Long-term tissue response to bioabsorbable poly-L-lactide and metallic screws: an experimental study

Area of Science:

• Biomaterials Science
• Orthopedic Surgery
• Tissue Engineering

Background:

• Late inflammatory reactions have been reported with bioabsorbable poly-l-lactide (PLLA) bone fixation devices.
• Understanding long-term tissue response to PLLA implants is crucial for clinical safety.

Purpose of the Study:

• To compare the long-term tissue response of bioabsorbable PLLA screws versus metallic screws in cancellous bone.
• To evaluate the biocompatibility and degradation of PLLA screws over extended follow-up periods.

Main Methods:

• Utilized rabbit femora models with PLLA and metallic screws, alongside intact bone controls.
• Employed radiography, microradiography, histology, histomorphometry, and oxytetracycline labeling.
• Follow-up assessments were conducted at 36 and 51 months.

Main Results:

• Both PLLA and metallic screws elicited a bone walling-off response.
• Connective tissue formed between bone and implant only in the PLLA group, with no significant difference in layer thickness over time.
• No significant differences in trabecular bone volume or osteoid formation were observed between screw types and controls.
• PLLA material diminished over time, indicating slow degradation accompanied by fibrous tissue formation and macrophage activity.

Conclusions:

• Bioabsorbable PLLA and metallic screws demonstrate comparable long-term biocompatibility in cancellous bone.
• PLLA screws undergo slow degradation with associated fibrous tissue formation, but without significant inflammatory foreign-body reactions.
• The observed tissue responses suggest inertness for both PLLA and metallic screws within the study's follow-up timeframe.