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Why Manual Spinal Manipulation Works

Updated: Aug 2, 2021

This post is the first in a multiple-part series on manual spinal manipulation, also known as an

adjustment. The series will cover the safety, effectiveness and current theory of why

manipulation works.

It’s a controversial topic within the schools of Chiropractic because they still

teach specificity of the joints. Research proves the accuracy claimed in schools is incorrect but

providers still hold onto their own belief system. I recently attended a continuing education

seminar and one of the providers actually said the reason chiropractors are different is because

our manipulation is focused on the intersegmental motion. This provider still uses x-rays to

identify the area he needs to adjust on his patients, which is absolutely ridiculous! The best part

Is, this provider is now a diplomate in sports chiropractic and rehabilitation.

Before I end up down a rabbit hole, let’s get into this post. A topic that comes up in different

variations is cervical manipulation. A patient may express concern about strokes, or say they

heard on the news a chiropractor caused a stroke, or they just don’t want their necks adjusted. I

understand not wanting to have a stroke. I get it. In the current political climate, it is easy to

manipulate a story on the news, putting a spin or slant to it. I fear this will be a topic that comes

up again and again but let’s bring as many players to the table as we can.

Some background information about the technique. Before D.D. Palmer “invented” chiropractic

medicine on September 18, 1895 (yes, it has a birthday), the technique was known as bone

setting and was performed by an individual who manipulated joints, reset dislocated bones and

set fractures. Often, the practice was passed down from family member to family member

similar to metalwork (tin smith, goldsmith, bronzesmith, sword makers, etc.). Keeping this as

narrow as possible, bone setting has different names within the various cultures and languages,

but they all perform relatively the same techniques. The earliest known medical text that

describes this therapy is Edwin Smith of papyrus in 1552. He described bone-related injuries

being tended to by an Egyptian practitioner. This was often cultural but my specialty is within

Burmese martial arts and I know a few things within this culture. Most, if not all warriors were

trained in yoga, massage, stretching and soft tissue treatments. After battles, injured warriors

needed to continue to fight the following day so bo staffs, canes, liniments and ropes were all

used to provide relief from soreness and to promote healing. In ancient times, it was normal for

most people to have a baseline knowledge of farming, herbology and basic medicine to treat

infections. The more rural, the more information people had, and of course, the healer, medicine

man or shaman had the most.

What was the point of the last paragraph? To illustrate that manual spinal manipulation is not

new but it has changed names throughout the centuries. In 2009, the American Physical

Therapy Association lobbied to have the rights to perform spinal manipulation. They wanted it to

be included in their scope of practice, and they got it. Shortly after, the athletic trainers said, “we

can do it” and the American Medical Association said, “we are medical doctors, of course we

can perform this.” Osteopaths have been performing this therapy since 1874. That makes five

providers who practice manual spinal manipulation. The logical question is, if this therapy is so

dangerous then why would three more professions want to perform this? That’s a great

question! I AM SO GLAD YOU ASKED! I have no idea….

Joking. Because it is not dangerous. What happened in the beginning of reporting strokes with

this therapy, was that other professions stated they performed a Chiropractic

manipulation/technique even though they were in a different profession. That is a slightly shady

thing to do but it happened and happened for quite a while. Someone finally caught on and

started to correct the data but the damage was done.

Let’s move into the safety aspect. How safe is it? The research shows there is no correlation

causation to cervical manipulation and stroke. In 2010, an article published by Michael

Schneider DC, PhD used four publications to sum up this answer: the best available evidence

shows cervical mobilization and manipulation to be relatively equivalent therapies with respect

to their benefits and risks. David Cassidy in 2008 concluded VBA stroke is a very rare event in

the population. The increased risk of VBA stroke associated with chiropractic and PCP visits is

likely due to patients with headache and neck pain from VBA dissection seeking care before

their stroke. We found no evidence of excess risk of VBA stroke associated chiropractic care

compared to primary care.

This final one was published in the Neurologist and they concluded “Ultimately, the acceptable

level of risk associated with a therapeutic intervention like CMT must be balanced against

evidence of therapeutic efficacy.”

Now let’s talk about the other side of the spectrum. Many articles say this therapy places undue

stress on the artery and increases the risk of damaging an already dissected artery. Do an

Internet search for cervical manipulation safety and the answers will appear as recent as 2018.

Of course, chiropractic was mentioned in all of these. A teacher at my Chiropractic school, Dr.

