1. Scoliosis: More Than Just Cobb Angles
Joseph R. Grajo, MD1
Ryan Murtagh, MD, MBA1
Juan Uribe, MD2
1Department of Radiology
2Department of Neurologic Surgery
University of South Florida
Morsani College of Medicine
Tampa, FL

2. Disclosures Joseph R. Grajo, MD: None Ryan Murtagh, MD, MBA: None
Juan Uribe, MD: Nuvasive® (consultant, research grants, speaker bureau, royalties) - no stocks

3. Goals and Objectives Introduce a 3-dimensional approach to scoliosis
Discuss the various spinal and pelvic imaging parameters that play a significant role in patient outcomes after spinal surgery
Discuss surgical approaches used to restore normal coronal and sagittal balance with representative pre- and post-operative cases

4. Target Audience
General Radiologists
Neuroradiologists

5. Scoliosis
Historically, surgeons have focused on coronal alignment (scoliosis) and surgery to correct coronal deformity
Recent findings show that sagittal alignment correlates highly with quality of life scores2 and that failure to correct sagittal deformity can lead to poor outcomes
We are also finding that the position of the pelvis plays a significant role in spinal alignment
As a result, there is a more global, 3-dimensional approach to spinal deformity with increased emphasis on correction of both spinal and pelvic deformities
2Glassman, et al, Spine (Phila Pa 1976) 30:682–688, 2005
1Dubousset “Cone of Economy” taken from
Ames, et al, J Neurosurg: Spine / March 23, 2012

6. Spinal imaging parameters
Spinal parameters – Pelvic parameters
Spinal imaging parameters
Coronal spinal parameters
Scoliosis - measured by Cobb angles
Coronal plane decompensation
Sagittal spinal parameters
Thoracic Kyphosis (TK)
Lumbar Lordosis (LL)
Spinal Vertical Alignment (SVA)

7. Spinal parameters – Pelvic parameters
Cobb angles
26 degrees of dextroscoliosis

8. Coronal Plane Decompensation
Spinal parameters – Pelvic parameters
Coronal Plane Decompensation
Measure by
Drawing plumb line from C7 midpoint
Then measure distance from plumb line to midpoint of S1
In neutral, plumb line intersects midpoint of sacrum +/- 2 cm right or left
Plumb line
Central sacral vertical line
Ames, et al, J Neurosurg: Spine / March 23, 2012

9. Coronal plane decompensation
Spinal parameters – Pelvic parameters
Coronal plane decompensation
4.6 cm

10. Spinal parameters – Pelvic parameters
Thoracic Kyphosis
Normal is 30-40o in males years old (increases with age)
Approx 40o in women of same age
Fon, et al, AJR 1980
Ames, et al, J Neurosurg: Spine / March 23, 2012

11. Lumbar Lordosis Average in adults is 33.2 +/- 12.1 degrees
Spinal parameters – Pelvic parameters
Lumbar Lordosis
Average in adults is / degrees
Increases with age
Lin, et al, J Formos Med Assoc, 1992
Ames, et al, J Neurosurg: Spine / March 23, 2012

12. Spinal Vertical Alignment
Spinal parameters – Pelvic parameters
Spinal Vertical Alignment
Measured as:
Distance between plumb line from mid point of inferior endplate of C7 and supero-posterior corner of S1
In neutral SVA, plumb line from C7 intersects with supero-posterior corner of S1
Mean in asymptomatic adults is 0.5 cm +/- 2.5 cm3
Ideal SVA is less than +/- 5 cm4
Increases with age (“anterior imbalance”)
3Jackson and McManus. Spine 1994;19:1611–8
4Schwab, et al. Spine (Phila Pa1976) 35:2224–2231, 2010
6Malfari, et al, AJR 2010;194:S8–S22
Ames, et al, J Neurosurg: Spine / March 23, 2012

13. Normal and abnormal SVA
Spinal parameters – Pelvic parameters
Normal and abnormal SVA
Normal/Neutral
Positive SVA

14. Spinal parameters – Pelvic parameters
Parameters in adjacent zones of the spinopelvic axis are interdependent
Pelvic zone affects the lumbar zone (and vice-versa)
Lumbar zone affects the thoracic zone5
Position of pelvis plays important role in upright sitting and standing postures
Failure to address abnormal pelvic alignment increases risk of spinal malalignment, decompensation and treatment failure
Pelvic parameters consist of
Pelvic Incidence (PI)
Pelvic Tilt (PT)
Sacral Slope (SS)
Pelvic Obliquity (PO)
5Berthonnaund, et al. J Spinal Disord Tech 2005;18:40–7.

15. Spinal parameters – Pelvic parameters
Pelvic Incidence
Angle between line from femoral head(s) to midpoint of sacrum and line perpendicular to superior endplate of sacrum
This is a morphologic parameter – descriptor of how much sacrum is angled in a person. Basically, it describes the shape of the sacrum that you were born with
Stays constant throughout life except for slight change in puberty
Important for its relationship to lumbar lordosis (LL)
Ideally LL = PI +/- 9 degrees3
Can use a patient’s PI as pre-operative guide for amount of lordosis that should be introduced at surgery
Ames, et al, J Neurosurg: Spine / March 23, 2012
3Schwab, et al. Spine (Phila Pa1976) 35:2224–2231, 2010

