Nuclear Medicine Imaging of Joint Prosthesis Infections

Abstract

Replacement of diseased or injured joints with artificial prosthetic components is commonly employed to reduce the pain and disability associated with many orthopedic conditions including arthritis, congenital deformities, trauma and other diseases of bone and joint tissues. The most successful type of joint replacement procedure is the replacement of both sides of a diseased joint (total joint arthroplasty). Other types of joint replacement include hemi-arthroplasty and surface arthroplasty, where the surface of the joint is covered by a foreign material which provides a smooth articulating surface. The most commonly replaced joints are hips and knees: the results are now excellent with 10-year survival rates of 91.5% for hips and 96.5% for knees [1]. The materials used (stainless steel, cobalt-chrome, molybdenum alloy, titanium-aluminum-vanadium alloy, and ceramics) in prosthetic implants are considered biocompatible, nevertheless they represent a foreign body. These components usually articulate with plastic components (often composed of ultra-high molecular polyethylene) which may have a metal backing. Joint replacement failure may be due to the failure of structural materials, such as fatigue fracture of a metal prosthetic stem or the rapid destruction of a polyethylene cup. But a more common cause of arthroplasty failure is aseptic loosening of the implant. This complication is usually associated with late implant failure, occurring several years after the implant has been in situ and functioning reasonably. Both mechanical and biological factors contribute to the pathogenesis of aseptic loosening. Although relatively uncommon, another important cause of orthopedic implant failure and loosening of implant components is infection (septic loosening) [2, 3]. Distinguishing clinically between aseptic and septic loosening is often difficult. An accurate diagnosis is important, however, as both the surgical management and outcome may differ depending on whether the arthroplasty loosening is infective or mechanical in origin.