William Lauretti, said if this therapy was so dangerous why aren’t the people who adjust their

own necks having strokes? There would be PSA’s all over the place advising to stop doing this

immediately or you will die. I have used this statement endlessly to give patients perspective. A

study looked at the vertebral artery of people who died in car accidents. There was massive

trauma to the body but the artery was intact. It concluded the forces from cervical

manipulation were nowhere near as strong. An undamaged artery can handle a controlled

thrust. An Osteopathy group showed the blood flow with ultrasound during manipulation and the

flow did not change. In 2018 the Medical Science Monitor concluded both the rotational angle

and atherosclerotic disease can affect the blood flow of the internal carotid artery. However,

cervical rotary manipulation does not cause adverse effects on hemodynamics in cynomolgus

monkeys with mild carotid atherosclerosis and appears to be a relatively safe technique. A

2019 article in the British Medical Journal concluded: Our results are in accordance with

previous work, which has shown a decrease in blood flow and velocity in the contralateral

vertebral artery with head rotation. This may explain why we also observed a decrease in blood

velocity with manipulation because it involves neck rotation. Our work is the first to show that

cervical manipulation does not result in brain perfusion changes compared with a neutral neck

position or maximal neck rotation. The changes observed were found to not be clinically

meaningful and suggest that cervical manipulation may not increase the risk of

cerebrovascular events through a haemodynamic mechanism.

Safety has been established but what does the magical snap, crackle, and pop during a

manipulation mean? I did an interview recently and the other doctor in the video had no idea

about the latest research of the proposed mechanisms of manipulation. It reinforced my mindset

of staying current with the research. (Thank you to Paul Dougherty DC, Ph.D. for making me a

decent provider before I graduated and stressing the value of research). Tribonucleation, a

known process where opposing surfaces resist separation until a critical point where they then

separate rapidly, creates gas cavities. The crack is actually the formation of gas in the joint.

Pretty awesome. In school, we were taught it was pressure releasing and instructors used

opening a can of soda to make the analogy. Times change, and even though we don’t have all

the information, it is important to understand that the theoretical understanding of this therapy is changing.

The four proposed mechanisms to manipulation are mechanical, neurological, biochemical, and

psychological. I was listening to a podcast on Gestalt Education talking about the soft tissue

reflex that occurs with manipulation. At the area adjusted, the soft tissue has a reflexive release,

adding additional value to the therapy. This would fall under the mechanical category. The

neurological change is the increased range of motion after the adjustment. Yes, this can be

temporary, but rehabilitation can make this last longer for better results. The biochemical is a

complicated explanation that makes readers fall asleep. It activates the receptors in the brain to

process pain differently and affects opioids in the brain to help reduce pain. This is a very

watered-down explanation, so if you are a provider reading this...relax. The psychological

component is the interaction with the patient. Interestingly, sham adjustments showed

improvements with patients because the patient believed the provider treated the painful area

and the patient felt better.

Now the fun stuff. The topic that will anger almost every chiropractor that reads this. We are not

specific with adjustments. We are not even sure where the sound came from. In school, we are

taught that manipulation can be specific and must be specific to the area treated. If you are

trying to adjust the upper cervical spine, you must set up the patient in a way that maximally

targets the joints. It was a song and dance, especially with the upper cervical spine, because

there are some groups who believe the upper cervical spine is the gate to the body. If you

correct this area everything in the body will improve with better nerve flow to the body. I wish I

was making up the previous statement but I am not. Sadly, these folks have a following on

YouTube and are a perfect example of people who will follow someone who acts like they know

what they are doing, ignoring the person with actual knowledge. A provider I met a few years

ago said we don’t have the time for social media because we are so busy running the office.

Most of the time, unless they have a dedicated social media person, this statement is true.

Circling back to the cracking sounds, we know it is the formation of the gas bubble that creates

the crack, but from what joint? There are multiple studies that confirm we don’t have any idea

where the sound originates. One study said that target and adjacent motion segments undergo

facet joint gapping during manipulation and that intervertebral ROM is increased in all three

planes of motion after manipulation. Another study found that most subjects produced 3-4 pops

per manipulation. My favorite article conclusion so far is that the location of cavitation sounds

does not appear to have a relationship with the type of manipulative technique selected.

What does this all mean? Basically, cervical manipulation is a tool and not everyone needs this.

Yes, I am a chiropractor that said not every patient needs spinal manipulation. There are factors

to consider that would exclude certain patients: surgical fusion, upper cervical instability from

consecutive tissue disorders, myelopathy, rheumatoid arthritis, infection or tumor. Clinical

correlation is another skill to have. Drop attacks, sudden onset of a severe headache, new type

of headache, double vision or difficulty speaking would exclude patients from manipulation and

calling 911 would be the best option. Or drive the patient to the hospital yourself because these

are signs of a stroke. (Being a paramedic has its benefits when it comes to recognizing a

stroke.) Another thing to explain is that manipulation is a spectrum and a provider can perform

mobilizations all the way to cracking a joint. These are known as grades and the definition of

grade I is a small amplitude rhythmic oscillating mobilization in the early range of movement.

