Feature | Ultrasound Imaging | December 01, 2015

Ultrasound Reveals Knuckle-Cracking Fireworks

Results suggest cracking sound, bright flash observed on ultrasound are related to dynamic pressure changes associated with gas bubble in the joint

knuckle cracking, ultrasound study, RSNA 2015

The top image shows a knuckle joint on ultrasound prior to cracking, and below at the moment it cracks, showing a burst of light across the ultrasound image in the joint.

December 1, 2015 — Research presented at the 2015 annual meeting of the Radiological Society of North America (RSNA) tackles one of life's great mysteries: what causes a knuckle to "crack" out loud?

Watch video of a cracking knuckle

"It's extremely common for joints to crack, pop and snap," said Robert D. Boutin, M.D., professor of radiology at University of California, Davis (UC Davis) Health System. "We were interested in pursuing this study because there's a raging debate about whether the knuckle-cracking sound results from a bubble popping in the joint or from a bubble being created in the joint."

In the first study of its kind, researchers recorded simultaneous audio and visual evidence of knuckles cracking. Forty healthy adults, including 17 women and 23 men (age range 18-63), were examined at UC Davis with ultrasound imaging, as they attempted to crack the knuckle at the base of each finger, known in medical parlance as the metacarpophalangeal joint (MPJ). The participants included 30 individuals with a history of habitual knuckle cracking and 10 without.

While some participants stated that they had never intentionally cracked their knuckles, other participants did it frequently every day – up to 20 times per day for the past 40 years.

Orthopedists blinded to the participants' knuckle-cracking history evaluated the participants for grip strength, range of motion and laxity of each MPJ both before and after the ultrasound examination.

Using a small transducer, a sonographer recorded video images of 400 MPJs, as participants attempted to crack their knuckles. The sonographer also captured static images of each MPJ before and after participants tried their hands at cracking.

Two radiologists interpreted the ultrasound images, looking for sonographic evidence that would correlate with the audible cracks, which occurred in 62 of the 400 joints imaged.

"What we saw was a bright flash on ultrasound, like a firework exploding in the joint," Boutin said. "It was quite an unexpected finding."

Using the flashes on the ultrasound images, the radiologists were able to identify the joints with audible cracks with at least 94 percent specificity.

"There have been several theories over the years and a fair amount of controversy about what's happening in the joint when it cracks," Boutin said. "We're confident that the cracking sound and bright flash on ultrasound are related to the dynamic changes in pressure associated with a gas bubble in the joint." As for which comes first — the cracking sound or the flash of light — Boutin said that more research is needed.

The physical examinations revealed no immediate pain, swelling or disability in the knuckle-cracking group and no immediate difference in laxity or grip strength between the participants who cracked their knuckles and those who didn't.

"We found that there was no immediate disability in the knuckle crackers in our study, although further research will need to be done to assess any long-term hazard – or benefit – of knuckle cracking," Boutin said.

The ultrasound system used in the study was the GE Logic E9.

Co-authors on the study are Anuj Netto, M.D., M.P.H., David Nakamura, M.D., Cyrus Bateni, M.D., Michael S. Cronan, R.T., Robert Szabo, M.D., M.P.H., and Abhijit J. Chaudhari, Ph.D.

For more information: www.radiologyinfo.org

Related Content

Greater Left Ventricular Mass Increases Risk of Heart Failure
News | Cardiac Imaging | October 21, 2019
Elevated left ventricular mass, known as left-ventricular hypertrophy, is a stronger predictor of coronary artery...
GE Healthcare and Premier Inc. Developing One-stop Breast Clinic Model for U.S.
News | Mammography | October 21, 2019
GE Healthcare and Premier Inc. have announced a collaboration to develop a model to bring a same-day breast cancer...
Laurel Bridge Software Celebrates 20th Anniversary
News | Enterprise Imaging | October 21, 2019
Laurel Bridge Software recently celebrated its 20th anniversary of helping healthcare providers and original equipment...
Densitas Breast Density Assessment Software Joins Nuance AI Marketplace
News | Breast Density | October 21, 2019
Densitas Inc. announced that its U.S. Food and Drug Administration (FDA)-cleared densitas densityai breast density...
FDA Clears AiCE Image Reconstruction on Canon's Aquilion Precision CT

Image courtesy of Canon Medical Systems

Technology | Computed Tomography (CT) | October 21, 2019
Canon Medical Systems USA Inc. has received U.S. Food and Drug Administration (FDA) 510(k) clearance on its Advanced...
The Revolution Apex intelligent computed tomography (CT) scanner

The Revolution Apex intelligent computed tomography (CT) scanner. Image courtesy of GE Healthcare.

News | RSNA | October 18, 2019
At the 2019 annual meeting of the Radiological Society of North America (RSNA 2019), Dec. 1-6 in Chicago, GE Healthcare...
Selecting an AI Marketplace for Radiology: Key Considerations for Healthcare Providers
Feature | Artificial Intelligence | October 18, 2019 | Sanjay Parekh, Ph.D.
October 18, 2019 — As the nascent market for...
Surgical Institute of Reading Chooses RamSoft's PowerServer Lite PACS
News | PACS | October 18, 2019
Surgical Institute of Reading recently selected RamSoft’s PowerServer Lite PACS (picture archiving and communication...
MaxQ AI's Intracranial Hemorrhage Software to be Integrated on Philips CT Systems
News | Artificial Intelligence | October 18, 2019
Medical diagnostic artificial intelligence (AI) company MaxQ AI announced that its Accipio intracranial hemorrhage (ICH...
Siemens Healthineers Announces First U.S. Install of Multix Impact Digital Radiography System
News | Digital Radiography (DR) | October 18, 2019
DHR Health in Edinburg, Texas, recently became the first healthcare facility in the United States to install the Multix...