title: Real-time visualization of joint cavitation.
abstract: Cracking sounds emitted from human synovial joints have been attributed historically to the sudden collapse of a cavitation bubble formed as articular surfaces are separated. Unfortunately, bubble collapse as the source of joint cracking is inconsistent with many physical phenomena that define the joint cracking phenomenon. Here we present direct evidence from real-time magnetic resonance imaging that the mechanism of joint cracking is related to cavity formation rather than bubble collapse. In this study, ten metacarpophalangeal joints were studied by inserting the finger of interest into a flexible tube tightened around a length of cable used to provide long-axis traction. Before and after traction, static 3D T1-weighted magnetic resonance images were acquired. During traction, rapid cine magnetic resonance images were obtained from the joint midline at a rate of 3.2 frames per second until the cracking event occurred. As traction forces increased, real-time cine magnetic resonance imaging demonstrated rapid cavity inception at the time of joint separation and sound production after which the resulting cavity remained visible. Our results offer direct experimental evidence that joint cracking is associated with cavity inception rather than collapse of a pre-existing bubble. These observations are consistent with tribonucleation, a known process where opposing surfaces resist separation until a critical point where they then separate rapidly creating sustained gas cavities. Observed previously in vitro, this is the first in-vivo macroscopic demonstration of tribonucleation and as such, provides a new theoretical framework to investigate health outcomes associated with joint cracking.
authors: Department of Physical Therapy, Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, Alberta, Canada.
authors: Gregory N
authors: GN
authors: Kawchuk
authors: Private Practice, Nanaimo, British Columbia, Canada.
authors: Jerome
authors: J
authors: Fryer
authors: Department of Radiology and Diagnostic Imaging, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada.
authors: Jacob L
authors: JL
authors: Jaremko
authors: Department of Chemical and Materials Engineering, Faculty of Engineering, University of Alberta, Edmonton, Alberta, Canada.
authors: Hongbo
authors: H
authors: Zeng
authors: School of Medicine and Public Health, University of Newcastle, Callaghan, New South Wales, Australia.
authors: Lindsay
authors: L
authors: Rowe
authors: Department of Biomedical Engineering, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada.
authors: Richard
authors: R
authors: Thompson
mesh_terms: D001175:Arthrography; D006801:Humans; D007592:Joint Diseases / Q000000981:diagnostic imaging / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D008662:Metacarpophalangeal Joint / Q000000981:diagnostic imaging / Q000473:pathology*; D013582:Synovial Fluid / Q000000981:diagnostic imaging