Degradation of Unsintered Hydroxyapatite and Poly-L-Lactide Composite Sheets In Vivo and In Vitro

Bioabsorbable sheet-shaped implants made of forged composites of unsintered hydroxyapatite and poly-L-lactide (F-u-HA/PLLA) have been used for orbital fracture repair with good results. This is the first report using multiple specimens implanted in the human orbit to demonstrate the biodegradation and loss of strength of F-u-HA/PLLA sheets. Among the patients who underwent various facial fracture repairs with F-u-HA/PLLA sheets implanted in their orbits, those whose sheets were subsequently extracted were included in the study. Viscosity-average molecular weight, crystallinity, and bending strength of the extracted implants were measured. An in vitro degradation test was also performed for comparison. Among the 111 patients who underwent F-u-HA/PLLA sheet implantation, 13 subsequently underwent surgical extraction of implants; the majority were due to secondary correction of complex fractures. One patient developed an infection; none developed foreign body reactions. Overall, 11 specimens from 10 patients with consent were examined. The time from implantation to extraction ranged from 43 to 632 days (median: 210 d). Compared with the results of the in vitro degradation test, the viscosity-average molecular weight and bending strength had a slower decrease. The F-u-HA/PLLA sheets retained more than 50% of their initial bending strength after 12 months. Crystallinity varied widely. F-u-HA/PLLA sheets implanted in human orbits did not degrade faster than those of in vitro testing. Sheet-shaped implants made of forged composites of unsintered hydroxyapatite and poly-L-lactide can be considered appropriate reconstructive materials for orbital fractures as they retained sufficient strength to support the orbital contents at 12 months postoperatively, and no case of delayed foreign body reactions was observed.