Posterior Elbow Dislocation: Nerve Injuries, Symptoms, and Recovery

What nerves are injured in a posterior elbow dislocation?

Posterior elbow dislocations primarily risk injury to the ulnar nerve, followed by the median nerve, and less commonly, the radial nerve, due to the significant forces and displacement involved during the traumatic event.

Understanding Posterior Elbow Dislocation

A posterior elbow dislocation occurs when the bones of the forearm (radius and ulna) are displaced backward relative to the humerus (upper arm bone). This is the most common type of elbow dislocation, typically resulting from high-energy trauma, such as a fall onto an outstretched hand. While the primary concern is the integrity of the joint and surrounding ligaments, the close proximity of major neurovascular structures makes nerve injury a significant complication that requires immediate assessment.

Key Nerves Around the Elbow

To understand potential injuries, it's crucial to be familiar with the major nerves traversing the elbow joint:

• Ulnar Nerve: This nerve runs along the medial (inner) side of the arm, passing behind the medial epicondyle of the humerus (the "funny bone") through a tunnel called the cubital tunnel. It supplies sensation to the little finger and the ulnar half of the ring finger, and innervates many of the small muscles within the hand responsible for fine motor movements.
• Median Nerve: Located on the anterior (front) aspect of the elbow, the median nerve passes through the cubital fossa (the crease of the elbow). It is responsible for sensation in the thumb, index, middle, and radial half of the ring finger, and controls muscles involved in forearm pronation, wrist flexion, and thumb opposition.
• Radial Nerve: The radial nerve courses along the posterior aspect of the humerus, spiraling around the bone, before passing anteriorly near the elbow joint. It primarily supplies the extensor muscles of the forearm, responsible for wrist and finger extension, and provides sensation to the back of the hand over the thumb, index, and middle fingers.

Nerves Most Susceptible to Injury

Due to the biomechanics of a posterior elbow dislocation, certain nerves are more vulnerable:

• Ulnar Nerve Injury:
  • Mechanism: This is the most frequently injured nerve in elbow dislocations. The ulnar nerve's superficial position behind the medial epicondyle makes it highly susceptible to stretching, compression, or contusion as the olecranon (part of the ulna) displaces posteriorly and often medially. During the dislocation event or subsequent reduction, the nerve can be directly impinged or stretched.
  • Symptoms: Patients may experience numbness or tingling (paresthesia) in the little finger and the ulnar half of the ring finger. Weakness may be observed in the intrinsic hand muscles, affecting finger spreading (abduction) and bringing together (adduction), and overall grip strength.
• Median Nerve Injury:
  • Mechanism: While less common than ulnar nerve injury, the median nerve can be stretched or compressed as it crosses the elbow joint anteriorly, particularly with significant displacement of the forearm bones. Direct contusion or entrapment by bone fragments or hematoma are also possibilities.
  • Symptoms: Sensory deficits typically include numbness or tingling in the thumb, index, middle, and radial half of the ring finger. Motor weakness may manifest as difficulty with thumb opposition, forearm pronation, or wrist flexion.
• Radial Nerve Injury:
  • Mechanism: Injury to the radial nerve is the least common among the three major nerves in isolated posterior elbow dislocations. Its deeper and more protected course makes it less vulnerable. However, it can be injured in more complex fracture-dislocations, where bone fragments may directly impinge upon it, or in cases of severe traction.
  • Symptoms: The hallmark of radial nerve injury is "wrist drop," an inability to extend the wrist and fingers. Sensory loss would typically be felt on the dorsal (back) aspect of the hand over the thumb, index, and middle fingers.

Mechanisms of Nerve Injury in Dislocation

Nerve injury in the context of an elbow dislocation can occur through several mechanisms:

• Stretch or Traction: The most common mechanism, where the nerve is pulled and stretched beyond its physiological limit as the joint dislocates.
• Compression: The nerve can be compressed between the dislocated bones, surrounding soft tissues, or by a hematoma (collection of blood) that forms after the injury.
• Contusion/Direct Impact: A direct blow to the nerve during the traumatic event.
• Laceration: While rare in pure dislocations, sharp bone fragments in associated fractures can directly cut the nerve.
• Ischemia: Disruption of blood supply to the nerve due to vascular injury or severe compression.

Recognizing Nerve Injury: Clinical Signs and Symptoms

Prompt recognition of nerve injury is paramount for optimal outcomes. Healthcare professionals perform a thorough neurovascular assessment immediately after the injury and again after reduction of the dislocation. Key signs to watch for include:

• Sensory Deficits: Numbness, tingling, or a pins-and-needles sensation (paresthesia) in the areas supplied by the affected nerve.
• Motor Deficits: Weakness or complete paralysis of the muscles innervated by the injured nerve, leading to difficulty with specific movements (e.g., wrist drop, inability to make a fist).
• Pain: Neuropathic pain, which can be sharp, burning, or shooting, may also be present.

It's important to note that nerve symptoms can sometimes be delayed, developing hours or days after the initial injury due to swelling or hematoma formation.

Diagnosis and Management

Diagnosis of nerve injury typically involves a comprehensive clinical examination.

• Immediate Assessment: A detailed neurological examination focusing on motor function and sensation in the hand and forearm is crucial immediately following the injury and after the elbow has been successfully reduced.
• Imaging: X-rays are used to confirm the dislocation and identify any associated fractures. If nerve symptoms persist or are severe, MRI may be considered to visualize soft tissue damage and nerve integrity.
• Electrodiagnostic Studies: If nerve symptoms do not resolve spontaneously within a few weeks, electrodiagnostic tests such as electromyography (EMG) and nerve conduction studies (NCS) may be performed to assess the extent and location of nerve damage.

Management depends on the severity of the nerve injury:

• Conservative Management: Most nerve injuries associated with elbow dislocations are neurapraxia (temporary nerve stunning) and often resolve spontaneously over weeks to months. Initial management typically involves observation, rest, and protection of the nerve.
• Surgical Intervention: Surgical exploration may be indicated for more severe nerve injuries (axonotmesis or neurotmesis) that show no signs of recovery, or if there's evidence of persistent nerve compression by bone fragments or scar tissue.

Prognosis and Rehabilitation

The prognosis for nerve recovery following an elbow dislocation varies significantly based on the type and severity of the nerve injury. Neurapraxia has the best prognosis, with most individuals experiencing full recovery. More severe injuries, such as axonotmesis (axon damage) or neurotmesis (complete nerve transection), have a longer and less predictable recovery path, often requiring more intensive rehabilitation or surgical repair.

Rehabilitation plays a vital role in recovery, focusing on:

• Maintaining Range of Motion: Preventing joint stiffness.
• Strengthening Exercises: Restoring muscle strength as nerve function returns.
• Nerve Gliding Exercises: To prevent adhesions and promote nerve mobility.
• Sensory Re-education: For persistent sensory deficits.

Conclusion

Posterior elbow dislocations are significant injuries with a notable risk of associated nerve damage, particularly to the ulnar and median nerves. Prompt and thorough neurological assessment by a healthcare professional is essential immediately following the injury and after reduction to identify any nerve deficits. While many nerve injuries are temporary, persistent symptoms warrant further investigation and potentially specialized management to ensure the best possible functional outcomes and prevent long-term complications.