Keywords
spondylosis - spine - lumbar pain - classification - radiography
Introduction
The analysis of radiographic parameters for sagittal pelvic alignment has become critical
to the evaluation and treatment of adult spinal deformity (ASD).[1] The importance of these radiographic parameters lies in their strong correlation
with quality of life and functional capacity indicators,[2]
[3]
[4] which was the basis for the classification system most used for ASD, called Scoliosis
Research Society-Schwab (SRS-Schwab).[5] More recently, the clinical relevance of the SRS-Schwab classification system has
been demonstrated, and the degree of functional limitation and the choice of treatment
are influenced by SRS-Schwab subtypes and its modifiers.[6]
The frequency of ASD is related to age, with a higher prevalence in older subjects.[7]
[8] Thus, as expected in the elderly population, other conditions may be concurrent
with ASD, potentially confusing the functional limitation of these subjects. These
conditions include lumbar degenerative disease (LDD), whose pathophysiology involves
anatomical and structural changes in intervertebral discs, facet joints and vertebral
bodies.[9] Such degenerative changes may be associated with spinal deformities, instabilities,
such as spondylolisthesis, and canal or foraminal narrowing. In addition, they may
lead to compression of neural elements, resulting in significant axial low-back pain
and/or radicular pain.[10]
There is a lack of studies evaluating the interference of LDD in spinopelvic radiographic
parameters, as well as the correlation of these parameters with symptoms and functional
limitation. Our aim was to evaluate the relationship between the severity of the LDD
and sagittal spinopelvic alignment.
Materials and Methods
Population
The present is a cross-sectional study with a cohort of subjects recruited prospectively
and non-consecutively from an outpatient facility. The study was approved by the Ethics
in Research Committee of our institution (under CAAE 18013219.7.0000.5463), and the
patients signed an informed consent form. Adult patients (aged ≥ 18 years) complaining
of low-back pain with or without radiculopathy symptoms and LDD radiographic signs
were included. The exclusion criteria were: previous spinal or central nervous system
surgery; neurological or neuromuscular diseases; history of spinal trauma or neoplastic
disease; hip/knee/ankle/foot disability potentially altering joint positions; and
inadequate radiography, not enabling visualization from the second cervical vertebra
(C2) to the head of the femur, or with insufficient resolution to analyze the radiographic
signs of LDD.
Determination of the Severity of Degenerative Lumbar Disease
Images in frontal and lateral views of the lumbar spinal segment, extracted from total
(panoramic) spinal radiographies, were analyzed. Only digitalized images in the digital
imaging and communications in medicine (DICOM) format were considered, since they
enable magnification while maintaining quality and resolution, with greater precision
for the assessment by level of the entire lumbar segment. All tests were performed
at the same radiology service, following a standardized technique: comfortable, orthostatic
posture, with shoulders at 45° of elevation and flexed elbows, resting the fingertips
on the clavicles or face.[11]
The severity of the LDD was defined using the recently-published scale based on a
total spinal radiography.[12] This scale determines severity by analyzing the presence or not of the main radiographic
signs of the disease, including marginal osteophytosis at the vertebral body, loss
of height in the intervertebral disc, sclerosis and subchondral cysts in end plates,
and the number of vertebral segments affected.[12] The absence or presence of scoliosis or signs of objective instability, including
spondylolisthesis and laterolisthesis, was also considered. Each radiograph was evaluated
by two independent examiners, both orthopedists under training for spine surgery (with
one and two years of experience). According to these criteria, the patients were graded
as follows ([Figure 1]):
Fig. 1 Illustration of the radiographic grade scale for lumbar degenerative disease (LDD).
(A) Grade 0; (B) grade I; (C) grade II; (D) grade III.
-
Grade 0: no signs of LDD.
-
Grade I: presence of signs of LDD in one or two segments, with no scoliosis or signs
of instability.
-
Grade II: presence of signs of LDD in three or more segments, with no scoliosis or
signs of instability.
-
Grade III: presence of signs of LDD with scoliosis (coronal inclination ≥ 30°, measured
by the Cobb technique) and/or signs of instability, such as laterolisthesis (> 2 mm)
and spondylolisthesis (at least grade 2).
