A level-1 pilot study to evaluate of ultraporous β-tricalcium phosphate as a graft extender in the posterior correction of adolescent idiopathic scoliosis

The objective of this study is to compare the clinical and radiographic results of ultraporous β-tricalcium phosphate (β-TCP) versus autogenous iliac crest bone graft (ICBG), through prospective randomized pilot study (EBM-Level 1), as graft extenders in scoliosis surgery. In the posterior correction of scoliosis, local bone resected as part of the procedure is used as the base bone graft material. Supplemental grafting from the iliac crest is considered the gold-standard in posterior spinal fusion. However, autograft is not available in unlimited quantities, and bone harvesting is a source of significant morbidity. Ultraporous β-TCP might be a substitute for ICBG in these patients and thus eliminate donor site morbidity. A total of 40 patients with adolescent idiopathic scoliosis (AIS) were randomized into two treatment groups and underwent corrective posterior instrumentation. In 20 patients, ICBG harvesting was performed whereas the other half received β-TCP (VITOSS^®) to augment the local bone graft. If thoracoplasty was performed, the resected rib bone was added in both groups. Patients were observed clinically and radiographically for a minimum of 20 months postoperatively, with a mean follow-up of 4 years. Overall pain and pain specific to the back and donor site were assessed using a visual analog scale (VAS). As a result, both groups were comparable with respect to the age at the time of surgery, gender ratio, preoperative deformity, and hence length of instrumentation. There was no significant difference in blood loss and operative time. In nine patients of the β-TCP group and eight patients of the ICBG group, thoracoplasty was performed resulting in a rib graft of on average 7.9 g in both groups. Average curve correction was 61.7% in the β-TCP group and 61.2% in the ICBG group at hospital discharge (P = 0.313) and 57.2 and 54.3%, respectively, at follow-up (P = 0.109). Loss of curve correction amounted on average 2.6° in the β-TCP group and 4.2° in the comparison group (P = 0.033). In the ICBG group, four patients still reported donor site pain of on average 2/10 on the VAS at last follow-up. One patient in the β-TCP group was diagnosed with a pseudarthrosis at the caudal end of the instrumentation. Revision surgery demonstrated solid bone formation directly above the pseudarthrosis with no histological evidence of β-TCP in the biopsy taken. In conclusion, the use of β-TCP instead of ICBG as extenders of local bone graft yielded equivalent results in the posterior correction of AIS. The promising early results of this pilot study support that β-TCP appears to be an effective bone substitute in scoliosis surgery avoiding harvesting of pelvic bone and the associated morbidity.