The French paradox regarding cemented femoral components has not been resolved, so we compared the mechanical behavior of a French stem, the CMK stem (Biomet, Warsaw, IN, USA), with a collarless, polished, tapered stem (CPT, Zimmer, Warsaw, IN, USA) using an original biomechanical instrument. Two size-3 CPT stems and two size-302 CMK stems stems were fixed with bone cement into a composite femur soaked in vegetable oil to simulate wet condition. The composite femur was attached to a biomechanical testing instrument after stem implantation, and a 1-Hz dynamic sine wave load (3000 N) was applied to the stems for a total of 1 million cycles. An 8-hour unload period was set after every 16 hours of load. Femur temperature was maintained at 37°C during testing. The femoral canal was prepared for the CPT stems by standard rasping; for the CMK stems, however, the French method was used, in which cancellous bone was removed with a reamer. One CMK stem (CMK-1) was inserted into a femur without collar contact (>2 mm above the calcar), and the other (CMK-2) was inserted into a femur with collar contact. Stem subsidence was measured at the stem shoulder. Compressive force and horizontal cement movement were measured via rods set at the cement–bone interface on the medial, lateral, anterior, and posterior sides of the proximal and distal portions of the composite femurs.Introduction
Materials and Methods
