Pre-manipulative VBI Testing Worthless
By Dr John Reggars

In March 2004 the jury in the Canadian Coronial Inquest into the death of Lana Lewis, who died some 17 days after receiving chiropractic manipulation to her neck, recommended that pre-manipulative screening tests for vertebrobasilar ischemia (VBI) have not been shown to be of benefit and should not be performed.¹

Also, last year the Australian Physiotherapy Association updated its guidelines on pre-manipulative testing, stating that the minimum testing includes sustained end range movements only and that further VBI testing is to be guided by the clinical reasoning of the physiotherapist.²

Now a recent review by Thiel and Rix³ opines that as these tests have been shown to have little validity and reliability in detecting patients at risk of vertebrobasilar stroke and that they in themselves may increase the risk of stroke: “Practitioners might well now consider whether provocative testing provides any real benefit to any of these patient populations”.

Thiel and Rix state that the pre-manipulative tests fail to satisfy the necessary requirements of a “screening test”, in that they fail to identify the pre-symptomatic condition they were designed to detect. The authors put forward several different vertebrobasilar stroke pathophysiological mechanisms and the relative validity and reliability of VBI testing for each scenario:

Vertebral Artery Dissection
The authors argue that the most commonly accepted theory relating to stroke associated with spinal manipulative therapy is that of vertebral artery dissection. That even if the dissection was due to pre-symptomatic congenital or acquired arterial weakness that positional testing will not provide the practitioner with any useful information regarding the possible risk of injury. Furthermore, based on the research of Symons⁴, the reviewers point out that pre-manipulative tests place more mechanical stress on the vertebral artery than the actual manipulation and therefore performing these tests may increase the risk of injury to the vertebral artery.

Arterial Vasospasm
With respect to the hypothesis that vessel spasm resulting from spinal manipulative therapy (SMT) is the cause of arterial occlusion, Thiel and Rix state, “Again, for the same reason as dissection, it is hard to see how on biologically plausible grounds, a positional pre-manipulation test could assess for the possibility of an impending vasospasm. In summary, the construct validity of the tests with these pathologies in mind is poor”.

Embolism
It has also been postulated that SMT related stroke may be due to embolisation from pre-existing thrombus formation in the vertebral artery. Thiel and Rix suggest, that even though pre-manipulative testing may detect sufficient alteration to arterial blood flow to produce ischemic brainstem symptoms, in an artery with sufficient atherosclerosis, it could also dislodge an embolus resulting in stroke.

Hypoplastic Artery
In the case where a hypoplastic artery has been hypothesized to play a part in SMT related stroke, the authors suggest that there is no evidence that a hypoplastic artery has a greater predisposition to dissection but that identifying a hypoplastic artery via these tests may be of benefit where the contralateral artery suffers injury. However, according to Thiel and Rix, a review of the literature on this mechanism, in particular in vivo Doppler studies, shows inconclusive, inconsistent and even contradictatory results and that pre-manipulative testing lacks the necessary sensitivity in order to be valid and dependable predictors of risk.

The authors conclude with several observations and recommendations that include:

• In many cases the only presenting symptom of vertebral artery dissection (VAD) may be neck pain alone and without signs and symptoms of VBI.
• If there is a strong likelihood of VAD, provocative pre-manipulation tests should not be performed.
• In a patient presenting with VBI symptoms due to non-dissection stenotic vertebral artery pathologies, provocative testing is very unlikely to provide any useful additional diagnostic information.
• In a patient with unapparent vertebral artery pathology provocative testing is very unlikely to provide any useful information in assessing the risk of SMT related stroke.
• Practitioners might well now consider whether provocative testing provides any real benefit to any of these patient populations.

Although the evidence is moving towards showing that VBI screening tests appear to be of little predictive value the expectation may be different from a medico-legal perspective and hence it may be judicious to carefully perform such a test to comply with expected standards of care.

References:
1. Reggars J. The Jury’s verdict. COCA News, March 2004.
2. Reggars J. Physiotherapists issue new guidelines for cervical spine manipulation. COCA News, December 2004.
3. Thiel H, Rix George. Is it time to stop functional pre-manipulation testing of the cervical spine? Manual Therapy, (in press).
4. Symons B, Leonard T, Herzog W. Internal forces sustained by the vertebral artery during spinal manipulative therapy. J. Manip Physiol, 2002; 25:504-10.