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Open Access

Peer-reviewed

Research Article

Systematic review on biomechanical effects of high-velocity, low amplitude spinal manipulation

  • Anke Langenfeld ,

    Roles Conceptualization, Methodology, Project administration, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing

    anke.langenfeld@balgrist.ch

    ‡ These authors share first authorship on this work.

    Affiliation Integrative Spinal Research Group, Department of Chiropractic Medicine, University Hospital Balgrist and University of Zurich, Zurich, Switzerland

    ⨯
  • Mirjam Baechler ,

    Roles Conceptualization, Methodology, Project administration, Writing – original draft, Writing – review & editing

    ‡ These authors share first authorship on this work.

    Affiliation Department of Chiropractic Medicine, University Hospital Balgrist and University of Zurich, Zurich, Switzerland

    ⨯
  • Jaap Swanenburg,

    Roles Data curation, Methodology, Writing – review & editing

    Affiliations Integrative Spinal Research Group, Department of Chiropractic Medicine, University Hospital Balgrist and University of Zurich, Zurich, Switzerland, Faculty of Medicine, Institute of Aerospace Medicine, University of Zurich, Zurich, Switzerland

    ⨯
  • Malin Mühlemann,

    Roles Data curation, Writing – review & editing

    Affiliation Integrative Spinal Research Group, Department of Chiropractic Medicine, University Hospital Balgrist and University of Zurich, Zurich, Switzerland

    ⨯
  • Luana Nyirö,

    Roles Writing – review & editing, Data curation

    Affiliations Integrative Spinal Research Group, Department of Chiropractic Medicine, University Hospital Balgrist and University of Zurich, Zurich, Switzerland, Department of Chiropractic Medicine, University Hospital Balgrist and University of Zurich, Zurich, Switzerland

    ⨯
  • Daniel Streuli,

    Roles Conceptualization, Data curation, Writing – review & editing

    Affiliation Integrative Spinal Research Group, Department of Chiropractic Medicine, University Hospital Balgrist and University of Zurich, Zurich, Switzerland

    ⨯
  • Brigitte Wirth,

    Roles Conceptualization, Methodology, Project administration, Supervision, Writing – original draft, Writing – review & editing

    Affiliation Integrative Spinal Research Group, Department of Chiropractic Medicine, University Hospital Balgrist and University of Zurich, Zurich, Switzerland

    ⨯
  • Petra Schweinhardt

    Roles Data curation, Methodology, Project administration, Supervision, Writing – original draft, Writing – review & editing, Conceptualization

    Affiliations Integrative Spinal Research Group, Department of Chiropractic Medicine, University Hospital Balgrist and University of Zurich, Zurich, Switzerland, Department of Chiropractic Medicine, University Hospital Balgrist and University of Zurich, Zurich, Switzerland

    ⨯

Abstract

Background

Spinal manipulative therapy uses high-velocity low-amplitude (HVLA) thrusts which are clinically effective, but underlying mechanisms are still unknown.

Objective

To summarize the evidence for biomechanical effects of HVLA thrusts in asymptomatic and symptomatic humans as well as for a possible link between biomechanical effects and clinical effectiveness.

Study design

Systematic review of randomized controlled trials.

Methods

An information specialist conducted systematic literature searches in six databases [Medline (OvidSP), Premedline (PubMed), CINAHL, EMBASE, Cochrane, and Biosis]. Studies were selected by two authors and classified using the revised Cochrane risk-of-bias tool for randomized trials (RoB 2). Results were qualitatively summarized per biomechanical output [range of motion (ROM) according to the spinal region where HVLA thrusts were applied, facet joint gapping, and spinal stiffness].

