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Correlation of the Clinical and In Vitro Degradation Characteristics of a Poly(l-Lactic Acid): Poly(Glycolic Acid) Copolymer by Mini Meta-analysis

AbstractAbsorbable internal fixation devices have built a successful clinical history in a variety of applications throughout the skeleton. Their appeal lies in their ability to lose strength and mass in a predictable reproducible manner, consistent with the healing process. Most of the evidence for their degradation properties, however, is derived from in vitro and animal studies. These methods approximate only the human clinical condition, and there are few such data available directly from patients. To better understand the absorption profile of an 85:15 poly(l-lactic acid):poly(glycolic acid) copolymer in humans, a “mini meta-analysis” was performed on 2 published studies: (1) a clinical study that followed reduction in CT image density of a cross-pin for ligament reconstruction over a 2-year interval, and (2) an in vitro study that measured the hydrolysis and strength loss of test specimens over a 10- to 11-month interval in a phosphate-buffered saline at 37°C. The CT image density profile grossly approximated the in vitro tensile modulus profile with both quantities retaining at least half of their initial value at 44 to 52 weeks, but bore little resemblance to the rapid decreases in inherent viscosity (a measure of average molecular weight) and elongation to break (a measure of ductility), which were at half their initial values by 32 to 36 weeks. Because of the inherent difficulty in directly measuring absorbable implant degradation in patients on a routine basis, investigators should seize opportunities such as this in an effort to close the knowledge gap regarding absorbable implant degradation in humans as much as possible.