Hip Dislocations: Understanding Types, Causes, and Management

What are the 3 types of hip dislocations?

Hip dislocations are severe orthopedic injuries characterized by the displacement of the femoral head from the acetabulum, primarily categorized into three types based on the direction of the femoral head's displacement: posterior, anterior, and central.

Understanding Hip Dislocation

A hip dislocation occurs when the head of the femur (thigh bone), which normally sits securely within the acetabulum (the socket in the pelvis), is forced out of its normal position. This is a high-energy injury, often resulting from significant trauma, and constitutes a medical emergency requiring immediate attention due to the potential for serious complications.

Anatomy of the Hip Joint

The hip is a classic ball-and-socket synovial joint, designed for both mobility and stability. The "ball" is the spherical head of the femur, and the "socket" is the acetabulum, a deep cup-shaped depression formed by the fusion of three pelvic bones (ilium, ischium, and pubis). Strong ligaments, a joint capsule, and surrounding muscles provide significant stability. The blood supply to the femoral head, particularly from the medial circumflex femoral artery, can be compromised during dislocation, leading to potential long-term issues.

The Three Primary Types of Hip Dislocations

The classification of hip dislocations is based on the direction in which the femoral head dislocates relative to the acetabulum.

1. Posterior Hip Dislocation

• Prevalence: This is by far the most common type, accounting for approximately 90-95% of all traumatic hip dislocations.
• Mechanism of Injury: Posterior dislocations typically occur when a force is applied along the long axis of the femur while the hip is in a flexed, adducted, and internally rotated position. A classic example is the "dashboard injury" in a motor vehicle accident, where the knee strikes the dashboard, driving the femur backward. Other causes include falls from significant heights or sports injuries where a direct impact forces the knee towards the chest.
• Clinical Presentation: The affected leg typically appears shortened, internally rotated, and adducted. The patient experiences severe pain and is unable to move the leg. There is often a palpable prominence posteriorly due to the dislocated femoral head.
• Associated Injuries: Sciatic nerve injury (foot drop, numbness) is a significant concern due to the nerve's proximity. Fractures of the posterior wall of the acetabulum are also common, as are femoral head fractures.

2. Anterior Hip Dislocation

• Prevalence: Anterior dislocations are much less common, making up about 5-10% of cases.
• Mechanism of Injury: These dislocations usually result from a forceful abduction and external rotation of the hip, often combined with extension. A direct blow to the posterior aspect of the hip or a fall with the leg in an abducted and externally rotated position can cause this.
• Clinical Presentation: The affected leg typically appears abducted, externally rotated, and slightly flexed. The femoral head may be palpable anteriorly (e.g., in the groin or pubic region).
• Subtypes:
  • Obturator Type: The femoral head is displaced inferiorly and medially, often palpable in the obturator foramen region.
  • Pubic/Iliac Type: The femoral head is displaced superiorly and medially, palpable near the pubic bone or iliac crest.
• Associated Injuries: Femoral head fractures, femoral neck fractures, or injury to the femoral artery or nerve can occur, though neurovascular compromise is less common than with posterior dislocations.

3. Central Hip Dislocation (Acetabular Fracture-Dislocation)

• Prevalence: Pure central dislocations without an associated acetabular fracture are rare. More commonly, this presentation is an acetabular fracture-dislocation.
• Mechanism of Injury: This type occurs when a direct lateral force is applied to the greater trochanter (the bony prominence on the side of the hip), driving the femoral head medially and through the acetabulum into the pelvic cavity. This mechanism almost invariably causes a fracture of the acetabulum.
• Clinical Presentation: The leg may appear normal in length or slightly shortened, but the patient experiences intense pain and is unable to bear weight. Swelling and bruising around the hip are common.
• Associated Injuries: Significant acetabular fractures are inherent to this type of injury, often requiring surgical intervention. Internal organ damage within the pelvis (e.g., bladder, bowel) is a serious concern due to the medial displacement of the femoral head.

Causes and Mechanisms of Injury

Hip dislocations are almost exclusively the result of high-energy trauma. Common scenarios include:

• Motor Vehicle Accidents (MVAs): The most frequent cause, especially "dashboard injuries" leading to posterior dislocations.
• Falls from Heights: Significant vertical impact can transmit forces up the femur.
• Sports Injuries: High-impact sports like football, rugby, or skiing can lead to dislocations if specific forces are applied.
• Industrial Accidents: Crushing injuries or falls.

Symptoms and Diagnosis

A hip dislocation is characterized by:

• Sudden, excruciating pain in the hip, groin, or thigh.
• Inability to move the affected leg.
• Visible deformity of the leg (e.g., shortened, rotated, adducted/abducted) specific to the dislocation type.
• Swelling and bruising around the hip.

Diagnosis is typically made through a thorough clinical examination and imaging studies. X-rays (AP pelvis and lateral views) are crucial for confirming the diagnosis, determining the type of dislocation, and identifying any associated fractures. A CT scan may be performed after reduction to assess for subtle fractures, incarcerated bone fragments, or soft tissue injuries.

Immediate Management and Treatment Principles

Hip dislocation is an orthopedic emergency. Prompt treatment is critical to minimize complications, especially avascular necrosis of the femoral head.

• Emergency Medical Attention: Transport to an emergency department immediately.
• Closed Reduction: The primary treatment is closed reduction, where a physician manually manipulates the femoral head back into the acetabulum without surgical incision. This is typically performed under sedation or general anesthesia to relax the muscles and minimize pain.
• Neurovascular Assessment: Before and after reduction, a thorough assessment of the nerves and blood vessels in the leg is crucial.
• Open Reduction: If closed reduction is unsuccessful, or if there are significant associated fractures, an open reduction (surgical intervention) may be necessary.

Recovery and Rehabilitation Considerations

After successful reduction, the focus shifts to protecting the joint and beginning rehabilitation.

• Immobilization: Brief immobilization (e.g., with crutches and protected weight-bearing) is often recommended initially.
• Rehabilitation Program: A structured physical therapy program is vital to:
  • Restore range of motion.
  • Regain strength in the hip and surrounding muscles.
  • Improve proprioception and balance.
  • Gradually progress weight-bearing.
• Prevention of Complications: Close monitoring for potential complications such as:
  • Avascular Necrosis (AVN): Death of bone tissue due to interruption of blood supply to the femoral head, a severe long-term complication.
  • Post-Traumatic Arthritis: Degenerative changes in the joint over time.
  • Recurrent Dislocation: Though less common after initial traumatic dislocations, it can occur, especially if there are underlying ligamentous laxity issues or unaddressed fractures.
  • Sciatic Nerve Palsy: If the nerve was injured during dislocation.

Conclusion: A Serious Orthopedic Emergency

Hip dislocations are severe injuries that require immediate medical attention. Understanding the three primary types—posterior, anterior, and central—is crucial for diagnosis and initial management. While the mechanisms and specific presentations differ, all types share the common need for prompt reduction to preserve joint function and mitigate long-term complications. Recovery is a lengthy process involving careful rehabilitation to restore strength, mobility, and stability to the joint.