Forces required to cause cavitation during spinal manipulation of the thoracic spine

The purpose of this study was to measure the forces exerted during spinal manipulative therapy of the thoracic spine simultaneously with corresponding cavitation signals. Forces were measured using a thin, flexible pressure mat which was placed on patients over the contact area between doctor and patient. Cavitation signals were measured using a skin mounted accelerometer on the spinous process of a vertebral body adjacent to the manipulated vertebral body. Mean forces of spinal manipulative therapy at the instant of cavitation were 364 N with a standard deviation of 106 N. These values are considerably larger than corresponding values reported for cavitation at metacarpophalangeal joints. The precise factors causing cavitation of the spinal joints could not be determined. Study designs which may allow identification of these factors are suggested.