Results

The thirty-three included studies were heterogeneous regarding participant characteristics, intervention frequency and outcomes. Twenty-seven studies reported on the effects of HVLA thrusts on spinal ROM. There is evidence increased cervical ROM following cervical HVLA thrusts on cervical ROM [9/15 studies with a positive treatment effect (5 low risk of bias/4 some concern) and increased cervical ROM following thoracic HVLA thrusts [8/8 studies (4 low risk of bias/4 some concern)]. The effects of a thoracic and lumbar HVLA thrusts on the respective ROM were less clear. Three (2 low risk/1 some concern) studies on facet joint gapping showed increased gapping following HVLA thrusts compared to side-posture positioning, and a single study (some concern) on spinal stiffness showed no effect of HVLA thrusts. Only one study (some concern) linked the biomechanical to clinical outcomes.

Conclusion

HVLA thrusts, either applied to the cervical or the thoracic spine, appear to increase cervical ROM, based on studies with low risk and studies with some concern regarding risk of bias. For all other outcomes, the included studies were too heterogeneous and too few to draw any sound conclusion. Future studies on the biomechanical effects of HVLA thrusts should link the biomechanical to clinical outcomes such as pain and disability.

PROSPERO registration

CRD42018096963.

Citation: Langenfeld A, Baechler M, Swanenburg J, Mühlemann M, Nyirö L, Streuli D, et al. (2025) Systematic review on biomechanical effects of high-velocity, low amplitude spinal manipulation. PLoS One 20(7): e0328048. https://doi.org/10.1371/journal.pone.0328048

Editor: Anthony Demont, National Institute of Health and Medical Research: INSERM, FRANCE

Received: November 9, 2023; Accepted: June 25, 2025; Published: July 18, 2025

Copyright: © 2025 Langenfeld et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data are within the manuscript and its Supporting Information files.

Funding: The author(s) received no specific funding for this work.

Competing interests: The authors have declared that no competing interest exist.

Introduction

High-velocity, low-amplitude (HVLA) thrusts are widely used by chiropractors, physical therapists, osteopaths, and medical doctors [1]. SMT using HVLA thrusts are thought to be clinically effective and is recommended in recent guidelines for the management of acute and chronic low back pain (LBP) [2], neck pain [3], cervical [4], and lumbar radiculopathy [5]. The effects of HVLA thrusts on pain and function in patients with neck and LBP are comparable to other recommended treatment options, like medication and exercise [6–8].

HVLA thrusts can be applied manually, by a hand-held instrument (instrument-applied manipulation, IAM), or by a robot-like apparatus [9,10]. The manual procedure is characterized by a force application through the hands of the practitioner directed to the intervertebral joints [11–13]. The target joint is brought to the end of its range of motion (ROM) by the application of a preload force, followed by a high-velocity thrust over a short-amplitude [9,14]. This application targets the intervertebral joint but the forces are also transmitted to the surrounding soft tissues [15]. For IAM, which is clinically effective and safe, a force is delivered to the spine by a spring-loaded hand-held instrument with a small rubber tip [16]. For research, a robot-like apparatus has been developed that can apply a thrust to the human spine in a standardized manner with different force-time profile settings [10].

The effects of HVLA thrusts have been categorized as neurophysiological or biomechanical, e.g., increased range of motion, or reduced muscle activity, with the overall effects being most likely a complex interplay between the two [15,17,18].

Previous systematic reviews have investigated the biomechanical effects of HVLA thrusts directed to the cervical or thoracic spine on cervical range of motion (ROM) [19–21]. HVLA thrusts directed to the cervical or thoracic spine were shown to increase cervical ROM [19–21]. In contrast, systematic reviews on lumbar HVLA thrusts found no effect on lumbar ROM [19]. No review has examined the effects of thoracic HVLA thrusts on thoracic ROM or other biomechanical outcomes. Additionally, information linking biomechanical effects of HVLA thrusts to clinical outcome is missing [1,9].

Therefore, this systematic review aimed to summarize the evidence for biomechanical effects of an HVLA thrusts in asymptomatic and symptomatic humans as well as to explore a possible link between these biomechanical effects and clinical effectiveness.

Materials and methods

This systematic review is reported in accordance with the Preferred Reporting Items of Systematic Review and Meta-Analysis guidelines [22]. The protocol of this systematic review was registered at the International Prospective Register of Systematic Reviews (PROSPERO: CRD42018096963).

