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

Investigations Provided

Laboratory Results

Test	Result	Normal Range	Interpretation
Hb	138 g/L	130-180 g/L	Normal
WCC	11.2 ×10⁹/L	4-11 ×10⁹/L	Mildly elevated (stress response)
Platelets	286 ×10⁹/L	150-400 ×10⁹/L	Normal
Creatinine	88 μmol/L	60-110 μmol/L	Normal
Coagulation	Normal	-	Safe for procedure
Group & Screen	Complete	-	Available for transfusion

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

What is your diagnosis and what is the urgency of treatment?

What are the classification systems for hip dislocation and associated injuries?

Describe your technique for closed reduction of posterior hip dislocation.

The CT shows a small posterior wall fragment (15%). What is your management?

What are the complications of posterior hip dislocation and how do you monitor for them?

What if closed reduction fails? Describe your approach to open reduction.

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:

Feature	Posterior	Anterior
Frequency	90%	10%
Mechanism	Dashboard	Abduction/ER force
Position	SIA (shortened, IR, adducted)	Extended, ER, abducted
Associated injuries	Posterior wall, sciatic nerve	Femoral head, femoral nerve

Critical Management Points

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

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:

Artery	Source	Importance
Medial femoral circumflex artery	Profunda femoris	MAIN supply (80%)
Lateral femoral circumflex artery	Profunda femoris	Minor contribution
Ligamentum teres artery	Obturator	Variable, minor

In posterior dislocation:

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

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

Dashboard injury triad:

Posterior hip dislocation - as discussed
Patella fracture - direct impact
PCL injury - posterior tibial translation
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.

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:

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

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

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.

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

Posterior Hip Dislocation