Effect of Whitlockite as a new bone substitute for bone formation in spinal fusion and ectopic ossification animal model

Abstract

Background: Bone substrates like hydroxyapatite and tricalcium phosphate have been widely used for promoting spinal fusion and reducing the complications caused by autograft. Whitlockite has been reported to promote better bone formation in rat calvaria models compare with them, but no study investigated its effect on spinal fusion yet. Also, the higher osteoinductivity of whitlockite raised concern of ectopic ossification, which was a complication of spinal fusion surgery that should be avoided.

Methods: In this study, we compared the osteoinductivity of whitlockite, hydroxyapatite, and tricalcium phosphate porous particles with SD rat spine posterolateral fusion model and investigated whether whitlockite could induce ectopic ossification with SD rat abdominal pouch model.

Results: The micro-CT result from the posterolateral fusion model showed whitlockite had slightly but significantly higher percent bone volume than tricalcium phosphate, though none of the materials formed successful fusion with surrounding bone tissue. The histology results showed the bone formed on the cortical surface of the transverse process but did not form a bridge between the processes. The result from the abdominal pouch model showed whitlockite did not induce ectopic bone formation.

Conclusion: Whitlockite had a potential of being a better bone substrate hydroxyapatite and tricalcium phosphate in spinal fusion with low risk of inducing ectopic ossification.

Keywords: Bone; Calcium phosphate; Hydroxyapatite; Whitlockite.

Fig. 1

Experiment images of abdominal pouch model. a the abdominal skin was opened without interrupting muscle tissue. b six pouches in the muscle tissue was made without hurting peritoneum. c 15 mg bone substitute was implanted in the muscle pouch. d, the muscle was sutured, and the defect was closed layer by layer

Fig. 2

Experiment images of PLF model. a L4-L5 level was exposed and the transverse processes were decorticated. b 50 mg of bone substitutes was implanted in the decorticated site and the soft tissue was closed layer by layer

Fig. 3

Micro-CT images of rat PLF model. No bone was formed in sham group. All three groups with implant showed bone formed on the surface of decorticated surface and encompassed some implant particles. No significant difference could be observed between the groups. No group formed bridge between the transverse processes

Fig. 4

Image of undecalcified H&E staining histology section. All three groups showed bone formation on the decorticated surface. The implant particles were encompassed by the newly formed bone. None of the group showed formation of bridge between the transverse processes

Fig. 5

Images of decalcified H&E staining histology section. No bone formation could be observed around the implanted material