Search strategy

An a priori search strategy was agreed on at the beginning of the project by three of the authors (DS, PS, BW). The initial literature search was undertaken by an information specialist at the University of Zurich, Zurich, Switzerland. All articles published until June 14, 2018, were included. No time restriction regarding the start date was applied. The literature search was updated three times for the times June 2018 – October 2020, October 2020 – March 2023 and March 2023 – November 2024 by the same information specialist using the same search strategy (see appendix). Databases were Medline, CINAHL, EMBASE, PubMed, Cochrane, and Biosis.

Inclusion and exclusion criteria

This review focused on peer-reviewed publications reporting on randomized controlled trials in English that investigated biomechanical effects, changes in ROM, changes in the distance between articular surfaces of the zygapophyseal joint [gapping] [23], and resistance to elastic deformation of a joint (stiffness) [24], following manual, instrumented, or apparatus HVLA thrust in symptomatic or asymptomatic humans.

Studies exclusively reporting neurophysiological or subjective outcomes or using any modeling, such as finite element models, were excluded. The review included studies that used HVLA thrusts either as a standalone or combined intervention, provided that the effect of the HVLA thrusts could be isolated [e.g., HVLA thrusts plus electrotherapy versus electrotherapy alone]. Studies involving mobilization were included when mobilization was used as a control intervention against HVLA thrusts. Since the key difference between mobilization and HVLA thrusts is the application of a thrust, mobilization is considered an appropriate control intervention.

Study selection

After removing duplicate articles, two reviewers independently screened titles and abstracts to determine eligibility. If eligibility could not be determined, the full text was consulted. If articles were deemed eligible during abstract and title screening, the full text was assessed, and data was extracted if included in the review. Discrepancies were resolved through discussion between the two reviewers. If discrepancies could not be resolved, a third reviewer (PS) was consulted.

Risk of bias assessment

The revised Cochrane risk-of-bias tool for randomized trials (RoB 2, beta version, 15 March 2019) was used to assess the quality of the included studies in five bias categories, i.e., randomization process, deviations from intended interventions, missing outcome data, outcome measurement, and selection of reported results, as well as an overall bias classification. Each of the categories allows for a classification of ‘low risk’, ‘some concerns’, or ‘high risk’ [25]. Two reviewers from the pool [all listed authors] were randomly allocated to studies and independently classified each study, and discrepancies in any of the bias categories were resolved through discussion between the two reviewers. If a consensus could not be reached, a third reviewer (PS) was involved. To determine the best evidence, studies deemed ‘high risk’ were excluded from the narrative synthesis.

Data extraction

Data to be extracted was defined prior to the study and included subject characteristics, treatment region, description of intervention and control interventions, timing of assessment relative to intervention, biomechanical outcomes, and main biomechanical results. Extracted data was verified by a second researcher and summarized per biomechanical output (range of motion (ROM) according to the spinal region where HVLA thrust was applied, facet joint gapping, and spinal stiffness).

Results

Study selection and study quality

Titles and abstracts were screened based on predefined inclusion and exclusion criteria by two independent reviewers. The PRISMA flowchart outlines the selection process (Fig 1). A total of 4,228 studies were identified, 1,714 (40.5%) duplicate records were removed, 2,514 (59.4%) records were screened, and 2,376 (56.1%) records were excluded. The remaining 138 (3.2%) full-text articles were assessed, leading to the exclusion of 94 (2.2%) studies. The assessment of study quality resulted in 16 (0.3%) articles with ‘low risk’ [26–41], 17 (0.4%) articles with ‘some concerns’ (Fig 1), and 11 articles (0.2%) with ‘high risk’ [42–52]. The level of agreement of ‘high risk’ (excluded studies) vs ‘low risk’ or ‘some concerns’ (included studies) was moderate (ĸ = 0.58). A quantitative analysis (meta-analysis) was not performed due to the high heterogeneity of data with regard to participant characteristics, intervention frequency, and outcomes.

