Minimally invasive screw fixation is as stable as anterior plating in acetabular T-Type fractures – a biomechanical study

Abstract

IntroductionOperative treatments of T-type acetabular fractures are challenging surgical procedures. Open reduction and internal fixation is the standard method for the operative management of these fractures, however this is associated with high blood loss, long hospital stay and longer rehabilitation. Anterior subcutaneous pelvic fixation (internal fixation=INFIX) and retrograde pubic screw fixation have shown promising results in minimally invasive treatment of pelvic ring fractures. For T-type acetabular fractures, however, minimally invasive treatment concepts are still rare. Therefore we performed a mechanical in vitro study to:– investigate the potential favorability of minimally invasive treatment options over the already established open anterior locking plate osteosynthesis of acetabular T-fractures regarding biomechanical stability and post-surgical stiffness;– explore the biomechanical feasibility of the INFIX;– assess its potential ability to reduce the anterior acetabular column. HypothesisA minimally invasive treatment of acetabular T-type fractures is biomechanically equivalent to an open anterior plate osteosynthesis. MethodsTwenty-four synthetic hemipelvis specimens with a T-type acetabular fracture were divided in four groups. A posterior column screw was placed in every pelvis of every group. The anterior column was fixed with:– anterior column screw;– anterior column screw incl. INFIX;– INFIX alone;– 14-hole angular stable locking plate (standard fixation method).Displacement of the anterior column was reduced in group 2+3 using the INFIX. All specimens were cyclically loaded with 200N until a maximum of 600N. Movement/displacement of the fracture fragments were detected with a 3D-ultrasound measuring system. Displacement (mm) and Stiffness (N/mm) of the construction were analyzed. ResultsStatistical assessment showed no significant differences between the four fixation types (p>0.05). The 14-whole locking plate (group 4) displayed the overall highest stability with a displacement of 1.3±0.04mm and stiffness of 76.3±2.4N/mm. Anterior screw fixation (group 1) proved to be the minimally invasive fixation method with the least displacement and highest stiffness (1.5±0.2mm, 68.3±6.8N/mm). The combination of an INFIX and an anterior column screw (group 2), showed a mean stiffness of 62.1±6.0N/mm and a mean displacement of 1.7±0.2mm. INFIX only (group 3) presented a displacement of 1.6±0.1mm and a stiffness of 64.5±4.5N/mm. DiscussionMinimally invasive fixation techniques for T-type acetabular fractures show promising biomechanical stability in non- or slightly displaced fractures. Furthermore, INFIX could be a feasible tool for the reduction of the anterior acetabular column. Level of evidenceIII, case control prospective experimental study.