Chance Fracture

A Chance fracture is a flexion distraction injury of the thoracolumbar spine in which a horizontal fracture splits the vertebral body, pedicles and posterior elements (spinous process and laminae) in a transverse plane, so that the whole vertebra fails under tension. The fulcrum of flexion lies anterior to the vertebral body, which was classically the lap seat belt without a shoulder strap.

It accounts for 1 to 3% of thoracolumbar fractures. It occurs most often at L1 to L3 (L2 in 40%), in adults and children involved in road traffic collisions (children are at higher risk because the pelvis is a poor anchor for the lap belt, and the anterior abdominal wall absorbs force). Variants include bony (through the bone only), ligamentous (through the posterior ligamentous complex and disc), and mixed forms. Falls from height and farm accidents are other causes.

Associated abdominal injury occurs in 40 to 60% (small bowel perforation, mesenteric tear, pancreatic and duodenal injury, aortic and renal injury), and neurological deficit in 10 to 15% (more with ligamentous and fracture dislocation forms). Complications are delayed diagnosis of bowel injury, kyphosis, instability, neurological injury, wound infection and venous thromboembolism.

Pathophysiology.

When the lap belt restrains the pelvis, sudden deceleration flexes the trunk over the belt and the spine fails in tension from posterior to anterior. The posterior elements, pedicles and the vertebral body fracture horizontally, with variable anterior compression of the vertebral body. The anterior longitudinal ligament may remain intact and act as a hinge. The same force compresses the abdominal contents against the belt and the spine, which explains the abdominal injuries.

Back pain with a palpable gap between spinous processes (an interspinous widening) and spinal tenderness, and the seat belt sign (transverse abdominal wall ecchymosis, in 30 to 60%). Abdominal pain, distension, tenderness, guarding, absent bowel sounds or haematuria suggest visceral injury, which may be masked by distracting spinal pain or a neurological deficit. Neurological symptoms (paraesthesia, weakness, sphincter dysfunction) are present in a minority.

Examine under spinal precautions with log rolling: seat belt marks, abdominal examination (repeat at intervals), full neurological examination including perianal sensation and anal tone, chest, pelvis and limbs, and haemodynamic state.

• CT of the thoracolumbar spine with sagittal and coronal reformats (the key test): horizontal fracture line through the body, pedicles and posterior elements, interspinous widening, loss of posterior vertebral height (the posterior wall remains intact in a pure Chance fracture), kyphosis, and associated injuries.
• The fracture may be missed on axial images alone and on anteroposterior radiographs, where a "empty vertebra" or a widened interspinous distance is a clue.
• MRI of the spine: ligamentous variant (posterior ligamentous complex and disc injury), cord or conus injury, epidural haematoma.
• CT of the chest, abdomen and pelvis with intravenous contrast in all patients with a seat belt sign or abdominal findings; FAST ultrasound at presentation; serial abdominal examination.
• Blood tests: full blood count, lactate, amylase and lipase, urinalysis, group and cross-match.

Differential diagnosis.

• Burst fracture and compression (wedge) fracture.
• Fracture dislocation and other flexion distraction injuries.
• Pathological fracture and transverse process fractures.
• Apophyseal injury and spondylolysis (children).

The first priority is to identify and treat life threatening abdominal and other injuries. The spinal injury is then stabilised to suit the fracture pattern.

Initial care. Airway, breathing and circulation with in line spinal precautions; massive transfusion for haemorrhage; early surgical review for suspected bowel injury; avoid hypotension (mean arterial pressure at least 85 mm Hg if cord injury is present).

Non-operative treatment (bony Chance fracture, intact posterior ligaments, minimal kyphosis under 15 to 20 degrees, no neurological deficit, no vertebral body displacement).

• Hyperextension casting or a thoracolumbosacral orthosis (extension brace) for 10 to 12 weeks, with early mobilisation; union rates are 90 to 100% in children and young adults.
• Radiographs standing at 1 to 2 weeks, 6 weeks and 12 weeks to monitor kyphosis.
• Children treated non-operatively have excellent healing.