Evaluation of Spinopelvic Radiographic Parameters
The radiographic parameters were measured using the Surgimap Spine (Nemaris, Inc.,
New York, NY, US) software, a validated tool for radiographic evaluation of the spine.[13] The following parameters were considered: sagittal vertical axis (SVA), calculated
as the distance between the plumb line of C7 and the posterosuperior corner of the
sacrum; pelvic tilt (PT), an angle between the line touching the upper sacrum plateau
and the horizontal plane; pelvic incidence (PI), an angle between a line perpendicular
to the center of the upper sacrum plateau and a line from the center of the upper
sacrum plateau to the center of the femur heads; lumbar lordosis (LL), a sagittal
Cobb angle between the upper plateau of L1 and the upper plateau of S1; and the discrepancy
between PI and LL (PI-LL).[1] These parameters were measured by two independent examiners (the same ones who determined
the severity of the LDD). If there were any discrepancies between the two measurements,
a third measurement was performed. The value of each parameter was obtained by the
average of the measures performed by the two examiners.
Statistical Analysis
The statistical analysis was performed using the R software (R Foundation for Statistical
Computing, Vienna, Austria), version 3.4.9. After determining the severity of the
LDD, the spinopelvic radiographic parameters of the four grades were compared by analysis
of variance (ANOVA) and a Bonferroni posttest. The level of significance was set at
5%, and statistically significant results presented p-values lower than 0.05.
Results
Population, Demographics and LDD Severity
From a total of 138 radiographic exams, 130 patients met the inclusion criteria and
had images with sufficient resolution. There were 97 (75%) female patients in total,
and the average age of the sample was of 57 years (standard deviation [SD]: 14.6 years),
ranging from 18 to 95 years. Regarding LDD severity, 12 (9%) patients were grade 0,
41 (32%) were grade I, 43 (33%) were grade II, and 34 (26%) were grade III. There
was a significant age difference among LDD grades (p < 0.001) ([Figure 2]), with grade-I patients (mean age: 51 years; SD: 10 years) older than grade-0 (mean
age: 33 years; SD: 13.6 years) (p < 0.001) subjects, grade-II (mean age: 63 years; SD: 10.6 years) patients older than
grade-I (p < 0.001) subjects, and no significant difference between grades II and III (mean
age: 65 years; SD: 12.2 years) subjects (p = 1).
Fig. 2 Age comparison according to LDD grades.
Spinopelvic Radiographic Parameters
The SVA differed according to LDD grades ([Figure 3]), and grade-III patients presented higher mean SVA values, that is, greater anterior
inclination of the trunk, than grade-I (p = 0.008) and grade-0 (p = 0.03) subjects ([Table 1]). The PT was also different according to LDD grades ([Figure 4]), and grade-III patients had higher mean PT values, that is, greater pelvic retroversion,
than grade-I (p <0.001) and grade-0 (p = 0.01) subjects ([Table 1]). The PI-LL values were also influenced by LDD grades ([Figure 5]), with average values higher in grade-III compared to grade-I (p = 0.04) patients.
There was no significant difference among LDD grades regarding PI and LL values ([Table 1]).
Fig. 3 Comparison of the sagittal vertical axis (SVA) in different LDD grades.
Fig. 4 Comparison of the pelvic tilt (PT) in different LDD grades.
Fig. 5 Comparison of the discrepancy between pelvic incidence and lumbar lordosis (PI-LL)
in different LDD grades.
Table 1
|
TOTAL
M (SD)
|
GRADE 0
M (SD)
|
GRADE I
M (SD)
|
GRADE II
M (SD)
|
GRADE III
M (SD)
|
p
|
|
SVA (mm)
|
−3.4 (32.8)
|
−21.1 (36.6)
|
−14.9 (27.7)
|
2.6 (26)
|
8.9 (38.4)
|
0.001
|
|
PT (°)
|
17 (11.4)
|
11.9 (9.6)
|
13.3 (10.4)
|
17.1 (9.4)
|
23.3 (12.8)
|
< 0.001
|
|
PI (°)
|
53.5 (14.8)
|
49.3 (19.3)
|
51.4 (16)
|
53.2 (12)
|
57.8 (14.3)
|
0.191
|
|
LL (°)
|
56.7 (13.3)
|
58.1 (10.5)
|
57.7 (13.5)
|
56.4 (11.7)
|
55.5 (15.8)
|
0.884
|
|
PI-LL (°)
|
−3.4 (14.8)
|
−8.7 (10.2)
|
−6.8 (13)
|
−3.3 (13)
|
2.3 (18.5)
|
0.03
|
Discussion
The current global demographic change, with aging in the population related to a higher
life expectancy, which results in a surge of age-related health problems.[7]
[8] Conditions often overlap, as in the spine, in which LDD is usually associated with
a loss of sagittal alignment.[14] Several articles[2]
[3]
[4]
[6]
[10]
[14] suggest an association between LDD and loss of sagittal alignment, resulting in
pain and functional disability, but there are no studies demonstrating the real relationship
between LDD severity and loss of sagittal alignment, nor the role of each component
in the etiology of the symptoms.
