Quantifying strain in the vertebral artery with simultaneous motion analysis of the head and neck: a preliminary investigation

High pillow and spontaneous vertebral artery dissection: A case-control study implicating "Shogun pillow syndrome"

INTRODUCTION

The underlying causes of spontaneous vertebral artery dissection (sVAD) remain insufficiently understood. This study aimed to determine whether high-pillow usage is associated with an increased risk of sVAD and evaluate the frequency of sVAD attributable to high-pillow usage.

PATIENTS AND METHODS

This case-control study identified patients with sVAD and age- and sex-matched non-sVAD controls (case-to-control ratio: 1:1) treated at a certified comprehensive stroke center in Japan between 2018 and 2023. The pillow height used at the onset of the index disease was measured and classified into three categories between 12 and 15 cm boundaries. Univariable logistic regression was performed to assess the odds ratio (OR) with a 95% confidence interval (CI) of high-pillow usage for sVAD development. A subgroup of sVAD attributable to high-pillow usage was defined with the following three conditions: high-pillow usage (⩾12 or ⩾15 cm); no minor preceding trauma; and wake-up onset.

RESULTS

Fifty-three patients with sVAD and 53 non-sVAD controls (42% women, median age: 49 years) were identified. High-pillow usage (⩾12 and ⩾15 cm) was more common in the sVAD group than in the non-sVAD group (34 vs 15%; OR = 2.89; 95%CI = 1.13-7.43 and 17 vs 1.9%; OR = 10.6; 95%CI = 1.30-87.3, respectively). The subgroup of sVAD attributed to high-pillow usage (⩾12 and ⩾15 cm) was found in 11.3% (95%CI = 2.7%-19.8%) and 9.4% (95%CI = 1.5%-17.3%), respectively.

CONCLUSION

High-pillow usage was associated with an increased risk of sVAD and accounted for approximately 10% of all sVAD cases. This tentative subgroup of sVAD may represent a distinct spectrum of disease-Shogun pillow syndrome.

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).

Angular Kinematics of Chiropractic Supine Cervical Spine Manipulation: Rotational Measures and Comparisons to Doctor and Recipient Perceptions

OBJECTIVES

The primary purposes of this study were to measure axial rotation during supine cervical spinal manipulative therapy (cSMT) and to record recipients' and doctors' perceptions of rotational magnitudes.

METHODS

Experienced doctors of chiropractic (DCs) provided supine cSMT and acted as recipients of cSMT. Participants who received SMT wore inertial measurement units attached to the forehead and sternum for motion capture. Afterward, recipients and DCs completed questionnaires asking about their perceptions of motion. Data were analyzed for magnitudes of axial rotation at peak thrust and correlations with patient and doctor perceptions. Secondary analyses included angular velocity, angular acceleration, and other kinematic variables.

RESULTS

We recorded 23 SMT events with 14 DCs. Rotation at thrust peaks averaged 32.4° (17.4°). Doctors' and recipients' perceptions of rotation were higher than measured values 45% and 50% of the time, respectively. Maximum angular velocity and acceleration averaged 221.9°/s (124.9) and 4786.5°/s² (2456.6), respectively. We found no correlation between perceptions and velocity or acceleration; doctors' perceptions had an inverse correlation with measurements.

CONCLUSION

On average, we found rotation during supine cSMT to be 32°. Both DCs and SMT recipients overestimated rotation compared with actual measurements. These factors should be considered in discussions of rotation and SMT.

Kinematics of the head and associated vertebral artery length changes during high-velocity, low-amplitude cervical spine manipulation

Background

Cervical spine manipulation (CSM) is a frequently used treatment for neck pain. Despite its demonstrated efficacy, concerns regarding the potential of stretch damage to vertebral arteries (VA) during CSM remain. The purpose of this study was to quantify the angular displacements of the head relative to the sternum and the associated VA length changes during the thrust phase of CSM.

Methods

Rotation and lateral flexion CSM procedures were delivered bilaterally from C1 to C7 to three male cadaveric donors (Jan 2016–Dec 2019). For each CSM the force–time profile was recorded using a thin, flexible pressure pad (100–200 Hz), to determine the timing of the thrust. Three dimensional displacements of the head relative to the sternum were recorded using an eight-camera motion analysis system (120–240 Hz) and angular displacements of the head relative to the sternum were computed in Matlab. Positive kinematic values indicate flexion, left lateral flexion, and left rotation. Ipsilateral refers to the same side as the clinician's contact and contralateral, the opposite. Length changes of the VA were recorded using eight piezoelectric ultrasound crystals (260–557 Hz), inserted along the entire vessel. VA length changes were calculated as D = (L₁− L₀)/L₀, where L₀ = length of the whole VA (sum of segmental lengths) or the V3 segment at CSM thrust onset; L₁ = whole VA or V3 length at peak force during the CSM thrust.

