Contribution of Lumbar Spine Pathology and Age to Paraspinal Muscle Size and Fatty Infiltration

TLDR: Lumbar muscle fat content, but not CSA, changes with age in individuals with pathology, and in women, this increase is more profound than age-related increases in healthy individuals.

Abstract: Author(s): Shahidi, Bahar; Parra, Callan L; Berry, David B; Hubbard, James C; Gombatto, Sara; Zlomislic, Vinko; Allen, R Todd; Hughes-Austin, Jan; Garfin, Steven; Ward, Samuel R | Abstract: Study designRetrospective chart analysis of 199 individuals aged 18 to 80 years scheduled for lumbar spine surgery.ObjectiveThe purpose of this study was to quantify changes in muscle cross-sectional area (CSA) and fat signal fraction (FSF) with age in men and women with lumbar spine pathology and compare them to published normative data.Summary of background dataPathological changes in lumbar paraspinal muscle are often confounded by age-related decline in muscle size (CSA) and quality (fatty infiltration). Individuals with pathology have been shown to have decreased CSA and fatty infiltration of both the multifidus and erector spinae muscles, but the magnitude of these changes in the context of normal aging is unknown.MethodsIndividuals aged 18 to 80 years who were scheduled for lumbar surgery for diagnoses associated with lumbar spine pain or pathology were included. Muscle CSA and FSF of the multifidus and erector spinae were measured from preoperative T2-weighted magnetic resonance images at the L4 level. Univariate and multiple linear regression analyses were performed for each outcome using age and sex as predictor variables. Statistical comparisons of univariate regression parameters (slope and intercept) to published normative data were also performed.ResultsThere was no change in CSA with age in either sex (P g 0.05), but women had lower CSAs than men in both muscles (P l 0.0001). There was an increase in FSF with age in erector spinae and multifidus muscles in both sexes (P l 0.0001). Multifidus FSF values were higher in women with lumbar spine pathology than published values for healthy controls (P = 0.03), and slopes tended to be steeper with pathology for both muscles in women (P l 0.08) but not in men (P g 0.31).ConclusionLumbar muscle fat content, but not CSA, changes with age in individuals with pathology. In women, this increase is more profound than age-related increases in healthy individuals.Level of evidence3.

Figures

Figure 3. R Panel C) an in both FSF the erector

Figure 1. F EGENDS low diagram of participant screening, exclusion, and analysis.

Table 2. Patient demographic characteristics.

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UC San Diego
UC San Diego Previously Published Works
Title
Contribution of Lumbar Spine Pathology and Age to Paraspinal Muscle Size and Fatty
Infiltration.
Permalink
https://escholarship.org/uc/item/4cc45524
Journal
Spine, 42(8)
ISSN
0362-2436
Authors
Shahidi, Bahar
Parra, Callan L
Berry, David B
et al.
Publication Date
2017-04-01
DOI
10.1097/brs.0000000000001848
Peer reviewed
eScholarship.org Powered by the California Digital Library
University of California

SPINE An International Journal for the study of the spine Publish Ahead of Print
DOI : 10.1097/BRS.0000000000001848
Contribution of lumbar spine pathology and age to paraspinal muscle size and fatty infiltration
Bahar Shahidi PT, PhD
1,2
; Callan L Parra BS
2
; David B Berry MS
3
; James C Hubbard MD
2
; Sara
Gombatto PT, PhD
4
; Vinko Zlomislic MD
2
; R. Todd Allen MD
2
; Jan Hughes-Austin PT, PhD
2
; Steven
Garfin, MD
2
; Samuel R. Ward PT, PhD
1,2,3
AFFILIATIONS:
1
University of California San Diego Department of Radiology
2
University of California San Diego Department of Orthopaedic Surgery
3
University of California San Diego Department of Bioengineering
4
San Diego State University Physical Therapy Program
CORRESPONDING AUTHOR:
Samuel R Ward PT, PhD
University of California San Diego
9500 Gilman Dr. MC0863
La Jolla, CA 92093
srward@ucsd.edu
Phone: (858) 534-4918
Fax: (858) 822-3807
Acknowledgement: April 29, 2016
Revise: July 8, 2016
Accept: July 22, 2016
The manuscript submitted does not contain information about medical device(s)/drug(s).
NIH (1TL1TR001443) grant funds were received in support of this work.
Relevant financial activities outside the submitted work: grants, payment for lectures,
travel/accommodations/meeting expenses.
Copyright © 2016 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.