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Fig 1. Prisma flow diagram for the whole study including searches 2018, 2020, 2023 and 2024.

https://doi.org/10.1371/journal.pone.0328048.g001

Thus, after the exclusion of the high-risk publications, 33 publications were included in the qualitative synthesis (Fig 2).

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Fig 2. Results of the quality assessment using the RoB 2 tool including studies with low risk and some concerns [high-risk studies excluded].

https://doi.org/10.1371/journal.pone.0328048.g002

The majority of the included studies (27/33) reported on the effects of HVLA thrusts on spinal ROM. These effects can be categorized as local effects where HVLA thrusts are applied in the same spinal region in which ROM is measured or regional effects where HVLA thrusts are applied in a region distant to where ROM is measured. Four studies reported on the effects of HVLA thrusts on gapping of the zygapophyseal [facet] joints [26,27,53] and one on spinal stiffness [54]. Post-treatment measurement time points varied. Eighteen (54%) studies performed measurements pre-treatment and immediately post-treatment [28,29,32–35,37–40,55–62]. Other studies measured 24 hours after treatment [61], 48 hours after treatment [31], one week after treatment [41], after the fifth visit [54], or at the end of each treatment phase [36]. Additionally, if treatment was applied over a period of time, measurements were taken at the end of the treatment series [37,63] (Tables 1–3).

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Table 1. Local effects of HVLA thrust on range of motion cervical spine.

https://doi.org/10.1371/journal.pone.0328048.t001

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Table 2. Regional effects of HVLA thrust on range of motion.

https://doi.org/10.1371/journal.pone.0328048.t002

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Table 3. Effects of HVLA thrust on facet joint gapping and spinal stiffness.

https://doi.org/10.1371/journal.pone.0328048.t003

Local effects of HVLA thrusts on ROM

Effects of cervical HVLA thrusts on cervical ROM.

16 (47%) studies investigated the effects of cervical HVLA thrust on cervical ROM in different patient populations, e.g., mechanical neck pain, chronic neck pain, and tension-type headache [32–36,39,41,55–60,64–66]. Seven studies (43.7%) were rated low risk and nine (56.2%) as some concerns [55–60,64–66]. Nine (56.2%) of these studies showed an increase in cervical range of motion (4 low-risk and 5 some concerns) [32,33,39,41,55,56,58,60,64]. Included studies were heterogeneous in terms of the movement planes considered, number of movement planes where an improvement was observed, treatment frequency, and time of measurement after HVLA thrust: treatment approaches ranged from one session with immediate post-treatment measurement to a maximum of eight sessions over four weeks [60] (Table 1).

Effects of thoracic HVLA thrusts on thoracic ROM.

Two studies (5.8%) with low risk of bias investigated the effect immediately after the thoracic spine manipulation on thoracic ROM. One [2.9%] study showed an immediate post-treatment improvement on active thoracic flexion but not on extension, of a single T9 HVLA thrust compared to a sham intervention in a sample of 22 participants. The other study (2.9%) [N = 52] investigated active thoracic excursion (i.e., full flexion to full extension) in patients with subacromial impingement syndrome of the shoulder and found no difference between a total of 6 HVLA thrusts applied to the upper, middle, and lower thoracic spine in a single session compared to a sham intervention [38] (Table 1).

Effects of lumbar HVLA thrusts on lumbar ROM.

Two studies (5.8%) rated some concerns of bias, investigated lumbar spine HVLA thrusts effects on lumbar ROM [63,67]. One study (2.9%) included 330 participants with chronic non-specific LBP at level L4/5, in three treatment arms, and measured the effects on active ROM using the modified Schober test. The patients underwent twelve treatment sessions (3x/week for four weeks) including lumbar spine HVLA thrusts plus laser plus exercises, or laser and exercises without HVLA thrust, or exercises only. The modified Schober test showed an improvement for the HVLA thrust group compared to the two other groups [63]. Another study (2.9%) with 14 participants with lumbar spinal stenosis investigated the effects of bilateral lumbar HVLA thrusts on active ROM [flexion, extension, left lateral flexion, right lateral flexion, left rotation and right rotation]. No within or between group differences pre- and post-treatment were reported [67] (Table 1).

