Biomechanical evaluation of the less invasive stabilization system for theinternal fixation of distal femur fractures

Objective: Comparison between a Less Invasive Stabilization System (LISS) u sing monocortical screws with angular stability and two conventional plate systems Condylar Buttress Plate (CBP) and Dynamic Condylar Screw (DCS) for the treatment of distal femoral fractures with respect to biomechanical pro perties. Design: Biomechanical study using paired cadaver femurs. In Test Configurat ion I (distal test), a ten-millimeter gap at the diaphysis-metaphysis junct ion simulates a supracondylar femoral fracture. Test Configuration 2 (proxi mal test) has the same configuration, but the gap was cut in the isthmic re gion. Proximal and distal plate ends were fixed to corresponding cortical b one fragments in both tests. Optical displacement transducers served to qua ntify the system's ability to withstand a stepwise increased load. Reversib le (deflection) and irreversible deformation (subsidence) of the bone-plate construct was investigated. Results: In Test Configuration 1, LISS showed less irreversible deformation in 72 percent of the left-right comparisons. No correlation between bone m ineral density, cross-section area of bones and the measured response of th e construct under load was found between pairs. In Test Configuration 2, 83 percent of the left-right comparisons showed less permanent deformation bu t a higher elastic deformation for LISS. Conclusions: These results suggest an enhanced ability to withstand high lo ads when using the monocortical screw fixation technique with angular stabi lity. A higher elastic deformation of LISS compared with conventional plati ng systems in distal femoral fractures can be explained by the lower bendin g stiffness caused by different design and material properties.