Modularity in total hip arthroplasty design has received increased citation in the clinical literature. The advantages of these systems include off-the-shelf flexibility for customizing proximal and distal canal filling, preservation of soft tissue structures, biomechanical restoration of offset, version and leg length, as well as accommodating difficult situations of femoral deformity and bone loss. Both mid-stem and distal neck modular femoral systems have been successfully employed for a variety of patient skeletal pathology. However, they are not without clinical concerns. The maintenance of anatomical stability within the femoral canal, structural compromise at metal-metal interconnections due to cyclic microdisplacements defined as fretting, decoupling of components in vivo, and increased potential for metallic wear debris generation and corrosion have all been reported. This handout describes a laboratory basis for the evaluation of modular femoral stem designs and suggests a thought process when considering their employ.