A recently-introduced LDD grading system is based on the analysis of lumbar-segment
findings in total (panoramic) spinal radiographs.[12] This scale was developed to precisely evaluate, in the same test, that is, a total
spinal radiograph, both LDD and sagittal pelvic alignment parameters.[12] The advent of digital analysis of radiographic images enables sufficient magnification
with no detriment to resolution to assess signs of degenerative disease in lumbar
segments.
The most used classification system for ASD is SRS-Schwab, which describes the deformity
pattern at the coronal plane and considers three radiographic parameters of spinopelvic
alignment as sagittal modifiers.[5] These modifiers include the SVA, PT and PI-LL, which are classified according to
the severity of the loss in sagittal alignment. Terran et al.[6] observed a strong correlation between worsened modifier values, meaning a deterioration
in spinopelvic sagittal alignment, with worse indicators of quality of life, as well
as with the decision regarding surgical treatment and the performance of more complex
surgeries.
Our study showed increased SVA, PT and PI-LL values, that is, the sagittal modifiers
from the SRS-Schwab classification, in patients with grade III LDD. The increase in
these parameters suggests a worsened spinopelvic sagittal alignment, with greater
anterior trunk inclination (SVA) and greater PT as a potential compensation mechanism
for the anterior inclination. In addition, the relationship between LL and PI is well
established, so, in each individual, the LL must be in harmony with the PI,[4]
[5] highlighting the importance of PI-LL. Higher PI-LL values mean LL loss in relation
to what is expected from the PI.[4]
[5] In the present study, grade-III patients tended to lose the spinopelvic sagittal
alignment, with increased SVA values, which denotes anterior trunk inclination, and
increased PT values, with pelvic retroversion as a potential compensatory mechanism.
In addition, there was an increase in PI-LL, which means a relative lack of LL in
relation to the PI value.
Grade-III patients were also older than grade-0 and I subjects, which may have influenced
the increase in SVA, PT and PI-LL values. A recent study[15] showed that asymptomatic individuals present increased SVA and PT as they age. In
another study, Lafage et al.[16] noted that even though sagittal alignment changes with age, it is not necessarily
related to the onset of symptoms and functional disability. As such, we must question
whether cut-off values for radiographic parameters considered as sagittal modifiers
in the SRS-Schwab classification system should be adjusted by age.[16]
So far, it is not known whether LDD findings would have any influence on the correlation
between loss of sagittal alignment and the occurrence of pain and functional disability,
as it has been demonstrated that age influences the correlation between sagittal alignment
and pain/functional disability. Some LDD findings, mainly those from grade-III patients,
including scoliosis and objective instability (spondylolisthesis and laterolisthesis),
could confuse this correlation, as they are predisposing factors per se for changes
in spinopelvic alignment parameters. This can generate a confounding factor regarding
what is most relevant for the loss of sagittal alignment, whether LDD advancement
or the presence of a deformity, warranting further studies.
However, the present study has some limitations, mainly because it is an observational
analysis using only images, with no consideration of clinical aspects, such as indicators
of quality of life, in this correlation of radiographic parameters for spinopelvic
alignment and LDD grades. In addition, there was a selection bias in the inclusion
of subjects, since all patients came from an orthopedic outpatient facility with some
spinal complaint, instead of being age-stratified asymptomatic individuals.
Conclusion
The present study on the correlation between LDD grades and radiographic parameters
of spinopelvic alignment showed that patients with more severe LDD tend to lose sagittal
alignment, with greater anterior inclination of the trunk, pelvic retroversion as
a potential compensatory mechanism, and lumbar hypolordosis regarding the PI value.
The LDD grade scale can be the basis for future studies aiming better understand the
role of LDD on sagittal alignment in asymptomatic, age-stratified individuals, regardless
of the the grade-III deformities.
