Endocrine Abstracts

Background: Bioresorbable screws for surgical fracture treatment are of great interest for the orthopaedic community. Such implants are designed to provide stability and compression of the fracture and should dissolve after healing, thereby making removal of surgical material obsolete. Magnesium implants are a new material option. So far, long-term follow-up of fracture healing and material decay has not been studied in human. Here, we present the results of the 2.5 year follow-up of 6 patients with medial malleolus fractures after surgical stabilization with magnesium screws.

Design and Methods: 6 patients with isolated, bimalleolar or trimalleolar ankle fractures were surgically treated using bioresorbable screws (magnesium 99.1%, calcium 0.45%, zinc 0.45%) with an initial volume of 243,3 mm3 (+/- 5). Fracture healing was assessed clinically after one year. Implant resorption was studied after 2.5 years with HR-pQCT (high resolution peripheral quantitative computed tomography). Screw residues were carefully evaluated in a binary approach for every slice (residual present vs not present). Zones of degradation without visible bone were contoured manually and the volume was evaluated.

Results: All patients showed clinical evidence of fracture healing confirmed by plain radiographs, with full weight bearing and absence of pain in the fractured ankle after 1 year. After 2.5 years, resorption of the implant material was almost complete. Of the 11 implants in 6 patients, 3 were dissolved without visible residuals whereas at 8 implantation sites minimal residuals were observed, as assessed by HR-pQCT. In 10% of slices (min. 0%; max. 33%) residuals were observed at implant sites. The degradation zones lacked visible ingrowth of new bone for the most part. Mean volume of degradation zones was 504.8 mm³ (min. 239.2 mm³; max. 1109.1 mm³).

Conclusion: Considering the successful fracture healing and excellent clinical outcome after one year, bioresorbable magnesium screws are a viable option for fracture fixation. Implant removal is not necessary and the 2.5 year follow-up showed the screw material largely resolved. However, enlarged degradation zones and the lack of new bone in these zones were observed.