Anterior Hip Dislocation

Anterior hip dislocation is displacement of the femoral head in front of the acetabulum. It accounts for about 10% of traumatic hip dislocations. It follows a high energy force on an abducted and externally rotated hip, such as a fall from height, a road traffic collision with the leg abducted, or a sporting collision.

Two types exist. The inferior or obturator type (about 70%) has the head lying in the obturator foramen, with the hip abducted, externally rotated and flexed. The superior type (iliac or pubic) has the head lying in front of the pubic ramus, with the hip extended, abducted and externally rotated.

Complications are femoral head impaction or osteochondral fracture (up to 25 to 50%), avascular necrosis (up to 10%, higher when reduction is delayed), femoral nerve and vascular injury (the femoral vessels are in front of the head), post-traumatic arthritis, heterotopic ossification and recurrent instability.

Pathophysiology.

Forced abduction and external rotation with extension levers the neck against the acetabular rim, and the head exits through the anterior capsule inferior to the iliofemoral ligament. In the obturator type the head compresses the obturator nerve and the pectineus. In the pubic type the head lies close to the femoral vein, artery and nerve, causing venous congestion or ischaemia.

Severe pain and an abducted, externally rotated and flexed leg (obturator type), or an extended leg held in abduction and external rotation (pubic type). The leg is not shortened. The head may be palpable in the groin or beside the pubis.

Check the femoral pulse and distal perfusion; swelling of the leg or a cool, pale or cyanosed limb implies femoral vessel compression. Assess femoral and obturator nerve function: knee extension, hip adduction, and sensation over the front of the thigh and the medial thigh.

• Anteroposterior pelvis radiograph: the head lies within or inferior to the obturator foramen, or in front of the pubic ramus. The femoral head appears larger than the contralateral side, and the leg is in external rotation (the lesser trochanter is in profile).
• Lateral view radiograph shows the head anterior to the acetabulum.
• CT after reduction defines head fracture, impaction (Hill-Sachs-like defect), intra-articular fragments and acetabular rim fracture.
• CT or conventional angiography when pulses are absent or perfusion is poor.

Differential diagnosis.

• Posterior hip dislocation and femoral neck fracture.
• Acetabular fracture and pubic ramus fracture.
• Femoral head fracture dislocation and dislocated hip prosthesis.
• Femoral vessel injury from other causes.

Reduction within 6 hours of injury under sedation with muscle relaxation or general anaesthesia.

• Allis method (modified): the assistant stabilises the pelvis, traction is applied along the line of the femur with the hip in slight flexion and abduction, then the thigh is gently adducted and internally rotated while the head is pushed laterally and posteriorly into the socket.
• Captain Morgan or lateral traction methods may also be used. Reduction is confirmed by a clunk and radiographs.
• Irreducible hip (interposed capsule, rectus femoris, iliopsoas, buttonholing through the capsule): open reduction by an anterior approach.

Reduction under sedation. Ketamine 1 to 2 mg/kg intravenously over 1 to 2 minutes as a single dose (a further 0.5 to 1 mg/kg after 10 minutes if needed; 4 to 5 mg/kg intramuscularly without access).

Give it by a clinician skilled in airway care with continuous oximetry and capnography, after fasting where time allows. Avoid with raised intracranial pressure, psychosis or acute upper airway infection. General anaesthesia with a muscle relaxant gives the best conditions for a difficult reduction.

After reduction.

• CT to confirm a congruent joint. Surgery is needed for an incongruent reduction, loose bodies, a displaced head or acetabular fracture, or femoral vessel injury (vascular repair by the vascular surgeon).
• Simple dislocations: protected weight bearing for 4 to 6 weeks with a hip abduction restriction (avoid extension, abduction and external rotation) and then progressive strengthening.
• Avascular necrosis: MRI at 3 to 6 months and 12 months. Early disease is treated with protected weight bearing; collapse needs hip replacement.

Operative antibiotic prophylaxis. Cefazolin 2 g intravenously (3 g when weight is 120 kg or over) within 60 minutes before incision as a single dose (repeat after 4 hours or blood loss over 1500 mL).

With severe penicillin allergy, use vancomycin 15 mg/kg intravenously starting 90 to 120 minutes before incision as a single dose, with levels and creatinine checked in prolonged cases.

Thromboprophylaxis. Enoxaparin 40 mg subcutaneously once daily, started within 12 hours after reduction or surgery once bleeding is controlled, and continued for 28 to 35 days or until the patient is mobile.

Dose adjustments: 20 mg once daily at creatinine clearance under 30 mL/min; adjust by anti-Xa level in obesity and renal impairment. Check the platelet count on days 5 to 14 for heparin induced thrombocytopenia. Use mechanical prophylaxis until then.

Analgesia.

• Paracetamol 1 g orally or intravenously every 6 hours (maximum 4 g daily; 3 g daily when weight is under 50 kg, with chronic alcohol use or hepatic impairment).
• Morphine 2.5 to 5 mg intravenously every 5 to 10 minutes as needed before reduction, titrated to pain (halve the dose with age over 75 or eGFR under 30 mL/min/1.73 m2; reassess after 10 mg). Monitor respiratory rate, oxygen saturation and blood pressure continuously.
• Afterwards oral morphine 5 to 10 mg every 4 hours as needed for up to 3 days with a laxative (avoid exceeding 60 mg in 24 hours without senior review).
• Ibuprofen 400 mg orally every 8 hours with food for up to 5 days (maximum 1200 mg daily); avoid with eGFR under 30 mL/min/1.73 m2, peptic ulcer, heart failure or anticoagulant use.

Monitoring. Femoral pulses, distal perfusion and femoral nerve function before and after reduction and every 4 hours in the first 24 hours. Radiographs at 2 weeks, 6 weeks, 3 months, 6 months and 12 months. MRI at 3 to 6 months and 12 months for avascular necrosis. Hip function at each visit. Heterotopic ossification on radiographs at 6 to 12 weeks.

Referral and escalation. Emergency: refer to orthopaedics on diagnosis and arrange reduction within 6 hours. Immediate escalation for limb ischaemia or femoral venous congestion (vascular surgery), failed closed reduction, open injury, or neurological deficit.

Special groups.

• Children: reduce urgently; avascular necrosis risk is lower than in adults.
• Older adults: low energy injury suggests prosthetic hip dislocation or bone disease.
• Pregnancy: left lateral tilt of 15 degrees and obstetric input.
• Kidney impairment: avoid ibuprofen and reduce morphine doses.