Ectopic bone formation in the pelvis after combined anterior and posterior fusion of the spine with osteogenic protein-1 use: a case report.

Case report. We report the first described case of ectopic bone formation with osteogenic protein-1 (OP-1) use occurring in the pelvis after combined anterior and posterior spinal fusion. OP-1 is a member of the transforming growth factor-β superfamily of extracellular proteins involved in bone growth and formation. Potential side effects of OP-1 are not yet fully understood, and clinical data have failed to show significant adverse effects of OP-1. The patient had flat-back syndrome with symptomatic junctional degenerative disease below the level of fusion and underwent staged anterior and posterior reconstruction. OP-1 was used in conjunction with local bone graft and crushed cancellous allograft in both anterior and posterior procedures. Bone grew adjacent to the left superior pubic rami, extending through the left rectus sheath and into the left psoas muscle. Subsequently, complete excision of the ectopic bone was performed. No local recurrence was noted at postoperative visits up to 5 months after excision. At that time, the patient had returned to work and was pleased with the level of function. Caution is justified with the use of OP-1. Clinical studies must be conducted to ensure appropriate dosing to prevent ectopic bone formation and deleterious effects.