1 Introduction topenlarge
Managing high grade spondylolisthesis requires good knowledge of lumbosacral anatomy.
The goals of the surgical management are:
- Solid fusion across L5-S1
- Neural decompression
- Ensure sagittal balance
- Prevent further slippage
- Reduce pain
- Maintain neurological integrity
Levels of instrumentation
In some cases (in high grades) where a more rigid instrumentation is needed, the fusion can be extended proximally to L4 and distally to Pelvis.
Identification of anatomical landmarks
Due to the distorted anatomy care must be taken to confirm correct fusion levels. Typically the L5 pedicle is extremely anterior, hidden beneath the sacral alar.
Intraoperative fluoroscopy or spinal navigation is used to facilitate identification of correct levels.
2 Pedicle screw insertion topenlarge
Pedicle screw insertion in L5 and S1 (L4 if needed) is performed in a standard fashion, ensuring that the proximal facet is not breached by the pedicle screw.
3 Spine decompression topenlarge
A wide posterior spinal decompression is performed by carefully removing the L5 mobile lamina and the ligamentum flavum using sequential Kerrison rongeurs. The dural sac and the L5 and S1 nerve roots are identified.
4 Reduction topenlarge
The inferior facet of L5 and part of the S1 superior facet is removed bilaterally to give access to the L5-S1 disk space.
Care is taken not to injure the L5 nerve.
The disc is removed by incising the anulus fibrosis and using a series of rongeurs and curettes forward to the anterior anulus. Care is taken not to disrupt the anterior anulus.
The endplates are cleared for all traces of cartilaginous material to ensure fusion.
If the sacral endplate is domed, the dome is flattened.
Mobilization of disk space
Interbody trials / spacers are inserted bilaterally in incremental fashion to loosen the annulus and anterior longitudinal ligament to achieve indirect foramina decompression by increasing the inter vertebral hight.
The focal lumbosacral kyphosis must be corrected during this maneuver.
The Listhesis can also be corrected to improve anterior vertebral apposition however care must be taken as anatomical reduction has been associated with L5 nerve root injury.
During this maneuver the L5 nerve roots EMG's must be monitored to avoid postoperative foot drop.
Once the satisfactory reduction is achieved, the spacer is replaced by the corresponding cage.
Care must be taken to ensure that the cage is resting between both endplates. A structural graft can also be used instead of a cage.
The graft or cage should be placed as anterior as possible in order to achieve more lordosis.
High grade listhesis are at higher risk of graft extrusion.
Rods are contoured to accommodate the pedicle screws. The rods must respect the achieved regional lordosis.
The achieved correction, listhesis and kyphosis are stabilized by securing the rod to the pedicle screws.
Optional: reduction with Schanz pins
Special 6 mm double-threaded Schanz screws are inserted in the L5 pedicle on each side. The Schanz screws have a 3 cm long threaded part in their shaft.
Two rods about 8 cm long are contoured to the desired lumbosacral lordosis. The rods are mounted to the Schanz pins in L5 with a rotule and then the rods are pushed into the screws of L4 and S1 where they are fixed.
Two threaded sleeves are sleeved over the Schanz screws. By tightening the sleeve along the threaded part of the Schanz screws, the vertebra of L5 is gradually reduced towards the rod.
When reduction is satisfactory, all clamps are tightened.
The reduction sleeve is removed.
The Schanz pins are cut to the appropriate length.