J Manipulative Physiol Ther. 1986 Sep; 9(3): 189-95.

Analysis of the joint crack by simultaneous recording of sound and tension.

In order to elucidate the significance of the noise often associated with a chiropractic adjustment, the joint crack has been analyzed using a simultaneous sound and tension recording system. It was found that, during the crack, which is a consistent double-peak wave, a drop in tension occurred immediately after the first sound wave, indicating separation of the articular surfaces (adjustment). The significance of the crack as an integral part of a chiropractic adjustment, where separation of the articular surfaces is desired, is then discussed.