Chiropractic care involves manual treatments designed to improve musculoskeletal function, often focusing on the spine. A common technique is high-velocity, low-amplitude (HVLA) cervical manipulation, often called a neck adjustment. This procedure uses a quick, controlled thrust to a joint, frequently resulting in a popping sound. Concerns exist regarding a rare but serious adverse event: the potential link between this specific neck adjustment and a particular kind of stroke. This article examines the scientific evidence surrounding this association, focusing on the biological mechanisms, the statistical debate, and risk minimization measures.
The Mechanism of Arterial Dissection
The biological event hypothesized to link cervical manipulation and stroke is an arterial injury called a dissection, involving a tear in the inner lining (intima) of an artery wall in the neck. The two arteries of primary concern are the vertebral arteries (VA) at the back of the neck and the internal carotid arteries (ICA) at the front. The VAs are relevant as they travel through bony canals in the cervical vertebrae before forming the basilar artery, which supplies blood to the brainstem and cerebellum.
When a tear occurs, blood enters the space between the layers of the artery, causing the wall to separate. This dissection can lead to an ischemic stroke in two ways. The expanding wall can narrow the vessel, restricting blood flow, or the injury site can promote the formation of a blood clot (thrombus).
A piece of this clot can break off, becoming an embolus, which travels into the smaller vessels of the brain. When the clot lodges, it blocks oxygen and nutrient supply, causing an ischemic stroke. If the vertebral artery is involved, the resulting stroke is called a vertebrobasilar artery (VBA) stroke. This sequence is considered a rare occurrence.
Biomechanical studies conclude that the strain exerted by a skilled manipulation is significantly lower than the force required to mechanically disrupt a healthy artery. For a dissection to occur, it is hypothesized that the artery must have a pre-existing weakness, such as an underlying connective tissue disorder or a spontaneous injury already in progress. A healthy vessel is highly resilient, capable of withstanding forces associated with normal movements.
Distinguishing Correlation from Causation in the Data
The association between cervical manipulation and stroke is a complex epidemiological issue centering on the distinction between correlation and causation. Studies explore whether the adjustment causes the dissection or merely occurs shortly before stroke symptoms become obvious.
Evidence supports the hypothesis that many patients experiencing an arterial dissection are already symptomatic when they seek chiropractic care. A developing vertebral artery dissection commonly presents with a new or unusual headache and neck pain before neurological symptoms appear. These non-specific symptoms are often the reasons a patient seeks a manual therapist for relief.
Large-scale population studies compared the risk of VBA stroke following a visit to a chiropractor versus a primary care physician (PCP). These studies consistently found a similar association between VBA stroke and a visit to either type of provider. This suggests the elevated risk is not specific to the manipulation but rather to the patient’s underlying condition that prompted the visit.
The manipulation is thus correlated with the stroke’s timeline, not necessarily its cause, because the patient was already experiencing the early stages of the dissection. The scientific consensus from systematic reviews is that there is insufficient evidence to establish a definitive causal link between cervical manipulation and a dissection in a healthy artery.
Identifying Patients at Elevated Risk
Preventing a serious adverse event relies on the practitioner’s ability to identify patients who may already have a developing arterial dissection or a predisposition to one. Patient history taking is the most important screening tool, as specific symptom patterns serve as red flags suggesting a non-musculoskeletal origin for the pain. Chiropractors are trained to differentiate a common mechanical neck complaint from a potential vascular injury.
The most concerning symptom is the sudden onset of severe, unusual head or neck pain, often localized to one side or the back of the head. Patients frequently describe this as the “worst headache of their life,” indicating a vascular event. Any report of recent minor trauma, such as a neck strain or sudden jarring movement, should also raise immediate suspicion.
Other concerning symptoms that signal a disruption of blood flow to the brainstem include neurological deficits. These may manifest as:
- Dizziness or vertigo that is not positional.
- Visual disturbances like double vision.
- Difficulty with swallowing.
- Slurred speech.
Patients with underlying conditions, such as connective tissue disorders (e.g., Ehlers-Danlos syndrome) or a history of vascular disease, have an inherently elevated risk. The presence of any red flag symptom or predisposing condition necessitates immediate cessation of manipulation and an urgent medical referral.
Immediate Warning Signs and Emergency Protocol
Recognizing the definitive symptoms of a stroke immediately following a cervical manipulation is essential for patient safety. Stroke symptoms caused by a vertebral artery dissection typically affect the brainstem and cerebellum, leading to specific signs. These include a sudden onset of severe, persistent dizziness or vertigo, significant imbalance, or difficulty coordinating movements.
The widely recognized acronym F.A.S.T. applies to all types of stroke and should be used to quickly assess the situation. This involves observing for facial drooping, arm weakness or numbness, and speech difficulties, such as slurred words. A severe, thunderclap headache that peaks rapidly and is accompanied by any neurological signs is a medical emergency.
The emergency protocol must be implemented immediately. If a patient experiences any definitive neurological symptom or severe, unusual pain during or shortly after the adjustment, treatment must be stopped. The practitioner must call local emergency services. Informing responders and hospital staff about the recent cervical manipulation is critical for rapid diagnosis.