The mobility of the sacroiliac joint in healthy subjects.

A three-dimensional stereophotogrammetric method is described for measuring the mobility of the sacroiliac joint, which was based on preliminary two-dimensional in vitro experiments. The investigations were carried out with intraosseous markers in 24 healthy volunteer male (15) and female (9) subjects having an age range of 20 to 50 years. Considerable intra- and inter-individual variability was found for both the measurements of rotation and translation. The position and direction of the movement axes showed wide variations, but a basic pattern could always be recognized. The average values for rotation and translation were low, being 1.8 degrees / 0.7 mm for the males and 1.9 degrees / 0.9 mm for the females. No statistically significant differences could be demonstrated with respect to either sex or age. On the basis of the measurement results, it is postulated that there is pathological sacroiliac joint movement when rotation is more than 6 degrees and translation more than 2 mm. This increased mobility seems to be of greater clinical significance than reduced mobility.