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

Abstract

The objective of this study is to compare the clinical and radiographic results of ultraporous beta-tricalcium phosphate (beta-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 beta-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 beta-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 beta-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 beta-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 degrees in the beta-TCP group and 4.2 degrees 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 beta-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 beta-TCP in the biopsy taken. In conclusion, the use of beta-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 beta-TCP appears to be an effective bone substitute in scoliosis surgery avoiding harvesting of pelvic bone and the associated morbidity.

Fig. 1

Posteroanterior radiographs of a 16-year-old girl (at the time of surgery) out of the β-TCP group (without thoracoplasty) showing a King I scoliosis with a thoracic curve of 54° from T6 to T12 and a lumbar curve of 58° from T12 to L4 and the instrumentation from T6 to L4 at last follow-up, 52 months after surgery

Fig. 2

Postoperative and follow-up posteroanterior radiographs (3-, 7-, 11-, and 52-months) of the patient presented in Fig. 1 with focus on the lumbar curve demonstrating a progressive resorption of the β-TCP morsels and the formation and maturation of a continuous bony fusion mass visible at the curve’s concavity

Fig. 3

Postoperative radiographs of a 24-year-old girl (at the time of surgery) out of the TCP group with a pseudarthrosis at the caudal end of the instrumentation at T12: close-up view 1 week after surgery, 2 months postoperatively showing a slight lucency around the right pedicle screw (arrow), and 10 months after surgery with progression of the lucency confirmed by computed tomography

Fig. 4

Biopsy taken from the fusion mass at T10/11 in the patient with the pseudarthrosis at T11/12 presented in Fig. 3 showing solid bone formation without evidence of β-TCP

Fig. 5

Number of patients who experienced donor site pain after ICBG harvesting and average pain intensity evaluated by a visual analogue scale (0–10) during follow-up