If we’ve said it once, we’ve said it a million times: chiropractors don’t ‘crack’ backs and necks. We carefully adjust, often in gentle ways (depending on the needs and nervous system of the person under care). But beyond the experience of getting adjusted, what can we actually say about the force measures used to deliver these adjustments to the spine in order to correct these subluxations? It’s a question recently put under the proverbial microscope in order to clear this up.
Now before we start, an important thing to note: the force used to deliver an adjustment is measured in Newtons – that is the level of force applied to a mass. But what on earth does that mean in practical terms? One Newton is the force it takes to move one kilogram one metre per second. It’s also the force exerted by 100 grams at rest on, say, a flat surface – so think a large kiwi fruit or an apple mouse. If you hold one of these items in your hand, you are feeling the force of one Newton. Being that chiropractors are not trying to move patients by a metre, but rather adjust patients who are lying on a table (for example), think of the kiwi fruit as you read the article!
So let’s talk about the study!
A recent study published in the Journal of Clinical Chiropractic focuses on the thrust force measurement of chiropractic supine (lying on the back, face upward) cervical adjustments (SCA). Studying the force levels applied during cervical manipulation is relevant to claims that cervical manipulation may cause injury. We’ve stared down these accusations before, and chiropractic has been shown to be remarkably safe, but adding this study into the mix only strengthens those claims [1,2].
One of the things chiropractors do in day-to-day practice is ensure that the force applied during adjustments is appropriate for each patient’s needs. Too much force can cause discomfort or injury, while too little force may not address the underlying issue effectively. Routinely, force measures are decreased to consider the age, fragility or tensile strength of the person under care (for example, in infancy or in a person’s older years). Many chiropractors operate off the concept of eliciting the most change with the least force. Still, the results of this study will contribute to an increased understanding of forces experienced by patients in clinical settings.
The research focused specifically on measuring the thrust force applied during cervical adjustments performed while the patient is lying on their back (supine position). This position allows chiropractors to access the cervical spine more comfortably and is commonly used in clinical practice.
Doctors of Chiropractic (DCs) from Parker University volunteered to either administer or receive supine cervical adjustments (SCAs). DCs performing adjustments were instructed to wear a specialised finger-mounted splint designed by the researchers. This splint had a flat surface to house a pressure sensor, ensuring accurate force measurements during the adjustments. It prevented any bending or distortion of the sensor, thus maintaining precise readings. The design ensured that only the splint’s surface touched the patient during the adjustment, minimising the risk of applying force beyond the intended area. The splint consisted of a 3D-printed plastic frame shaped to fit the index finger and secured with a velcro strap. A Tekscan Flexiforce pressure sensor was attached to the frame and connected to a small amplifier positioned on the forearm.
Data collection was facilitated using Noraxon MR3 software and subsequently exported to Microsoft Excel to convert millivolts to Newtons of force using calibration factors and to capture the peak force of each thrust. Results showed a total of 13 successful force recordings were obtained, revealing an average peak force of 79.5 Newtons (standard deviation: 27.0), with values ranging from a maximum of 125.4 N to a minimum of 46.8 N.
The peak force levels observed in this examination of supine cervical adjustments, averaging 79.5 N, fall within the lower range compared to findings from other research. The finger splint proved highly effective, with none of the participants experiencing any discomfort, and the doctors reported that the splint did not impede their ability to maintain contact or administer the thrust.
The confidence in the validity of force determinations may not be absolute (and certainly, it would be difficult to get exact measures that represent every chiropractor). This particular type of pressure sensor, despite its widespread use, needs a warm-up procedure before data recording, and it is not certain that the procedure was duplicated consistently in each session. In a world where individuals are accustomed to the sophistication of modern phone apps, it’s important to understand that measuring force levels during adjustments is not straightforward. Calibration before each session helped ensure accurate conversion of sensor readings to force, even when conditions varied from day to day and among practitioners.
There had previously been a limited amount of investigation of the peak forces applied to patients’ necks during supine cervical adjustments. In addition to advancing our understanding of chiropractic care, this research represents an important contribution to the scientific literature on chiropractic care. By quantifying the force dynamics of chiropractic adjustments, the study helps to standardise and refine these techniques, ultimately proving and improving the safety record of our wonderful profession
References:
- Church, E. W., Sieg, E. P., Zalatimo, O., Hussain, N. S., Glantz, M., & Harbaugh, R. E. (2016). Systematic Review and Meta-analysis of Chiropractic Care and Cervical Artery Dissection: No Evidence for Causation. Cureus, 8(2), e498. https://doi.org/10.7759/cureus.498
- Todd A, Carroll M, Robinson A, Mitchell E, (2015), “Adverse Events Due to Chiropractic and Other Manual Therapies for Infants and Children: A Review of the Literature,” Journal Manipulative and Physiological Therapeutics, Volume 38, Issue 9, November-December 2015, pp. 699-712, http://www.sciencedirect.com/science/article/pii/S016147541400178X
- Russell, B., Owens, E., Hosek, R., & Keller, M., (2024). Thrust force measurement of chiropractic supine cervical adjustments. Journal of Contemporary Chiropractic. Vol 7. Is 1. 2024 https://journal.parker.edu/article/112921-thrust-force-measurement-of-chiropractic-supine-cervical-adjustments