Surgery (ligamentous or mixed injuries, posterior ligamentous complex disruption, kyphosis over 20 degrees, translation, neurological deficit, abdominal injury preventing bracing, or failure of non-operative care).

• Short segment posterior pedicle screw fixation with compression across the fracture (one level proximal and one distal), usually with fusion; the fracture is stabilised in extension.
• Posterior wiring or tension band constructs in selected cases; anterior reconstruction is seldom needed.
• Decompression for neurological deficit with canal compromise. Laparotomy for visceral injury is done first or concurrently when the patient is unstable; spinal fixation is delayed until the patient is stable, with the spine protected.
• Results are good, with union in over 90%; complications include infection, implant failure and chronic pain.

Operative antibiotic prophylaxis. Cefazolin 2 g intravenously (3 g when weight is 120 kg or over; 30 mg/kg to a maximum of 2 g in children) within 60 minutes before incision, repeated after 4 hours or blood loss over 1500 mL.

With severe penicillin allergy, clindamycin 10 mg/kg (maximum 900 mg) intravenously or vancomycin 15 mg/kg intravenously starting 90 to 120 minutes before incision as a single dose.

With bowel injury, add metronidazole 500 mg intravenously every 8 hours (children 7.5 mg/kg every 8 hours, maximum 500 mg) and the antibiotics chosen by the surgical team.

Tranexamic acid. Tranexamic acid 15 mg/kg (maximum 1 g) intravenously over 10 minutes before incision, repeated once after 3 hours if bleeding continues (maximum 2 g). Avoid with a history of thromboembolism, active intravascular clotting, seizures, or recent coronary stent. Reduce the dose at creatinine clearance under 50 mL/min.

Thromboprophylaxis. Mechanical prophylaxis from admission. Enoxaparin 40 mg subcutaneously once daily (adolescents and adults) started 24 to 72 hours after injury or surgery once haemostasis is secure and bleeding from abdominal injuries is controlled (20 mg at creatinine clearance under 30 mL/min). Check the platelet count on days 5 to 14. It is not used routinely in children under 14 years.

Analgesia.

• Adults: 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).
• Oral morphine 5 to 10 mg every 4 hours as needed for severe pain for up to 3 to 5 days (start 2.5 to 5 mg with age over 75 or eGFR under 30 mL/min/1.73 m2). Monitor sedation and respiration. Laxative.
• Avoid NSAIDs in suspected visceral injury, bleeding, or when fusion is awaited.
• Children: paracetamol 15 mg/kg orally or intravenously every 4 to 6 hours (maximum 75 mg/kg daily and not exceeding 4 g daily).
• Oral morphine 0.1 to 0.2 mg/kg every 4 hours as needed (maximum 10 mg a dose), or intravenous morphine 0.05 to 0.1 mg/kg every 4 hours as needed in the acute phase.
• Neuropathic pain: gabapentin 300 mg orally at night in adults, increased to 300 to 600 mg three times daily (maximum 3600 mg daily; reduce at creatinine clearance under 60 mL/min). In children, 5 mg/kg at night (maximum 300 mg), increased to 5 to 10 mg/kg three times daily.

Monitoring. Repeated abdominal examination and haemoglobin in the first 48 hours (delayed bowel perforation can present after 24 to 72 hours). Neurological examination every 4 hours at first. Wound and brace skin checks. Review at 2 weeks, 6 weeks, 3 months, 6 months and 12 months with radiographs or CT. Flexion and extension films at the end of bracing. Psychological support after the collision.

Referral and escalation. Every suspected Chance fracture needs spinal precautions, a trauma team review and a spinal surgical opinion the same day, with general surgical review for abdominal injury. Emergency referral for peritonitis, haemodynamic instability, neurological deficit, or progressive kyphosis.

Special groups.

• Children: higher rate of abdominal injury and of multi-level fractures; restraint with age appropriate child seats and three point belts prevents the injury.
• Pregnancy: lap belt injuries risk placental abruption; foetal monitoring and obstetric review; limit radiation; MRI without gadolinium.
• Older adults and osteoporosis: longer fixation, bone protective therapy.
• Prevention: correct use of three point seat belts and child restraints.