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Hip Dislocations and Displaced Fractures of the Hip

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PART 1 - HIP DISLOCATIONS

Overview

• Posterior dislocations: >90% of all hip dislocations
• Anterior dislocations: ~10% (superior/pubic or inferior/obturator)

Hip dislocation is an orthopaedic emergency. Reduction should occur within 6 hours. AVN risk rises from <10% at <10 hours to ~25% when delay extends to 15 hours.

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Anatomy of Dislocation

• Posterior dislocations: Capsule torn posteriorly or inferoposteriorly. The Y ligament (iliofemoral) is generally intact but stripped from its acetabular attachment.
• Anterior dislocations: The psoas acts as a fulcrum; capsule is disrupted anteroinferiorly. Femoral vessel injury, though rare, can occur in high-energy injuries.

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1A. Posterior Hip Dislocation

• Limb shortened, adducted, and internally rotated (key distinguishing feature from femoral neck fracture, which is externally rotated)
• Associated injuries: acetabular fracture, femoral neck fracture, femoral shaft fracture, knee ligament injury
• Sciatic nerve injury in ~10% of cases

• AP + lateral pelvis radiograph
• CT of acetabulum and femur after identification

• Allis maneuver (most common): In-line traction with simultaneous hip flexion and internal rotation
• Multiple techniques described; EM physician should be proficient in more than one
• Anterior dislocations require OR reduction

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Classification of Posterior Hip Dislocations

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1B. Anterior Hip Dislocation

• Superior (pubic/subspinous): Hip extended at time of injury
• Inferior (obturator): Hip flexed at time of injury

• Limb in abduction and external rotation (opposite of posterior)
• Femoral artery or nerve injury possible - full neurovascular exam required

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Indications for Open Reduction

• Failed closed reduction
• Unsatisfactory reduction
• Complex fracture-dislocations
• Irreducible dislocations

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PART 2 - DISPLACED FRACTURES OF THE HIP

Anatomy of Fracture Sites

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2A. Femoral Neck Fractures (Intracapsular)

• AVN risk: 15-35% with displaced intracapsular fractures
• ~15% of fractures are radiographically subtle initially
• Occult fractures: if weight-bearing is limited at 24 hours, MRI is the investigation of choice (specific and sensitive)

• Garden 1 & 2 (undisplaced): Internal fixation with dynamic hip screw or multiple cannulated screws (especially in patients <60 who were independently mobile)
• Garden 3 & 4 (displaced): Hemiarthroplasty; or total hip replacement in patients who were independently mobile before fracture
• Interruption of trabecular lines on X-ray = subtle fracture; use lateral view and MRI to confirm

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2B. Intertrochanteric Fractures (Extracapsular)

• Run between the greater and lesser trochanters
• Blood supply is preserved - lower AVN risk
• Can be treated with plate and dynamic screw fixation or intramedullary nailing
• Severely comminuted fractures are easily identified on X-ray
• Subtle/minimally displaced fractures may be missed - air trapped in skin crease of groin can mimic or mask a fracture
• Approximately 1% are initially occult on plain X-ray; if not detected and patient mobilizes, fracture may displace

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2C. Subtrochanteric Fractures (Extracapsular)

• Below the lesser trochanter, extracapsular
• Treated by intramedullary nailing
• Lower AVN risk compared to intracapsular fractures

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PART 3 - COMPLICATIONS

• AVN risk from hip dislocation increases from <10% at <10 hours delay to ~25% at 15 hours delay
• Outcomes are measured with Harris Hip Score, WOMAC, and Merle d'Aubigne scores; overall health with SF-12 and SMFA

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Summary Table

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