Regional effects of HVLA thrusts on ROM

Effects of thoracic HVLA thrusts on cervical ROM.

Eight studies investigating the effects of thoracic spine HVLA thrusts on cervical ROM showed an increase in cervical ROM [28,30,37,40,61,62,68,69]. Four (50%) were rated as low risk of bias [28,30,37,40] and four (50%) as having some concerns for risk of bias [61,62,68,69]. Five (62.5%) included acute or chronic neck pain patients [28,30,37,68,69], two (25%) included cervical radiculopathy patients with or without neck pain [40,61], and one (12.5%) included healthy participants [62]. One (12.5%) study only measured cervical rotation and consequently only reported an increase of rotation [28]. The other studies (87.5%) measured all planes of cervical ROM, with two (25%) reporting increased ROM in all planes [30,68] and five (62.5%) in different cervical planes [37,40,61,62,69]. Six studies (75%) measured immediately post-treatment [28,37,40,61,62,68], and two studies (25%) reported an increase of cervical ROM lasting up to one [30,69] or two weeks [68]. Treatment approaches ranged from one session with one to two HVLA thrusts on one site [28,37,61,62,69] or multiple sites [40,69] to multiple sessions of HVLA thrusts [68] (Table 2).

Effects of thoracic and cervical HVLA thrusts on cervical ROM.

One study with low risk of bias compared HVLA thrusts with mobilization of the upper cervical and the upper thoracic region on the passive range of cervical rotation of C1/2 in a neck pain population and reported a significantly greater increase in both rotation directions for the HVLA thrust compared to the mobilization group 48 hours after the intervention [31] (Table 2).

Effects of HVLA thrusts on facet joint gapping

Three studies compared the effects of lumbar side-posture HVLA thrusts with pure side-posture positioning on gapping of the lumbar facet joints as measured by MRI before and after application of the HVLA thrusts [26,27,53]. Two studies (66%) were rated as low risk of bias and one (33%) as having some concerns for risk of bias. Two larger follow-up studies, also in healthy participants, showed statistically significant differences in gapping between the subjects receiving side-posture HVLA thrusts and those receiving side-posture positioning only, but only when the MRI following HVLA thrusts was conducted in side-posture. In patients with acute LBP (N = 112) [26], at onset, pure side-positioning resulted in more gapping than HVLA thrusts [delivered with the most painful side positioned up] followed by side-positioning. In contrast, after two weeks of chiropractic treatment, facet joint gapping after HVLA thrusts was greater than after side-positioning (Table 3).

Effects of HVLA thrust on spinal stiffness

One study rated some concerns for risk of bias and investigated spinal stiffness after the application of IAM HVLA thrusts to T7 in chronic thoracic pain patients [54]. This four-arm trial (N = 81) included three HVLA thrust groups using different dosages of applied force magnitude, impulse duration, and rate of force application, and a control group. The treatment regime was three sessions over two to three weeks. Spinal stiffness was measured before and after HVLA thrusts over the spinous processes of T6, T7, and T8. Displacement of vertebrae was measured using an indenter device during exhalation using the following procedure: after application of a posterior-to-anterior load of 5N on the spinous process, the load was gradually increased with an 18 N/s rate of force application to 45 N. Terminal and global spinal stiffness coefficients were calculated using the force and displacement data recorded during each spinal stiffness trial. Terminal stiffness was defined as the ratio of the load divided by the displacement between 10 and 45 N, and global stiffness was defined as the slope of the straight-line best fitting the data over the same load interval. Stiffness was reduced after the intervention in all groups, including the control group, but no statistically significant difference was found between the groups (Table 3).

