Authors of section

Author

Jean Ouellet

General Editor

Luiz Vialle

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Posterior fusion of L5-S1

1. Introduction

Basic principles

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
posterior fusion of l5 s1

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. Prepartation and approach

This procedure is performed through the Wiltze approach with the patient placed prone.

posterior fusion of l5 s1

3. Pedicle screw insertion

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.

posterior fusion of l5 s1

4. Spine decompression

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.

posterior fusion of l5 s1

5. Reduction

Facet removal

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.

posterior fusion of l5 s1

Disk removal

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.

posterior fusion of l5 s1

The endplates are cleared for all traces of cartilaginous material to ensure fusion.

If the sacral endplate is domed, the dome is flattened.

posterior fusion of l5 s1

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.

posterior fusion of l5 s1

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.

posterior fusion of l5 s1

Rods are contoured to accommodate the pedicle screws. The rods must respect the achieved regional lordosis.

posterior fusion of l5 s1

The achieved correction, listhesis and kyphosis are stabilized by securing the rod to the pedicle screws.

posterior fusion of l5 s1

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.

posterior fusion of l4 s1 with or without pelvic fixation or ala

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.

posterior fusion of l4 s1 with or without pelvic fixation or ala

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.

posterior fusion of l4 s1 with or without pelvic fixation or ala

When reduction is satisfactory, all clamps are tightened.

posterior fusion of l4 s1 with or without pelvic fixation or ala

The reduction sleeve is removed.

posterior fusion of l4 s1 with or without pelvic fixation or ala

The Schanz pins are cut to the appropriate length.

posterior fusion of l4 s1 with or without pelvic fixation or ala

6. Posterior lateral fusion

Posterior lateral fusion should be carried out across the transverse process of L5 (and L4) to the sacral ala.

Bone graft is impacted in the lateral gutters.

spondylolisthesis type 6

7. Aftercare

Detailed postoperative neural assessment must be conducted, specifically looking at the integrity of the L5 nerve root as well as sacral nerves controlling bowel and bladder.

Patients with high grade spondylolisthesis that have been reduced are at high risk of postoperative foot drops secondary to neuro traction injury. To minimize such injuries patients are immediately placed in bed with knees and hips flexed. As long as no neuro injury can be identified the leg can be gradually extended after day two. If neuro injury can be identified, the period of flexion should be extended.

Patients are made to sit up in the bed on the first day after surgery. Bracing is optional. Patients with intact neurological status are made to stand and walk on the second day after surgery. Patients can be discharged when medically stable or sent to a rehabilitation center if further care is necessary. This depends on the comfort levels and presence of other associated injuries.

Patients are generally followed with periodical x-rays at 6 weeks, 3 months, 6 months, and 1 year looking for spinal fusion.

Patients with a diagnosis of dysplastic spondylolisthesis run a higher risk of cauda equina and require closer monitoring of their neurological status during and after surgery.