INTRODUCTION. The L5 transverse processes articulating with the sacrum and/or pelvis, described as Bertolotti's syndrome, can be related to low back pain and sacroiliac joint dysfunction. We report the surgical intervention in two consecutive cases where Bertolotti's syndrome became symptomatic after lumbar interbody fusion due to stress transfer to adjacent segments.METHODS. Patients who developed persistent sacroiliac joint dysfunction post-fusion failed initial non-operative therapy consisting of aggressive exercise program, NSAID's and a lidocaine/steroid injection placed under fluoroscopic guidance into the symptomatic pseudoarticulation. Injections were diagnostic as they temporarily relieved the symptoms of sacroiliac pain. After recurrence of the symptoms, patients underwent surgical excision of the L5-S1 pseudoarticulation. The L5 transverse process and sacral ala were exposed via lateral muscle splitting approach. The enlarged L5 transverse process was subsequently osteomized with a high-speed burr or small osteotome. Kerrison rongeurs and curettes were used to complete the resection of the transverse process-sacral pseudoarticulation. Bone wax was rubbed into the exposed cancellous bone.RESULTS. Osteotomy of the L5 transverse process articulating with the sacrum diminished forces transferred to the ipsilateral sacroiliac joint. Thus, the sacroiliac joint became and remained mobile, functional and pain-free.DISCUSSION. Patients with sacroiliac joint dysfunction rarely fail to respond to non-operative intervention. In the described cases, the surgery was only performed after all non-operative options had been exhausted. The pseudoarticulation excision procedure as described provides a simpler, less biomechanically damaging answer to otherwise intractable severe sacroiliac pain