A Biomechanical Comparison of Bosworth and Poly-L Lactic Acid Bioabsorbable Screws for Treatment of Acromioclavicular Separations

Abstract

The purpose of this study was to determine the failure load of intact coracoclavicular ligaments and the pullout strength of a poly-L lactic acid screw (PLLA, Linvatec, Largo, FL) compared with a titanium screw (Bosworth, Stryker Howmedica Osteonics, Allendale, NJ) in the repair of fifth-degree acromioclavicular separations. Biomechanical cadaveric study. The ultimate tensile strength of coracoclavicular ligaments was determined using a servohydraulic testing machine (MTS, Eden Prairie, MN) by creating grade V acromioclavicular separations. Titanium Bosworth screws and Linvatec PLLA screws were placed across the reduced coracoclavicular joint and through the base of the coracoid process of right and left matched cadaveric shoulder specimens, respectively. The axial pullout strength was determined by MTS uniaxial tensile testing along the screw axis to determine the ultimate fixation failure load at a rate of 1 mm/second. Intact coracoclavicular ligaments required an axial load of 340.15 +/- 100.77 N to fail. The bioabsorbable PLLA screw provided fixation strength that was significantly less than the Bosworth screw fixation strength: 272.01 +/- 63.26 and 367.01 +/- 111.54 N, respectively (P < .05, paired t test). The titanium Bosworth screw restored strength to the acromioclavicular joint equivalent to the intact coracoclavicular ligament; however, the bioabsorbable PLLA screw fixation was significantly weaker than the intact ligaments and the Bosworth repair. Titanium Bosworth screws supply more strength of fixation in grade V acromioclavicular separations than the PLLA screw tested in this study.