Can an external frame fixation reduce the movements in the sacroiliac joint? A radiostereometric analysis of 10 patients.

To evaluate whether a Hoffmann-Slätis frame can reduce movements in the sacroiliac joints, 10 patients (7 women) with severe posterior pelvic pain of long duration were externally stabilized. The movements were analyzed with radiostereometric analysis (RSA) in supine and standing positions, preoperatively and postoperatively with the frame applied. In 2 patients, there was no reduction in the movements with the frame, perhaps because it was not properly tightened. In the remaining 8 patients, the median reduction in rotation was 55% on the left side and 63% on the right side around the helical axes, and 74% around the x-axes on the left side and 66% on the right side. Our data suggest that external fixation using the Hoffmann-Slätis frame, substantially reduces sacroiliac joint mobility in some patients, which must be considered when using the frame as a diagnostic tool. Pre-stressing the frame by tightening the vertical bars before the compression bar is applied is recommended to reduce the risk of this shortcoming.