What's The "Crack" Sound?

real-time_visualization_of_joint_cavitation.pdf
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Highlights

•  Looking at the Modern History of Understanding the “Crack”
  • 1947: The prevailing evidence was a decrease in joint pressure, forming a gaseous bubble.  This was an observation from pre and post x-rays of a distracted finger:
    • “…distraction forces decrease pressure within the synovial fluid to the point were dissolved gas comes out of solution.” {2}
  • 1971: Using similar methods to the above observation, a new conclusion arose.  It was shown to be the collapse of the bubble, not the formation:
    • “…but rather cracking was caused by the subsequent collapse of the bubble… [or] through ligamentous recoil” {3,4}
  • 2015: Using a motion MRI (cine MRI), new observations could be made to chart changes 310 milliseconds and 2mm apart leading to “Viscous Adhesion” (aka Tribonucleation):
    • “…a process that occurs when 2 closely opposed surfaces are separated by a thin film of viscous liquid.  When these surfaces are distracted, viscous adhesion or tension between the surfaces resist their separation.  Then, as distraction forces overcome the adhesive forces, the surfaces separate rapidly creating a negative pressure.  This negative pressure, combined with the speed with which the surfaces separate, can create a vapor cavity within fluid”. {1}
• Purpose of Experiment

To provide “direct evidence to resolve the differing perspectives regarding the mechanism of joint cracking… using real-time cine magnetic resonance imaging (cine MRI)… [to show] the mechanism of joint cracking is related to cavity formation rather than bubble collapse.” {1}

• Events consistent with Tribonucleation observed {1}

Definition of tribonucleation: Opposing surfaces resist separation until a critical point where they separate rapidly resulting in vapor cavities

1. Minimal joint surface separation in the resting phase prior to joint cracking followed by rapid joint separation during the crack itself.
   1. Joint space (1) prior to and (2) after crack:

                     1- 0.93 mm +/- 0.73 mm STD
                     2- 1.89 mm +/- 0.59 mm STD
     2.   Joint duration was less than the duration of single frame (<310 milliseconds)
     3.   Rapid cavity inception associated with crack and joint separation
     4.   Fluid brings in gas in solution for formation of air region
     5.   Results show joint cracking is the result of cavity inception within synovial fluid
     6.   Resultant cavity (air region) never collapsed past the point of sound production

Safety of tribonucleation in physiologic conditions:

1. Distraction force must be applied to overcome tension within the synovial fluid (not within the soft tissues) before cracking can occur
2. The inherent tension forces that kept the joint surfaces together add stability to the joint itself

• Discussion from Authors

1. Is it good/bad?
   1. Signs of cartilage health

                      i. “Cine MRI revealed a new phenomenon preceding joint cracking: a transient bright signal in the intra-articular space… We speculate this phenomenon may be related to changes in fluid organization between cartilaginous joint surfaces and specifically may result from evacuation of fluid out of the joint cartilage with increasing tension.  If so, this sign may be indicative of cartilage health and therefore provide a non-invasive means of characterizing joint status.” {1}

1. Signs of joint degeneration

                     i.Chronic knuckle cracking has not been shown to exceed the threshold for damage {5,6}

• Conclusions from authors {1}
  • Data:
    • “…supports the view that tribonucleation [viscous adhesion] is the process which governs joint cracking
    • …provides a new theoretical framework to investigate health outcomes associated with joint cracking.  This framework will allow scientists to compare and contrast this process…[to] revel how joint cracking affects cartilaginous joint surfaces.
    • Ultimately, by defining the process underlying joint cracking, its therapeutic benefits, or passible harms, may be understood.”

