Vertebral arteries do not experience tensile force during manual cervical spine manipulation applied to human cadavers

Background: The vertebral artery (VA) may be stretched and subsequently damaged during manual cervical spine manipulation. The objective of this study was to measure VA length changes that occur during cervical spine manipulation and to compare these to the VA failure length. Methods: Piezoelectric ultrasound crystals were implanted along the length of the VA (C1 to C7) and were used to measure length changes during cervical spine manipulation of seven un-embalmed, post-rigor human cadavers. Arteries were then excised, and elongation from arbitrary in-situ head/neck positions to first force (0.1 N) was measured. Following this, VA were stretched (8.33 mm/s) to mechanical failure. Failure was defined as the instance when VA elongation resulted in a decrease in force. Results: From arbitrary in-situ head/neck positions, the greatest average VA length change during spinal manipulation was [mean (range)] 5.1% (1.1 to 15.1%). From arbitrary in-situ head/neck positions, arteries were elongated on average 33.5% (4.6 to 84.6%) prior to first force occurrence and 51.3% (16.3 to 105.1%) to failure. Average failure forces were 3.4 N (1.4 to 9.7 N). Conclusions: Measured in arbitrary in-situ head/neck positions, VA were slack. It appears that this slack must be taken up prior to VA experiencing tensile force. During cervical spine manipulations (using cervical spine extension and rotation), arterial length changes remained below that slack length, suggesting that VA elongated but were not stretched during the manipulation. However, in order to answer the question if cervical spine manipulation is safe from a mechanical perspective, the testing performed here needs to be repeated using a defined in-situ head/neck position and take into consideration other structures (e.g. carotid arteries). Keywords: Spinal biomechanics; cerebrovascular accidents; spinal manipulation; stroke; vertebral artery dissection

Spinal mobilization force-time characteristics: A scoping literature review

Background: Spinal mobilization (SMob) is often included in the conservative management of spinal pain conditions as a recommended and effective treatment. While some studies quantify the biomechanical (kinetic) parameters of SMob, interpretation of findings is difficult due to poor reporting of methodological details. The aim of this study was to synthesise the literature describing force-time characteristics of manually applied SMob. Methods: This study is reported in accordance with the Preferred Reporting Items for Scoping Reviews (PRISMA-ScR) statement. Databases were searched from inception to October 2022: MEDLINE (Ovid), Embase, CINAHL, ICL, PEDro and Cochrane Library. Data were extracted and reported descriptively for the following domains: general study characteristics, number of and characteristics of individuals who delivered/received SMob, region treated, equipment used and force-time characteristics of SMob. Results: There were 7,607 records identified and of these, 36 (0.5%) were included in the analysis. SMob was delivered to the cervical spine in 13 (36.1%), the thoracic spine in 3 (8.3%) and the lumbopelvic spine in 18 (50.0%) studies. In 2 (5.6%) studies, spinal region was not specified. For SMob applied to all spinal regions, force-time characteristics were: peak force (0-128N); duration (10-120s); frequency (0.1-4.5Hz); and force amplitude (1-102N). Conclusions: This study reports considerable variability of the force-time characteristics of SMob. In studies reporting force-time characteristics, SMob was most frequently delivered to the lumbar and cervical spine of humans and most commonly peak force was reported. Future studies should focus on the detailed reporting of force-time characteristics to facilitate the investigation of clinical dose-response effects

Indication for spinal sensitization in chronic low back pain: mechanical hyperalgesia adjacent to but not within the most painful body area

Introduction: In 85% of patients with chronic low back pain (CLBP), no specific pathoanatomical cause can be identified. Besides primary peripheral drivers within the lower back, spinal or supraspinal sensitization processes might contribute to the patients' pain. Objectives: The present study conceptualized the most painful area (MP) of patients with nonspecific CLBP as primarily affected area and assessed signs of peripheral, spinal, and supraspinal sensitization using quantitative sensory testing (QST) in MP, a pain-free area adjacent to MP (AD), and a remote, pain-free control area (CON). Methods: Fifty-nine patients with CLBP (51 years, SD = 16.6, 22 female patients) and 35 pain-free control participants individually matched for age, sex, and testing areas (49 years, SD = 17.5, 19 female participants) underwent a full QST protocol in MP and a reduced QST protocol assessing sensory gain in AD and CON. Quantitative sensory testing measures, except paradoxical heat sensations and dynamic mechanical allodynia (DMA), were Z-transformed to the matched control participants and tested for significance using Z-tests (α = 0.001). Paradoxical heat sensations and DMA occurrence were compared between cohorts using Fisher's exact tests (α = 0.05). The same analyses were performed with a high-pain and a low-pain CLBP subsample (50% quantile). Results: Patients showed cold and vibration hypoesthesia in MP (all Ps < 0.001) and mechanical hyperalgesia (P < 0.001) and more frequent DMA (P = 0.044) in AD. The results were mainly driven by the high-pain CLBP subsample. In CON, no sensory alterations were observed. Conclusion: Mechanical hyperalgesia and DMA adjacent to but not within MP, the supposedly primarily affected area, might reflect secondary hyperalgesia originating from spinal sensitization in patients with CLBP

Musculoskeletal Biomechanical and Electromyographical Responses Associated with Spinal Manipulation

The primary goal of this thesis was to systematically describe biomechanical and electromyographic (EMG) responses of the human musculoskeletal system associated with cervical and upper thoracic spinal manipulation (SM). The overarching hypotheses were that: i) greater three-dimensional (3D) movements of the head and neck would be associated with larger vertebral artery (VA) strains; and ii) SM applied with greater force and more quickly would result in larger EMG responses. In the first project, a basic science methodology was used to measure: i) 3D movements of the head and neck and associated VA strains during cervical SM applied to human cadaveric donors; and ii) the elongation required for mechanical failure of the VA. Pre-positioning of the head and neck resulted in the largest changes in angular kinematics and arterial strain, while small changes occurred during the thrust. There were correlations between angular displacements and VA strains during cervical SM, however these were variable in direction (positive vs. negative) and strength (negligible to high). Arterial strains during cervical SM did not exceed those required to produce tensile stretch; therefore, it is unlikely the procedures delivered in this study could result in mechanical disruption of a healthy vessel wall. In the second project, an applied methodology was used to investigate: i) reflexogenic effects of cervical and upper thoracic SM in asymptomatic and neck pain participants; and ii) the relationship between SM kinetics and EMG responses. In asymptomatic participants, cervical and upper thoracic SM was often associated with EMG responses. However, responses occurred less frequently in symptomatic participants, suggesting that the reduction in EMG responses may be associated with pain-induced reflex inhibitions. Further, when two thrusts were delivered to the same spinal segment, following one another in quick succession, the second thrust was delivered more forcefully and more quickly, resulting in greater peak EMG responses and shorter neuromuscular delays. Collectively, the data in this thesis demonstrate that high-velocity, low-amplitude (HVLA) cervical and upper thoracic SM causes biomechanical and EMG responses within the musculoskeletal system. Further, these studies provide important safety and mechanistic data on cervical and upper thoracic SM