Minimally invasive screw plates for surgery of unstable intertrochanteric femoral fractures: a biomechanical comparative study.

BACKGROUND: This study presents the first biomechanical comparison of two minimal invasive screw plates used in the treatment of intertrochanteric fractures of the femur.
METHODS: Six fresh cadaveric pairs of human femur were included, following dual energy X-ray absorbsiometry analysis to obtain two cohorts of homogenous femurs. In each pair, unstable four-part trochanteric fractures were created and reduced. In each cohort, one femur was randomly selected to undergo instrumentation using one of the two minimal invasive devices, and the other femur was instrumented using the other device (minimally invasive screw system (MISS) or per cutaneous compression plate (PCCP)). Femurs were positioned at 25 degrees of adduction in order to simulate the anatomical loading during one-legged stance. Biomechanical tests were performed using a single vertical compressive load applied on the femoral head. Cycling loading was applied with three-dimensional fracture motions with stereophotogrammetric analysis and global displacement analysis throughout the cyclic test. Intact femurs after cyclic loading were tested to failure. Failure mode was diagnosed with macroscopic or radiographic analysis.
FINDINGS: Significant difference were detected between PCCP and MISS in sliding of the lag screw. Global vertical displacement of the femoral head during cyclic loading was higher for the PCCP. No statistically significant difference was noted in three-dimensional inter fragmentary displacement and load to failure between these two devices. Failure mode in both devices mainly consisted in fracture impaction, but no cut-out was noted.
INTERPRETATION: PCCP and MISS appear to be mechanical devices that may improve clinical outcomes and reduce the risk of co-morbidities associated with unstable trochanteric fractures without increased risk of mechanical failure.