Fingerknacken Why our fingers crack

Researchers discover causes of cracking fingers

04/16/2015

For a long time people have been arguing about the causes of finger-biting in the professional world. Now, an international research team led by lead author Professor Greg Kawchuk of the Department of Rehabilitation Medicine at the University of Alberta, Canada has discovered that cracking is actually triggered. They have the results of their study in the journal „PLoS One“ released.

After decades of debate about what happens when the joints crack, Professor Kawchuk's scientists, using MRI scans, were able to observe for the first time how a tensile force in the joint quickly forms a cavity that causes the fingers to snap. The joint surfaces surrounding the joint capsule (ends of the bones) are separated by a gap which is filled with viscous synovial fluid. When pulled on the finger, this gap widens significantly and suddenly there is a cavity in the synovial fluid, which is connected to the clicking sound.

Contradictory theories about finger-clicking
For the first time in 1947 British researchers had identified the formation of gas bubbles within the joint as the cause of the finger-cracking, but later studies came to a different conclusion, according to the University of Alberta. In the 1970s, scientists at the University of Leeds suspected collapsing gas bubbles as the cause of the cracking, but here also lacked the clear evidence. All that was agreed was that gas bubbles form in the joint when tensile forces act. What causes the crackling noise has remained controversial ever since. Now, the international research team led by Professor Kawchuk has provided information through modern imaging techniques.

Fingerknacken observed on MRI
For their investigations, the researchers first needed someone who could crack their ten fingers at will. Fortunately, a colleague who had this ability was found in their ranks and they pushed this, lying on his stomach and with his finger first in the MRI tube. At the tip of his finger, they attached a pulling device, which allowed a clear view of the joint during the following shots. Afterwards, they pulled on the researcher's finger until the crackling sound was heard. The MRT recorded the events in 3.2 frames per second, so that a film was created, on which the process could be followed exactly. At low tensile forces, according to the researchers initially no changes in the joint could be found, but was pulled sufficiently strong on the finger, widened the joint space and it was very sudden a gas-filled cavity in the synovial fluid (synovial fluid).

Formation of a vacuum in the joint
„It's a bit like a vacuum is forming“, explains Professor Kawchuk in the press release from the University of Alberta. As the interfaces separate at once, there is insufficient fluid available to fill the increasing volume, creating a void. This event was based on the MRI scans unequivocally attributable to the emergence of the crack, while the regression of the bladder after releasing the finger was noiseless. Thus, the researchers have confirmed the original thesis of the British scientists in 1947 and clearly disproved subsequent, different study results.

Identify threatening joint damage early?
However, Professor Kawchuk and colleagues also hope to contribute to exploring potential damage from finger-clicking. Because scientists have calculated that the amount of force when the joints crack, sufficient to cause damage to hard surfaces. However, there are also conflicting results in the room, which is why Kawchuk and his team want to investigate this in a next step. Cracking may also affect other joints in the body, including the spine, or may serve as an explanation for arthritis and joint injuries. In this context, also be the first recorded occurrence „a white flash just before the formation of the cavity“ Of particular interest, the scientists report. Professor Kawchuk emphasizes that he would like to use even more advanced MRI technology to understand what happens in the joint space after cracking and what that means for health. Maybe you can „we use the new discovery to see problems as they start - long before symptoms occur or patients go to the doctor“; so Kawchuk. Joint problems could possibly be treated before they begin, concludes the study director. (Fp)