Results

Irrespective of the type of CSM, the side or level of CSM application, angular displacements of the head and associated VA length changes during the thrust phase of CSM were small. VA length changes during the thrust phase were largest with ipsilateral rotation CSM (producing contralateral head rotation): [mean ± SD (range)] whole artery [1.3 ± 1.0 (− 0.4 to 3.3%)]; and V3 segment [2.6 ± 3.6 (− 0.4 to 11.6%)].

Conclusions

Mean head angular displacements and VA length changes were small during CSM thrusts. Of the four different CSM measured, mean VA length changes were largest during rotation procedures. This suggests that if clinicians wish to limit VA length changes during the thrust phase of CSM, consideration should be given to the type of CSM used.

Changes in internal carotid and vertebral arterial wall stiffness with head movement can be detected with shear wave elastography

Background: Safe practice is important for patients with neck pain, with the potential for injury to cervical arteries. Cervical manipulation or end range techniques/positions may place considerable strain on the arteries. Altered integrity of the arterial wall may render them more susceptible to minor trauma, particularly in the upper cervical region. Screening of blood flow velocity is limited for predicting those at risk. Examining properties of the cervical arterial wall (stiffness characteristics) and their response to head movement may provide an alternate measure of arterial susceptibility.Objectives: To investigate whether shear wave ultrasound elastography can detect any changes in internal carotid (ICA) and vertebral (VA) arterial wall stiffness in neutral compared with contralateral head rotation.Design: Observational studyMethods: Shear wave ultrasound elastography was used to measure the stiffness of the ICA and VA. Shear wave velocity (m/s), indicative of arterial stiffness, was measured in both arteries proximally (C3-4) and distally (C1-2) in neutral and contralateral head rotation as were intimal thickness (mm) and flow velocity (cm/s).Results: Thirty participants (20-62 years) were successfully imaged. The VA was stiffer than ICA and it became significantly stiffer in contralateral rotation (p = 0.05). The ICA became significantly less stiff (p = 0.01). Effects were more apparent at C1-2 but significant in the ICA only (p = 0.03). Flow velocity and intimal thickness were unchanged in rotation.Conclusions: Changes in VA and ICA arterial wall stiffness can be measured with shear wave ultrasound elastography. This measure may ultimately help identify arteries with greater vulnerability to rotational stresses.

Force transmission between thoracic and cervical segments of the spine during prone-lying high-velocity low-amplitude spinal manipulation: A proof of principle for the concept of regional interdependence

BACKGROUND

Regional interdependence is conceptually based on observations that applying manual therapy to a remote anatomical region has an effect in the area of the patient's primary complaint. The current model for regional interdependence depends on force transmissibility within the body. This investigation sought to determine transmissibility between forces applied to the thoracic spine during prone-lying high-velocity low-amplitude spinal manipulative therapy and the cervical spine.

METHODS

A chiropractic treatment table was modified to allow (or disallow) translation of the headrest in the caudal-cephalad direction when unlocked (or locked). Prone-lying high-velocity low-amplitude spinal manipulative therapy was applied to the thoracic region of 9 healthy participants with the headrest in both configurations. Head and thorax kinematics and kinetics were measured at interfaces between participant and the external environment, which included the clinician's hands. Compressive forces at the cervicothoracic junction and angular kinematics of the cervical spine were derived. Ratios between the clinician-applied forces (input) and the cervical compressive force (output) were also determined.

FINDINGS

The cervical spine extended during all high-velocity low-amplitude spinal manipulative therapy trials. Force input-to-output ratios exceeded 1 for high-velocity low-amplitude spinal manipulative therapy trials performed with the headrest in the locked configuration, which was greater than ratios for the unlocked configuration.

INTERPRETATION

Forces imparted to thoracic spine during high-velocity low-amplitude spinal manipulative therapy were transmitted to the cervical spine, which provided a precursor for the regional interdependence model for manual therapy. Friction between the participant's face and the treatment table's head rest likely amplified cervical compressive forces.

Changes in Vertebral Artery Hemodynamics Associated With McKenzie Therapeutic Cervical Movements: An Exploration Using Duplex Ultrasound Imaging

OBJECTIVE

The purpose of this study was to explore vertebral artery hemodynamic changes associated with McKenzie therapeutic cervical movements in healthy individuals.

METHODS

A single-group repeated-measure design was used to examine 20 healthy participants aged 22.05 (1.69) years, mean (standard deviation). Vertebral artery volume flow, diameter, resistive index, time-averaged maximum velocity, and pulsatility index were measured using Duplex ultrasound. Vertebral artery hemodynamics were measured at cervical neutral positions then compared against vertebral artery hemodynamics measured during end-range loading and after repeated McKenzie therapeutic movements. Wilcoxon signed rank tests were used for comparisons, and standardized mean differences (SMDs) were calculated to quantify the changes in size.

RESULTS

Repeated retraction with extension in a sitting position and end-range retraction with extension in supine position were significantly associated with an increase in vertebral artery volume flow, P ≤ .01, and the SMD suggests small-medium changes in size. Statistical significant vertebral artery dilation was observed in the sitting position with protraction, combined retraction with extension, and flexion, P ≤ .01, yet the SMD suggested small changes in size. End-range flexion was significantly associated with a reduction in vertebral artery pulsatility index, and the SMD suggested large changes in size. Repeated retraction with extension in supine position was significantly associated with an increase in vertebral artery time-averaged maximum velocity, yet the SMD revealed no clinically important difference.

