BackWards - Unveiling the brain's topographic organization of paraspinal sensory input.

Cortical reorganization and its potential pathological significance are being increasingly studied in musculoskeletal disorders such as chronic low back pain (CLBP) patients. However, detailed sensory-topographic maps of the human back are lacking, and a baseline characterization of such representations, reflecting the somatosensory organization of the healthy back, is needed before exploring potential sensory map reorganization. To this end, a novel pneumatic vibrotactile stimulation method was used to stimulate paraspinal sensory afferents, while studying their cortical representations in unprecedented detail. In 41 young healthy participants, vibrotactile stimulations at 20 Hz and 80 Hz were applied bilaterally at nine locations along the thoracolumbar axis while functional magnetic resonance imaging (fMRI) was performed. Model-based whole-brain searchlight representational similarity analysis (RSA) was used to investigate the organizational structure of brain activity patterns evoked by thoracolumbar sensory inputs. A model based on segmental distances best explained the similarity structure of brain activity patterns that were located in different areas of sensorimotor cortices, including the primary somatosensory and motor cortices and parts of the superior parietal cortex, suggesting that these brain areas process sensory input from the back in a "dermatomal" manner. The current findings provide a sound basis for testing the "cortical map reorganization theory" and its pathological relevance in CLBP.

In vivo measurements of spinal stiffness according to a stepwise increase of axial load.

BACKGROUND: The spine has a complex motor control. Its different stabilization mechanisms through passive, active, and neurological subsystems may result in spinal stiffness. To better understand lumbar spinal motor control, this study aimed to measure the effects of increasing the axial load on spinal stiffness. METHODS: A total of 19 healthy young participants (mean age, 24 ± 2.1 years; 8 males and 11 females) were assessed in an upright standing position. Under different axial loads, the posterior-to-anterior spinal stiffness of the thoracic and lumbar spine was measured. Loads were 0%, 10%, 45%, and 80% of the participant's body weight. RESULTS: Data were normally distributed and showed excellent reliability. A repeated-measures analysis of variance with a Greenhouse-Geisser correction showed an effect of the loading condition on the mean spinal stiffness [F (2.6, 744) = 3.456, p < 0.001]. Vertebrae and loading had no interaction [F (2.6, 741) = 0.656, p = 0.559]. Post hoc tests using Bonferroni correction revealed no changes with 10% loading (p = 1.000), and with every additional step of loading, spinal stiffness decreased: 0% or 10-45% loading (p < 0.001), 0% or 10-80% loading (p < 0.001), and 45-80% (p < 0.001). CONCLUSION: We conclude that a load of ≥ 45% of the participant's body weight can lead to changes in the spinal motor control. An axial load of 10% showed no significant changes. Rehabilitation should include high-axial-load exercise if needed in everyday living.

Healthy women show more experimentally induced central sensitization compared with men.

ABSTRACT: Women more often experience chronic pain conditions than men. Central sensitization (CS) is one key mechanism in chronic pain that can differ between the sexes. It is unknown whether CS processes are already more pronounced in healthy women than in men. In 66 subjects (33 women), a thermal CS induction protocol was applied to the dorsum of one foot and a sham protocol to the other. Spatial extent [cm 2 ] of secondary mechanical hyperalgesia (SMH) and dynamic mechanical allodynia were assessed as subjective CS proxy measures, relying on verbal feedback. Changes in nociceptive withdrawal reflex magnitude (NWR-M) and response rate (NWR-RR) recorded through surface electromyography at the biceps and rectus femoris muscles were used as objective CS proxies. The effect of the CS induction protocol on SMH was higher in women than in men (effect size 2.11 vs 1.68). Nociceptive withdrawal reflex magnitude results were statistically meaningful for women (effect size 0.31-0.36) but not for men (effect size 0.12-0.29). Differences between men and women were not meaningful. Nociceptive withdrawal reflex response rate at the rectus femoris increased in women after CS induction and was statistically different from NWR-RR in men (median differences of 13.7 and 8.4% for 120 and 140% reflex threshold current). The objective CS proxy differences indicate that dorsal horn CS processes are more pronounced in healthy women. The even larger sex differences in subjective CS proxies potentially reflect greater supraspinal influence in women. This study shows that sex differences are present in experimentally induced CS in healthy subjects, which might contribute to women's vulnerability for chronic pain.

Limited prognostic value of pain duration in non-specific neck pain patients seeking chiropractic care.

BACKGROUND: Pain chronicity is considered an important prognostic factor for outcome. Here, it was investigated whether pain duration influences outcome when only chronic patients (pain >3 months) are considered. Secondary aims were to determine, in patients of any pain duration, how much variance in outcome is explained by pain duration and whether pain duration truly predicts outcomes, that is out-of-sample prediction in independent data. METHODS: Secondary analysis of a cohort study of neck pain patients. Patients were assessed before start of treatment and at 1-week, 1-, 3-, 6- and 12-month follow-up. Outcomes were patient global impression of change (PGIC) and percent change in patients' perceived pain intensity, rated on a numerical rating scale (NRS). Regression analyses (linear and logistic) and supervised machine learning were used to test the influence of pain duration on PGIC and percent NRS change at 1-week, 1-, 3-, 6- and 12-month follow-up within sample and out-of-sample. Separate analyses were performed for the full sample (n = 720) and for chronic patients (n = 238) only. RESULTS: No relationship between pain duration and outcome was found for chronic patients only. For the full sample, statistical relationships between pain duration and outcomes were observed at all tested follow-up time points. However, the amount of variance in outcome explained by pain duration was low and no out-of-sample prediction was possible. CONCLUSIONS: Pain duration did not emerge as an important predictor of outcome in this database of 720 neck pain patients receiving chiropractic treatment. SIGNIFICANCE STATEMENT: The relatively large dataset of neck pain patients challenges the widely accepted wisdom that pain duration is an important predictor of pain outcomes and that very chronic patients might only have a small likelihood of getting better. It is postulated that these results are important for the attitude of the first encounter between healthcare professionals and chronic patients.