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one substitute.Material and MethodTitanium alloy Meridian ST Femoral Components (Stryker Orthopaedics, NJ) with aningrowth surface and 1/8” holes drilled into the medial, anterior and posterior aspects.Synthetic composite femurs (Pacific Research Labs, WA) with gaps created in 32% offemoral canal [1].Typical surgical recommendations were followed for creating the femoral bone canal. Thetest group (n=3) had an injectable HA bone substitute pressed into the gaps (Figure 1, A). Thecontrol group (n=3) was tested without HA filler. Femur was shortened distally and oriented at0Ëš flexion and 0Ëš varus/valgus. Metal probes were placed in the 1/8” holes and LVDTs weremounted to the bone via a custom frame (Figure 1, B). Vertical LVDTs collectedsuperior/inferior displacement. Horizontal LVDTs collected medial/lateral displacement fromthe anterior and posterior probes and anterior/posterior displacement from the medial probe.Mechanical loading included an axial compressive load (0-1000 N at 200 N/s) followed by tentorsional cycles (8 N-m external torque to 6 N-m internal torque at 0.5 Hz). Calculations wereused find the interfacial micromotion which occurring at the bone/implant interface [2].ResultsData collected from anterior and medial horizontal probes showed axial compression producedgreater micromotion in control group than test group (Figure 2). During torsional loading, testgroup had reduced motion for anterior, medial and posterior probes. For both groups there wasan increase in micromotion at medial probe when compared to anterior and posterior probes forboth axial and torsional loading. This indicated the implant tended to tilt in medially duringtesting.Translational motion was calculated from vertical probes and summed for axial and torsionalloading. The control group had larger total micromotion than the test group. The translationalcomponent of micromotion was greater than the rotational component.DiscussionThe purpose of this study was to determine whether the use of an injectable HA bone substitutewould reduce initial micromotion of a cementless press-fit hip implant. The addition of thebone substitute in the gaps significantly reduced both translational and rotational micromotion.This stabilizing feature along with the inductive properties of the HA can make it a valuableasset in orthopaedic implantation. The test was conducted for basic research and it does notrecommend the use of this product as described. The bone substitute is meant as a bone gapfiller and not for mechanical stability. Further research is necessary to determine the usefulnessof the bone substitute as a grouting agent.References1. Wu, L. et. al. J Zhejiang Univ. Science, 5;10:1270-1278 (2004).2. Yanoso-Scholl, L. et. al. ASME 2009, Lake Tahoe, CA.FiguresFigure 1 Figure 2 Figure 3file:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]