Decisions and Expectations with Osteotomy Surgery for Fixed Sagittal Imbalance Syndromes: Smith-Petersen vs Pedicle Subtraction
Fatigue pain from neck, hip extensors.
Effect on levels above/below - predisposes to early degeneration.
Post-traumatic - fusing the thoracolumbar or lumbar spine in kyphosis.
-Scoliosis - don't shorten the anterior column (Zielke, Dwyer) or lengthen the posterior column (HR, other).
-Degenerative - don't fuse segmental kyphosis without correction; will produce fall-off above.
-Post-traumatic - don't fuse the spine in kyphosis without correction.
-Long fusion if pullout of posterior segmental spinal instrumentation (PSSI) or displacement of structural grafts anteriorly.
-Settling of long fusion done without structural grafting or 4-point fixation of sacrum/pelvis. Settling = loss of anterior column height and subsequent kyphosis.
-LDK (Lumbar Degenerative Kyphosis).
- Ankylosing spondylitis and related disorders.
Indications for Osteotomy:
Fixed kyphosis associated with pain/pseudarthrosis,
Definition of balance/out of balance; see definition below.
Emotionally stable patient with family support
Spectrum of Deformity:
Type I (compensated) - patient segmentally flat but globally in balance. Able to compensate by hyperextending segments above/below. Discs below are not severely degenerated but appear triangular on a standing x-ray (abnormal) and trapezoidal on a supine x-ray (normal). Triangular = markedly convergent posteriorly or anterior height by > 5 mm -- posterior height.
Type II (decompensated) - patient segmentally and globally flat and out of balance. C7 in front of L5-S 1. Patient unable to compensate by hyperextending segments below.
Get long cassette lateral x-ray with the patients hips and knees extended and his or her hands just in front of the waist. Drop a plumb from C7 to produce the sagittal vertical axis (SVA). SVA anterior to L5/Sl disc = positive sagittal balance. SVA posterior to L5/Sl disc = negative sagittal balance. SVA through the L5/S1 disc = neutral sagittal balance. Physiologic = neutral or slightly negative SVA.
Shortens posterior column.
Hinges on middle column.
Lengthens anterior column.
May require structural grafting of anterior column.
If there is significant residual deformity/rotation/ scoliosis, it may shorten the concavity, lengthen the convexity, and displace the patient towards the concavity.
Indications for Multiple Smith-Petersen Osteotomies Without Anterior
Fusing short of sacrum (usually type I deformity).
Excellent bone stock.Mild/moderate correction at several levels.
Fat discs anteriorly.
Physiologic sagittal restoration achievable.
Excellent segmental fixation achievable.
Indications for Anterior Releases/Morselized Graft Then Multiple Smith-Petersen
Osteotomies. No Structural Grafting Needed.
Narrow or ossified discs need anterior release.
If pseudos exist, an anterior procedure is advisable to 8 surface area for fusion.
Weight-bearing line behind the osteotomies post-operatively if so, may not need structural grafting if there are not big gaps anteriorly.
Indications for Posterior Smith-Petersen Osteotomies with Structural
Grafting Anteriorly [Cages, Fresh Frozen Femoral Rings, Tricortical Iliac Graft
(Auto or Allo)]:
Big gaps (> 10 mm) anteriorly after osteotomies.
Incomplete sagittal restoration.
If extending fusion to sacrum, structurally graft at least 4-5 and 5-1, too.
Transpedicular Three-Column (Pedicle/Vertebral Body Subtraction) Osteotomy:
Anticipate 30E correction at one level.
One approach (posterior).
No gap anteriorly.
The anterior column is not opened up as in a Smith-Petersen osteotomy.
All 3 columns should be bone on bone at the completion.
Do it at L1 or below.
Blood loss variable, but usually more than with Smith-Petersen osteotomy because of work on the floor of the canal (epidural veins) + the vertebral body (very vascular).
Do at apex if possible - OK to do even if a rotational deformity exists there.
Shortens posterior and middle column; hinges on anterior column.
Should open up/enlarge the canal centrally (as one would for a Simmons cervical-thoracic osteotomy) if not being done through a previous fusion or if any hint of subluxation.
Step-by-Step Technique of PSO:
Step 1. The extent of the osteotomy indicated with shade.
Step 2. The posterior columns resected but the pedicles
preserved. The pedicles surrounded medially/laterally/ superiorly/inferiorly.
Step 3. A cavity created under the pedicles.
Step 4. The pedicles resected and the posterior vertebral body wall resected. Thin the posterior vertebral body wall with a curette until it is wafer thin. Then resect the lateral portions with a Kerrison or Leksell. Greenstick the posterior cortex centrally with a Woodson or reverse angled curette.
Step 5. The lateral vertebral body wall resected
at the level of the pedicles.
Step 6. The osteotomy closed*
*If the canal is at all stenotic centrally, then a wide posterior column decompression
should be performed centrally, the osteotomy should be open centrally and only
closed laterally along the foramen bilaterally.
Step 7. The spine reconstructed.**
**Potential fixation points include screws and hooks. Closing forces
are cantilever and compression.
Need 30E more lumbar lordosis than thoracic kyphosis, i.e. match 30E lumbar lordosis with OE thoracic kyphosis, 70E lumbar lordosis (TI2-S1) with 40E thoracic kyphosis (T3-T12).
Assume 1E correction per mm bone resected with SPO (10-15 mm per level).
Assume 30E-35E correction per PSO.
Assume 30E-35E of lordization/correction is needed to posteriorly displace the plumb/SVA from C7 12-15 cm.
Complications of Osteotomies:
Wound - may be significant if there have been multiple previous surgeries. Do TPN!
CSF leak - always a risk, but rarely a problem if the osteotomies are closed tightly.
Blood loss - may want to stage procedures 5 days apart. Stand/walk patient between. Use catheter and hyperal if not able to do in one day.
Loss of fixation - rare.
Non-union - rare at osteotomy level(s) if enough correction and stability is achieved. More likely in segments being added to the fusion. Those distal lumbar segments being added should be structurally grafted!
Slow recovery by the patient in some cases due to magnitude of the surgery.
Neurologic: SSEP, MEP, multiple wake-up tests advised.
Coronal decompensation - more likely with SPO than PSO - especially if done at apex with residual rotation.
Results of Osteotomies:
Fusion rate: high if osteotomy closed posteriorly, stable fixation, and sagittal restoration.
Patient satisfaction: high if sagittal restoration complete without complications and patient comorbidities are low. (Booth, Bridwell et al, SRS 1998, AAOS 1999, Spine 1999.)
Patient satisfaction lower if:
-Poor family/social support.
Patient motivation is important.
Surgeon should prepare the patient and patient family for the worst.
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