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Posterolateral Decompression



- Discussion:
    - most indicated for unstable burst frx w/ cord impingement along w/dural tear and nerve root entrapment from frx of posterior elements;
    - most effective at the thoracolumbar junction and in the lumbar spine as more direct means of reducing the bony fragments;
    - procedure involves hemilaminectomy and removal of portions of one pedicle w/ high speed burr to allow posterolateral decompression 
          of the dura along its anterior aspect.
    - w/ angled instruments, the bone can be curetted out of the canal or tapped back into the vertebral body;
    - in thoracic spine, where less room is available for cord, this technique may involve increased risk to the neural elements;
    - following decompression, it is necessary to select implant for fixation
          as well as number of levels to be fused;
          - consider pedicle screw implants in lumbar levels to preserve motion, where as hook implants can be used in the thoracic levels (where
                 significantly less motion occurs);
          - rod long / fuse short philosophy: disadvantages;
                 - unclear how long hardware needs to remain in place;
                 - damage to facet capsules usually occurs w/ hook insertion;
                 - facet immobilization may lead to joint fibrosis or degeneration;

- Standard Posterior Approach:
    - longitudinal incision over the spinous processes of involved level;
    - after noting precise location of tips of spinous processes, incise superficial fascia, lumbodorsal fascia, & supraspinous ligament 
           longitudinally;
    - erector spinae (sacrospinalis) is subperiosteally dissected off lumbar spines intervening interspinous ligament, and laminae;
           - erector spinae group consists of the spinalis, longissimus, and the iliocostalis;
           - the multifidus and quadratus lumborum lie below the erector spinae musculature;
    - move periosteal elevator proximally and laterally to place erector spinae under tension;
    - using cautery,  subperiosteally strip muscles off lateral surface of spinous process, again moving in a distal to proximal direction;
            - pack each segment w/ sponge after exposure to lessen bleeding;
    - place the end of elevator at junction of spinous process & lamina at the next higher (more proximal) level & continue the dissection;
           - if exposure in opposite direction is attempted, dissection will tend to follow direction of the fibers into the muscle, creating 
                more hemorrage;
    - expose the posterior surface of the laminae and the articular facets;
    - retract muscles laterally using crank retractor - Laminotomy:

- Laminotomy:
    - at appropriate level,  ligamentum flavum is incised and cut away with part adjacent laminae, as necessary to expose the extra 
           dural space;
    - denude the lamina and ligamentum flavum with a curet;
    - ligamentum flava must be very carefully incised since Dura may lie immediately adjacent;
           - ligamentum itself may be as much as 5 mm thick;
           - avoid damaging the dura and the contained nerve roots;
   - remove the flap of ligamentum flavum by sharp dissection;
   - grasp the ligamentum flavum with an Allis or Kocher clamp and incise it w/ bayonet pointed knife where it fuses w/ interspinous 
           ligament;
           - during dissection of the ligament keep the point of the knife in view so that the dura will not be nicked;
   - w/ angulated Kerison rongeur carefully remove small shelving portion of ligamentum flavum left laterally