Neurosurgery notes/Spine/Deformity/Classification-Spinal deformity/Roussouly classification

Roussouly classification

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Classification-Spinal deformity

General

  • Made with normal looking spine
  • It is based on the observation that there are characteristic sagittal profiles that occur as a consequence of the orientation of the pelvis, sacrum, and lumbosacral junction.
    • Variations in the lower arc of lordosis are determined by
      the sacral slope.
      • When the sacral slope increases → lower arc of lordosis increases → global curvature of lordosis increases as well.
      • When the sacral slope decreases, two reciprocal changes in the lower arc of lordosis can occur:
        • The lower arc of lordosis can decrease as the apex moves inferiorly OR
        • The lower arc of lordosis can flatten as the radius of curvature increases
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  • Sagittal alignment of the human spine and pelvis in a standardised standing position is highly variable in different individuals.
    • The correlations between the various parameters of lumbar and pelvic alignment indicate that characteristics of the lumbar lordosis are most dependent on the orientation of the sacral slope and the pelvis.
    • The upper arc of lumbar lordosis remains relatively constant, with an average value of approximately 20° in all proposed types of sagittal alignment.
    • The lower arc of lumbar lordosis is the most important determinant of the global lordosis: (This is also why L4-S1 lordosis can help characterise the spinal curvature so well)
      • Lordosis tilt angle
      • Position of the apex
      • Number of lordotic vertebrae
Image
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Roussouly
Type 1
Type 2
Type 3
Type 4
SS
(fixed)
< 35°, which is usually associated with a low pelvic incidence
Sacral slope < 35°
Between 35° and 45°
> 45°, which is associated with a high pelvic incidence
PI
(fixed)
< 40º
Between 40º and 50º
Between 50º and 60º
> 60º
Lumbar lordosis apex
(fixed)
Center of L5 vertebral body.
 
Base of the L4 vertebral body.
Center of the L4 vertebral body.
 
Base of the L3 vertebral body or higher.
% of lordosis at L4-S1
 
80%
65%
60%
50-60%
Vertebrae in lordosis
3
5
5
> 5
Inflection point (lordosis-kyphosis transition junction)
L2
 
T12-L1
T12
T11
Lower arc of lumbar lordosis
Minimal, decreasing toward zero as the sacral slope approaches the horizontal.
Relatively flat
The lower arc of lordosis becomes more promi-
nent.
The lower arc of lordosis is prominent, and the
lordosis tilt angle is zero or positive.
Thoracic kyphosis
Long extending into the lumbar spine
 
 
 

Classes

Type 1 Lordosis.
  • Sacral slope < 35°, which is usually associated with a low pelvic incidence
  • Lumbar lordosis apex: center of L5 vertebral body.
  • Lower arc of lumbar lordosis is minimal, decreasing toward zero as the sacral slope approaches the horizontal.
  • Inflection point is low and posterior, creating a short lordosis with a negative lordosis tilt angle.
  • The upper spine has a significant kyphosis of the thoracolumbar junction and thorax.
 
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  • : Possible evolution of type 1 shape. (“Life is a kyphosing event.” - D. Polly)
    • Occurs by adding kyphosis to the Type 1 shape
    • When the kyphosing event occurs in a type 1, compensation is done below in the lumbar spine by increasing more the lordosis on a short segment (accentuating the type 1).
    • On the other hand, when compensation mechanisms are consumed, LL disappears and extension in the normally kyphotic thoracolumbar area is insufficient, giving raise to “global kyphosis” type with a very small PI
      •  
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Type 2 Lordosis.
  • Sacral slope < 35°.
  • Lumbar lordosis apex: base of the L4 vertebral body.
  • Lower arc of lordosis is relatively flat.
  • The inflection point is higher and more anterior, decreasing the lordosis tilt angle but increasing the number of vertebral bodies included in the lordosis.
  • The entire spine is relatively hypolordotic and hypokyphotic.
 
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  • : Possible evolution of type 2 shape. (“Life is a kyphosing event.” - D. Polly)
    • Type 2 spines have a little range of compensation.
    • When the kyphosing event affects the thoracolumbar area or lumbar area, either
      • LL increases on a small arch generating a type 1 spine (thoracolumbar kyphosis), OR
      • Lumbar spine lordosis disappears generating “lumbar kyphosis” type (if the thoracic spine could compensate with a hypokyphosis) OR
      • “Global kyphosis type” (with a low PI)
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Type 3 Lordosis.
  • The sacral slope is between 35° and 45° (Figure 5).
  • The apex of lumbar lordosis is in the center of the L4 vertebral body.
  • The lower arc of lordosis becomes more prominent.
  • The inflection point is at the thoracolumbar junction, and the lordosis tilt angle is nearly zero.
  • An average of 4 vertebral bodies constitute the arc of lordosis.
  • The spine is well balanced.
 
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  • : Possible evolution of type 3 shape. (“Life is a kyphosing event.” - D. Polly)
    • Loss of lordosis in lumbar spine in type 3 spines → compensation begins in the mobile spine above (loss of TK) and evolves enough to create retroversion with a straight spine with decrease in SS giving raise to false type 2.
    • When thoracic spine is not mobile enough, thoracic hypokyphosis does not occur giving raise to false type 2 + TK with the only compensation being the increase in PT (retroversion of the pelvis).
    • The ultimate evolution of type 3 is global kyphosis (with high PI) maximally retroverted pelvis
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Type 4 Lordosis.
  • The sacral slope is > 45°, which is associated with a high pelvic incidence.
  • The apex of the lumbar lordosis is located at the base of the L3 vertebral body or higher.
  • The lower arc of lordosis is prominent, and the lordosis tilt angle is zero or positive.
  • The number of vertebrae in a lordotic orientation is > 5, and a state of segmental hyperextension exists.
 
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  • : Possible evolution of type 4shape. (“Life is a kyphosing event.” - D. Polly)
    • Decrease in lordosis in type 4 spines induces a type 3 shape with retroverted pelvis, the false type 3 spine.
    • Subsequent evolution is identical to type 3 spines
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Assessment

  • A lateral radiograph of the spine and pelvis is made with the subject in a controlled standing position.
  • The hands are placed on rests, and the patient is asked to stand in a comfortable but erect posture.
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  • Roussouly classification is use to classify a normal spine so trying to do it for a deform spine will be difficult so use the following two methods
      • AO spine:
      • Flow chart helps to define each class with Pelvic Incidence and the location of the Lordosis and Kyphosis.
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      Sebaaly 2020:
      • Low-PI group (< 50°) restored to types 1 and 2
      • High-PI (≥ 50°) group restored to types 3 and 4
      Bari 2020:
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Clinical importance of Roussouly classification

  • Basi 2020
    • Odds ratio for not correcting spine parameters with respect to Roussouly classification for revisional surgery is
      • 1.68 for univariate
      • 4.73 for multivariate
  • Sebaaly 2020:
    • PJK occurred in (p = 0.01) with an OR = 4.6.
      • 13.5% in cases when Roussouly was respected
      • 41.4% in cases where Roussouly was not respected
  • Pizonnes 2019:
    • Rate of mechanical complications
      • 72% in patients not matching the ideal Roussouly type
      • 15% in patients where the Roussoly type was matched.
 

Strengths:

  • Understanding a patient's Roussouly type can help in planning the appropriate inflection point for their surgery

Weaknesses/Limitations:

  • Moderate interobserver reliability, ranging from 0.4 to 0.683.
  • A drawback is that it categorises patients by PI, despite PI describing a continuum rather than discrete categories
  • Does not directly account for thoracic kyphosis (TK) or C2 Tilt8.