Fracture of the Dens (Type 1)

24 Year old male came with motor vehicle accident with pain in neck, Sagittal T1 W and Coronal STIR MRI images of cervical spine shows an oblique fracture in the tip of odontoid process (arrow). No cord compression.

Discussion:

• Most dens fractures are caused by motor vehicle accidents and falls
• About 1/3 of C-spine injuries occur at C2 and about ½ at C6-C7
• As expected, most fatal cervical spine injuries occur at C1 or C2
• Most odontoid fractures occur with flexion, extension and rotation.

• Classification of dens fractures:
• About 15% of all cervical spine fractures
• Classified by location (Anderson and D’Alonzo classification)
• Type I (<5%)
• Tip of dens at insertion of alar ligament which connects dens to occiput
• Usually stable but may be associated with atlanto-occipital dislocation
• Type II (>60%)
• Most common dens fractures
• Fracture at base of dens at its attachment to body of C2
• Type III (30%)
• Subdentate—through body of C2
• Does not actually involve dens
• Unstable fracture as the atlas and occiput can now move together as a unit
• Other fractures include a rare longitudinal fracture through dens and body of C2

• Imaging findings
• Conventional radiography is frequently first used as it tends to be most available
• CT is better at demonstrating fractures
• MRI is used for evaluation of ligamentous, disk, spinal cord and soft tissue injuries
• Posterior displacement of the fractured dens into the spinal canal is more common than other displacements
• Lateral view on conventional radiography is most useful as most (85-90%) of injuries can be seen on lateral view
• Cervicothoracic junction visibility assures that the entire cervical spine is visualized
• Soft tissue findings may include >5 mm of prevertebral soft tissue at C3 or less than half of the AP diameter of the adjacent vertebra
• At level of C6, prevertebral soft tissue should be no more than 22 mm in adults and 14 mm in children younger than 15 years
• Widening of the predentate space to greater than 3 mm is abnormal
• Pitfalls
• A mach line may appear to traverse the base of the dens on the open-mouth (aka as the atlantoaxial or odontoid) view but should be recognized by the superimposed base of the occiput
• The mach line will not be present on the lateral view of the dens
• A smooth and sclerotic edge to the “fracture” usually indicates either congenital non-union or acquired non-union of the dens to the body of C2
• Treatment
• Type I fractures are usually treated with a hard collar for 6-8 weeks
• Type II fractures can be treated with
• Immobilization for 12-16 weeks
• Operative fixation (odontoid screw)
• Arthrodesis of C1 to C2
• Type II fractures can be treated with a halo or surgically, as Type II fractures
• Complications
• Non-union
• Due to limited vascular supply
• May occur in 30-50% of Type II fractures, especially in elderly
• Malunion
• Pseudarthrosis
• Affected by age of patient, amount of displacement.

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Spine fracture in Ankylosing Spondylitis

38 year old male patient with ankylosing spondylitis met with mild trauma following which he presented with para paresis, Sagittal T2 weighted MR image showing anterior displacement of C6 over C7 (Arrow head) and multiple syndesmophytes in all the cervical levels (short arrow). There is cord hyperintensity at the levels of C6, C7 and D1 suggestive of cord contusion due to fracture.

The diffuse paraspinal ossification and inflammatory osteitis of advanced ankylosing spondylitis creates a fused, brittle spine that is susceptible to fracture. Even minor trauma can produce an unstable injury as a result of disruption of the ossified supporting ligaments.

Thoracolumbar fractures are reported less frequently than cervical injuries in patients with ankylosing spondylitis.Three recognized patterns are simple vertebral compression fractures, transversely oriented shear fractures, and stress fractures associated with pseudoarthrosis. Transversely oriented shear fractures are acute fractures of the ankylosed spine that invariably disrupt the ossified supporting ligaments and usually traverse the disk space. Disruption of all three columns of the spine predisposes the fracture to displacement and neurologic injury. Stress fractures associated with pseudoarthrosis are subacute injuries that constitute part of the spectrum of spondylodiscitis, a destructive discovertebral (“Andersson”) lesion, that tends to occur in the thoracolumbar region. End-plate erosions and disk height changes, with vertebral sclerosis or osteolysis, can be seen radiographically.

Shiny corner sign in Ankylosing Spondylitis

38 year old male with recently diagnosed ankylosing spondylitis, lateral lumbar spine radiograph showing increased density (arrow) in the anteroinferior part of L3 vertebral body suggetive of shiny corner sign. MR STIR image shows increased signal in anteroinferior parts (arrows) of L3 and L5 bodies.

Shiny corner sign, also known as a Romanus lesion, is an early spinal finding in ankylosing spondylitis. These represent small erosions at the superior and inferior endplates (corners on lateral radiograph) of the vertebral bodies, with surrounding reactive sclerosis. Eventually the vertebral bodies become squared.

On MRI the 'shiny corners' appear as areas of increased T1 signal due to focal fatty marrow as a result of chronic inflammation. MRI however can detect changes earlier than x-ray manifestations, when there is initially increased T2 signal on STIR and decreased signal on T1WI. At this stage plain films appear normal.