Mechanical characteristics of poly-L-lactic acid absorbable screws and stainless steel screws in basilar osteotomies of the first metatarsal.

The purpose of this study is to evaluate the structural characteristics of 3.5-mm. stainless steel cortical screws and poly-L-lactic acid (PLA) absorbable screws in oblique closing base wedge osteotomies of the first metatarsal. Six pairs of frozen first metatarsal bones were excised from the specimen group. An oblique base wedge osteotomy was performed and fixated with either a 3.5-mm. stainless steel or PLA screw. Specimens were loaded to failure with the Bionix Material Testing System at a constant rate of 0.166 mm./sec. A Student's t test for paired samples with a 95% confidence interval was used to measure differences in ultimate load, ultimate displacement, and structural stiffness. The following results (mean +/- standard deviation) were obtained: Structural stiffness, PLA 12.35 +/- 3.82 N/mm. and stainless steel 10.13 +/- 5.74 N/mm.: ultimate displacement, PLA 7.39 +/- 3.23 mm. and stainless steel 10.89 +/- 7.91 mm.; ultimate load, PLA 57.95 +/- 1.01 N and stainless steel 51.49 +/- 5.22 N. In this fracture model, there were no statistically significant differences in the structural characteristics of PLA 3.5-mm. screws and stainless steel screws in oblique closing base wedge osteotomies of the first metatarsal.