Residency · Residency · Neurosurgery

Thoracolumbar Fractures: Classification and Fixation

Overview

The thoracolumbar junction spanning T11 to L2 is the most common site of spinal fractures, accounting for approximately 60 percent of all spinal column injuries. This predilection reflects the biomechanical transition between the rigid thoracic spine, which is stabilized by the rib cage, and the mobile lumbar spine below. Common mechanisms include motor vehicle accidents, falls from height, sports injuries, and in the elderly population, osteoporotic compression fractures from minimal trauma. Neurological injury accompanies approximately 15 to 20 percent of thoracolumbar fractures. Treatment spans a wide spectrum from simple bracing for stable injuries to complex instrumented fusion for unstable patterns with neurological compromise.

Anatomy

Three-Column Model

The Denis three-column model, introduced in 1983, provides the conceptual framework for understanding thoracolumbar fracture stability. The anterior column comprises the anterior longitudinal ligament and the anterior half of the vertebral body and disc. The middle column includes the posterior half of the vertebral body and disc along with the posterior longitudinal ligament. The posterior column encompasses the pedicles, facet joints, laminae, spinous process, and the posterior ligamentous complex. In this model, disruption of the middle column is the key determinant of instability, and failure of two or more columns defines an unstable fracture.

Posterior Ligamentous Complex

The posterior ligamentous complex consists of the supraspinous ligament, interspinous ligament, ligamentum flavum, and facet joint capsules. The integrity of this complex is the single most important factor in determining whether a fracture requires operative or non-operative treatment. Disruption of the PLC indicates instability and typically mandates surgical stabilization regardless of other fracture characteristics.

Classification Systems

AO Spine Thoracolumbar Classification

The AO Spine classification system, published in 2013, categorizes fractures into three major types based on mechanism and morphology.

Type A injuries are compression injuries with an intact posterior tension band. These range from A0, a minor non-structural fracture, through A1, a compression or wedge fracture involving a single endplate, to A2, a split or pincer fracture involving both endplates, to A3, an incomplete burst fracture with single endplate and posterior wall involvement, and finally A4, a complete burst fracture with both endplates disrupted and retropulsed fragments.

Type B injuries involve tension band disruption with either posterior or anterior distraction. B1 is a Chance-type bony fracture through the posterior elements. B2 represents disruption of the PLC as a ligamentous distraction injury. B3 is an anterior distraction injury from hyperextension through the disc and anterior elements.

Type C injuries involve translation or rotation in any plane, indicating complete disruption of all columns. These represent the highest degree of instability regardless of the underlying fracture morphology.

Neurological Modifier

The AO system includes a neurological modifier ranging from N0 for neurologically intact, N1 for a transient deficit that has resolved, N2 for radiculopathy, N3 for incomplete spinal cord injury or cauda equina syndrome, N4 for complete spinal cord injury, and NX when assessment is not possible such as in an intubated patient.

TLICS Score

The Thoracolumbar Injury Classification and Severity Score is a point-based system that directly guides management decisions. Points are assigned in three categories. For morphology, compression receives 1 point, burst adds 1 additional point for a total of 2, translation or rotation receives 3 points, and distraction receives 4 points. For PLC integrity, an intact complex scores 0, a suspected or indeterminate injury scores 2, and a confirmed injury scores 3. For neurological status, intact scores 0, nerve root injury scores 2, incomplete cord or conus or cauda equina injury scores 3, and complete cord injury scores 2 points.

Treatment recommendations based on total score are straightforward: a score of 0 to 3 indicates non-operative management, a score of 4 falls in a gray zone where surgeon judgment determines the approach, and a score of 5 or greater indicates operative treatment.

Older Classifications

Historical systems include the Denis classification dividing injuries into compression, burst, flexion-distraction, and fracture-dislocation patterns; the McAfee classification distinguishing stable from unstable burst fractures; and the Ferguson and Allen mechanistic classification based on force vectors.

Specific Fracture Types

Compression Fractures

Compression fractures, classified as AO A1, involve anterior wedging of the vertebral body with an intact posterior wall and intact PLC. They are stable injuries typically treated conservatively. However, kyphotic deformity exceeding 30 degrees or loss of more than 50 percent of vertebral body height may indicate occult PLC injury and should prompt further evaluation with MRI.

