Background & Aims

Spinal manipulative therapy (SMT) can help many patients relieve pain and improve function, however, the precise mechanisms underlying SMT’s effects remain unclear. A potential mechanism associated with clinical benefits of SMT may involve alterations in lumbar proprioceptive function, which is mainly controlled by muscle spindles. Proprioceptive weighting (PW), which is the central nervous system’s capability to selectively prioritize the most reliable proprioceptive inputs from body stabilizers like ankle and paraspinal muscles, is crucial for proprioceptive function. PW capacity is often impaired in LBP patients with increased ankle-steered weighting. Interestingly, animal studies have demonstrated that SMT-like loads can increase paraspinal muscle spindle discharge, suggesting that SMT might enhance PW from paraspinal muscles in humans. However, evidence for such a neurophysiological effect and its link to clinical outcomes of SMT in patients with LBP does not yet exist.

Methods

171 participants (pain-free adults (N=129): mean age = 26.3y, 81 females; patients with chronic non-specific LBP (N = 42): mean age = 30.2y, 29 females) were pseudorandomized to three groups (1:1:1 allocation ratio): 1) lumbar SMT (LMANIP, high-velocity low-amplitude SMT at the L4/L5 level), 2) lumbar spinal mobilization (LMOB, Grade III mobilization), or 3) no intervention (NI). PW assessments were conducted pre- and immediately post-intervention by intervention-blinded staff, using a force plate to track postural sway on two surfaces (stable/foam) and applying vibrotactile stimulation (60Hz) at the lumbar longissimus and triceps surae muscles. The primary outcome was the PW ratio calculated from changes in the center of pressure in the anteroposterior direction (PW near “1” = greater dependence on ankle proprioception, near “0” = more reliance on lumbar proprioception). Mixed (including both groups) and regression (only patients) models were used for statistical analysis.

Results

Mixed model results yielded significant main effects for “surface” and ”time point” (p`s < 0.001), but no main effect for “group” (p = 0.415). Post-hoc t-tests for the interaction effect "intervention x time point" showed a significant effect for LMANIP (p = 0.001, corrected for multiple comparisons), characterized by a significant decrease in the PW ratio after LMANIP. Such an effect was not observed for LMOB or NI (p`s > 0.575). The regression results (adjusted R2=0.154) revealed that LMANIP was associated with a significantly greater reduction in pain (pre-/post-intervention mean difference = 1.85, SD = 1.91) compared to both LMOB and NI (p’s < 0.017). Additionally, significant interactions were observed between the pre-intervention PW ratio and “intervention”, driven by LMANIP, which showed significant differences when compared with both NI (p = 0.015) and LMOB (p = 0.042). No significant interactions were found for the post-intervention PW ratio.

Conclusions

These results from a controlled study with blinded outcome assessors indicate that a single SMT intervention has an immediate effect on lumbar proprioceptive function irrespective of health status. Notably, these findings provide the first evidence that paraspinal proprioceptive input is ‘up-weighted’ following SMT, aligning with and extending findings from pre-clinical research on SMT-like interventions in animal models. Furthermore, our data suggest that the initial PW status may have predictive value for the analgesic response following SMT. These results lay the groundwork for future investigations into the long-term impact of this mechanism in patients with chronic LBP, specifically focusing on its potential to predict therapeutic outcomes which offers a promising avenue for developing more personalized treatment approaches.

References

Brumagne, S., Cordo, P. & Verschueren, S. Proprioceptive weighting changes in persons with low back pain and elderly persons during upright standing. Neurosci Lett 366, 63–66 (2004).

Pickar, J. G. & Wheeler, J. D. Response of muscle proprioceptors to spinal manipulative-like loads in the anesthetized cat. Journal of Manipulative & Physiological Therapeutics 24, 2–11 (2001).

Bertrand-Charette, M., Perron, M.-P., da Silva, R. A. & Beaulieu, L.-D. Vibration-induced postural reactions: a scoping review on parameters and populations studied. Frontiers in Human Neuroscience 17, (2024).

Claeys, K. et al. Young individuals with a more ankle-steered proprioceptive control strategy may develop mild non-specific low back pain. Journal of Electromyography and Kinesiology 25, 329–338 (2015).

Presenting Author

Luana Nyriö

Poster Authors

Michael Meier

PhD

University of Zurich

Lead Author

E-mail

Luana Nyriö

DCM

Balgrist University Hospital

Lead Author

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Petra Schweinhardt

University of Zurich

Lead Author

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Tobias Potthoff

DCM

Balgrist University Hospital

Lead Author

E-mail

Mena Suter

Balgrist University Hospital

Lead Author

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Monika Dörig

Balgrist University Hospital

Lead Author

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Topics

  • Mechanisms: Biological-Systems (Physiology/Anatomy)