A method of injection molding an orthopedic device comprising: injection molding a polymeric orthopedic device having a length along a longitudinal axis; and deliberately inducing, in the device, a material property change along the longitudinal axis by varying a molding parameter during the injection molding. The material property may be, for example, elastic modulus and/or density. The molding parameter varied during the injection molding may be a supply material pressure. The orthopedic device may be an elongated rod-shaped element, such as a spinal fixation rod, which may or may not have a substantially uniform cross-section, and may or may not have a metallic core. A corresponding apparatus is also described.