Oral Presentation 50th International Society for the Study of the Lumbar Spine Annual Meeting 2024

Quantifying Full Spine Paraspinal Muscle Volume, Intramuscular Fat and Fat-free Muscle (A)symmetry in Adolescent Idiopathic Scoliosis (#MP-8e)

Phoebe Duncombe 1 2 , Taylor JM Dick 2 , Phoebe Ng 2 3 , Maree T Izatt 4 5 6 , Peter Pivonka 7 , Labrom Robert 4 5 6 , Kylie Tucker 2
  1. The University of Queensland, Brisbane, QUEENSLAND, Australia
  2. School of Biomedical Sciences, The Faculty of Medicine , The University of Queensland, Brisbane , Queensland , Australia
  3. KK Women’s and Children’s Hospital, Singapore, Singapore
  4. Queensland Children’s Hospital, Brisbane, Queensland, Australia
  5. School of Mechanical, Medical and Process Engineering, Queensland University of Technology, Brisbane , Queensland, Australia
  6. Biomechanics and Spine Research Group, QUT at Centre for Children’s Health Research, Brisbane, Queensland, Australia
  7. ARC Training Centre for Joint Biomechanics, Queensland University of Technology , Brisbane, Queensland, Australia

INTRODUCTION

Adolescent idiopathic scoliosis (AIS) is characterized by an atypical 3D spinal curvature that develops/progresses between 10-18 years of age. Asymmetry in paraspinal muscle size and quality influences force-generation capacity and may contribute to asymmetrical vertebral growth (1). We aimed to determine if paraspinal muscle volume and intramuscular fat asymmetry, assessed across many vertebrae, differed between female adolescents with AIS and age-matched controls.

 

METHODS

T1-weighted and mDixon MRI scans were performed on 23 female adolescents with primary-right-convex thoracic scoliosis [Cobb angle: 40±16°; age: 13.8±1.5 years]; and 20 adolescents without scoliosis [age: 13.1±1.8 years]. Paraspinal muscle volumes (only multifidus and longissimus shown here) were determined from the 6th Thoracic [T6] to 4th lumbar [L4] vertebral levels. Fat-fraction maps from mDixon scans were co-registered with muscle volumes to determine intramuscular fat proportions. Muscle volume, intramuscular fat proportion and fat-free muscle volume asymmetry indices [ln(concave/convex)] were determined (2).  

 

RESULTS

The asymmetry in paraspinal muscle volume, intramuscular fat and fat-free volume were greater in AIS than controls at multiple vertebral levels (For p<0.05, see fig. 1, 2).

Muscle volume: Multifidus volume was significantly greater (p<0.05) on the concave than the convex-side of the primary thoracic curve across 6 thoracic vertebral levels; and greater on the concave than convex-side of the secondary/compensatory lumbar curve across 4 lumbar vertebral levels). Very little asymmetry in muscle volume was identified for the longissimus.

Intramuscular fat: Greater (p<0.05) fat was observed on the concave than the convex-side around the thoracic scoliotic curve apex, and in the lumbar region for both muscles (fig. 1B and 2B).

Fat-free volume: Multifidus fat-free muscle volume three vertebral levels above the apex was significantly greater on the concave than the convex-side (p<0.05) and was greater on the convex than the concave-side at the 5th vertebral level below the apex (fig. 1C). For longissimus only at the 3rd vertebral level above the apex was the fat-free muscle volume greater on the convex than the concave-side (p<0.05, fig. 2C).

 

DISCUSSION

Compared to the control group, participants with AIS have significant asymmetry in multifidus volume, intramuscular fat, and fat-free muscle, across multiple vertebral levels around the thoracic curve apex and in the lumbar spine. Longissimus also had significant asymmetry in intramuscular fat levels around the apex of the thoracic curve and in the lumbar spine.  This provides evidence of an imbalance in the force-producing capacity of paraspinal muscles in AIS, particularly in the deep paraspinal muscle which apply forces to the transverse and spinous processes of the vertebrae. The next step in this data collection is to determine if these asymmetries are correlated with curve severity, future progression of curve, and bony asymmetries identified in our participants with AIS.

Crucially, all of these muscle-focused factors are modifiable (3). By identifying and targeting imbalances in muscle size, quality and activation during adolescence, when the bones are still growing, we may be able to re-balance the forces applied to the spine and promote symmetrical growth. Further investigation into how these asymmetries influence paraspinal muscle force-generating capacity is warranted.

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  1. Stokes IA, Spence H, Aronsson DD, Kilmer N (1996) Mechanical modulation of vertebral body growth: Implications for scoliosis progression. Spine (Phila Pa 1976) 21:1162-1167. doi: 10.1097/00007632-199605150-00007
  2. Cole TJ, Altman DG (2017) Statistics Notes: Percentage differences, symmetry, and natural logarithms. BMJ 358:j3683. doi: 10.1136/bmj.j3683
  3. Hughes DC, Ellefsen S, Baar K (2018) Adaptations to Endurance and Strength Training. Cold Spring Harb Perspect Med 8. doi: 10.1101/cshperspect.a029769