Introduction Bioabsorbable materials were invented to address issues with synthetic implants including migration growth disturbance rigidity radioopacity infection need for implant removal operations Indications include but are not limited to pediatric orthopaedics transphyseal SR PLGA 80/20 screws only cause temporary growth arrest in rabbits (unlike nonbioabsorbable implants) osteomyelitis antibiotic eluting PLA carriers for growth factors rhBMP2 and rhBMP7 augmentation of bone healing at iliac crest bone harvest site Types of Bioabsorbable Materials Polyglycolic acid (PGA) hydrophilic, crystallic glass transition temperature 36degC becomes malleable if this temperature is exceeded disadvantages early degradation and strength loss login to view 1 more bullet intraoperatively, must be heated to adapt to implantation surface, and cooled login to view 1 more bullet Polylactic acid (PLA) more hydrophobic than PGA L-isomer or poly-L-lactic acid (PLLA) login to view 4 more bullets D-isomer login to view 2 more bullets Co-polymers P(L/D)LA copolymers mixture of D- and L-isomers of PLA hydrophobic and crystallic resistant to hydrolysis and degradation adding D-isomers results in less tightly packed polymer chains login to view 1 more bullet example is P(L/D)LA 70/30 in oral-maxillofacial surgery simple and self-reinforced forms PLGA copolymers combination of PLA and PGA low crystallinity used in oral-maxillofacial surgery simple and self-reinforced forms Self reinforcing (SR) composite structure made from partially crystalline/amorphous material made of orientated fibers/fibrils and binding matrix better biomechanical properties improved rigidity and strength along longitudinal axis malleable at room temperature login to view 1 more bullet can withstand 4 times bending minimal "memory" (tendency to return to previous shape after bending) can be sterilized by gamma irradiation login to view 3 more bullets Biodegradation Primary mechanisms of biodegradation poly-hydroxy-acid degradation breakdown is by random hydrolysis of ester bonds, which leads to login to view 3 more bullets kidney excretion PDS and PGA products can be excreted by the kidney enzyme breakdown enzymes are involved with PLA and PGA degradation lowered pH polymer breakage produces products that lower pH accelerating the breakdown material crystallinity determines hydrophobicity and degradation speed amorphous and hydrophillic materials degrade faster login to view 1 more bullet crystalline and hydrophobic materials degrade slower login to view 1 more bullet Additional variable that affect degradation chemical composition and molecular weight fiber orientation (SR or simple) monomer concentration (in polymers) stereoisomerism and conformation pores and surface area/volume ratio sterilization method (gamma irradiation vs others) Degradation method (enzymatic vs hydrolysis) Histopathology Granulomatous inflammation cellular reactions around bioabsorbale implants are characterized by T lymphocytes (CD4>CD8) plasma cells endothelial cells birefringent polymer debris thin macrophage layer multinucleated giant cells Capsule formation a capsule forms around implants that consists of internal cell layer login to view 2 more bullets external fibrous layer login to view 2 more bullets Stages begins with infiltration of neutrophils tissue reaction to trauma followed by CD4 T lymphocytes infiltration macrophages infiltration is last Adverse Tissue Reactions Incidence 3% in pediatrics up to 60% in adults (more common in adults) Presentation symptoms fluid accumulation, fluctuant papules login to view 1 more bullet symptoms appear late in materials with low degradation rate login to view 1 more bullet physical exam synovitis discharging sinus Labs fluid cultures are sterile unless there is secondary bacterial infection after bursting Radiography osteolysis is seen in up to 60% of cases Treatment nonoperative observation login to view 1 more bullet operative aspiration and/or surgical debridement implant removal login to view 2 more bullets arthrodesis login to view 1 more bullet