Hip Dislocation

Snapshot

• A 27-year-old woman presents to the emergency room with severe hip pain after being a passenger in a head-on motor vehicle accident. On physical exam, she has significant pain and deformity in her left hip. Her left hip is adducted, flexed, and internally rotated.

Introduction

• Clinical definition
  • condition in which the femoral head is pushed out of the acetabulum
    • in adults, almost always occurs in the setting of significant trauma
• Epidemiology
  • incidence
    • rare injury
    • most common mechanism of injury is motor vehicle accident
    • 90% of dislocations are posterior
    • 10% of dislocations are anterior
  • demographics
    • 4:1 male-to-female ratio
    • most commonly affects adolescents and adults aged 16-40
  • risk factors
    • significant trauma
• Etiology
  • traumatic
  • developmental
    • developmental dysplasia of the hip
  • neuromuscular
    • cerebral palsy
• Pathoanatomy
  • normal anatomy
    • hip joint is inherently stable due to
      • bony ball-and-socket architecture
      • soft tissue constraints
        • labrum, joint capsule, and hip musculature
    • significant trauma is therefore required to overcome the inherent stability of the joint
  • mechanism
    • axial loading on adducted femur predisposes to posterior dislocation
      • dashboard injury
    • axial loading on abducted and externally rotated femur predisposes to anterior dislocation
• Associated conditions
  • 95% incidence of concomitant injuries to other areas of the body
    • acetabular and femoral head or neck fractures
    • knee ligamentous and meniscal injuries
    • closed head injuries
• Prognosis
  • favorable
    • anterior dislocations 
• simple dislocations (no associated fractures)

Presentation

• Symptoms
  • severe pain and immobilty in the affected hip
  • may also complain of lower back, thigh, knee, or lower leg pain
• Physical exam
  • hip position
    • posterior dislocation
      • hip will be flexed, adducted, and internally rotated 
    • anterior dislocation
      • hip will be flexed, abducted, and externally rotated
  • pain with passive or active movement
• thorough head-to-toe examination following Advanced Trauma Life Support (ATLS) protocols must be performed given high incidence of concomitant head and extremity injuries

Imaging

• Radiographs
  • indication
    • anteroposterior (AP) pelvis radiograph always indicated when hip dislocation is suspected
  • finding
    • posterior hip dislocation 
      • femoral head smaller than contralateral side and superior to acetabulum
      • femur appears adducted
      • internal rotation of femur noted as lesser trochanter will be poorly visualized
    • anterior hip dislocation 
      • femoral head appears larger than contralateral side and inferior to acetabulum
      • femur appears abducted
      • external rotation of femur noted as lesser trochanter will be in full profile
• Computerized tomography (CT) scan
  • indication
    • high suspicion for associated fractures
  • finding
• associated fractures to acetabulum, femoral head, and femoral neck

Differential

• Femoral neck fracture
  • hip will remain in acetabulum on AP pelvis radiograph
• Acetabular fracture
• hip will remain in acetabulum on AP pelvis radiograph

Treatment

• Conservative
  • closed reduction under conscious sedation
    • indication
      • closed reduction should be attempted in all traumatically dislocated hips 
• Operative
  • open reduction 
    • indication
• failure of closed reduction

Complications

• Avascular necrosis of femoral head
• Sciatic nerve injury 
• Post-traumatic osteoarthritis