CONCLUSION

For the healthy participants in this study, McKenzie cervical movements were mostly associated with an increase in vertebral artery hemodynamics.

Shear wave elastography of the cervical arteries: A novel approach to the assessment of cervical arterial wall stiffness. An investigation of psychometric properties and intra-rater reliability

BACKGROUND

Cervical arterial dissection, can occur spontaneously and is a rare but catastrophic adverse event associated with neck manipulation. Pathophysiology involves altered integrity of the arterial wall increasing its vulnerability to minor trauma. Those at risk are difficult to detect. Previous screening investigated blood flow but altered mechanical properties as stiffness of cervical arterial wall could provide a more valid indication of arterial integrity or even early dissection.

OBJECTIVES

To investigate suitability and intra-rater reliability of shear wave ultrasound elastography to measure mechanical properties of the cervical arterial wall. Suitability was assessed by ability to track arteries along their length and measurement accuracy.

DESIGN

Observational and intra-rater reliability study.

METHODS

Internal carotid (ICA) and vertebral arteries (VA) of healthy participants were examined with shear wave elastography. Shear wave velocity (m/s) indicative of wall stiffness was measured with the head in the neutral position: proximally (C3-4) and distally (C1-2) where injuries have been more commonly reported. Proximal measures were repeated to assess intra-rater reliability.

RESULTS

Thirty healthy participants (13 female), mean age of 29 (±12.8) years were imaged. Mean VA wall stiffness (3.4 m/s) was greater than ICA (2.3 m/s) (p < 0.000). Intra-rater reliability for ICA was ICC 0.81 (CI 0.52 to 0.92) and for VA ICC 0.76 (CI 0.38 to 0.9). Standard error of measurement was 0.16 for ICA and 0.34 for VA.

CONCLUSIONS

Shear wave ultrasound elastography appears a suitable and reliable method to measure cervical arterial wall stiffness, justifying further research into its use for screening arterial integrity.

A risk-benefit assessment strategy to exclude cervical artery dissection in spinal manual-therapy: a comprehensive review

Cervical artery dissection refers to a tear in the internal carotid or the vertebral artery that results in an intramural haematoma and/or an aneurysmal dilatation. Although cervical artery dissection is thought to occur spontaneously, physical trauma to the neck, especially hyperextension and rotation, has been reported as a trigger. Headache and/or neck pain is the most common initial symptom of cervical artery dissection. Other symptoms include Horner's syndrome and lower cranial nerve palsy. Both headache and/or neck pain are common symptoms and leading causes of disability, while cervical artery dissection is rare. Patients often consult their general practitioner for headache and/or neck pain, and because manual-therapy interventions can alleviate headache and/or neck pain, many patients seek manual therapists, such as chiropractors and physiotherapists. Cervical mobilization and manipulation are two interventions that manual therapists use. Both interventions have been suspected of being able to trigger cervical artery dissection as an adverse event. The aim of this review is to provide an updated step-by-step risk-benefit assessment strategy regarding manual therapy and to provide tools for clinicians to exclude cervical artery dissection. Key messages Cervical mobilization and/or manipulation have been suspected to be able to trigger cervical artery dissection (CAD). However, these assumptions are based on case studies which are unable to established direct causality. The concern relates to the chicken and the egg discussion, i.e. whether the CAD symptoms lead the patient to seek cervical manual-therapy or whether the cervical manual-therapy provoked CAD along with the non-CAD presenting complaint. Thus, instead of proving a nearly impossible causality hypothesis, this study provide clinicians with an updated step-by-step risk-benefit assessment strategy tool to (a) facilitate clinicians understanding of CAD, (b) appraise the risk and applicability of cervical manual-therapy, and (c) provide clinicians with adequate tools to better detect and exclude CAD in clinical settings.

The potential dangers of neck manipulation & risk for dissection and devastating stroke: An illustrative case & review of the literature

Chiropractic cervical manipulation is a common practice utilized around the world. Most patients are never cleared medically for manipulation, which can be devastating for those few who are at increased risk for dissections. The high velocity thrust used in cervical manipulation can produce significant strain on carotid and vertebral vessels. Once a dissection has occurred, the risk of thrombus formation, ischemic stroke, paralysis, and even death is drastically increased. In this case report, we highlight a case of a 32-year-old woman who underwent chiropractic manipulation and had vertebral artery dissection with subsequent brainstem infarct. She quickly deteriorated and passed away shortly after arrival to the hospital. Although rare, one in 48 chiropractors have experienced such an event. We utilize this case to highlight the risk associated with cervical manipulation and urge open dialogue between chiropractors and physicians. Receiving medical clearance prior to cervical manipulation in potential at risk patients would drastically reduce morbidity and mortality.