1 Introduction top
- Review patient's clinical data and blood exams.
- Estimate the surgical blood loss and determine the need for blood transfusion or the use of cell saver.
- Estimate the correction to be around 40-50° or 50% of the curve in deformities above 90°
- Check X-rays for possible pedicle abnormalities and draw the surgical strategy on a template
Selection of upper instrumented level
There are currently two commonly used options for the upper instrumented level.
- End vertebra of the deformity
- The first lordotic vertebra cranial to the deformity
Using the first lordotic vertebra will reduce the risk of getting junctional kyphosis. However, insertion of pedicle screws at the cervico thoracic junction is technically demanding.
In the case illustrated the end vertebra of the kyphosis is T3, while the optimal fixation point is at T1, the first lordotic vertebra cranial to the deformity.
Selection of lower instrumented level
The distal point of fixation has traditionally been the vertebra below the first lordotic disc in the lumbar area, usually L1 or L2
Another option is to use the most proximal vertebra touched by a line drawn vertically from the posterior superior corner of the sacrum on the lateral radiographs.
Curves more than 90° or smaller curves which do not correct more than 50% in hyperextension films will require a release. This may be an anterior release, a posterior osteotomy, or a combination of both.
Most cases can be managed with a posterior osteotomy and pedicle screw instrumentation. The main indications for anterior release is advanced disk degeneration and anterior osteophytes.
2 Anterior release topenlarge
The anterior release consists of a thorough discectomy resection of annulus of the apical intervertebral discs and release of the anterior longitudinal ligament within the proposed instrumented area of the spine.
Generally a minimum of 5 apical intervertebral discs are excised.
The annulus is incised from the lateral aspect of the spine with a scalpel. The disc is removed using curettes and rongeurs.
Removal of the posterior annulus is optional.
The ALL (anterior longitudinal ligament) is usually thickened at this region and cutting it increase the release and posterior correction of the deformity.
End plate excision
The cartilaginous end plate is excised using a curette, a periosteal elevator or a chisel in order to reduce the risk of pseudoarthrosis.
Morselized rib graft supplemented with bone substitutes or iliac crest bone graft is placed in the interbody space.
3 Pedicle screw insertion topenlarge
Bilateral pedicle screws are inserted at the three cranial and caudal vertebrae. This is performed prior to any posterior osteotomies to reduce the risk of accidental injury to the spinal cord during screw insertion.
On the remaining vertebrae, unilateral pedicle screws may be used switching sides at each level.
Alternatively either laminar or transverse hooks can be inserted at the upper end of the construct.
At the most caudal levels reduction screws may be inserted to facilitate rod insertion and deformity correction.
4 Posterior release (posterior column osteotomy) topenlarge
PCO in the thoracic spine is called Ponte osteotomy.
The inferior aspect of the spinous process is removed followed by the removal of the inter spinous ligament utilizing a standard rongeur.
Then bilateral facet joints are removed either with a Kerrison rongeur or a high speed burr.
Care should be taken not to tear the dura or the nerve roots so as not to compromise the neurological function.
5 Reduction of the deformity topenlarge
The rod curvature should approximate the planned correction (to achieve 40-50° of kyphosis).
Overcorrection will increase the risk of decompensation either proximal or caudal.
After rod insertion is completed, gradual compression between the screws towards the apex of the deformity will provide further correction.
The goal of compression is to close the osteotomy sites and to reduce the posterior length of the spine.
6 Spinal fusion topenlarge
The laminae and the transverse processes are decorticated with an osteotome.
Care should be taken to always point the osteotome away from the spinal canal.
Alternatively, the decortication may be performed with a powered burr.
Bone graft (allograft, autograft, or bone substitutes) is copiously placed over the entire decorticated area.
Optional: Vancomicin powder (1gram) is distributed over the surgically exposed area.
Transverse connectors may be inserted one at each end of the construct at the surgeons discretion.
7 Intraoperative imaging top
Prior to wound closure intraoperative imaging should check:
- Fusion levels
- Screw position
- Overall coronal and sagittal correction and alignment