The locking attachment plate for proximal fixation of periprosthetic femur fractures-a biomechanical comparison of two techniques

Mechanical properties of a locking attachment plate construct (LAP-LCP), allowing bicortical screw placement laterally to the prosthesis stem, are compared to a cerclage-LCP construct. Eight right synthetic femora with implanted uncemented hip endoprosthesis were cut distally and fixed with LCP, monocortical locking screws and either LAP (n = 4) or cerclage (n = 4). Cyclic testing was performed with monotonically increasing sinusoidal load until failure. Relative movements at the plate-femur interface were registered by motion tracking. Statistical differences were detected by unpaired t-test and general linear model repeated measures. Stiffness of the LAP-LCP was significantly higher at the beginning (875.4 N/mm +/- 29.8) and after 5000 cycles (1213.0 N/mm +/- 101.1) compared to the cerclage-LCP (644.96 N/mm +/- 50.1 and 851.9 N/mm +/- 81.9), with p = 0.013. Relative movements for AP-bending (B) and axial translation (T) of the LAP-LCP at the beginning (0.07A degrees A +/- 0.02, 0.20 mm +/- 0.08), after 500 cycles (0.16A degrees A +/- 0.10, 0.26 mm +/- 0.07) and after 5000 cycles (0.26A degrees A +/- 0.11, 0.31 mm +/- 0.07) differed significantly from the cerclage-LCP (beg.: 0.26A degrees A +/- 0.04, 0.28 mm +/- 0.05; 500 cyc: 0.47A degrees A +/- 0.03, 0.53 mm +/- 0.07; 5000 cyc.: 0.63A degrees A +/- 0.18, 0.79 mm +/- 0.13), with B: p = 0.02, T: p = 0.04. Relative movements for medial bending were not significantly different between the two constructs. Cycles to failure (criterion 1 mm axial translation) differed significantly between LAP-LCP (19,519 +/- 1,758) and cerclage-LCP (11,265 +/- 2,472), with p = 0.035. Biomechanically, the LAP-LCP construct improves proximal fixation of periprosthetic fractures compared to the cerclage-LCP construct.