Endocrine Abstracts

Background: Bioresorbable implants should provide stability for fracture healing and resorb thereafter to make implant removal obsolete. Here, we report follow-up data of 6 patients treated with bioresorbable magnesium screws following medial malleolus fractures.

Purpose: Assessment of the implantation site and implant resorption of 11 implants in 6 patients with HR-pQCT (high resolution peripheral quantitative computed tomography).

Methods: Isolated, bimalleolar or trimalleolar ankle fractures were surgically treated with bioresorbable screws (Magnesium 99.1%, Calcium 0.45%, Zinc 0.45%) in 20 patients. After at least 2.5 years patients were clinical assessed and HR-pQCT-scans were performed. Screw residuals were evaluated in a binary approach for every axial slice generated by the HR-pQCT (residual present vs. not present). Evaluations included total volume, bone volume, and volume of the trabeculae-free space.

Results: All patients showed clinical evidence of fracture healing without clinical complications twelve weeks after the surgery. With full weight bearing and absence of pain in the fractured ankle. After 2.5 years, all observed implants were resorbed for the most part. Of 11 implants, 3 were dissolved without visible residuals. Minor residuals were present in 10% of slices (0%-33%). However, in 2 female study participants >50 years secondary expansions of the drilling channel were observed, where trabeculae were absent. Screw volume before implantation was 243.3 mm³, and the trabeculae-free cavities were 596.1 mm³ in mean size (239,2–1109,1mm³) with the largest cavities in the bone with the lowest bone volume per total volume (BV/TV).

Conclusion: Bioresorbable magnesium screws for fracture fixation are providing fracture healing and satisfactory clinical outcome after one year. Surgical removal is not necessary. Especially in patients with decreased bone mineral density the dynamic and impact of implant resorption needs to be studied further.

Keywords: HRpQCT, bioresorbable implant, magnesium screw, ankle fracture