External fixation of the pelvic girdle as a test for assessing instability of the sacro-iliac joint

External fixation of the pelvic girdle was used in a consecutive series of ten female patients suffering from suspected chronic instability of the sacro-iliac joint. The condition was attributed to pelvic relaxation after pregnancy in seven patients and to trauma in three. External fixation of the pelvis with a trapezoid frame reduced the average radiographic displacement of the symphysis from 5.0 to 2.4 mm in eight patients, relieved the dorsal pain in seven, and markedly improved walking ability in five. Seven of the ten patients were subsequently subjected to an anterior sacro-iliac joint arthrodesis in which square compression plates and autogenous bone grafts were used. At follow-up examination five of these patients were improved, and two unchanged. The results suggest that external fixation of the pelvis is useful in assessing painful sacro-iliac joint instability and should precede surgical intervention.