A 45-year-old man sustains an acetabular fracture in a motor vehicle accident. CT scan shows a posterior wall fracture with 40% involvement of the posterior wall and an associated posterior dislocation of the hip that has been reduced. What is the indication for surgical fixation in this case?

• A Only if the hip redislocates after reduction under anaesthesia stress testing
• B Never; posterior wall fractures should always be managed conservatively if the hip is concentrically reduced
• C Posterior wall involvement >20-25%, as fractures of this size are associated with hip instability ✓
• D Only if the patient is aged <60 years

Explanation

Posterior wall acetabular fractures involving >20-25% of the posterior wall are associated with hip instability and require open reduction and internal fixation (ORIF). Biomechanical studies show that >25% posterior wall loss results in hip instability with normal physiological loads. This patient has 40% involvement — a clear surgical indication. A dynamic examination under anaesthesia or CT may be used to confirm instability in borderline cases (15-25%), but 40% is unambiguously unstable. Conservative treatment of large posterior wall fractures leads to post-traumatic osteoarthritis from incongruence and instability. Age alone is not the determining factor.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.