Relationship between biomechanical and patient-rated outcomes

Sixteen (47%) of the included studies used patient-rated outcome measures such as pain [visual analogue pain scale, numeric pain rating scale, 9-point faces pain scale] [28,30,34,37,41,57,59,60,64–66,68,69] and/or disability [neck pain and disability scale, neck disability index, Northwick Park neck pain questionnaire, jaw functioning limitation scale] [30,32,40,41,56,64,66,69] as primary outcome measures. One study, rated some concerns for risk of bias, statistically linked these patient-rated outcomes to biomechanical measures. This study reported an association between neck pain at rest and the improvement in ROM, i.e., the greater the increase in ROM, the greater the improvement in neck pain.

Discussion

This systematic review found evidence in support for local effects of HVLA thrusts to the cervical spine on cervical ROM and for regional effects of thoracic HVLA thrusts on cervical ROM. This indicates that cervical ROM can be increased by HVLA thrusts to either the cervical or the thoracic spine. In contrast, evidence regarding local effects of HVLA thrusts to the thoracic and lumbar spine remains inconclusive. Similarly, it is not yet clear whether HVLA thrusts lead to facet joint gapping or reduce spinal stiffness. Most studies investigated pain and/or disability as patient-reported outcomes, but only one analyzed their relationship to the biomechanical measures.

Local effects of HVLA thrusts on ROM

The finding of HVLA thrusts increasing cervical spinal ROM is in line with previous systematic reviews [19,20]. Although the heterogeneity of the studies regarding treatment approaches and participant characteristics hinders comparison, there appears to be an immediate effect of HVLA thrust to the cervical spine on increased cervical ROM. This also holds true when only considering studies delivering HVLA thrust-SMT to the upper cervical spine: the study that did not show an effect included patients with temporomandibular joint dysfunction [66], while the positive studies included patients with tension-type headache [32], cervicogenic headache [36] or chronic neck pain [58]. Patients with temporomandibular joint dysfunction might not necessarily have upper cervical joint dysfunctions and adding HVLA-SMT to the comparison treatment of suboccipital release and exercise might not change the biomechanical results. Overall, as studies differed with relation to measuring active or passive ROM and with relation to which planes were measured, no clear pattern emerged of which movement planes of cervical ROM are affected most or most often by HVLA thrust-SMT directed to the cervical spine.

As for the two studies [29,38] on the immediate, local effects of a single thoracic HVLA thrusts applied to the thoracic spine compared to a sham intervention. Ditcharles and colleagues applied a single thrust to T9 in patients with subacromial pain and showed an increase of thoracic flexion as measured by inclinometer [assessor-blinded] [29]. Kardouni and colleagues applied a total of six thoracic thrusts to young healthy adults and did not report any effect on thoracic spine extension and thoracic excursion using an electromagnetic motion capture system [38]. Thus, given the fact that only electromagnetic studies were available for the local effects of HVLA thrusts on the thoracic spine, the local effect of thoracic spine HVLA on thoracic ROM remains unclear and underlines the notion that research on the thoracic spine is scarce [70]. Two studies examining the local effects of HVLA thrusts on the lumbar spine showed divergent findings [63,67]. The larger study’s HVLA group demonstrated a significant reduction in pain and an improvement in function [63]. The smaller study did not find any effect of a single HVLA thrusts in patients with spinal canal stenosis [67]. In addition to being underpowered, as suggested by the authors, it is conceivable that it is more difficult in patients with spinal canal stenosis to increase ROM. Thus, several factors might be contributing to the divergent findings, including variations in the number of interventions administered (three session over four weeks vs. one single session with one single thrust), as well as differences in the sample size (n = 330 vs. n = 14) and type of the study populations (patients with uncomplicated chronic low back pain, lumbago, sciatica, with pain localized in L4/L5 vs. degenerative lumbar stenosis).

