CIM Case: Posterior Hip Dislocation

Clinical Scenario

Patient: 55-year-old male truck driver Presentation: Right hip pain following motor vehicle accident (hitting a cow at 100km/hr), unable to move right leg, brought to ED by ambulance Relevant history: Unrestrained driver, dashboard impact to right knee, no loss of consciousness, GCS 15, no other injuries identified in primary survey, no significant past medical history Examination findings:

• Right lower limb shortened, internally rotated, and adducted (classic attitude)
• Flexed hip position
• Unable to actively move right hip
• Severe pain with any attempted movement
• No obvious external wounds
• Palpable knee contusion (dashboard injury)
• Sciatic nerve examination: Ankle dorsiflexion 5/5, plantar flexion 5/5, sensation intact
• Pedal pulses palpable bilaterally
• Left hip and both knees appear normal
• No spinal tenderness

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Investigations Provided

Laboratory Results

Imaging

Image 1: AP Pelvis Radiograph

Radiological features:

• Right femoral head not in acetabulum
• Femoral head appears smaller on right (superior displacement)
• Lesser trochanter not visible on right (internal rotation)
• Shenton's line disrupted
• No obvious acetabular fracture visible on AP view
• No obvious femoral head fracture visible
• Left hip normal
• Pubic symphysis and SI joints intact

Image 2: Post-Reduction CT Scan (after closed reduction)

CT findings:

• Femoral head concentrically reduced in acetabulum
• Small posterior wall fragment (15% of acetabular articular surface)
• No intra-articular loose bodies
• No femoral head fracture
• No other pelvic injuries
• Joint space symmetric to contralateral side

Questions & Model Answers

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Key Teaching Points

Pattern Recognition

This pattern suggests Posterior Hip Dislocation:

• Dashboard mechanism (knee strike with hip flexed)
• Classic SIA position: Shortened, Internally rotated, Adducted
• Severe pain, unable to move hip
• High-energy mechanism

Compare with Anterior Dislocation:

Critical Management Points

1. Time is critical - reduce within 6 hours to minimise AVN risk
2. Document sciatic nerve - before AND after reduction
3. CT scan is mandatory - after reduction, assess for fractures and loose bodies
4. Assess stability - dynamic testing under anaesthesia
5. Long-term follow-up - AVN may appear up to 2 years post-injury
6. Open reduction if needed - don't persist with multiple closed attempts

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Common Examiner Follow-ups

Q: "What is the blood supply to the femoral head and why is AVN a concern?"

Blood supply to femoral head:

In posterior dislocation:

• Medial femoral circumflex artery is stretched/kinked
• Posterior capsule ruptures, further compromising blood supply
• Longer dislocation = longer ischemia = higher AVN risk

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Q: "What associated injuries must you exclude with dashboard mechanism?"

Dashboard injury triad:

1. Posterior hip dislocation - as discussed
2. Patella fracture - direct impact
3. PCL injury - posterior tibial translation
4. Femoral shaft fracture - axial load

Also consider:

• Acetabular fracture
• Femoral head fracture
• Patellar tendon rupture
• Tibial plateau fracture

Always examine the ENTIRE limb and obtain appropriate imaging.

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Q: "The patient develops footdrop after reduction. What is your management?"

Post-reduction sciatic nerve palsy:

Causes:

• Traction injury during reduction
• Contusion from dislocation
• Incarceration (rare)

Management:

1. Document - which component affected (peroneal vs tibial)
2. Expectant management - most (70-80%) recover spontaneously
3. Splint - AFO for footdrop
4. Physiotherapy - maintain ROM, strengthening
5. EMG/NCS - at 6 weeks if no recovery
6. Observe 12-18 months - for spontaneous recovery
7. Consider exploration - if no recovery and incarceration suspected

Most sciatic injuries from dislocation are neuropraxia and recover. Surgery is rarely needed.

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Q: "How does management differ if there is an associated femoral neck fracture?"

Pipkin Type III - Dislocation with femoral neck fracture:

This is a devastating injury:

• AVN rate very high (often >50%)
• Union of neck fracture compromised
• Usually requires total hip arthroplasty

Management:

• Young patient: Attempt reduction and internal fixation of neck (emergently)
• Older patient or delayed presentation: Primary THA
• Must reduce dislocation first to assess neck fracture

This is one of the worst combinations in hip trauma - counsel patient about poor prognosis.

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Related Topics

• Acetabular Fractures
• Femoral Head Fractures
• Hip Dislocation After THA
• Kocher-Langenbeck Approach
• Sciatic Nerve Injury
• AVN of Femoral Head