16. Spinal parameters – Pelvic parameters
Pelvic Tilt
Angle between a line from midpoint of femoral heads to center of superior endplate of sacrum and a vertical plumb line to midpoint of femoral heads
This is a positional parameter, meaning that unlike the PI, it can change
Compensatory mechanism – as spine tilts forward (i.e. as you lose lordosis and increase kyphosis), subject tries to maintain neutral alignment by pelvic retroversion4
Increased work to retrovert pelvis and patients become uncomfortable leading to poor outcomes
Ideally PT is less than 20 degrees3
Increased PT after surgery implies residual postoperative spinal deformity and negatively affects function and thus postoperative outcomes (highly correlated with outcomes)3
1Ames, et al, J Neurosurg: Spine / March 23, 2012
3Schwab, et al. Spine (Phila Pa1976) 35:2224–2231, 2010
4Jackon and McManus. Spine 1994;19:1611–8

17. Spinal parameters – Pelvic parameters
Pelvic Tilt
Recall that parameters in adjacent zones of the spinopelvic axis are interdependent
Therefore  As SVA increases, the result is a compensatory increase in PT
Study by Schwab, et al6 on patients compared changes in SVA vs pelvic tilt
Negative SVA (<0) – average PT = 10o
Neutral SVA (0-5 cm) – average PT = 16o
Positive SVA (> 5 cm) – average PT = 21o
6Schwab, et al, Spine 2006;31:E959–67.

18. Increasing PT to maintain neutral
Spinal parameters – Pelvic parameters
Increasing PT to maintain neutral
Low pelvic tilt but positive SVA
Now has normal SVA but high PT, lots of energy to maintain
Retroversion
Increasing SVA  increase in PT  greater energy expenditure and greater disability
Image from Ames, et al, J Neurosurg: Spine / March 23, 2012

19. Two examples of abnormal PT
Spinal parameters – Pelvic parameters
Two examples of abnormal PT
35 degrees
31 degrees
(note positive SVA)
*this is good example showing that sometimes it is hard to align femoral heads. Attempt to use midpoint if not aligned.

20. What is the significance???
Spinal parameters – Pelvic parameters
What is the significance???
Retroverted/compensated patients are not happy patients
Patients with positive sagittal balance fight to maintain neutral by
Pelvic retroversion
Flex hips and knees
More work to stay upright!!
Patients with sagittal balance + scoliosis had better outcomes when both fixed versus just scoliosis fixed7
Another study showed best radiographic predictor of outcome was not scoliosis curve but sagittal balance8
7Schwab, et al, Spine 2008; 33:2243–2247
8Glassman, et al, Spine 2005; 30:682–688

21. Sacral Slope Measurement that is not as commonly used
Spinal parameters – Pelvic parameters
Sacral Slope
Measurement that is not as commonly used
Angle between line drawn along superior endplate of S1 and a horizontal reference line
PI = PT + SS
As PT increases, SS decreases (pelvic retroversion)
Ames, et al, J Neurosurg: Spine / March 23, 2012

22. Summary of pelvic parameters by age
Spinal parameters – Pelvic parameters
Summary of pelvic parameters by age
3Schwab, et al. Spine (Phila Pa1976) 35:2224–2231, 2010

23. Spinal parameters – Pelvic parameters
Pelvic obliquity
Important part of coronal correction strategy
In similar fashion to the relationship between PT/retroversion in sagittal balance, PO is compensatory mechanism to improve coronal balance
Presence of PO can suggest other problems like leg length discrepancy, and these should be addressed if present
Ames, et al, J Neurosurg: Spine / March 23, 2012

24. Spinal parameters – Pelvic parameters
Pelvic obliquity
Pelvic obliquity (tilt) to the right as compensatory mechanism to maintain neutral coronal balance

25. How is positive balance/retroversion treated surgically?
Spinal parameters + Pelvic parameters = The Big Picture
How is positive balance/retroversion treated surgically?
With positive SVA, neutral sagittal balance can be restored through increase in lumbar lordosis
Lordosis can be increased by:
taking away height from the back (osteotomy, such as pedicle subtraction osteotomy)
adding height to the front (ALIF with introduction of cages to increase height)
Location can have variable results
More inferior – greater increase in LL with osteotomy or cage
More superior – requires larger osteotomy or cage for same lordosis
Flat back – before surgery
Post op - increased lordosis with osteotomies and cages restores sagittal balance
Ames, et al, J Neurosurg: Spine / March 23, 2012

26. Before and After BEFORE Positive sagittal balance of 12 cm PT of 22o
Osteotomies increase LL from 28o to 60o
SVA of 3 cm
PT of 9o
Ames, et al, J Neurosurg: Spine / March 23, 2012

27. Before and After Dextroscoliosis 55o Pelvic obliquity 7o

28. Before and After
SVA 10.9 cm
SVA 3.4 cm

29. Before and After
Pelvic tilt 35 degrees
Pelvic tilt 22 degrees

30. Gone too far?

31. Bringing it all together
In summary, like it or not, we are in an age where radiology is fighting relevancy in many major areas
Imperative that radiologist develop larger role in surgical decision making process
A little extra effort on something as simple as scoliosis series can go a long way
As the radiologist, you should address the following in your report for scoliosis films
On the frontal view - where is the scoliosis and what are the Cobb angles of the primary and secondary curves?
How much coronal plane decompensation is there and is there any compensatory pelvic obliquity?
On the lateral view, what is the SVA and how much is the pelvic tilt? Conclude if there is compensation/pelvic retroversion (PT > 20o).
Is there a significant difference between the lumbar lordosis and the pelvic incidence? LL should be within 9o of the PI. If significant difference, can increase LL with osteotomy and/or cages.

32. Thanks!
Contact Information
Joseph R. Grajo, MD:
Ryan Murtagh, MD:
Juan Uribe, MD: