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Posterior Approach: Distraction Systems

- See: Multisegmented Hook Instrumentation

- Discussion:
     - reduction of retropulsed bone from the canal requires that posterior longitudinal ligament be intact to provide tension;
          - when distracted, ligament pulls bone out of the canal anteriorly toward the body;
          - this technique is generally not successful if surgery is delayed for weeks (or even days) or w/ severely comminuted fractures;
     - indirect method from posterior approach usually involves distraction instrumentation and three- or four-point fixation to realign spine;
           - rods are placed at least 3 levels above & 2 levels below level of injury;
     - rods are contoured to provide anterior vector force across the fracture;
     - in 75% of cases, adequate canal decompression can be acheived by posterior instrumentation alone;
            - in neurologically intact pt, residual canal compression is ignored since canal remodeling will remodel impinging fragments;
            -  w/ incomplete neurologic injury & residual canal compromise > 25% consider secondary anterior decompression;
- Implants:
    - Harrington Rods:
    - CD:

- Pearls:
    - enhanced stabilization may be obtained by the addition of sublaminar or spinous process wires;
         - although sublaminar wires gives more rigid fixation, their passage in a neurologically comprimised patient increases the risk of further
                injury, particularly if spinal cord edema is present;
    - consider restoring spinal column stability with posterior dual Harrington distraction rods;
    - rods are loaded by 4 point bending and prevent the spine from flexing into more kyphosis;

- Pitfalls:
    - attempt to restore saggital plane alignment;
    - avoid overdistraction (esp w/ three column failure);
    - most frequent mode of failure w/ dual Harrington distraction rods has been cut out or dislodgement of a Hook;
    - common difficulty w/ posterior instrumentation is to obtain enough length for 4 point bending of the posterior rods;
          - need to include two levels above & below the injury site which is a disadvantage in the lumbar spine;
    - multiple pieces of bone retropulsed into the canal may not be completely reduced by distraction instrumentation;
    - intraoperative assessment of adequacy of reduction is difficult;

- Misc:
     - Denis type A burst fx can be reduced 80%
     - all type As may reduce by posterior instrumentation alone;
     - type B burst fx will reduce 50% by distraction alone;
          - w/ > 60% canal comprimise in neurologically incomplete pts need to undergo simultaneous anterior & posterior approaches

Vertebral burst fractures: An experimental, morphologic, and radiographic analysis.

Reduction of the intracanal fragment in experimental burst fractures.