208, No. Multidetector CT is an excellent supplemental imaging tool for evaluating a hip prosthesis (note that although some investigators prefer the term multichannel, multidetector is the more commonly used term). The components are the individual parts used to build a prosthesis. Loose femoral stem in a left resurfacing type total hip prosthesis. Most often, you will be asked to lie flat on your back with your arms over your head. Total hip prostheses, most commonly used as a treatment for arthritis, have one or two bearing surfaces. The number of bearing surfaces and the materials of which they are made vary depending on prosthesis type and design. However, they can be of great importance if they are present in large or increasing amounts (Fig 12) and should be closely monitored (29). (b) Scout radiograph shows a radiolucent band that corresponds to the finding indicated by the solid arrows in a. (b) What are the components? This procedure usually takes approximately 15 to 30 minutes. Other complications include neurovascular injury, leg length discrepancy, periprosthetic fracture, dislocation or subluxation, osteolysis, loosening, heterotopic ossification, pseudobursa formation, metal sensitivity or toxicity, and wear or breakage of hardware. In rare cases, it can also be caused by cancer. When optimized to reduce metal artifact, CT scans can aid in the assessment of the implant hardware, component fixation, and the host bone and soft tissues. Radiologists should carefully review prior radiographs and develop a systematic approach to the interpretation of the CT scans. Prosthetic hips can dislocate for a variety of reasons, and recurrent dislocation is a common indication for revising a prosthesis (1). Therefore, it may become critical to recognize distinguishing features of a bipolar hemiprosthesis, such as a bipolar head that has a slightly greater than hemispheric shape or lacks screw holes (Figs 2, 3). Pseudocysts occur as a result of granulomatous reaction to debris from polyethylene wear. 97, No. (d) Total hip prosthesis with an uncemented cup. We use a smoother reconstruction algorithm (medium or soft-tissue filters) and slightly thicker reconstruction sections when evaluating prosthetic hips to decrease the conspicuousness of streak artifacts in the soft tissues (13,15). The distal aspect of the stem (not shown) was fixed at revision surgery. The resurfacing type implant has a relatively small acetabular cup (note the slight step-off of the acetabular cup and femoral head [black arrow in a]). In addition, asymmetric hardware geometry produces nonuniform artifacts that are most severe in the direction of the hardware’s greatest cross-sectional profile. 46, No. Often your doctor can determine that you have a hip fracture based on your symptoms and the abnormal position of your hip and leg. Sagittal reformatted CT image shows a metal fatigue fracture of the femoral stem (solid arrow). 1, 16 January 2017 | Current Radiology Reports, Vol. (a) Unipolar hemiprosthesis fixed with cement (arrows) and with the stem in varus position. Also, the wear rate and types of complications vary with different bearing surfaces (20–25). Unlike radiography, CT eliminates overlapping shadows that can obscure or simulate disease. Radiography is also the initial imaging modality of choice for evaluating symptomatic hip implants for potential complications. Thus. One of them had a knee replacement and the other had a hip replacement. Radiographs are obtained for routine surveillance to document prosthesis position and fixation and the status of the adjacent bone. Pitch is probably the most important parameter affecting the quality of implant images (13). ... CT Scan. However, if the bipolar head of a hemiprosthesis has worn down the acetabular cartilage and protrudes into the subchondral bone plate, it could be misinterpreted as an acetabular cup in a reamed acetabulum from total hip arthroplasty. 5, No. 62, No. This study describes the normal and pathologic patterns of a bone scan and exemplifies ten common situations that can cause pain in patients with hip … Figure 15 Cement mantle fracture. Coronal reformatted CT images show a small area of osteolysis adjacent to the track of an acetabular screw (arrow in a) and endosteal scalloping at the cement-bone interface of a femoral stem (arrows in b). 78, No. These scans provide three-dimensional images of bony structures. Cement (usually polymethylmethacrylate) is used to fill the spaces between the bone and hardware, creating a “mantle” around the hardware that produces a uniform fit with evenly distributed forces. CT allows better detection, characterization, and quantification of osteolysis around the cup, as well as more accurate estimation of the total amount of the cup that is fixed to bone (Fig 17) (6–10,37). These include hip and knee replacements, plates, screws, and rods to treat limb fractures, and dental fillings. Virtual colonoscopy is a minimally invasive scan. As mentioned earlier, soft-tissue findings can help identify an infected prosthesis (41). The technologist will always be able to see and hear you during your exam. 39, No. Osteolysis.—CT is particularly useful in evaluating periprosthetic bone around the acetabular cup, where assessment with radiography is difficult. Note the superior location of the right greater trochanter. Viewer (c) Are there abnormalities of the host bones or soft tissues? A lower pitch (<1) allows z-axis oversampling of data, which decreases cone beam and splay artifacts and improves overall image quality, albeit at the expense of increased patient dose. 212, No. Over time, hip prostheses have become more complicated because of modular designs and the use of multiple materials. During the scan, which takes less than an hour, you … A basic understanding of hip reconstruction and hip implants is required for proper image interpretation. Laboratory tests. Hip pain is fairly common. In this article, we discuss the fundamentals of primary hip reconstruction and the basic classification of hip prostheses; the performance and interpretation of multidetector CT examinations of patients with hip prostheses; the components, bearing surfaces, and methods of fixation used for primary hip reconstruction, with emphasis on specific features that are relevant to CT; and a method for systematically evaluating hip prostheses and detecting complications using multidetector CT. Radiography is the only imaging technique used for routine surveillance of a hip implant, and it is the modality of choice for the initial imaging workup of a patient with a symptomatic prosthesis (1,3,4). (b) Axial noncontrast CT scan obtained in a different patient with a metal-on-metal implant shows periprosthetic collections lined by dense debris (arrows), findings that proved at surgery to represent metallosis. The fluid collection proved to be a hematoma. Total hip prostheses can be conventional or resurfacing types (Fig 3). Usually, in replacement surgeries, titanium implants are used. For … The scanner is open at the back and the front, allowing you to see out. Although the person performing the imaging has no control over the hardware as such, these hardware-related factors should be considered when setting scanning parameters that can be modified. β The areas of bone in-growth (also called struts or “spot welds”) are recognized on radiographs and CT scans by the presence of trabecular bone that extends all the way to the metal component surface (Fig 10).Figure 10 Solid fixation from bone in-growth in a patient with a right total hip prosthesis. After completing this journal-based CME activity, participants will be able to: List appropriate indications for multidetector CT in the evaluation of hip prostheses. 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