section name header

Information

 Differential Diagnosis of Skull and Spine Disorders

Function:

  1. to restore anatomic alignment in fractures (fracture reduction)
  2. to stabilize degenerative disease
  3. to correct congenital deformities (scoliosis)
  4. to replace diseased / abnormal vertebrae (infection, tumor)

Posterior Fixation Devices  !!navigator!!

using paired / unpaired rods attached with

  1. Sublaminar wiring
    = passing a wire around lamina + rod
  2. Interspinous wiring
    = passing a wire through a hole in the spinous process; a Drummond button prevents the wire from pulling through the bone
  3. Subpars wiring
    = passing a wire around the pars interarticularis
  4. Laminar / sublaminar hooks
  5. used on rods for compression / distraction forces to be applied to pedicles / laminae
    1. upgoing hook curves under lamina
    2. downgoing hook curves over lamina
  6. Pedicle / transpedical screws
    • connected by plates / rods spanning single / multiple segments
    • crossbars (for additional strength)
  7. Rods
    1. Luque rod = straight / L-shaped smooth rod 6–8 mm in diameter
    2. O-ring fixator, rhomboid-shaped bar, Luque rectangle, segmental rectangle = preshaped loop to form a flat rectangle
    3. Harrington distraction rod
    4. Harrington compression rod
    5. Knodt rod = threaded distraction rod with a central fixed nut (turnbuckle) and opposing thread pattern
    6. Cotrel-Dubousset rods = a pair of rods with a serrated surface connected by a cross-link with ≥4 laminar hooks / pedicle screws
  8. Plates
    1. Roy-Camille plate
      = simple straight plates with round holes
    2. Luque plate
      = long oval holes with clips encircling the plate
    3. Steffee plate = straight plates with long slots
  9. Translaminar / facet screw
    = cancellous screws for single level fusion when posterior elements are left intact
  10. Percutaneous pinning
    = (hollow) interference screws placed across disk level

Anterior Fixation Devices  !!navigator!!

  1. Dwyer device
    = screws threaded into vertebral body over staples embedded into vertebral body connected by braided titanium wire; placed on convex side of spine
  2. Zielke device
    = modified Dwyer system replacing cable with solid rod
  3. Kaneda device
    = 2 curved vertebral plates with staples attached to vertebral bodies with screws, plates connected by 2 threaded rods attached to screw heads
  4. Dunn device
    (similar to Kaneda device, discontinued)

Reconstruction after Diskectomy / Corpectomy  !!navigator!!

  1. Auto- / allograft bone block
  2. Allograft strut (eg, fibula, humerus)
  3. Interbody spacers: titanium / radiolucent material (eg, polyetheretherketone)
    1. ramp
    2. bone graft cage: open structure filled with bone graft material
      • 2 radiopaque markers for assessment of spacer position: posterior marker should be ≥2 mm anterior to posterior vertebral body margin
  4. Vertebral body replacement device
    1. expandable hollow cylinder packed with bone graft / cement (Synex cage)
    2. mesh (Moss cage)
    3. stackable carbon-fiber-reinforced polymer cages held together by metallic rods
  5. Disk replacement device
    Indication: pain from disk degeneration only
    Contraindication: facet joint degeneration, <4 mm residual disk height, significant endplate degeneration

Complications of Spinal Instrumentation  !!navigator!!

  1. Pseudarthrosis
    • corticated linear lucency across graft material
    • focally increased signal on T2WI
    • increased tracer activity on bone scintigraphy
  2. Malpositioned pedicle screws (2.4% complication rate)
    • nerve root irritation (medial angulation of screw)
    • disruption of cortical bone
      1. medial deviation
      2. lateral deviation
      3. penetration of anterior cortex (exception are sacral screws which may be anchored in anterior cortex of the sacrum for additional stability)
    • lucent rim around screw threads ← loosening
  3. Malpositioned anterior cervical plate
    • penetration into adjacent disk space / foramen transversarium / spinal cord / nerve roots
  4. Herniation of graft material
    • anteriorly / posteriorly displaced graft
  5. Postoperative hematoma
  6. Surgery at wrong level
  7. Accelerated degenerative changes / ligamentous instability / fracture at adjacent levels
  8. Superficial / deep infection (diskitis, osteomyelitis)
  9. Arachnoiditis

Assessment of Bridging Spinal Fusion

Time from surgery: 6–9 months

  • <3° of intersegmental positional change on lateral flexion + extension views
  • visible bone formation in / about graft material
  • minimal loss of disk height
  • absence of lucency around implant
  • absence of fracture of device / graft / vertebra

 Outline