The end results is tip of the iceberg…
The Anatomy of an Adjustment: Why Chiropractic Technique Is Never One-Size-Fits-All
To a patient, an adjustment can look deceptively simple: a quick, well-placed movement, sometimes a "crack," and relief. Underneath that simplicity sits a layered clinical decision — which region needs to move, which technique will move it safely, how much force a particular body can absorb, and what the exact line of drive should be. None of it depends on making noise. It depends on intent.
What a Spinal Adjustment Actually Is
A chiropractic adjustment, more formally termed spinal manipulative therapy (SMT), is usually delivered as a high-velocity, low-amplitude (HVLA) thrust — a fast, small-magnitude force applied to a specific joint to take it briefly beyond its usual passive range. The prevailing scientific model treats this mechanical input as the first step in a chain reaction, not the end point. A brief mechanical force to the tissue triggers peripheral, spinal, and supraspinal neurophysiological responses — changes in muscle spindle and paraspinal reflex activity, altered pain processing at the dorsal horn, and central pain-modulation effects — which is what is now thought to produce the clinical benefit, rather than any single structural "correction" alone. This comprehensive mechanism-based model, first proposed by Bialosky and colleagues and refined in subsequent neurophysiological reviews, is central to understanding why the same-looking thrust can be applied so differently between practitioners and still be clinically appropriate.
The Purpose of Adjusting Different Regions
The spine is not a uniform structure, and neither is the reasoning behind adjusting each part of it.
| Region | Typical purpose of adjustment | Biomechanical note |
|---|---|---|
| Cervical spine | Restoring segmental motion for neck pain, cervicogenic headache, and referred upper-limb symptoms | Systematic review evidence shows cervical HVLA thrusts reliably increase cervical range of motion; the vertebral arteries' course through the transverse foramina also makes this the region requiring the most careful vascular screening |
| Thoracic spine | Improving rib cage and mid-back mobility, often used to indirectly benefit neck and shoulder mechanics | Interestingly, thoracic HVLA thrusts have also been shown to increase cervical range of motion, and generally require a different force profile than cervical work due to the added stability of the rib cage and larger surrounding musculature |
| Lumbar spine | Addressing segmental stiffness, facet-related low back pain, and disc-related presentations (with appropriate technique modification) | Larger paraspinal muscle mass and more mechanically robust segments typically require greater peak force and a more deliberate preload than cervical adjusting |
| Sacroiliac joint / pelvis | Addressing pelvic asymmetry and SIJ-related pain patterns | Often suited to drop-table or side-posture delivery, which uses table mechanics and body weight rather than raw practitioner force to achieve the same corrective vector |
Notably, research measuring joint gapping and range-of-motion changes after HVLA thrusts has found clearer, more consistent effects in the cervical and thoracic spine than in the lumbar spine, reinforcing that technique and expected response genuinely differ by region rather than being interchangeable.
Why So Many Different Techniques Exist
Chiropractic has never settled on one single delivery method, and that's by design rather than inconsistency. Each named technique represents a different way of solving the same underlying problem — restoring motion to a specific segment — using a different combination of contact point, force, and mechanical assistance.
- Diversified technique uses a specific, pre-determined line of drive for each manual thrust, aiming to correct a biomechanical restriction directly with the practitioner's hands.
- Gonstead technique places heavy emphasis on a structured pre-adjustment analysis (static and motion palpation, temperature instrumentation, imaging) to identify one precise segment, then applies a highly specific contact and line of drive to that level alone rather than a broader regional approach.
- Activator and other instrument-assisted methods deliver a controlled, low-force mechanical impulse, useful where a lower-force, highly repeatable input is clinically preferable.
- Thompson (drop-table) technique uses a table mechanism that yields fractionally as the thrust is delivered, reducing the raw force the practitioner needs to generate manually while still achieving joint motion — often favoured around the pelvis and lower lumbar spine.
None of these is universally "stronger" or "better" — the appropriate choice depends on the segment involved, the tissue and joint findings on assessment, and the patient in front of the practitioner.
What a Chiropractor Considers Before Adjusting Any Spine
Before technique is even discussed, every adjustment is filtered through a safety screen. The primary concern is always ruling out pathology that would make manipulation inappropriate or dangerous — spinal cord involvement, vertebral artery dissection risk, unstable fractures, tumour, infection, or cauda equina syndrome are all recognised contraindications that require referral rather than treatment. Vascular screening is particularly important in the cervical spine given the vertebral arteries' anatomical path, and case literature on vertebral artery dissection following cervical HVLA — while rare — is part of why thorough history-taking and red-flag screening precede manipulation of this region specifically.
Once serious pathology has been excluded, a second layer of clinical reasoning shapes how the adjustment is actually delivered:
- Body size and tissue depth: greater soft-tissue thickness over a joint changes how much force is required to reach and move that segment, and alters where the practitioner's contact point needs to sit.
- Line of drive: the exact vector of the thrust relative to the joint's plane of motion, which determines whether the force actually moves the intended segment or is dissipated into surrounding tissue. Controlled research on thoracic HVLA delivery has shown that even small changes in practitioner starting position and body mechanics measurably change the peak force and rate of force delivered — underscoring how much the "how" of a thrust matters, independent of the target itself.
- Purpose of the adjustment: whether the goal is restoring a hypomobile segment, reducing muscle guarding, or supporting a broader rehabilitation plan changes the force and technique chosen.
- Intent: the practitioner's clinical reasoning for that specific contact, at that specific segment, in that specific direction — which is what actually differentiates a therapeutic adjustment from a generic, forceful movement.
