Decisions and Expectations with Osteotomy Surgery for Fixed Sagittal Imbalance Syndromes: Smith-Petersen vs Pedicle Subtraction

Problems with Fixed Kyphosis:
• Cosmesis awful.
• Function poor.
• Fatigue pain from neck, hip extensors.
• Effect on levels above/below - predisposes to early degeneration.

Diagnosis/Etiology:
• Post-traumatic - fusing the thoracolumbar or lumbar spine in kyphosis.
• Post fusion.

-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).

• Systemic.

- JRA.
- Ankylosing spondylitis and related disorders.
- Osteoporosis.

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 patient’s 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.

Smith-Petersen Osteotomies:

• Shortens posterior column.

smith-peterson osteotomy

• 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 Surgery:
Fusing short of sacrum (usually type I deformity).
• Young patient.
• 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.

3-column pedicle subtraction osteotomy
 

• 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.

pedicle subtraction osteotomy
 

Step 2. The posterior columns resected but the pedicles preserved. The pedicles surrounded medially/laterally/ superiorly/inferiorly.

pedicle subtraction osteotomy
 

Step 3. A cavity created under the pedicles.

 
pedicle subtraction osteotomy

 

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.

pedicle subtraction osteotomy
 

 Step 5. The lateral vertebral body wall resected at the level of the pedicles.

pedicle subtraction osteotomy
 

Step 6.  The osteotomy closed*

pedicle subtraction osteotomy
 

*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.**

pedicle subtraction osteotomy
 

**Potential fixation points include screws and hooks. “Closing” forces are cantilever and compression.

Calculations:
• 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:

-Wound infection.
-Coronal imbalance.
-Poor family/social support.

Patient motivation is important.

Surgeon should prepare the patient and patient family for “the worst.”

Bibliography:

1. Booth KC, Bridwell KH, Lenke LG, Baldus CR, Blanke KM: Complications and predictive factors for the successful treatment of flatback deformity (fixed sagittal imbalance). Spine 1999;24:1712-20.

2. Bradford DS: Thomasen osteotomy. Section 11, Special Techniques. In: McCarthy RE (ed), Spinal Instrumentation Techniques Manual, Vol. 2. Rosemont, IL, Scoliosis Research Society, June, 1998.

3. Bradford DS, Tribus CB: Vertebral column resection for the treatment of rigid coronal decompensation. Spine 1997;22:1590-9.

4. Bridwell KH: "Pedicle subtraction" (three column) osteotomy. Section 11, Special Techniques. In: McCarthy RE (ed), Spinal Instrumentation Techniques Manual, Vol. 2. Rosemont, IL, Scoliosis Research Society, June, 1998.

5. Burton DC, Asher MA, and Amundson GM: The Heinig “eggshell” procedure for the treatment of thoracic and lumbar kyphosis. Paper #68 presented at the Scoliosis Research Society, San Diego, CA, September 23-25, 1999.

6. Denis F: The iatrogenic loss of lumbar lordosis. The flat back and flat buttock syndromes. In: Farcy JPC (ed), Complex Spinal Deformities. Spine: State of the Art Reviews, Vol. 8, No. 3, Philadelphia, Hanley & Belfus, Inc., 1994, pp. 659-680.

7. Farcy JPC, Schwab FJ: Management of flatback and related kyphotic decompensation syndromes. Spine 1997;22(20):2452-7.

8. Hehne H-J, Zielke K: Correction of long, curved deformities in ankylosing spondylitis. Chapter 19. In: Bridwell KH, DeWald RL (eds), The Textbook of Spinal Surgery, 1st ed. Vol. 1. Philadelphia, JB Lippincott Company, 1991, pp. 547-555.

9. Kostuik JP, Maurais GR, Richardson WJ, Okajima Y: Combined single stage anterior and posterior osteotomy for correction of iatrogenic lumbar kyphosis. Spine 1988;! 3: 257-66.

10. LaGrone MO, Bradford DS, Moe JH, Lonstein JE, Winter RB, Ogilvie JW: Treatment of symptomatic flatback after spinal fusion. J Bone Joint Surg 1988;70A:569-80.

11. Leatherman KD, Dickson RA: Two-stage correction surgery for congenital deformities of the spine. J Bone Joint Surg 1979;61B:324.

12. Leong JCY, Ma A, Yau AC: Spinal osteotomy for fixed flexion deformity. Orthop Trans 1978;2:271.

13. Shufflebarger HL, Clark CE: Thoracolumbar osteotomy for postsurgical sagittal imbalance. Spine 1992;17(8S):S287-90.

14. Smith-Petersen MN, Larson CB, Aufranc OE: Osteotomy of the spine for correction of flexion deformity in rheumatoid arthritis. J Bone Joint Surg 1945;27: 1-11.

15. Thiranont N, Netrawinchien P: Transpedicular decancellation closed wedge vertebral osteotomy for treatment of fixed flexion deformity of the spine in ankylosing spondylitis.  Spine 1993; 18:2517-22.

16. Thomasen E: Vertebral osteotomy for correction of kyphosis in ankylosing spondylitis. Clin Orthop 1985;194:142-52.

Updated on: 09/26/12
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