Enhanced Release of Calcium Phosphate Additives from Bioresorbable Orthopaedic Devices using Irradiation Technology is Non-Beneficial in a Rabbit Model

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Abstract

Objectives
Bioresorbable orthopaedic devices with calcium phosphate (CaP) fillers are commercially available on the assumption that increased calcium locally drives new bone formation but the clinical benefits are unknown. Electron beam (ebeam) irradiation of polymer devices has been shown to enhance the release of calcium. The aims of this study were to (1) establish the biological safety of ebeam surface modified bioresorbable devices, (2) test the release kinetics of CaP from a polymer device and (3) establish any subsequent beneficial effects on bone repair in vivo.

Materials and Methods
ActivaScrew™ Interference (Bioretec Ltd.) and PLGA orthopaedic screws containing 10 wt% β-tricalcium phosphate (β-TCP) underwent ebeam treatment. In vitro degradation over 36 weeks was investigated by recording mass loss, pH change and calcium (Ca) release. Implant performance was investigated in vivo over 36 weeks using a lapine femoral condyle model. Bone growth and osteoclast activity were assessed by histology and enzyme histochemistry.

Results
Ca release doubled in the electron beam treated group before returning to a level seen in untreated samples at 28 weeks. Extensive bone growth was observed around the perimeter of all implant types along with limited osteoclastic activity and no statistical significant differences between groups.

Conclusion
The higher than normal dose of ebeam used for surface modification did not adversely affect tissue response around implants in vivo. Surprisingly, incorporation of β-TCP and subsequent accelerated release of Ca had no significant effect on in vivo implant performance calling into question the clinical evidence base for these commercially available devices.
Original languageEnglish
Pages (from-to)266–274
JournalBone and Joint Research
Volume8
Early online date08 Feb 2019
DOIs
Publication statusPublished - 28 Jun 2019

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