Grade V (high velocity low amplitude) is a small amplitude, quick thrust at end of the available

range of movement. Read more about the grades here.

The patient’s presentation is the key to providing the best evidence-based approach. Like I said

before, if you ask the provider why and they can’t give you a reason besides what they believe,

then it is time to leave that office.


  1. Anderst WJ;Gale T;LeVasseur C;Raj S;Gongaware K;Schneider M;, William, et al. “Intervertebral Kinematics of the Cervical Spine before, during, and after High-Velocity Low-Amplitude Manipulation.” The Spine Journal : Official Journal of the North American Spine Society, U.S. National Library of Medicine, Dec. 2018,

  2. Dunning J;Mourad F;Barbero M;Leoni D;Cescon C;Butts R;, James; Firas; Marco; Diego; Corrado; Raymond. “Bilateral and Multiple Cavitation Sounds during Upper Cervical Thrust Manipulation.” BMC Musculoskeletal Disorders, U.S. National Library of Medicine, Dec. 2013,

  3. Dunning J;Mourad F;Zingoni A;Iorio R;Perreault T;Zacharko N;de Las Peñas CF;Butts R;Cleland JA; “CAVITATION SOUNDS DURING CERVICOTHORACIC SPINAL MANIPULATION.” International Journal of Sports Physical Therapy, U.S. National Library of Medicine, Jan. 2013,

  4. Mourad F;Dunning J;Zingoni A;Iorio R;Butts R;Zacharko N;Fernández-de-Las-Peñas C; “Unilateral and Multiple Cavitation Sounds During Lumbosacral Spinal Manipulation.” Journal of Manipulative and Physiological Therapeutics, U.S. National Library of Medicine, Jan. 2019,

  5. SM;, Ross JK;Bereznick DE;McGill. “Determining Cavitation Location during Lumbar and Thoracic Spinal Manipulation: Is Spinal Manipulation Accurate and Specific?” Spine, U.S. National Library of Medicine, July 2004,

  6. W;, Herzog. “The Biomechanics of Spinal Manipulation.” Journal of Bodywork and Movement Therapies, U.S. National Library of Medicine, July 2010,

  7. JM;, Flynn TW;Childs JD;Fritz. “The Audible Pop from High-Velocity Thrust Manipulation and Outcome in Individuals with Low Back Pain.” Journal of Manipulative and Physiological Therapeutics, U.S. National Library of Medicine, Jan. 2006,

  8. Beffa, R., & Matthews, R. (n.d.). Does the adjustment cavitate the targeted joint? an investigation into the location of cavitation sounds. DEFINE_ME.

  9. JM;, F. T. W. C. J. D. F. (n.d.). The audible pop from high-velocity thrust manipulation and outcome in individuals with low back pain. Journal of manipulative and physiological therapeutics.

  10. Michaud, T. (n.d.). Uneventful upper cervical manipulation in the presence of a damaged vertebral artery.

  11. Wuest, S., Seymons, B., Leonard, T., & Herzog, W. (n.d.). Preliminary Report: Biomechanics of Vertebral Artery Segments C1-C6 During Cervical Spinal Manipulation.

  12. Haneline, M., & Triano, J. (n.d.). Cervical Artery Dissection. A Comparison of Highly Dynamic Mechanisms: Manipulation versus Motor Vehicle Collision.

  13. Quesnele, J., Triano, J., Noseworthy, M., & Wells, G. (n.d.). Changes in Vertebral Artery Blood Flow Following Various Head Positions and Cervical Spine Manipulation.

  14. Chung, C., Cote, P., Stern, P., & L'Espérance, G. (n.d.). The Association Between Cervical Spine Manipulation and Carotid Artery Dissection: A Systematic Review of the Literature.

  15. Cagnie, B., Jacobs, F., Barbaix, E., Vinck, E., Dierckx, R., & Cambier, D. (n.d.). Changes in Cerebellar Blood Flow After Manipulation of the Cervical Spine Using Technetium 99m–Ethyl Cysteinate Dimer.

  16. Ernst, E. (2007, July). Adverse effects of spinal manipulation: a systematic review. Journal of the Royal Society of Medicine.

  17. Wood, T., Colloca, C., & Matthews, R. O. (n.d.). A pilot randomized clinical trial on the relative effect of instrumental (MFMA) versus manual (HVLA) manipulation in the treatment of cervical spine dysfunction.

Alan Alda PBS 2001 broadcast, The criticism took place during a segment (“Adjusting the joints”) of Scientific American Frontiers

Up to 40% of patients have experienced continued pain after surgery, which is often referred to as Failed Back Surgery Syndrome (FBSS)


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