Pseudotumor is a known complication of Metal-on-Metal (MOM) total hip arthroplasty (THA). MRI is usually used to visualize pseudotumor formation. However, small pseudotumors close to the THA components may not be observed using MRI due to image distortion by the interaction between the metallic objects and the magnetic fields. The CT image quality also degrades because MOM THA components can induce X-ray beam-hardening effects. Therefore, we evaluated contrast-enhanced (CE) tomosynthesis. Tomosynthesis is known as an X-ray tomography technique that provides images with fewer metal artifacts and lower X-ray doses for the patients. The aim of this report was to investigate the detectability of pseudotumors by tomosynthesis. A 71-year-old woman had undergone unilateral cementless large-diameter MOM THA using a couple of Conserve Plus acetabular cup and Profemur Z femoral component (Wright Medical, Memphis, Tennessee) for primary arthritis of the left hip at our hospital. She presented with severe hip, groin and buttock pain and swelling at fifteen months after surgery. Therefore, she was examined MRI and tomosynthesis using Sonialvision-Safire X-ray Radiography/Fluoroscopy System (Shimadzu Corporation, Japan). Plain tomosynthesis was obtained before the contrast media injection and followed by CE-tomosynthesis. Then, subtraction tomosynthesis between plain and CE-tomosynthesis were calculated in order to increase the image contrast. The subtraction tomosynthesis image enhanced the pseudotumor visibility, which was considered to be equal to that depicted using MRI (Fig. 1 and 2). However, using MRI, cystic lesions in the pseudotumor appeared as a very high signal in the T2 weighted images, whereas CE-tomosynthesis resulted in no image contrast (Fig. 3). The tomosynthesis image resulted in less image distortion and fewer metal artifacts than MRI, even in the area close to the hip implants.Introduction
Case Report
Frontal and lateral plain radiographs are the first choice for follow-up observations of the osteotomy boundary that faces the femoral and tibial components of a TKA. However, as plain radiographs provide no information in the image depth direction, it is difficult to determine the exact position of early-stage bone radiolucent lines. A new tomosynthesis technique, which uses both iterative reconstruction and metal extraction methods, has recently attracted attention. We report that this technique provides multi-slice images of the boundary between the metallic implant and the osteotomy surface, which is difficult to observe using conventional multi-slice imaging methods such as CT and MRI, and permits semi-three-dimensional evaluations of polyethylene wear.
We propose digital tomosynthesis with a new reconstruction method, a combination of iterative reconstruction (IR) with metal extraction, in order to reduce metal artifacts with compatibility of high spatial resolution for post-TKA follow-up examination. For comparison of metal artifact reduction efficiency, three images were respectively reconstructed by conventional filtered back projection (FBP), FBP with modified kernel and proposed method. Proposed method provides higher resolution images with remarkably less metal artifacts than others, where we can observe the structure of trabecular bone in the region very close to a metal prosthesis. We demonstrate some clinical applications.
