Table 3 Factors included across biopsychosocial domains in primary and secondary analyses.

Factors used in primary data-analytic methods

Grey matter volumes (mm³)

Medial frontal cortex, amygdala, thalamus, insula, caudate, putamen, anterior cingulate cortex, hippocampus, precentral gyrus (primary motor cortex), supplementary motor cortex, post-central gyrus (primary somatosensory cortex) and parietal operculum (secondary somatosensory cortex) pooled across left and right sides

Functional connectivity (z)

Medial prefrontal cortex to nucleus accumbens

Posterior cingulate cortex to angular gyrus

Pressure-pain thresholds (kg/cm²)

Forearms, lumbar spine, and posterior calves pooled across left and right sides

Temporal summation (change in vNRS; 0–10)

Forearms, lumbar spine, and posterior calves pooled across left and right sides

Exercise induced hypoalgesia (change in pressure pain thresholds; kg/cm²)

Forearms, lumbar spine, and posterior calves pooled across left and right sides

Other

Central sensitisation inventory (0–100)

Intervertebral disc height (mm)

Average height across all lumbar levels (from middle three slices surrounding the spinous process)

Intervertebral disc volume (cm³)

Average disc volume across all lumbar levels

Intervertebral disc T2 (ms)

Average T2 across all lumbar levels (from central three slices at the spinous process)

Vertebrae fat fraction (%)

Average fat fraction across all lumbar levels (from three highest contiguous slices)

Paraspinal muscle volume (cm³)

Average volume of the multifidus, erector spinae, psoas major and quadratus lumborum across the lumbar levels pooled across sides

Paraspinal muscle fat fraction (%)

Average fat fraction of the multifidus, erector spinae, psoas major and quadratus lumborum across the lumbar levels (from middle three slices at each level) pooled across sides

Radiographic grading

Average Pfirrmann grading across all lumbar levels (1–5)

Average facet joint grading across lumbar levels (0–3)

Average pars grading across all lumbar levels (0–4)

Average disc bulge grade across all lumbar levels (0–3)

Trunk muscle endurance (s)

Maximal trunk flexion and extension endurance

Trunk muscle strength (kg)

Maximal trunk extension strength

PROMIS questionnaires

Anxiety (8–40)

Depression (8–40)

Cognitive function (8–40; higher scores are better)

General self-efficacy (10–50; higher scores are better)

Satisfaction in social roles and activities (8–40; higher scores are better)

Social isolation (8–40)

Emotional support (8–40; higher scores are better)

Instrumental support (8–40; higher scores are better)

Other factors that do not fit the three domains

Nordic musculoskeletal questionnaire – average number of pain sites over the last 7 days and 12 months

Body mass index (kg/m²)

Factors used in secondary data-analytic methods^a

Grey matter volumes (mm³)

Medial frontal cortex, amygdala, thalamus, insula, caudate, putamen, anterior cingulate cortex, hippocampus, precentral gyrus (primary motor cortex), supplementary motor cortex, post-central gyrus (primary somatosensory cortex) and parietal operculum (secondary somatosensory cortex) side specific

Functional connectivity (z)

Medial prefrontal cortex to nucleus accumbens

Posterior cingulate cortex to angular gyrus

Pressure-pain thresholds (kg/cm²)

Forearms, lumbar spine, and posterior calves side specific

Temporal summation (change in verbal numeric rating scale; 0–10)

Forearms, lumbar spine, and posterior calves side specific

Exercise induced hypoalgesia (change is pressure pain thresholds; kg/cm²)

Forearms, lumbar spine, and posterior calves side specific

Other

Central sensitisation inventory (0–100)

Intervertebral disc height (mm)

Lumbar level specific disc height (from middle three slices surrounding the spinous process)

Intervertebral disc volume (cm³)

Lumbar level specific disc volume

Intervertebral disc T2 (ms)

Lumbar level specific T2 across (from middle three slices surrounding the spinous process)

Lumbar level specific nucleus only T2 across (from middle three slices surrounding the spinous process)

Lumbar level specific average T2 across (across whole disc)

Vertebrae fat fraction (%)

Lumbar level specific fat fraction (from three highest contiguous slices)

Paraspinal muscle area (mm²)

Lumbar level specific muscle size (from middle three slices at each level)

Paraspinal muscle fat fraction (%)

Lumbar level specific fat fraction (from middle three slices at each level)

Radiographic grading

Highest Pfirrmann grading across all lumbar levels (1–5)

Highest facet joint grading across lumbar levels (0–3)

Highest pars grading across all lumbar levels (0–4)

Highest disc bulge grade across all lumbar levels (0–3)

Trunk muscle endurance (s)

Maximal trunk flexion and extension endurance

Trunk muscle strength (kg)

Maximal trunk extension strength

PROMIS questionnaires:

Anxiety (8–40)

Depression (8–40)

Social isolation (8–40)

Cognitive function (8–40; higher scores are better)

General self-efficacy (10–50; higher scores are better)

Satisfaction in social roles and activities (8–40; higher scores are better)

Emotional support (8–40; higher scores are better)

Instrumental support (8–40; higher scores are better)

Other Factors that do not fit the three domains:

Nordic musculoskeletal questionnaire – average number of pain sites over the last 7 days and 12 months

Body mass index (kg/m²)