An in vitro comparison of an adjustable bone fixation system

Purpose: The purpose of this study was to biomechanically compare an adjustable plating system and several variations with an inverted-L pattern of 3 bicortical screws to fix a bilateral sagittal split osteotomy. Materials and Methods: Sixty polyurethane mandible replicas (Synbone, Laudquart, Switzerland) were used in this study. Ten uncut mandibular replicas served as control models. Fifty experimental synthetic mandibles had bilateral sagittal split osteotomies created with a 7-mm advancement. Fixation modalities included 3 bicortical screws in an inverted-L pattern, a 4-hole sagittal split plate with adjustable slider (slide 0), an adjustable plate with an additional bicortical screw (slide 1), an adjustable plate with 2 additional bicortical screws (slide 2), and an adjustable plate with 3 additional bicortical screws (slide 3). The alloplastic mandibles were secured in a custom fabricated jig and subjected to vertical loads at the incisal edge and torsional loading at the molar region by an Instron 1331 (Instron, Canton, MA) servohydraulic mechanical testing unit. Mechanical deformation data within a 0- to 900-N range were recorded. Yield load, yield displacement, and stiffness were determined. Means and standard deviations were derived and compared for statistical significance using a Fisher's Protected Least Significant Differences Test with a confidence level of 95% (P < .05). Second-order best-fit polynomials were created for the experimental data curves. Results: For incisal edge loading, the control was significantly greater for yield load than the experimental models. No significant difference was noted between slide 0, slide 1, and slide 2, but significant differences were seen with slide 3 and the inverted-L. There were no significant differences between slide 1, slide 2, slide 3, and inverted-L. For molar load, the control was significantly different than the experimental models. However, there was no significant difference between the experimental models. Conclusions: Mandibular advancements of 7 mm in a synthetic mandible fixed with a 4-hole sagittal split plate with adjustable slider alone is resistant to torsional forces and comparable to that seen with 3 bicortical screws placed in an inverted-L fashion. However, when loading at the incisal edge, additional bicortical screws are necessary to achieve the similar resistance to vertical load as that seen with 3 bicortical screws.