Denis Classification

Issues of Concern

Under the Denis classification system, the spine gets subdivided into three columns with the included elements:  

Anterior Column

• Anterior longitudinal ligament (ALL)
• Anterior two-thirds of the vertebral body and annulus

Middle Column

• Posterior one-third of the vertebral body and annulus
• Posterior vertebral wall
• Posterior longitudinal ligament (PLL)

Posterior Column

• All structures posterior to the PLL, including the posterior bony arch and the posterior ligamentous complex (supraspinous ligament, interspinous ligament, capsule, and ligamentum flavum)

The impetus in creating this third column was to describe the inherent instability of this middle column.[1][3] Fractures involving the middle column were considered unstable with injury to the posterior longitudinal ligament in addition to the posterior annulus fibrosis, while isolated complete disruption of the posterior ligamentous complex was insufficient to prompt frank instability.[4][5][6][7][8]

Clinical Significance

Based on the findings in his study, Denis went on to classify thoracolumbar injuries into four major types, based on column involvement and mechanisms of injury:

1. Compression

Structures involved:

• Fracture of the anterior column of the vertebral body with an intact middle column
• Failure of the anterior column in compression
• May involve the superior or inferior endplate, or both

Mechanism

Anterior flexion & axial loading  

2. Burst

Structures involved:  

• Compression fractures of the anterior and middle columns.  The posterior column may or may not be involved if lamina fractures are present or if dural tears or nerve entrapments occur
• May involve the superior or inferior endplate, or both  

Mechanism

Axial compression  

3. Flexion-Distraction (Seatbelt-Type)

Structures involved:  

• Usually involvement of all three columns
• No associated translation

Mechanism

Flexion injuries to the middle and posterior columns with distraction posteriorly from tensile forces.  The ALL serves as the axis of rotation, and the anterior column may fail secondary to compression.  

4. Fracture-Dislocation

Structures involved:  

• Involvement of all three columns

Mechanism

Variable mechanisms: shear, rotation, compression, and tension   

The classification systems for thoracolumbar injuries have evolved over time. However, there is no universally accepted system yet at this time.  As such, there is not a current standardized treatment algorithm explicitly designed for the Denis classification.  Instead, general treatment principles may be applied to the following fractures, although significant controversy still exists in operative indications:  

Compression Fractures

Nonoperative:

Bracing, kyphoplasty/vertebroplasty  

Operative:

Posterior instrumentation and fusion

• Indications[9]:
  • 30 degrees traumatic kyphosis 
  • 50% vertebral body height loss

Burst Fractures

Nonoperative:Bracing  

Operative:

Anterior/posterior decompression and instrumented fusion

• Indications:
  • Neurologic deficit
  • Spinal canal compromise
  • Degree of deformity
  • Disruption of the posterior ligamentous complex

Flexion-Distraction Injuries

Nonoperative:

Bracing

• Indications: minimally displaced bony or ligamentous injuries

Operative[10]:

Posterior instrumentation, with or without fusion

• Indications: kyphotic deformity greater than 20 degrees

Fracture Dislocation Injuries

Operative:

All require open reduction with instrumented fusion

Nursing, Allied Health, and Interprofessional Team Interventions

Nursing staff in orthopedic or neurosurgical practice should be familiar with the Denis classification so they can appropriately counsel patients regarding their condition, speak confidently and knowledgeably with other providers about cases, and alert clinicians to potential issues of concern should they be the first to encounter them.