- 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;
