Abstract
Positional testing for vertebrobasilar insufficiency (VBI) is used by physiotherapists as part of pre-manipulative screening protocols. Recently, the validity of the tests have been questioned because a negative test does not infer safety with cervical manipulative therapy but the reasoning surrounding this opinion may be questioned. While the positional tests were developed to test vertebral artery flow contralateral to the direction of head movement and the subsequent effect on cerebral blood supply, as inferred by symptom reproduction, ultrasound studies have shown that vertebral artery flow is inherently variable. Rather, the tests should be considered as testing for adequacy of collateral flow in particular head positions rather than decreased blood flow in a particular artery, with more attention to characteristics of symptom reproduction. We contend that positional testing for VBI remains valuable for testing adequacy of collateral flow, and also has an important place as part of the differential diagnosis of individuals with dizziness or imbalance. The physiotherapist’s ability to differentially diagnose dizziness and recognise the presence or not of VBI is not only critical for prompt medical investigation and management because it is a risk factor for transient ischaemic events and stroke, but has important influences over management decisions regarding cervical musculoskeletal treatment including exercise interventions. Importantly, the positional tests should not be considered as tests of arterial integrity and used to assess the risk of damage to the vertebral or internal carotid artery or presence of cervical arterial dissection. Urgent research is needed before we abandon positional testing prematurely.
Highlights
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Positional testing has an important role for screening and differential diagnosis.
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Positive tests via symptom reproduction determine inadequate collateral flow.
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Correct use and interpretation is vital as tests do not assess arterial integrity.
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Tests should not be abandoned but further research is needed.
1
Introduction
Currently, opinion is divided about the future of clinical positional tests for Vertebrobasilar Insufficiency (VBI). Some advocate abandoning VBI positional tests because they lack validity and do not inform about pre-manipulative risk ( ; ; ), others support their continued use ( ; ; ). The issue is that neither side has strong evidence for their positions. From a professional standpoint, this dichotomy needs to be discussed and future directions considered.
1.1
History of VBI positional testing
Positional testing was introduced in the 1950s as a means to test the adequacy of vertebral artery (VA) blood flow to the hindbrain when the head was placed in end range positions of cervical rotation and extension ( ; ) as these positions could be assumed with cervical manipulation or end range mobilisation techniques. The tests were adopted by the Australian Physiotherapy Association in 1988 ( ) as part of the first formal pre-manipulative testing protocol in Physiotherapy, with the growing awareness of the potentially serious side effects of cervical manipulation. The protocol was subsequently broadened to include differentiation of VBI from dizziness of other causes ( ). In 2017 the protocol was updated and broadened further to include recognition of cervical arterial dissection (CAD) ( ). The International Federation of Orthopaedic Manipulative Physical Therapist’s framework for assessing the risk of cervical arterial dysfunction was consensually agreed in 2012 and published in 2014. It included positional testing but noted that the predictive validity to detect those at risk of adverse event following cervical manipulative therapy was lacking ( ). first questioned whether it was time to stop functional pre-manipulative testing and this was subsequently supported by who suggested the tests should be abandoned. Recently, Hutting et al.( ) concluded that the sensitivity of positional tests was low in detecting those at risk, but their specificity to detect VBI was high. However performing them in an individual with a clear history of ischaemia/VBI might be hazardous. Thus the current situation is ambiguous.
1.2
Should VBI testing be abandoned?
The call for the abandonment of VBI position tests is based on four particular issues (i) conclusions that the tests lack validity to detect reduced blood flow, (ii) conflicting symptomatic responses when blood flow is reduced, or when positional tests are positive in the presence of normal flow (iii) the tests have no ability to predict or detect CAD and risk from manipulation, and (iv) the tests do not add value to the patient evaluation. Nevertheless, these conclusions can be questioned.
1.2.1
Lack of validity to detect reduced blood flow
Reduced blood flow has not been demonstrated during positional testing when based on studies measuring blood flow with Doppler ultrasound ( ) and this lack of validity provides one of the reasons for abandonment of positional tests. However, this reasoning can be refuted. In the first instance, ultrasound is not the reference standard for assessing the presence of VBI, rather the reference standard is digital subtraction angiography, although less invasive magnetic resonance (MRA) or computed tomography angiography (CTA) is often used ( ; ). Doppler ultrasound or transcranial Doppler is also used but shown to only pick up 50% of cases ( ). Doppler while a cheaper more available option, cannot visualise the full length of the artery and is highly operator dependent, which is particularly relevant when the vertebral artery (VA) is small and tortuous in its more vulnerable distal portions ( ; ).
Secondly, measures in earlier Doppler studies and in a more recent MRI study ( ) were mainly collected at C2-3 or a lower cervical level, in a single vessel and in healthy subjects ( ; ; ). Measuring flow in one vessel is not necessarily indicative of total cerebral inflow, as homeostatic flow to the brain is normally maintained via the Circle of Willis which enables compensation for any single vessel compromise ( ). Thus, imaging the whole cerebral circulation or at least more distal parts of the vessels above C2-3 will provide a better indication of the effects of head rotation on adequacy of flow downstream.
Interestingly, in single case and case series studies, when the more distal vessels i.e. posterior cerebral or basilar arteries were imaged dynamically with magnetic resonance angiography ( ; ) or transcranial Doppler ( ; ), in patients with symptomatic position-induced VBI (rotational vertebrobasilar ischaemia or occlusion syndrome), abnormal flow velocities have been confirmed in at least 80% of those studied. Although these types of studies are not the strongest design for generating evidence, Level 4 evidence ( ), their findings cannot be ignored and would support retaining positional testing in the clinical examination, albeit more targeted research is needed.
