are exceedingly rare, usually stemming from direct, high-energy trauma to the elbow.

Anatomy of the Elbow Joint

To understand elbow dislocations, it's essential to grasp the basic anatomy of this complex hinge joint. The elbow is formed by the articulation of three bones:

• Humerus: The upper arm bone.
• Ulna: The larger forearm bone, on the pinky finger side, which forms the main hinge joint with the humerus (trochlea of humerus articulating with the trochlear notch of the ulna). The olecranon process of the ulna forms the bony prominence at the back of the elbow.
• Radius: The smaller forearm bone, on the thumb side, which articulates with the capitellum of the humerus and also allows for forearm rotation.

The stability of the elbow is primarily maintained by:

• Bony Congruity: The snug fit of the ulna around the humerus.
• Ligaments:
  • Medial (Ulnar) Collateral Ligament (MCL): Provides stability on the inner side of the elbow.
  • Lateral (Radial) Collateral Ligament (LCL): Provides stability on the outer side.
  • Annular Ligament: Encircles the radial head, holding it against the ulna.
• Joint Capsule: A fibrous sac enclosing the joint.
• Muscles and Tendons: Dynamic stabilizers that cross the joint.

Understanding Elbow Dislocation

An elbow dislocation is a severe injury where the articular surfaces of the ulna and radius completely separate from the articular surfaces of the humerus. This often involves significant damage to the surrounding soft tissues, including ligaments and the joint capsule. Dislocation is distinct from a fracture, though fractures can often accompany dislocations.

Posterior Elbow Dislocation

Posterior elbow dislocation is the most common type of elbow dislocation, accounting for over 90% of all cases.

• Direction of Displacement: In a posterior dislocation, the ulna and radius are displaced posteriorly (backward) relative to the distal humerus. The olecranon process of the ulna typically moves behind the humerus.
• Mechanism of Injury: The most common mechanism is a fall onto an outstretched hand (FOOSH) with the elbow in hyperextension (straightened beyond its normal range) and often slight abduction or pronation. The force drives the ulna and radius backward, dislodging them from the humerus.
• Clinical Presentation:
  • Severe pain and swelling.
  • Obvious deformity of the elbow, often described as a "prominent olecranon" posteriorly, making the arm appear shortened.
  • Inability to move the elbow.
• Associated Injuries: Due to the forces involved, posterior dislocations frequently come with:
  • Ligamentous Tears: Especially the medial (ulnar) collateral ligament.
  • Fractures: Common concomitant fractures include the coronoid process of the ulna, radial head, or epicondyles of the humerus.
  • Neurovascular Compromise: While less common than with anterior dislocations, damage to the brachial artery or median/ulnar nerves can occur and requires immediate assessment.
• Prognosis: Generally good with prompt reduction and appropriate rehabilitation, though some residual stiffness is common.

Anterior Elbow Dislocation

Anterior elbow dislocation is an extremely rare injury, representing less than 1-2% of all elbow dislocations.

• Direction of Displacement: In an anterior dislocation, the ulna and radius are displaced anteriorly (forward) relative to the distal humerus. The olecranon process moves anterior to the humerus.
• Mechanism of Injury: This type of dislocation typically results from high-energy trauma, such as:
  • A direct blow to the posterior aspect of the elbow while the elbow is flexed.
  • A fall onto the elbow with the forearm pronated and the elbow flexed, driving the ulna forward.
• Clinical Presentation:
  • Intense pain and swelling.
  • The elbow may appear lengthened, and the olecranon fossa (the depression at the back of the humerus) may be prominent anteriorly.
  • The forearm may appear shortened.
  • Often associated with significant soft tissue damage.
• Associated Injuries: Due to the extreme forces required, anterior dislocations have a higher incidence of severe associated injuries:
  • Fractures: A fracture of the olecranon is very common, often occurring as the direct force impacts it. Fractures of the humerus shaft or epicondyles are also possible.
  • Neurovascular Injury: There is a much higher risk of damage to the brachial artery (leading to potential limb ischemia) and the median or ulnar nerves compared to posterior dislocations. This makes anterior dislocations a surgical emergency in many cases.
• Prognosis: The prognosis is often more guarded due to the higher incidence of severe associated injuries and potential for neurovascular complications.

Key Differences Summarized

Diagnosis and Treatment

Regardless of the type, an elbow dislocation is a medical emergency requiring immediate attention.

• Diagnosis:
  • Clinical Examination: Assessment of deformity, pain, range of motion, and crucially, neurovascular status (pulse, sensation, motor function).
  • X-rays: Crucial to confirm the direction of dislocation and identify any associated fractures.
  • CT/MRI: May be used to further assess complex fractures or soft tissue injuries if initial X-rays are inconclusive or surgery is planned.
• Treatment:
  • Reduction: The primary treatment is to reduce (relocate) the joint. This is typically done closed (without surgery) under sedation or anesthesia.
  • Immobilization: After reduction, the elbow is usually immobilized in a brace or cast for a short period (1-3 weeks) to allow initial healing of soft tissues. Prolonged immobilization is avoided to prevent stiffness.
  • Pain Management: Medications are prescribed to manage pain and swelling.
  • Surgical Intervention: May be necessary if the dislocation is unstable after reduction, if there are significant associated fractures that require fixation, or if there is neurovascular compromise.

Rehabilitation and Prevention

Rehabilitation is critical for restoring function and preventing long-term complications.

• Early Controlled Motion: Once initial healing allows, gentle, controlled range-of-motion exercises are initiated to prevent stiffness, a common complication of elbow injuries.
• Strengthening: Progressive strengthening exercises for the muscles surrounding the elbow and shoulder are introduced.
• Proprioception: Exercises to improve joint awareness and stability.
• Return to Activity: A gradual return to normal activities and sports, guided by a physical therapist, is essential.

Prevention primarily focuses on avoiding the mechanisms of injury:

• Fall Prevention: Being mindful of surroundings, using handrails, and maintaining good balance can reduce the risk of FOOSH injuries.
• Protective Gear: In high-impact sports, appropriate padding can help mitigate the effects of direct blows to the elbow.

Conclusion

While both posterior and anterior elbow dislocations involve the displacement of the forearm bones from the humerus, they differ significantly in their prevalence, mechanism of injury, and the spectrum of associated complications. Posterior dislocations are common and usually result from falls on an outstretched hand, while anterior dislocations are rare, high-energy injuries with a greater risk of severe neurovascular damage. Regardless of the type, immediate medical attention, accurate diagnosis, and comprehensive rehabilitation are paramount for optimal recovery and restoration of elbow function.