From the Research
Yes, when we crack our joints, it is indeed a release of gas from synovial fluid, specifically a cavitation process where dissolved gases, primarily carbon dioxide, form bubbles that rapidly collapse or burst, producing the characteristic cracking sound. This phenomenon occurs when you stretch or manipulate a joint, creating negative pressure within the joint capsule, as described in the study by 1. The gases released from the synovial fluid make up about 15% of the joint volume and consist of approximately 80% carbon dioxide.
Key Points
- The cavitation process is generated by an elastic recoil of the synovial capsule as it "snaps back" from the capsule/synovial fluid interface, as proposed by 1.
- Habitual joint cracking does not correlate with arthritic changes, but does correlate with loss of grip strength and soft-tissue swelling, as found in the study by 1.
- The temporary relief some people feel after cracking their joints may be due to the stretching of the joint capsule and temporary reduction in joint tension.
- A mathematical model of the events leading to the generation of the sound, developed by 2, resolves the dynamics of a collapsing cavitation bubble in the synovial fluid inside a metacarpophalangeal joint during an articular release, lending support for cavitation bubble collapse as the source of the cracking sound.
Clinical Implications
- Regular joint cracking does not cause arthritis, though excessive or forceful manipulation could potentially strain ligaments or tendons over time.
- The study by 2 provides a mathematical model that supports the available experimental data and sheds light onto the source of the cracking sound, which can inform clinical practice and patient education.
- The findings of these studies can help clinicians provide evidence-based advice to patients who habitually crack their joints, emphasizing the importance of gentle and controlled joint manipulation to avoid potential harm.