Double-Modular Hip Device Design Susceptible to Stress Corrosion Failure

Total hip replacements restore pain-free mobility to approximately 200,000 patients in the U.S. each year [1]. A typical hip system comprises a metal alloy stem, a femoral head (ceramic or metal alloy), and a polyethylene acetabular cup fit into a metal alloy backing. A modular press-fit Morse taper is commonly used to attach the femoral head to the stem. There are also more recent designs that incorporate a second interface at the neck-stem junction (Figure 1). Increased modularity in total hip replacement design allows the surgeon to intraoperatively preserve patient anatomy such as leg length and femoral anteversion and better balance the surrounding soft tissue for optimal biomechanics. However, modularity also increases the number of mechanical junctions and interfaces in the device which may lead to complications such as corrosion, wear, and fracture.