‘what causes ​“cracking” noises when being adjusted?

High-Velocity Thrust (HVT) in Manual Therapy: Benefits, Mechanisms, and Contraindications

A question that I am regularly asked is: 'what causes “cracking” noises when being adjusted?'. So, what is this “cracking” and why is it effective? 

High-Velocity Thrust (HVT) is a widely used technique in manual therapy designed to improve joint mobility and alleviate pain. It involves a quick, controlled thrust applied to a specific joint, often producing the characteristic "cracking" or "popping" sound. While this sound can be satisfying to hear, the primary benefit of HVT lies in its ability to restore joint function and reduce discomfort. However, HVT should be applied cautiously, as there are several contraindications to consider.

How HVT Works: Theories Behind the "Cracking" Sound

The cracking or popping sound that often accompanies HVT has been the subject of much scientific inquiry.

Tribunucleation (Viscous adhesion)

The current theory suggests that, joint distraction causes the pressure in the synovial fluid inside the synovial joints to decrease, as result a gas bubble is created and the pressure in the joint is decreased. This process is called Viscous Adhesion or Tribunucleation. Research using real-time MRI imaging has supported this theory, demonstrating bubble formation during joint manipulation.  

 In the past several theories attempt to explain the cause:

Cavitation Theory The most widely accepted explanation for the cracking sound is cavitation. When a joint is manipulated, the pressure inside the joint capsule drops, causing gases dissolved in the synovial fluid to form bubbles. When these bubbles rapidly collapse or “cavitate,” they produce the familiar sound. 

Tissue and Ligament Movement Another theory suggests that the cracking sound may result from the movement or repositioning of tendons, ligaments, or other soft tissues within the joint during HVT. As the joint is manipulated, these structures may snap back into place, creating an audible click or pop. Although less well-studied than cavitation, this theory is supported by observations of similar sounds occurring when tendons slip over bony structures .

Why HVT is Effective

The therapeutic benefits of HVT go beyond the audible sound, providing real physical improvements in joint function. HVT works by:

• Increasing Joint Mobility: HVT helps to restore motion in stiff or restricted joints, allowing for a greater range of movement. Studies have shown that spinal manipulation, including HVT, can improve joint flexibility and reduce biomechanical dysfunction .
• Reducing Muscle Tension: HVT may cause a reflexive relaxation of the surrounding muscles, reducing spasms and tension. This muscle relaxation contributes to pain relief and increased mobility .
• Alleviating Pain: By improving the alignment and function of the joints, HVT helps to alleviate pain. A study on spinal manipulative therapy demonstrated significant pain reduction in patients with chronic lower back pain after HVT treatments .
• Improving Nervous System Function: Some practitioners believe that spinal adjustments via HVT can reduce nerve compression, leading to improved nerve function and less pain. While this theory remains debated, certain studies suggest that HVT can positively influence the nervous system by reducing nerve impingement .

Contraindications of HVT

While HVT offers many benefits, it is not suitable for everyone. Certain conditions can increase the risk of complications, and in these cases, alternative therapies may be more appropriate. Contraindications include:

• Osteoporosis: Patients with weakened bones are at a heightened risk of fractures from forceful manipulations .
• Acute Inflammation: Conditions like rheumatoid arthritis or gout may worsen with HVT, especially during flare-ups .
• Spinal Instability: Patients with spinal instability, such as those with spondylolisthesis, are at a greater risk of injury if HVT is used .
• Recent Trauma: After recent fractures or ligament injuries, HVT may delay healing or cause further injury .
• Neurological Disorders: Conditions like spinal cord compression or cauda equina syndrome should not be treated with HVT due to the potential for worsening symptoms .
• Vascular Conditions: Individuals with vertebrobasilar insufficiency or aortic aneurysms are at risk during spinal manipulation, as sudden force could disrupt blood flow .

Conclusion

High-Velocity Thrust (HVT) is an effective and widely used manual therapy technique for improving joint function and alleviating pain. The characteristic cracking sound that accompanies the procedure is likely caused by bubble creation in the joint (Tribunucleation  or Viscous adhesion ) and as result the pressure in the joint is getting lower.

 Despite its benefits, HVT should be applied carefully, with a thorough assessment of the patient’s health to avoid risks, especially in cases where contraindications exist.

By understanding the mechanics of HVT and its contraindications, therapists can make informed decisions, ensuring safe and effective treatment tailored to each patient’s needs.

Some you tube videos  about HVT and the theory behind it 

https://www.youtube.com/watch?v=aJLU-4M-hdE

https://www.youtube.com/watch?v=BiDnCbxX-Ug

References

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