The Sound Myth: Why the "Pop" Isn't the Point
The audible release many people associate with an effective adjustment is a cavitation (or, per more recent biomechanical modelling, a tribonucleation event) — a rapid gas-related change within the joint's synovial fluid as the joint surfaces separate. It is a genuine physical phenomenon, but the research is remarkably consistent on one point: it is not what makes an adjustment work.
A landmark study found that an audible pop was not necessary for a successful high-velocity thrust manipulation in people with low back pain, with outcomes not differing based on whether a sound occurred. A subsequent systematic review pooling multiple prospective studies and a randomised trial concluded that regardless of which region of the spine was manipulated or how long follow-up lasted, there was no evidence that an audible pop improved pain outcomes. Neurophysiological research has extended this further: studies measuring brain activity and pain sensitivity after manipulation have found no meaningful difference in central nervous system response between thrusts that produced a pop and those that didn't, and hypoalgesic (pain-reducing) effects have been observed even in the absence of any sound at all.
The clinical implication: a correctly delivered adjustment — right region, right technique, right line of drive, right intent — can be completely silent and still achieve its purpose. Conversely, a loud cavitation produced without appropriate assessment, specificity, or reasoning behind it is, at best, a coincidental noise rather than a therapeutic outcome. What appears to matter clinically is precise, well-reasoned mechanical input to the right tissue — not decibels.
Bringing It Together
A well-delivered adjustment is the product of several layers of reasoning happening almost simultaneously: identifying which region actually needs to move and why, choosing a technique that suits that region and that patient's body, screening thoroughly for anything that would make manipulation unsafe, and executing a precise line of drive with clear clinical intent. The sound a joint may or may not make during that process is a side effect of physics — not a measure of whether the work was done well.
Frequently Asked Questions
Does a louder crack mean a better adjustment?
No. Multiple studies, including a systematic review across several regions of the spine, have found no relationship between the presence or loudness of an audible pop and improvement in pain or function.
Why do chiropractors use different techniques for different patients?
Because the force, contact point, and line of drive needed to move a segment safely and effectively change with the region being treated, the patient's body size and tissue depth, and the specific clinical goal of the adjustment.
What do chiropractors check for before adjusting the neck?
A thorough history and screening for red flags such as vertebral artery dissection risk, instability, fracture, or neurological signs, since the vertebral arteries pass directly through the cervical spine and require this region to be assessed particularly carefully.
Can an adjustment work without making a sound?
Yes. Research shows an audible pop is not necessary for a spinal manipulation to be clinically successful, and pain-reducing effects have been recorded after manipulations that produced no sound at all.
My chiropractor didn't crack my back. Is that normal?
Yes. A popping sound isn't needed for an adjustment to help. Mobilisation and low-force techniques often make no sound at all.
Can a chiropractor adjust without cracking?
Yes. Low-force options include drop table, Activator instrument and mobilisation techniques, which suit people who prefer not to have a thrust or a sound.
What should I avoid after a chiropractic adjustment?
There are no strict rules. Stay active, keep doing your exercises, and if you feel sore, hold off on unusually heavy or new strenuous activity for the rest of the day. Tell us about any side effects.
Curious what technique and approach would suit your spine? Our team at Spirit Chiropractic in Kogarah tailors every adjustment to your assessment, not a one-size-fits-all routine.
Call 0410 420 856- Bialosky JE, Bishop MD, Price DD, Robinson ME, George SZ. The mechanisms of manual therapy in the treatment of musculoskeletal pain: a comprehensive model. Manual Therapy. 2009;14(5):531-538.
- Bialosky JE, Beneciuk JM, Bishop MD, et al. Unraveling the mechanisms of manual therapy: modeling an approach. Journal of Orthopaedic & Sports Physical Therapy. 2018;48(1):8-18.
- Pickar JG. Neurophysiological effects of spinal manipulation. Spine Journal. 2002;2(5):357-371.
- Herzog W. The biomechanics of spinal manipulation. Critical Reviews in Physical and Rehabilitation Medicine. 2001;13(2-3).
- Gorrell LM, Conway PJ, Herzog W. Differences in force-time parameters and electromyographic characteristics of two high-velocity, low-amplitude spinal manipulations following one another in quick succession. Chiropractic & Manual Therapies. 2020;28:63.
- Efficacy of different biomechanical strategies for modulating force–time parameters of high-velocity low-amplitude manipulation of the thoracic spine: a randomized crossover experimental study. Chiropractic & Manual Therapies.
- Systematic review on biomechanical effects of high-velocity, low amplitude spinal manipulation. (Effects on cervical, thoracic and lumbar range of motion and facet joint gapping.)
- Flynn TW, Fritz JM, Wainner RS, Whitman JM. The audible pop is not necessary for successful spinal high-velocity thrust manipulation in individuals with low back pain. Archives of Physical Medicine and Rehabilitation. 2003;84(7):1057-1060.
- Impact of audible pops associated with spinal manipulation on perceived pain: a systematic review. Chiropractic & Manual Therapies. 2022;30:45.
- Bialosky JE, Bishop MD, Robinson ME, George SZ. The relationship of the audible pop to hypoalgesia associated with high-velocity, low-amplitude thrust manipulation: a secondary analysis of an experimental study in pain-free participants.
- The effect of a spinal thrust manipulation's audible pop on brain wave activity: a quasi-experimental repeated measure design.
- Case reports and reviews on vertebral artery dissection following cervical spinal manipulation, including red-flag screening frameworks for vertebral/carotid artery dissection in patients with neck pain or headache.
