Patients getting a spinal adjustment have come to expect a popping sound. But a study by a group of physiotherapists reports that this popping is not necessary for a successful treatment

The popping or cracking sound that comes with a forced thrust at the joint may be caused by cavitation. Cavitation is an engineering term. It refers to the buildup and collapse of gas. Cracking the knuckles is an example of cavitation. However, scientists aren't sure that the same thing happens when the knuckles are cracked as when the spine pops during manipulation.

Military therapists studied a group of patients between the ages of 18 and 60 who had low back pain. Each therapist had advanced training in spinal manipulation. Range of motion was measured before treatment and again two days later. There was no difference in motion between the group with a pop and the group without. Pain and disability levels were also unchanged. A pop occurred in about 70 percent of cases. The researchers aren't sure where the popping sound came from.

It turns out there's no link between a pop that can be heard and better spinal motion. Neither pain nor motion is affected by an audible pop during spinal manipulation. The authors conclude that health professionals who do spinal manipulation don't have to depend on a popping sound when treating patients.

Timothy W. Flynn, PT, PhD., et al. The Audible Pop is Not Necessary for Successful Spinal High-Velocity Thrust Manipulation in Individuals with Low Back Pain. In Archives of Physical Medicine and Rehabilitation. July 2003. Vol. 84. No. 7. Pp. 1057-1060.