Premanipulative Screening of Vertebral Arteries using Doppler Velocimetry
By Michael J Haynes

The majority of the following is based on a detailed analysis of the literature that was recently published¹ and which forms part of my PhD thesis².

In the past, screening procedures have been used to test vertebral arteries (VAs) prior to cervical manipulation, in order to reduce the risk of strokes that have a temporal relationship with neck manipulation. These tests were designed to provoke symptoms and signs of vertebrobasilar insufficiency, by rotating and/or extending the neck to occlude one or both of the VAs. There is mounting evidence indicating that the provocational tests yield unacceptably high false negative and false positive results and therefore are invalid.

Recently, Symons et al concluded from the results of their biomechanical study, that neck manipulation causes tensions on VAs that are within the limits of stretch applied to the arteries during range of motion testing³. This may lead some to believe that if neck manipulation causes no more stress to VAs than normal neck movements, then pre-manipulative testing of these vessels is unwarranted. The lack of validity for the provocational tests may also lend support to this attitude. To address these concerns, some analysis of the study by Symons et al is required, as well as a discussion on Doppler velocimetry of VAs.

Symons et al³ made in situ measurements of the tensions on the VAs, from fresh post-rigor human cadavers, during ROM testing and spinal manipulation at the C1/2, C3/4 and C6/7 levels. The measurements were made at the occiput – C1 and pretransverse segments of each VA. However, no measurements were made at the C1/2 level where maximal stresses can be applied to the artery during contralateral cervical rotation, nor at the C1/2 and C3/4 levels where thrusts of manipulation were applied. VAs are tethered along their course and so tensions are unlikely to be transmitted fully along their lengths. Hence, measurements by Symons et al may have been less than the stretch occurring at regions of maximal stress, ie the C1/2 and C3/4 levels. The fact that their study used cadavers aged 80-90 yrs, who may have suffered advanced degeneration in their cervical spines, further suggests that their findings probably do not apply to chiropractic patients, the majority of whom are aged less than 80 yrs. The cadavers’ necks were probably stiffer due to degenerative changes than those of typical younger chiropractic patients, which would have caused greater dampening of forces applied to the VAs from the manipulations. Since DJD has a predilection for the lower cervical spine, this has particular relevance to the manipulations that were made at the C6/7 level.

There is the need for practitioners of neck manipulation to check the patency of VAs, so as to assess the collateral supply in case one artery is injured and becomes occluded. If a VA was found not to be patent, this would suggest that preference be given to low force cervical techniques without full neck rotation, to reduce the risk of injury to the patent artery. In the event that the patient complained of symptoms suggesting possible vertebrobasilar ischaemia, the finding of VA stenosis would provide a greater incentive to refer for neurological assessment.

Another reason to check VA patency is that VA injury, in the form of dissection, can be neurologically silent, cause severe unilateral neck pain without torticollis, and frequently (94% of cases) causes major VA stenosis. This presentation of suspect VA dissection would indicate that neck manipulation is contraindicated, and that rapid medical referral for further assessment is required. If this presentation occurred after a neck manipulation, if the VA was previously found to be patent and especially if VBI symptoms had developed, medical referral would be particularly urgent in the attempt to prevent the onset of possible stroke, or at least reduce its severity.

VAs can become stenosed during cervical rotation and 2 studies have indicated that rotational stenosis of VA’s is an independent risk factor for stroke in the vertebrobasilar territory. A recent biomechanical study provided evidence to suggest that rotational stenosis of VA is primarily due to compression of the artery, which precedes any major stretch that may be induced. With a weakened VA due to an arteriopathy, compression of the vessel may be hazardous, especially if there is an associated stretching of the arterial wall. Detection of rotational (or other positional) stenosis, therefore could provide an indirect assessment of the mechanical stresses that are being applied to the artery during neck movement. This can assist the practitioner to select manipulative techniques that do not cause positional stenosis of the patient’s VAs and such an approach may reduce the risk of injury to these vessels. The practitioner would be also able to advise patients to be mindful of activities, such as certain sports, that may cause positional stenosis of the VAs.

During the 1980’s there were six studies, and another one in 2001, that demonstrated the high validity of small hand held Doppler ultrasound velocimeters in making preliminary assessment of VA patency. There is a recent study that indicated high validity of Doppler velocimetry to detect major VA rotational stenosis and another that indicated high inter-examiner reliability of the technique, even though one of the examiners had only 2 hours instruction in the examination procedure. There are a number of features of Doppler velocimetry that further make it suitable for pre-manipulative screening of VA’s. It is safe (no ionizing radiation), relatively quick (ie usually less than 2 minutes) and the Doppler instruments are relatively cheap (currently costing about $1,200).

Since there seems to be no legitimate evidence to suggest that practitioners of spinal manipulation can be excused from attempting to reduce the risks of strokes related to neck manipulation, pre-manipulative screening of VAs remains a procedure that is warranted. Furthermore, there is substantial indirect evidence to suggest that Doppler velocimetry is a valid, reliable and practical method for practitioners of spinal manipulation to screen the vertebral arteries of their patients.

*References available on request.