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AN17.1-3 | Hip Joint — SDL Guide (Part 2)

Hip Dislocation

Dislocation of the hip joint is uncommon due to the deep socket and strong ligaments, but when it occurs, it is usually due to high-energy trauma.

Posterior dislocation (most common, ~90%):
- Mechanism: dashboard injury in RTA — knee hits the dashboard with the hip in flexion → force drives the femoral head posteriorly out of the acetabulum
- Clinical picture: limb held in flexion, adduction, and internal rotation (the posterior capsule is lax in this position); limb appears shortened; femoral head not palpable in groin
- Complication: the sciatic nerve runs just posterior to the hip joint and is at risk → foot drop, loss of posterior thigh and below-knee sensation
- Treatment: urgent reduction under anaesthesia (within 6 hours to prevent AVN); check post-reduction for sciatic nerve function and acetabular fractures on CT

Anterior dislocation (rare, ~10%):
- Mechanism: forced external rotation in abduction (e.g., a fall straddling an object)
- Clinical picture: limb in flexion, abduction, and external rotation; femoral head palpable anteriorly in the femoral triangle
- Complication: femoral nerve and vessels at risk

Central fracture-dislocation: the femoral head is driven through the acetabular floor into the pelvis — requires CT and often open reduction.

Figure: Hip Dislocation

Figure: Central fracture-dislocation

Total Hip Replacement (Arthroplasty)

Total hip replacement (THR) replaces both the femoral head/neck (with a metal stem and ceramic/metal head) and the acetabular socket (with a metal/polyethylene cup). It is indicated for:
- Severe osteoarthritis (most common)
- Rheumatoid arthritis
- AVN of the femoral head
- Failed internal fixation of femoral neck fracture

Anatomical considerations for THR:
- Posterior approach (most common): detaches the short external rotators (piriformis, obturator internus, gemelli, quadratus femoris) to access the posterior capsule — these must be repaired to prevent posterior dislocation post-op; the sciatic nerve is protected
- Anterior approach (muscle-sparing): between sartorius/tensor fasciae latae (anterolateral) without detaching muscles; lower dislocation risk; steeper learning curve

Complications of THR:
- Dislocation — most common complication; more frequent with posterior approach; patients must avoid hip flexion >90° and internal rotation post-op
- DVT/PE — prophylaxis with anticoagulants is mandatory
- Infection — catastrophic; requires prosthesis removal
- Leg length discrepancy — improper implant sizing
- Aseptic loosening — long-term (>10 years); osteolysis from polyethylene wear particles

Figure: Total Hip Replacement (Arthroplasty)