S. B. Goodman, Stanford University, Stanford, CA

Summary: Total hip and knee replacement are two of the most successful and cost-effective procedures in all of surgery. In the elderly population, the current survivorship of hip and knee replacements is over 90% at 15 or more years. However, in the younger population, the revision rate is approximately 1% per year. Risk factors for revision include young age, high activity level, increased weight, male sex and a diagnosis of osteoarthritis. As the population is aging and generally becoming more active, the demands on joint replacement are ever increasing. How can surgeons and manufacturers provide a pain free, durable artificial joint replacement that will function normally over the lifetime of the patient? In order to answer this question one must examine why joint replacements fail. Excluding infection, the most common causes of clinical failure of joint replacements include wear of the bearing surfaces, loosening and periprosthetic osteolysis, dislocation (hips), malalignment (hips and knees) and stiffness (knees). These root causes of failure must be addressed to further improve implant longevity. Surgical technique must be improved to ensure repeatable prosthesis insertion in optimal position. In this regard, so called “minimally invasive surgery” with limited anatomical exposure has sometimes led to component malalignment. Computer navigation may hold the promise of more precise component placement, limiting outliers. Implants must obtain initial stability, which fosters rapid osseointegration. New “cancellous like” metallic surfaces, osteoconductive and potentially osteoinductive coatings may hasten bone ongrowth and ingrowth. New bearing surfaces such as metal-on-metal, highly cross-linked polyethylene, and ceramics have been shown to decrease wear, but new problems have arisen including excessive particle and ion production, hypersensitivity reactions, fatigue failure and implant fracture. Extensive remodeling of the surrounding bone in the presence of an implant also occurs, because of modulus mismatch. How can a joint replacement last a lifetime and yield normal function, including impact loading? This goal may be unobtainable at present, however ongoing research has the potential to improve implant longevity and function even further.