Posterior Dislocation: Acute & Long-Term Complications

What is the Complication of Posterior Dislocation?

Posterior dislocation, a less common but often more insidious form of joint displacement, carries a significant risk of acute and long-term complications, ranging from neurovascular damage and associated fractures to chronic instability and debilitating osteoarthritis.

Understanding Posterior Dislocation

A dislocation occurs when the bones that form a joint are forced out of alignment. Posterior dislocations, where the distal bone segment moves posteriorly relative to the proximal segment, are less frequent than anterior dislocations, particularly in the shoulder, but demand prompt recognition due to their potential for severe complications. While any joint can dislocate posteriorly, the glenohumeral (shoulder) and hip joints are the most clinically significant sites due to their mobility, load-bearing function, and proximity to vital neurovascular structures. The mechanism often involves a combination of adduction, internal rotation, and axial loading (e.g., direct blow to the front of the joint, falls, seizures, electrocution).

Acute and Immediate Complications

The immediate aftermath of a posterior dislocation can involve several serious issues that require urgent medical attention to prevent permanent damage.

• Neurovascular Injury: This is one of the most critical acute complications.
  • Nerve Damage: Depending on the joint, specific nerves are vulnerable. For the shoulder, the axillary nerve is most at risk, potentially leading to deltoid muscle weakness and sensory loss over the lateral shoulder. In hip dislocations, the sciatic nerve is frequently injured, causing foot drop (inability to dorsiflex the foot) and sensory deficits.
  • Vascular Damage: While less common than nerve injury, arterial damage (e.g., axillary artery in the shoulder, femoral artery in the hip) can lead to limb ischemia, requiring emergency surgical repair. Venous injury can also occur, contributing to swelling.
• Associated Fractures: The forces involved in a dislocation often cause bone fragments to break off.
  • Impaction Fractures: In the shoulder, a reverse Hill-Sachs lesion (an impaction fracture on the anterior aspect of the humeral head) is characteristic of posterior dislocations. In the hip, femoral head fractures (Pipkin fractures) can occur.
  • Avulsion Fractures: Ligaments or tendons can pull small pieces of bone away. For the shoulder, an avulsion of the lesser tuberosity (where the subscapularis muscle attaches) is common.
  • Articular Surface Fractures: Fractures of the glenoid rim (shoulder) or acetabular posterior wall (hip) can significantly compromise joint stability and congruence.
• Soft Tissue Damage: Beyond fractures, significant damage to the surrounding soft tissues is inevitable.
  • Ligamentous and Capsular Tears: The joint capsule and supporting ligaments (e.g., glenohumeral ligaments, iliofemoral ligament) are stretched or torn, leading to immediate instability.
  • Muscle and Tendon Tears: Rotator cuff tears (especially the subscapularis in the shoulder) are frequent.
  • Labral Tears: The labrum, a fibrocartilaginous rim that deepens the socket, can be torn (e.g., posterior labral tear in the shoulder, acetabular labral tear in the hip), contributing to instability and pain.
  • Articular Cartilage Damage: The forceful displacement can bruise or shear the smooth articular cartilage surfaces, laying the groundwork for future degenerative changes.

Long-Term and Chronic Complications

Even after successful reduction, posterior dislocations can lead to persistent problems that affect joint function and quality of life.

• Joint Instability and Recurrence: Damage to the joint capsule, ligaments, and labrum compromises the static stabilizers of the joint. This can lead to chronic instability, predisposing the joint to recurrent dislocations or subluxations (partial dislocations) with less force.
• Post-Traumatic Osteoarthritis (PTOA): Damage to the articular cartilage, changes in joint mechanics due to unreduced fragments, or chronic instability can accelerate the degenerative process, leading to premature osteoarthritis. Symptoms include chronic pain, stiffness, and reduced range of motion.
• Avascular Necrosis (AVN): This is a particularly devastating complication, especially in the hip. If the blood supply to the femoral head is compromised during the dislocation (e.g., by stretching or tearing the retinacular vessels), the bone tissue can die. This leads to collapse of the femoral head, severe pain, and rapid onset of osteoarthritis, often requiring joint replacement. The risk of AVN increases significantly with delayed reduction.
• Chronic Pain and Stiffness: Persistent pain can arise from nerve damage, ongoing inflammation, developing arthritis, or scar tissue formation. Stiffness (arthrofibrosis) is common due to capsular contracture and disuse, limiting the joint's range of motion.
• Muscle Weakness and Atrophy: Nerve injury, disuse during immobilization, or pain-inhibited movement can lead to significant muscle weakness and atrophy around the affected joint, further contributing to instability and functional deficits.

Joint-Specific Considerations

While many complications are common to all posterior dislocations, some are more prevalent or characteristic of specific joints.

• Shoulder Joint (Glenohumeral Joint):
  • Missed Diagnosis: Posterior shoulder dislocations are notoriously difficult to diagnose clinically and on standard anterior-posterior X-rays, often leading to delayed reduction and increased complication rates. Special views (e.g., axillary lateral, Y-scapular) are crucial.
  • High Incidence of Rotator Cuff Tears: Especially the subscapularis tendon, which can avulse its insertion at the lesser tuberosity.
  • Chronic Stiffness: The shoulder is prone to developing significant stiffness if not mobilized appropriately after reduction.
• Hip Joint:
  • High Energy Trauma: Posterior hip dislocations typically result from high-energy trauma (e.g., dashboard injury in a car accident), increasing the likelihood of multiple associated injuries.
  • Critical Risk of Avascular Necrosis (AVN): The hip joint's blood supply is highly vulnerable. The longer the hip remains dislocated, the higher the risk of AVN, making urgent reduction paramount.
  • High Incidence of Sciatic Nerve Injury: The sciatic nerve runs close to the posterior aspect of the hip joint.

The Importance of Timely Diagnosis and Management

Given the potential for severe complications, prompt and accurate diagnosis of a posterior dislocation is critical. This involves a thorough clinical examination and appropriate imaging studies (X-rays, CT scans, MRI). Delayed reduction significantly escalates the risk of complications, particularly avascular necrosis and chronic stiffness. Emergency reduction under appropriate sedation is the standard of care, followed by a comprehensive assessment for associated injuries.

Rehabilitation and Prevention Strategies

Following reduction, a structured rehabilitation program is essential to mitigate long-term complications. This typically involves:

• Initial Immobilization: To allow soft tissue healing.
• Gradual Range of Motion Exercises: To prevent stiffness and restore mobility.
• Strengthening Exercises: To rebuild muscle strength and dynamic joint stability, focusing on muscles that support the joint (e.g., rotator cuff in the shoulder, gluteal muscles in the hip).
• Proprioceptive Training: To improve joint awareness and control.
• Activity Modification: Advising patients on movements or activities to avoid that could lead to recurrence.

Surgical intervention may be necessary for irreducible dislocations, significant associated fractures, chronic instability, or severe avascular necrosis (e.g., joint replacement).

Conclusion

Posterior dislocation is a significant musculoskeletal injury with a complex array of potential complications, ranging from acute nerve and vascular damage to chronic instability, debilitating osteoarthritis, and avascular necrosis. While less common than anterior dislocations, their subtle presentation and often high-energy mechanism necessitate a high index of suspicion. Prompt diagnosis, urgent reduction, and a meticulous rehabilitation program are paramount in minimizing the risk and severity of these complications, ultimately aiming to restore optimal joint function and prevent long-term disability.