Burst Fractures

Burst fractures, classified as AO A3 or A4, result from axial loading that produces comminution of the vertebral body with retropulsion of fragments into the spinal canal. The middle column is involved by definition. The critical determinant of stability is PLC integrity, not the degree of canal compromise alone. Neurological deficit is present in 30 to 50 percent of cases. Importantly, canal compromise correlates poorly with neurological status due to neural plasticity and the phenomenon of canal remodeling over time.

Flexion-Distraction Injuries

Chance injuries, classified as AO B1 or B2, involve horizontal disruption through bone or ligaments from a distraction force. They are the classic seat belt injury. Associated abdominal injuries including bowel perforation, mesenteric tears, and aortic injury occur in 40 to 50 percent of cases, mandating thorough abdominal evaluation. Bony Chance fractures may heal with bracing because bone-to-bone healing is reliable, while purely ligamentous injuries require surgery because ligament-to-ligament healing is not.

Fracture-Dislocations

Type C fracture-dislocations represent the most unstable pattern with disruption of all three columns and translational displacement. They carry a high rate of complete neurological injury and always require surgical stabilization.

Assessing PLC Integrity

Clinical signs of PLC disruption include point tenderness over the spinous processes, a palpable gap between adjacent spinous processes, and subcutaneous hematoma over the midline. MRI is the best imaging modality for PLC assessment; T2 and STIR sequences reveal edema within the interspinous ligament or ligamentum flavum. CT findings suggestive of PLC injury include widened interspinous distance, facet subluxation, and transverse process fractures. PLC integrity determines operative versus non-operative management more than any other single factor in thoracolumbar trauma.

Non-Operative Management

Indications

Non-operative treatment is appropriate for patients with a TLICS score less than 4 who are neurologically intact. This includes stable compression fractures, burst fractures with intact PLC and no neurological deficit, and selected bony Chance fractures.

Treatment

A thoracolumbosacral orthosis worn for 8 to 12 weeks provides external stabilization. A hyperextension brace such as the Jewett orthosis is specifically designed for compression fractures. Activity modification and pain management supplement bracing. Serial standing radiographs at 2, 6, and 12 weeks monitor for progressive kyphosis, and progression greater than 10 degrees from the initial measurement indicates the need for surgery.

Vertebroplasty and Kyphoplasty

These procedures address painful osteoporotic compression fractures refractory to conservative care. Vertebroplasty involves injection of PMMA cement into the vertebral body under fluoroscopic guidance. Kyphoplasty uses a balloon tamp to create a cavity before cement injection, potentially restoring some vertebral height. These are typically considered after 3 to 6 weeks of failed conservative management. The INVEST and FREE trials showed mixed results, and their benefit remains debated. Contraindications include retropulsed fragments with canal compromise, burst fractures, infection, and coagulopathy. The most common complication is cement extravasation, followed by adjacent level fracture.

Operative Management

Indications

Surgery is indicated for a TLICS score of 5 or greater, neurological deficit with canal compromise in the setting of incomplete injury, PLC disruption, progressive kyphotic deformity, and fracture-dislocation patterns.

Posterior Pedicle Screw Fixation

Posterior pedicle screw fixation is the most common approach for thoracolumbar fractures. Short-segment fixation instructs one level above and one below the fracture using four screws. This preserves motion segments and is faster but carries a higher failure rate of up to 20 percent with loss of correction. Adding index-level screws through the fractured vertebral body significantly improves construct strength and is now widely recommended. Long-segment fixation extends two levels above and two below using eight screws. This provides superior biomechanical stability and is used for highly unstable patterns, poor bone quality, and fracture-dislocations at the cost of sacrificing more motion segments.

Posterior Decompression

Laminectomy is performed when posterior compression is present. Indirect reduction through ligamentotaxis uses distraction across the fracture to reduce retropulsed fragments back into the vertebral body. This technique is most effective within 72 hours of injury; beyond this window, fragments become adherent to the dura and surrounding structures and may require direct manipulation.

Anterior Approach

Corpectomy with strut graft and anterior plating is indicated for significant anterior column deficiency, failure of the posterior approach, and large retropulsed fragments not amenable to ligamentotaxis. The thoracolumbar junction is accessed via a thoracoabdominal or retroperitoneal approach. Anterior reconstruction may be combined with posterior fixation for 360-degree reconstruction in highly unstable patterns.

