Of seven cases of primary pyogenic infection of the sacro-iliac joint, three were due to staphylococci, one to streptococci, and the cause of three was not known. All seven patients made a complete recovery.
Due to the peculiar anatomy of the joint, a posterior approach will not drain an anterior abscess, and vice versa. In this small series of seven cases, the abscess formed anteriorly in six patients.
The author has found a new anterior approach valuable.