STRUCTURAL-ANALYSIS OF ABSORBABLE PIN AND SCREW FIXATION IN FIRST METATARSAL OSTEOTOMIES

The structural characteristics of 4.0-mm stainless steel screws compar ed with 4.0-mm poly-L-lactic acid absorbable screws and 2.0-mm stainle ss steel Steinmann pins compared with 2.0-mm poly-L-lactic acid absorb able pins in oblique closing base wedge; osteotomies of the first meta tarsal were evaluated. The authors performed oblique closing base wedg e using an osteotomy guide in six matched pairs of fresh frozen first metatarsal bones. Fixation was achieved with either a 4.0-mm stainless steel screw or poly-L-lactic acid absorbable screw. An additional fiv e pairs of matched specimens were used to compare 2.0-mm stainless ste el and poly-L-lactic acid absorbable pins with the same approach. Spec imens were loaded to failure with the Bionix Material Testing System(R )(1) at a constant rate of 0.166 mm/sec. A Student's t-test for paired samples was used with a 95% confidence interval to measure difference s in ultimate load, ultimate displacement, and structural stiffness. T here was not a significant difference in any of the parameters evaluat ed in the 4.0-mm poly-L-lactic acid absorbable versus stainless steel screw comparison (P > 0.05). Stainless steel 2.0-mm pins had significa ntly greater structural stiffness (P = 0.032) and less ultimate displa cement (P = 0.021) than their poly-L-lactic acid absorbable counterpar ts. There was not a significant difference in ultimate load in poly-L- lactic acid absorbable and stainless steel pins (P = 0.59).