ABSTRACT
Study Design: Retrospective chart analysis of 199 individuals aged 18-80 years scheduled for lumbar
spine surgery.
Objective: The purpose of this study was to quantify changes in muscle cross sectional area (CSA) and
fat signal fraction (FSF) with age in men and women with lumbar spine pathology and compare them
to published normative data.
Summary of Background Data: Pathological changes in lumbar paraspinal muscle are often
confounded by age-related decline in muscle size (CSA) and quality (fatty infiltration). Individuals
with pathology have been shown to have decreased CSA and fatty infiltration of both the multifidus
and erector spinae muscles, but the magnitude of these changes in the context of normal aging is
unknown.
Methods: Individuals aged 18-80 years who were scheduled for lumbar surgery for diagnoses
associated with lumbar spine pain or pathology were included. Muscle CSA and FSF of the multifidus
and erector spinae were measured from preoperative T2-weighted magnetic resonance images at the L4
level. Univariate and multiple linear regression analyses were performed for each outcome using age
and gender as predictor variables. Statistical comparisons of univariate regression parameters (slope
and intercept) to published normative data were also performed.
Results: There was no change in CSA with age in either gender (p>0.05), but women had lower CSA’s
than men in both muscles (p<0.0001). There was an increase in FSF with age in erector spinae and
multifidus muscles in both genders (p<0.0001). Multifidus FSF values were higher in women with
lumbar spine pathology than published values for healthy controls (p=0.03), and slopes tended to be
steeper with pathology for both muscles in women (p<0.08) but not in men (p>0.31).
Conclusions: Lumbar muscle fat content, but not CSA changes with age in individuals with pathology.
In women, this increase is more profound than age-related increases in healthy individuals.
Copyright © 2016 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.

Key Words: Lumbar Spine Pathology; Fatty Infiltration; Magnetic Resonance Imaging; Age; Cross
Sectional Area
Level of Evidence: 3
Copyright © 2016 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.

INTRODUCTION
Low back pain (LBP) is highly prevalent in the United States, with approximately 65-85% of
the general population experiencing some low back pain within their lifetime(1). Although most LBP is
considered self-limiting in nature, recent evidence suggests that a high proportion of individuals
develop recurrent symptoms, leading to poor functional outcomes and increased health care
utilization(1, 2). Changes in muscle size and fat content are often associated with LBP symptoms and
lumbar spine pathology (3, 4), however, the magnitude of these pathological changes are confounded
by natural age-related changes such as sarcopenia, fatty infiltration, and decreased torque production
(5). Muscle physiological cross sectional area is commonly used as an indicator for muscle force
production capacity (6), and cross sectional area (CSA) has been quantified using Magnetic Resonance
Imaging (MRI) region of interest segmentation analyses(7). Measures of total muscle size or volume in
isolation do not take into account fatty infiltration, which is associated with aging and pathology (8).
Since fatty infiltration in muscle decreases the proportion of contractile tissue capable of producing
force, it is important to understand how muscle size and fatty infiltration change, both with age, and in
the presence of pathology. Understanding muscle loss in the presence of lumbar spine pathology
requires an understanding of how muscle loss occurs with aging. If pathology yields unique rates of
muscle loss, new strategies for resolving muscle loss should be a clinical goal for functional
improvement, since standard exercise strategies do not appear to reverse these changes in this
population (9) (10-12).
Prior literature suggests that LBP and pathology alters CSA and fatty infiltration, with most
studies demonstrating decreases in muscle size and increases in fatty infiltration in those with
symptoms compared to their healthy counterparts(13-15). However, the extent of these morphological
changes is unclear when considering physiological declines observed with normal aging(16-18).
Effects of aging and pathology on muscle size and quality have been observed in other musculoskeletal
regions, such as the rotator cuff and thigh muscles. In the rotator cuff, there is evidence that muscle size
Copyright © 2016 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.