1.2.2
Conflicting symptomatic responses
The argument for abandonment of positional testing is also supported by evidence of conflicting symptom responses in situations when reduced blood flow has been demonstrated ( ; ; ; ) and when positional tests are positive in the presence of normal flow ( ). However, vertebral artery (VA) flow is highly variable, but usually adequately compensated by flow in the other three cervical vessels or by collateral flow from smaller vessels ( ). Thus the lack of VBI symptoms in studies of patients and healthy individuals where blood flow has been shown to be reduced could be explained by the preserved adequacy of collateral flow ( ; ; ). Similarly, positive positional tests in the presence of normal flow ( ) does confirm adequate collateral flow but suggests another cause of symptoms (e.g cervicogenic, vestibular). Hence, rather than focussing on reduced blood flow in the VA, it has been proposed that a positive VBI test should be determined by reproduction of specific symptoms and signs of ischaemia, as these suggest a critical reduction in cerebral flow ( ). Insufficient vertebrobasilar blood flow alone should not cause VBI if there is sufficient collateral flow ( ). In this context, positional tests are considered as tests of adequacy of collateral flow to the brain rather than flow reduction in one vessel. In the majority of individuals, tests will be negative, but it is possible they could be used to identify those persons with VBI symptoms from inadequate collateral blood flow so that appropriate care can be taken e.g. refer for medical evaluation or avoiding provocative head positioning when treating the person’s presenting neck pain disorder. More research is needed to determine the diagnostic utility of the tests for this purpose.
1.2.3
Inability to predict or detect cervical arterial dissection (CAD) and risk from manipulation
There is no argument against the conclusion that positional tests are unable to predict or detect CAD ( ; ). It is well recognised that positional tests are not tests of arterial integrity and they are unsuitable to determine the risk of CAD and safety to proceed with neck manipulation or other techniques. It was considered previously that identifying a change in blood flow in a VA between neutral and a particular head position might provide information about biomechanical strain on the artery imposed by the position ( ). More recent reviews have suggested haemodynamic parameters might act as a proxy for mechanical stress on the arteries ( ; ). However such theories can be dismissed as, with adequate collateral flow, symptoms may not arise even though the artery might undergo considerable mechanical strain. Rather CAD is more dependent on integrity of the arterial wall and positional tests cannot predict an arterial tear. Recognition of CAD is more likely to be gained from an indicative history (ie. acute onset of unusual headache or neck pain, recent trauma to the head or neck, and/or ischaemic signs and symptoms, in younger people under 50 years)( ; ). It is to be noted that the presentation of CAD could include signs and symptoms of VBI if the vertebrobasilar (posterior) circulation is involved but symptoms are often vague and transient in the early stages ( ). If a presentation of CAD is suspected, positional tests are more likely to be contra-indicated as they may extend the tear, cause the dissection flap to occlude the artery, or propagate an embolus ( ).
1.2.4
No added value to the patient evaluation
It has been concluded that the tests do not provide any additional value to the patient evaluation. ( , ; ). While positional tests have no place in CAD, the conclusion of their lack of added value for VBI is based on narrative reviews ( ; ; ) and a systematic review of four studies ( ). All four studies were of low quality due to various types of bias and non-representative participant inclusion. Two of the studies used ultrasound evaluation of a single VA which has been argued to be inadequate to make judgements on validity of positional tests. It is therefore suggested that studies to date may not have provided convincing enough evidence to abandon positional tests for VBI at this time. Screening for the effect of head movement on vascular haemodynamics and adequate collateral cerebral blood flow therefore may still be an important part of the evaluation of the patient ( ) and relevant to physiotherapy management. In addition the tests can be quickly incorporated into an active movement assessment and do not add substantially to the assessment time.
1.3
Should positional tests be retained?
There is no pretence that positional tests are fail safe tests for vascular supply to the brain. Positional tests are not unique to VBI. The symptoms they provoke (e.g. dizziness) could be of vascular, vestibular or cervicogenic origin ( ) and clinical reasoning across the patient’s history, presenting symptoms and onset as well as responses to positional tests is required for differential diagnosis ( ; ). However, if presenting the case for retaining positional tests from a vascular perspective, the question to consider is whether they add safety to treatment with cervical manipulative therapy. As argued, magnetic resonance angiography ( ; ) and transcranial Doppler ( ; ) have provided initial evidence of abnormal flow velocities in posterior cerebral or basilar arteries in patients with symptomatic position-induced VBI which supports the case for retaining the tests. However, rather than relating tests to the VA alone, it is more accurate to regard positional tests as tests of adequacy of collateral flow to the brain, rather than flow reduction in one vessel.
The position to retain positional tests in their evaluation of neck pain patients could be argued, especially if the patient presents with symptoms of dizziness that requires further differentiation or the clinician is considering the use of high velocity manipulative procedures or any end of range techniques which might compromise circulation as positional tests may have an important role in determining whether an individual has adequate collateral cerebral blood flow but more research is required. To this end, future studies must use appropriate dynamic imaging i.e. angiography or transcranial Doppler in different head positions, to capture the most informative images at the most relevant sites. The downstream effect of rotated head positions on blood supply to the brain needs to be evaluated in symptomatic rather than asymptomatic individuals and in those with confirmed vascular pathologies. In tandem there is a need for detailed characterisation of the timing and nature of symptom responses to the positional tests in those with vascular pathologies, healthy individuals, and those with other causes of dizziness, for a full understanding of their clinical interpretation and diagnostic utility.
2
Conclusion
The research evidence supporting the positions to either abandon or retain positional tests as initial screening tests for vertebrobasilar insufficiency is not strong for either standpoint. Targeted research is urgently needed to resolve this issue to help ensure best practice of cervical manipulative therapy into the future.
Appendix A
Supplementary data
The following is the Supplementary data to this article: Multimedia component 1
References
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