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Research Review

Jun et al. Chiropractic & Manual Therapies (2020) 28:15

Potential mechanisms for lumbar spinal stiffness change following spinal manipulative therapy: a scoping review


Introduction: In individuals having low back pain, the application of spinal manipulative therapy (SMT) has been shown to reduce spinal stiffness in those who report improvements in post-SMT disability. The underlying mechanism for this rapid change in stiffness is not understood presently. As clinicians and patients may benefit from a better understanding of this mechanism in terms of optimizing care delivery, the objective of this scoping review of current literature was to identify if potential mechanisms that explain this clinical response have been previously described or could be elucidated from existing data.

Methods: Three literature databases were systematically searched (MEDLINE, CINAHL, and PubMed). Our search terms included subject headings and keywords relevant to SMT, spinal stiffness, lumbar spine, and mechanism.

Inclusion criteria for candidate studies were publication in English, quantification of lumbar spinal stiffness before and after SMT, and publication between January 2000 and June 2019.

Results: The search identified 1931 articles. Of these studies, 10 were included following the application of the inclusion criteria. From these articles, 7 themes were identified with respect to potential mechanisms described or derived from data: 1) change in muscle activity; 2) increase in mobility; 3) decrease in pain; 4) increase in pressure pain threshold; 5) change in spinal tissue behavior; 6) change in the central nervous system or reflex pathways; and 7) correction of a vertebral dysfunction.

Conclusions: This scoping review identified 7 themes put forward by authors to explain changes in spinal stiffness following SMT. Unfortunately, none of the studies provided data which would support the promotion of one theme over another. As a result, this review suggests a need to develop a theoretical framework to explain rapid biomechanical changes following SMT to guide and prioritize future investigations in this important clinical area.

What does this mean and why is this important?
We know spinal manipulation typically produces short term transient positive outcomes, i.e. the patient feels better for a bit and then slips back a bit. We also know that spinal manipulation to low back reduces spinal stiffness, but what we do not know is why this reduction in spinal stiffness occurs and this is what this study tries to identify. This scoping review combines several studies which have tried to identify the ‘why’ however despite identifying common themes the quality of the evidence is not high enough to consider one over another.

What does this mean in clinic?
One of the most common questions we are asked is ‘how does manipulation work?’ and despite a lot of studies trying to identify this there is not the quality of evidence to identify a specific mechanism of action for spinal manipulative therapy.  Despite this we know that it does provide positive outcomes for patients when used as part of a comprehensive package of care.