Regional effects of HVLA thrusts on ROM

Eight studies investigating the effects of thoracic spine HVLA thrusts on cervical range of motion reported an improvement of cervical ROM, which is in line with findings of a previous systematic review [21]. A possible explanation for this finding might be that functional disturbances in the upper thoracic spine can lead to decreased muscle strength [71] and impaired ROM in the cervical spine. Thus, treating such functional disturbances in the upper thoracic spine by manual therapy to restore normal biomechanical function might normalize cervical ROM [71–74]. In addition, other phenomena might be contributing to the improvement of cervical ROM in response to thoracic HVLA thrusts, including those directed at the mid-thoracic spine. In particular, DNIC (diffuse noxious inhibitory controls)-like phenomena or non-specific treatment effects might be involved.

Effects on facet joint gapping and spinal stiffness

Inactivity, asymmetrical loads, and injury can lead to aberrant facet joint motion, hypomobility, and adhesion formation [14,23]. Thus, gapping the facet joints and breaking up adhesions might be one of the mechanisms of action of HVLA thrusts [14]. The three studies, all conducted by the same research group, investigated the effects of lumbar HVLA thrusts on gapping of the facet joints in an asymptomatic [27,53] and symptomatic LBP study population [26] provided some evidence that HVLA thrusts immediately gaps the lumbar facet joints, but only if followed by side-posture positioning, which suggests a short-lived effect.

A decrease in spinal stiffness has been shown in small studies after HVLA thrusts and has been related to changes in ROM, pain, pressure pain threshold, and spinal tissue behavior, e.g., by relaxation of the spinal connective tissues and/or changed motor reflexes [75]. However, the single study on spinal stiffness included in this review did not confirm these findings [54]. It has to be considered that posterior to anterior stiffness measurements are influenced by multiple factors — including soft tissue compliance and joint morphology — and do not provide a direct quantification of intrinsic segmental stiffness. [76–78].

Clinical considerations and recommendations for future studies

Interestingly, only one [58] of the included studies on ROM of any spinal region reported whether ROM was altered in the respective study population compared to norm values at baseline. This is a major shortcoming and hampers the interpretation of studies investigating the effect of a manual treatment that aims at improving ROM. Nevertheless, four articles refer to the minimal detectable change [MDC]: three studies report changes in ROM higher than the MDC [28,58,64] and one study changes lower than the MDC [40]. Future studies would benefit from quantifying a possible restriction of ROM beforehand and testing whether HVLA thrusts normalized ROM, considering the MDC or an alternative method to account for repeated measures effects. Furthermore, only one study investigated a possible relationship between biomechanical and patient-related outcomes such as pain or disability. For future studies, the incorporation of those links is strongly recommended and as long as such a link is not established, an increase in ROM alone should only be interpreted as a proxy for a successful outcome, when (painless) restricted ROM is one of the patients’ main complaints.

Limitations

In general, the RoB tool presents challenges because it focuses only on specific domains and does not assess the overall quality of the study [79]. The RoB tool, used as a checklist, aids in quality rating through its built-in algorithm while also allowing assessors to adjust the rating. However, it is a complex tool [80], that should only be used after intensive training [80], as was done in the present study. Nevertheless, the group of raters was heterogeneous in terms of expertise in conducting systematic reviews, and not all raters were involved in all review stages during the updates. Additionally, the literature search was limited to the English language which may have excluded some relevant studies. Lastly, due to the high heterogeneity of data with regard to participant characteristics, intervention frequency, and outcomes, no meta-analysis could be performed.

Conclusions

The main finding of this review, based on equal numbers of studies rated low-risk and some concerns, is that HVLA thrusts, applied to the cervical or the thoracic spine, increases cervical ROM, which is likely of clinical significance. However, the results on the local effects of an HVLA thrusts to the thoracic and lumbar spine, as well as on the effects of an HVLA thrusts on facet joint gapping and spinal stiffness, remain inconclusive. Future studies should quantify the outcome measures at baseline and assess potential relationships between the biomechanical effects of an HVLA thrust and clinical outcomes.

Acknowledgments

We thank the information specialist Martina Gosteli from the University Library of the University of Zurich, Zurich, Switzerland for conducting the literature search and Dr. Kayleigh Aymon from the Department of Chiropractic Medicine, Balgrist University Hospital and University of Zurich, Zurich, Switzerland for proofreading the manuscript.

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