Frequently asked questions

Q1. What have the authors contributed in "Contribution of lumbar spine pathology and age to paraspinal muscle size and fatty infiltration" ?

The purpose of this study was to quantify changes in muscle cross sectional area ( CSA ) and fat signal fraction ( FSF ) with age in men and women with lumbar spine pathology and compare them to published normative data. Copyright © 2016 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. 

Q2. What future works have the authors mentioned in the paper "Contribution of lumbar spine pathology and age to paraspinal muscle size and fatty infiltration" ?

Further research is required to elucidate the underlying mechanisms of age versus pathology related changes in muscle quality and their functional implications. 

Q3. What is the effect of age on fatty infiltrate in the lumbar spine?

Although CSA is greater in men than women, it does not decline with age, whereas fatty infiltrate increases with age and pathology in both muscles. 

Q4. What is the reason why the patients were excluded from the analyses?

From the initial 236 patients queried, 37 patients were excluded from the analyses; 17 patients were excluded due to existence of instrumentation at the L4 level affecting MR signal intensity analyses, 7 were excluded due to CPT codes unrelated to LBP or degenerative pathology (i.e. skinCopyright © 2016 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. 

Q5. What is the effect of age on muscle size and quality?

Prior literature suggests that LBP and pathology alters CSA and fatty infiltration, with moststudies demonstrating decreases in muscle size and increases in fatty infiltration in those with symptoms compared to their healthy counterparts(13-15). 

Q6. What was the CSA of the lumbar vertebra?

Regions of interest from T2-weighted axial magnetic resonance images taken from a singleslice estimated to be closest to the midlevel of the L4 vertebra were used to measure muscle CSA and fat content with custom written Matlab software (Mathworks, Natick MA). 

Q7. What was the trend for the slope of the erector spinae?

There was a trend towards a steeper slope in women with pathology compared to women without pathology for both multifidus (p=0.08) and erector spinae muscles (p=0.08), such that women with pathology displayed more age-related increases in FSF (Figure 4b,d). 

Q8. Why were there no comparisons between normal and pathological trajectories for CSA?

Due to differences in analytical methods for measuring muscle size, comparisons betweennormal and pathological trajectories for CSA were not performed (Figure 4). 

Q9. What were the predictors of FSF in the multifidus?

Age and gender were significant predictors of FSF in the multifidus (age β = 0.004, gender β = 0.0600; p<0.0001) whereas only age predicted FSF in the erector spinae (Age β = 0.0040, p<0.0001, gender β = 0.0201; p=0.15) muscle (Figure 3a-b). 

Q10. What was the CSA analysis of the lumbar spine?

For CSA measurements, regions of interest for both multifidus and erector spinae muscles were seeded and segmented bilaterally using Osirix software (22), based on fascial plane separations using the facet joint as a landmark between the multifidus and erector spinae, and the lumbosacral fascia posteriorly(23) (Figure 2a). 

Q11. What did the authors do to determine the effect of age on the slope of the ere?

Recognizing that differences in age range between the population in the current study and the healthy cohort may affect the results, the authors also performed sub-comparisons using only patients under the age of 65 (N=129), yielding similar main effects of age and sex. 

Q12. What was the effect of age on CSA?

Linear regression model results demonstrated no effect of age on muscle CSA (β = -0.0002 and -0.0118 for multifidus and erector spinae respectively, p>0.59), but a significant gender effect for multifidus (β = -2.26, p<0.0001) and erector spinae muscle CSA (β =-3.19, p<0.0001) where men displayed a larger CSA for both spine muscles (Figure 3c-d).