Timing of Surgery

Emergent surgery is required for progressive neurological deterioration. Urgent surgery within 24 hours is supported by growing evidence for incomplete spinal cord injury to maximize neurological recovery. Semi-elective surgery within 72 hours is ideal for stable fractures in neurologically intact patients, as this window optimizes the effectiveness of ligamentotaxis. For complete spinal cord injury, timing is less critical for neurological recovery, but early surgery may reduce systemic complications and hospital length of stay.

Special Populations

Osteoporotic Fractures

Osteoporotic compression fractures are extraordinarily common, with approximately 700,000 occurring annually in the United States. When surgical fixation is needed in osteoporotic bone, cement augmentation of pedicle screws reduces pullout failure. Vertebroplasty and kyphoplasty address isolated painful compression fractures that fail conservative management.

Ankylosing Spondylitis and DISH

In these conditions, the fused spine behaves as a long bone, and fractures are inherently highly unstable because they represent three-column disruption through a rigid lever arm. Even minor trauma can produce devastating fractures with a high rate of neurological injury. CT scanning of the entire spine is mandatory because fractures in ankylosed spines are notoriously easy to miss. Long-segment posterior fixation is required because the rigid spine demands long constructs to distribute forces. Complication rates are high, including epidural hematoma and delayed neurological deterioration.

Polytrauma Patient

Damage control principles apply: stabilize the spine early when feasible. Temporary external fixation may bridge patients who are too physiologically unstable for definitive surgery. All high-energy trauma patients should be screened for thoracolumbar fractures given the 10 percent incidence in polytrauma.

<image>Sagittal CT reconstruction of the thoracolumbar spine showing an L1 burst fracture (AO type A4) with comminution of the vertebral body, retropulsion of a posterior wall fragment into the spinal canal, and loss of vertebral body height, at the thoracolumbar junction</image>

<image>Axial CT scan at the level of an L1 burst fracture demonstrating comminution of the vertebral body with a large retropulsed bone fragment compromising approximately 50% of the spinal canal, and a sagittal split through the vertebral body</image>

<image>Sagittal STIR MRI sequence of the thoracolumbar spine in a patient with an L1 burst fracture, showing high signal intensity in the interspinous ligament and ligamentum flavum between T12 and L1, indicating disruption of the posterior ligamentous complex (PLC), upgrading this to an AO Type B injury</image>

<image>Postoperative AP and lateral radiographs of the thoracolumbar spine following short-segment posterior pedicle screw fixation from T12 to L2 with index-level screws through L1 for an L1 burst fracture, demonstrating restoration of vertebral body height and sagittal alignment</image>

Clinical Pearls

The PLC is the most important structure for determining stability and guiding management; always assess it with MRI using STIR or T2 sequences. The TLICS system provides a reliable, evidence-based scoring method for treatment decisions, with a score of 5 or greater generally warranting surgery. Short-segment fixation with index-level screws at the fracture level significantly reduces failure rates compared to short-segment fixation without index screws and should be standard practice. Canal compromise on CT alone does not determine the need for surgery; neurological status and PLC integrity are more important determinants. In ankylosing spondylitis, even minor trauma can cause highly unstable three-column fractures; maintain a high index of suspicion and CT the entire spine. Ligamentotaxis through distraction is most effective within 72 hours of injury; beyond this window, retropulsed fragments become adherent and may require direct decompression. Always evaluate for associated abdominal injuries in Chance fractures, as the seat belt mechanism produces bowel, mesenteric, or vascular injuries in 40 to 50 percent of cases.

References

1. Vaccaro AR et al. AOSpine thoracolumbar spine injury classification system. Spine. 2013;38(23):2028-2037.
2. Vaccaro AR et al. A new classification of thoracolumbar injuries: the importance of injury morphology, the integrity of the PLC, and neurologic status. Spine. 2005;30(20):2325-2333.
3. Denis F. The three column spine and its significance in the classification of acute thoracolumbar spinal injuries. Spine. 1983;8(8):817-831.
4. Konieczny MR et al. Epidemiology of fractures of the thoracolumbar spine. J Bone Joint Surg Br. 2011;93(2):232-237.
5. Oner FC et al. MRI findings of thoracolumbar spine fractures: a categorization based on AO spine injury classification. Spine. 2018;43(18):E1067-E1073.

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