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.



Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Wednesday, April 11, 2012 4:52 pm