Osteointegration of amorphous magnesium phosphate (AMP)-PEEK macroporous cranioplasty implants in a critical-size calvarial defect rat model.

Abstract

Calvarial defect reconstruction is vital for brain protection, neurological recovery, and esthetics. Polyetheretherketone (PEEK) is favored for its strength, radiolucency, and durability, but its limited osteointegration may compromise implant stability and long-term success. We hypothesized that addition of amorphous magnesium phosphate (AMP) to PEEK cranioplasty implants would enhance osteointegration. Critical-size calvarial defects (9 mm) were surgically created in 30 Lewis rats, and the defects were reconstructed using AMP-PEEK, PEEK, or autologous bone grafts (10 per group). Micro-computed tomography at 6- and 18-weeks assessed bone volume, bone volume/total volume, bone mineral density (BMD), tissue mineral density (TMD), and bone bridging. Histological exam and mechanical pull-out testing were performed at endpoint. At 6 weeks, AMP-PEEK had higher BMD than PEEK (60.3 vs. 57.7 mg/cc, p = 0.03). TMD increased from 6 to 18 weeks in both the groups (p < 0.01), with no difference between them at 18 weeks (p = 1.0). Bone bridging was the greatest in the autologous group at 6 and 18 weeks (61.4% and 62.6%) compared to AMP-PEEK (19.5%, 23.2%) and PEEK (14.7%, 20.2%) (p ≤ 0.03), respectively. Histology confirmed mineralized bone within implant pores and along the interface. Mechanical testing showed no differences in stability among the groups (p = 0.56). AMP coating enhanced early BMD suggesting accelerated initial mineralization but improve long-term bone volume or implant strength were not significantly improved compared to uncoated PEEK. Bone ingrowth within implant pores warrants further investigation to determine its potential positive impact on overall PEEK implant performance.