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Interpretation of postoperative orthopedic radiographs comprises a significant portion of the practice of not only subspecialized musculoskeletal radiologists but also general radiologists. A good foundation and understanding of the most common performed orthopedic procedures is essential for accurate interpretation of postoperative radiographs. This chapter reviews the basic concepts of joint replacement, spinal fusion, and fracture fixation, which are some of the most common procedures performed by orthopedic surgeons. In addition, the postoperative evaluation of various orthopedic hardware including the imaging findings for common complications will be discussed.
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Joint replacement is one of the most common orthopedic procedures performed. Generalized indications for joint replacement include severe osteoarthritis, avascular necrosis, trauma, and inflammatory arthropathies such as rheumatoid arthritis. Absolute contraindications for joint replacement include active local or systemic infection. Relative contraindications include obesity, remote infection, unrepaired ligamentous injuries, and neurologic impairment. Prior to the advent of joint replacement, surgical management of a painful or nonfunctional joint included joint arthrodesis (e.g., joint fusion), osteotomy, nerve division, and joint debridement. Patients were afforded significant improvement in quality of life with the development of joint replacement techniques; however, older joint replacement components often suffered from premature wear. Recent advances in biomaterials and joint replacement technology have led to marked improvements in the longevity of joint prostheses. Orthopedic surgeons can now choose between a vast array of prosthetic devices, many based on preference and familiarity. Though it is impossible for the radiologist to become familiar with all the different devices in the market, the structural material and complications are shared among the variety of different prostheses.
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The main components of any modern joint arthroplasty include a metal alloy and a plastic polyethylene liner. The low coefficient of friction between the metal alloy component and the polyethylene component simulates movements of normal joints. Alloys represent the metallic component of the prostheses. They are combinations of different metals such as chromium–cobalt, chromium–cobalt–titanium, or chromium–cobalt–molybdenum.1 These different alloys have individual biomechanical properties based on their metal composition, and differ in terms of their resistance to stress, strain, and tension. Polyethylene is the radiolucent liner of the prostheses. In other words, it is not seen on the radiograph. In order to secure the prosthesis, the prosthesis may either be press fit into the bone or cemented to the bone. Polymethylmethacrylate is the most commonly used cement to secure the prosthesis into the medullary cavity of the bone. Cement is seen as a radiopaque lining surrounding the prosthesis. Alternatively, porous-coated press-fit cementless prostheses demonstrate an irregular surface coated with lucent bone growth-stimulating material to ensure adherence to the surface.2 Another concept to be familiar with is the resistance of a prosthetic implant to motion, whether in the anteroposterior (AP) direction or the axial direction. A constrained prosthesis has two components that are directly linked together. As a result, there is full range of motion in only one ...