Improved intervertebral bone union in ALIF rat model with porous hydroxyapatite/collagen combined with platelet-rich plasma

Platelet-rich plasma (PRP) can accelerate bone union in spinal fusion surgery with an autogenous bone graft. However, it is unclear whether bone union can be obtained by using artificial bone and PRP together in spinal interbody fusion surgery.This study aimed to determine whether interbody fusion can be achieved by transplanting porous hydroxyapatite/collagen(HAp/Col) which is an artificial bone material frequently used in spinal fusion surgery, together with PRP in the intervertebral disc space in rats.A controlled laboratory study.A total of fourty 10-week old Sprague-Dawley rats were used in this study and assigned to three groups as follow: disc curettage only (control group, n=10), disc curettage + HAp/Col transplant (H group, n=10), and disc curettage + HAp/Col + PRP transplant (H+P group, n=10). The other 10 rats were sacrificed as blood donors for acquisition of PRP. Microcomputed tomography (μCT) examinations were performed to evaluate bone union, bone volume (BV), and bone mineral density (BMD) at 4, 8, and 12 weeks following surgery. Twelve weeks postoperatively, each group of three of L4-L5 spines was harvested to perform histological examination (hematoxylin & eosin stain) and the others were subjected to biomechanical testing (compression properties).The platelet count in PRP was approximately 4.1 times greater than that in whole blood (260.6±26.2 × 104 mg/dL and 64.3±2.9 × 104 mg/dL in PRP and whole blood, respectively). All the L4-L5 lumbar discs were fused in the H+P group, whereas only one case was fused in the H group and none in the control group at 12 weeks after surgery. BV was significantly higher in the H+P group than in the H group or control groups (both p<.01), although BMD was not significantly different among the three groups. Upon histological analysis, mature bone formation was observed at the transplanted space in all cases in the H+P group, whereas fibrous tissue was observed at the location in the H and control groups. Regarding biomechanical properties, the ultimate load to failure was significantly higher in the H+P group than in the H group or control group (p=.021 and .013, respectively), although stiffness was not significantly different between the three groups.The combination of porous HAp/Col and PRP at an appropriate concentration can promote bone union in the intervertebral disc space without using an autologous bone graft in the rat model. Bone tissue formation was histologically confirmed, and it was mechanically strong.This preclinical study showed that porous HAp/Col, when combined with PRP at an appropriate concentration, can induce bone union without autologous bone grafts. The results may eliminate the need for autologous bone collection for spinal fusion surgery in the future.