Balance restoration in the lumbar intervertebral space

Meisel HJ,

Branch C, Chopin D, Rauschning W

BG-Kliniken Bergmannstrost Halle, Germany

Merseburger Str. 165, 06112 Halle

Background:  Degenerated disc disease caused by degeneration or trauma leads to segmental instability.  Hyperplasia of adjacent structures, seen as a sign of autostabilization due to micromotion, leads to nerve root compression and spinal canal stenosis.

Study goal:  Study goal was the evaluation of cage positioning in the intervertebral space under posterior compression and of the preparation of the endplate. 

Method: Polyvinyl chlorate (PVC) and bone dowels identical to the size and form were chosen to compare the cages in implant positioning. 

Five human middle-aged cadavers were taken for the posterior lumbar implantation of PVC cages and bone dowels.

After discectomy and endplate preparation, the bone filled cages and bone dowels were brought into correct position under fluoroscopy and controlled with specially designed instruments. Lordosis was restored via transpedicular posterior fixation under compression. The cadaver was frozen to –70°C and the lumbar spine was cut out.  Two millimeter cuts from the resected area were taken for macroscopic onlight evaluation. 

Results:  Disc-form-adapted cages filled with bone brought into the prepared cage bed by impaction showed good bone-to-bone contact and precise anchorage on the posterior ring apophysis.  Disc height restoration to the selected cage height reopened (widened) neuroforaminal spaces.  Posterior decompression of spinal stenosis and neuroforaminal spaces leads to restoration of former dural sac diameters. Bone dowel implants show similar results.  Insufficient preparation of cage beds or endplates with remaining cartilage inhibit adequate bone-to-bone contact and further fusion.

Conclusions: Disc-shaped lumbar fusion cages with adequate bone-to-bone contact and precise anchorage on the posterior ring apophysis show remarkable balance restoration in the intervertebral space.  Posterior lumbar reconstructive compression via transpendicular fixation systems is mandatory to restore intravertebral balance. Posterior nerve decompression facilitates this reconstructive procedure.