Further Discussion from Dr. Hodges

• Comparison to Physics of the Chiropractic Adjustment
  • Definition of chiropractic adjustment
    • “The chiropractic application of a controlled directional force called a high-velocity low-amplitude (HLVA) designed to induce joint distraction and cavitation without exceeding the limits of anatomic joint motion” {7}
  • 2 Phases of Adjustment {8}
    1. Acceleration / Thrust: force employed by the doctor to reach the desired impact velocity
       • the product of the doctor’s mass and acceleration of the adjustive thrust (F = ma)
    2. Deceleration / Impact : the actual adjustive force produced by the doctor-patient interaction
       • the doctor’s mass multiplied by the deceleration (velocity initial – velocity final) / time
  • Many factors play a role in with determining forces during the adjustment: body types, conditions, age, preloading, set-up time, and clinical decision making {9}
  • Joint cavitation relationship to the adjustment {9}
    • Not the ultimate goal, although it does occur with a successful adjustment, but
    • Inexperienced practitioners, without proper instruction, will assume that when a “crack” is elicited, a successful adjustment has taken place.
      • Considerations with creating cavitation:
        • Using a short-lever arm vs a long lever arm
        • Too broad of doctor-contact
  • Improving results of the chiropractic adjustment {7,9}
    1. Specificity in Contacts and Angles (Short Lever Arms) – facilitates direct force through a combination of the center of mass of the vertebra and the plane lines of the 3D joint complex
    2. Pattern of Thrust – utilizing patient specific structure and biomechanics of joint being adjusted
    3. Holding – post-thrust hold the depth of thrust for a brief 1-2 seconds to affect the viscoelastic tissues

Conclusions from Dr. Hodges:
Old thought of the “cracking” noise experienced during distraction of a joint was based off xray static images with too long of time between images to accurately depict the events of the “crack”.  Then using cine MRI (motion xray of sorts), new evidence showed that it is the formation of gas bubbles from dissolved gas in a solution when distraction forces are applied (friction coefficient is exceeded).  I noticed the relationship between this phenomenon – Viscous Adhesion aka Tribonucleation, to what occurs during a chiropractic adjustment described by several authors in research and employed clinically in practice getting results.

1.  Viscous Adhesion / Tribonucleation is responsible for the audible “crack” that was demonstrated in distraction forces of a synovial joint
   • Joint is moving very small amounts ~1-2mm in cavitation
   • No harmful effects
   • Gives probable theory and application in cartilage health and management
2.  Using  Viscous Adhesion / Tribonucleation, a comparison can be established to what is experienced during the chiropractic HVLA described above on other synovial joints of the body
3. Using  Viscous Adhesion / Tribonucleation, a possible mechanism of what is seen clinically and shown in research as to how the chiropractic HVLA facilitates biomechanics and the impact on global health
4. Further research is needed to investigate joint structure change that creates a functional change to help global health in spinal dysfunction

References

1. Kawchuk GN, Fryer J, Jaremko JL, Zeng H, Rowe L, Thompson R (2015) Real-Time Visualization of Joint Cavitation. PLoS ONE 10(4): e0119470. Doi: 10.1371/journal.pone.0119470
2. Roston JB, Haines RW. Cracking in the Metacarpo-phalangeal Joint J Anat. 1947; 81: 165-73. PMID: 17105029
3. Unsworth A, Dowson D, Wright V. ‘Cracking Joints’ A Bioengineering Study of Cavitation in the Metacarpophalageal Joint. Ann Rheum Dis. 1971; 30: 348-358. PMID: 5557778
4. Brodeur R. The Audible Release Associated with Joint Manipulation. JMPT. 1995; 18: 155-164. PMID: 7790795
5. Wtason P, Kemohan WG, Mollan RA. A Study of the Cracking Sounds From the Metacarpophalngeal Joint. Proc Inst Mech Eng H. 1989; 203: 109-18. PMID: 2619836
6. Deweber K, Olszewski M, Ortolano R. Knuckle Cracking And Hand Osteoarthritis. J Am Board Fam Med. 2011; 24: 169-74. Doi: 10.3122/jabfm.2011.02.100156 PMID: 21383216
7. Gatterman MI. Foundations of Chiropractic: Subluxation Second Edition; 2005. Part One – Subluxation: The Articular Lesion Chapter 7, Chiropractic Technique pgs 144-146
8. Haas M. The Physics of Spinal Manipulation. Part I. The Myth of F = ma. J Manipulative Physiol Ther 1990; 13:204-206
9. Plaugher G. Textbook of Clinical Chiropractic: A Specific Biomechanical Approach. Philadelphia: Williams and Wilkins; 1993. Chapter 2, Clinical Anatomy And Biomechanics of the Spine p. 46-48