Acetabular Fracture ORIF - Posterior Wall

The single question. You operate on a posterior wall fracture when the hip is unstable or incongruent - and you prove that with the wall percentage, roof arc angles, a dynamic stress test, and the CT. A concentrically reduced, stable hip with a small wall fragment is treated non-operatively. Indications

• Unstable hip: posterior wall involvement over 40 percent, a positive dynamic stress test, subluxation on static imaging, or a failed closed reduction of a dislocation.
• Articular incongruity: intra-articular fragments preventing a concentric reduction, marginal impaction requiring elevation, or a step or gap over 2 mm on CT.
• Mechanical block: incarcerated labral tissue, osteochondral fragments blocking reduction, or an associated femoral head fracture (Pipkin).

Non-operative criteria and contraindications

• Non-operative requires ALL of: a concentrically reduced hip maintained, under 20 percent wall involvement, a negative dynamic stress test, and roof arc angles over 55 degrees on every view.
• Absolute contraindications: active infection, medically unfit for surgery, severe dementia with a non-ambulatory baseline, or posterior skin compromise precluding the approach.
• Relative: delay over 3 weeks with established callus, severe osteoporosis that will not hold fixation, a stable fracture under 20 percent, or an elderly low-demand patient with a concentrically reduced hip. Timing
• Hip dislocation is an emergency: reduce within 6 hours - AVN risk climbs steeply after 6-12 hours.
• Definitive ORIF: 3-10 days, after swelling resolves but before callus forms.
• Over 3 weeks: significantly more difficult; consider specialist referral.

The goal is an anatomic, stable reconstruction of the posterior wall through the Kocher-Langenbeck approach: identify and protect the sciatic nerve and the femoral head's blood supply, reduce the wall and any marginal impaction, hold it with lag screws and a buttress plate, and repair the posterior soft-tissue sleeve. The exposure is laid out in full below (and in depth on the Kocher-Langenbeck approach page).

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Rehabilitation protocol | Phase | Timing | Weight bearing | Motion | |-------|--------|----------------|--------| | 1 | 0-6 weeks | Toe-touch | Gentle passive ROM; no active flexion over 90 degrees and no resisted external rotation for 6 weeks (protects the rotator repair) | | 2 | 6-8 weeks | Partial, if healing on XR | Active-assisted ROM | | 3 | 8-12 weeks | Progress to full | Full ROM and strengthening | | 4 | 3+ months | Full | Return to function - desk work around 6 weeks, heavy labour 3-6 months | Hip precautions for 6 weeks: avoid combined flexion, adduction and internal rotation; use an abduction pillow; avoid low chairs and crossing the legs. Follow-up: wound check at 2 weeks, XR (AP pelvis and Judet) at 6 and 12 weeks, review at 6 months and 1 year (looking for arthritis and AVN), then annual surveillance.

Complications

Epidemiology. The posterior wall is the most common elementary acetabular fracture pattern, accounting for about 25-30 percent of acetabular fractures. It classically follows a dashboard injury - the flexed knee strikes the dashboard, driving force up the femoral shaft into a flexed hip - and is associated with a posterior hip dislocation in about 70 percent. It predominates in young, active adults, and the same mechanism often produces associated knee (PCL), femoral-shaft and spine injuries that must be sought. Letournel classification. Acetabular fractures divide into elementary (single-column or single-wall) and associated (combined) patterns. The posterior wall is an elementary pattern - the one most often operated on.

Pathoanatomy of marginal impaction. At the moment of posterior dislocation the femoral head drives into the posterior wall, shearing off the wall fragment and impacting a segment of articular cartilage and subchondral bone at the fracture edge. This marginal impaction - hidden behind the wall fragment and visible on CT as a double-density sign - is present in about 50 percent. Unless it is elevated back flush and supported with graft, the femoral head rides on a depressed surface and post-traumatic arthritis follows rapidly, even when the wall itself looks well reduced. This is the single most important technical point of the operation and a favourite viva topic. The stability rule and its basis. The "under 20 percent stable, over 40 percent unstable, 20-40 percent grey zone" rule rests on two cadaveric serial-osteotomy models - Keith (1988) and Vailas (1989) - which independently showed that small fragments leave the hip stable, large fragments destabilise it, and the mid-range depends on capsular and soft-tissue integrity. That mid-range dependence on the soft tissues is exactly why a dynamic stress test under anaesthesia is the arbiter for borderline walls. The full studies are summarised in the References below.

Further reading - Letournel E, Judet R (1993). Fractures of the Acetabulum, 2nd ed. Berlin: Springer-Verlag - the definitive classification and surgical-approach atlas (textbook reference, no PMID).

• Kreder HJ, Rozen N, Borkhoff CM, et al (2006). Determinants of functional outcome after simple and complex acetabular fractures involving the posterior wall. J Bone Joint Surg Br 88(6):776-82. PMID 16720773 - marginal impaction, comminution and residual displacement over 2 mm predict arthritis; consider primary THA in patients over 50 with marginal impaction and wall comminution.
• Brooker AF, Bowerman JW, Robinson RA, Riley LH (1973). Ectopic ossification following total hip replacement. J Bone Joint Surg Am 55(8):1629-32 - the Brooker HO grading system (classic reference).