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Synovial Fold Release and Joint Cracking

Synovial fold, tag, meniscoid

Synovial Fold Release and Joint Cracking : a New Hypothesis for the Sound Generator has been created

In 2013, much work on simulating the synovial joint was conducted and led to in-vitro testing using ddd models to demonstrate the sound.
The mechanism of a cracking joint sound was produced with two factors in place.  The precursory details required to create the environment to produce the sound of an audible release were:

polished simulated cartilage surface and elastomeric simulated synovial fold. No fluid or gas was required.
  1. Negative pressure was required to induce the noise
  2. Negative pressure was required to re-produce the noise
  3. Different sound characteristics (differing tones) were observed when different material properties were used for the fold—both in size, shape and intrinsic qualities (ie., elongation, tensile strength and durometer).
Points to support this suction release phenomenon in a vitro testing environment.
  1. The noise generated from a suction cup release is not a gas rushing into the negative space but the elastic recoil of the cup material itself.
  2. This noise is generated both without fluid (in air) and in fluid (in water). This provides support that the sound is irrespective of the environment and more related to the elastic properties of the simulated fold.
Other points.
  1. Audible releases have different sound signatures. Not all events are identical.
  2. Audible releases of differing synovial joints make different sounds. For example, a 5th MCP joint makes a different sound when distracted when compared to the 1st MCP. This is believed to be due to the shape of the fold/hyaline interface.

Clinical translation? Once we begin to identify the process of the noise generator, this will help lead us to better understand the pressures in and around the cartilage to improve mechanobiological therapies.

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