Imaging of porous polyethylene implant by using multidetector spiral computed tomography

The porous polyethylene implant (Medpor; Porex Surgical, Inc., Newnan, GA) is one of the most usable implants in clinical practice. Because it is radiolucent on both direct radiography and conventional computed tomography, visualization of the implant becomes an important issue. In this clinical study, availability of multidetector spiral computed tomography for visualization of the implant was evaluated. The technique was used in 15 patients who had Medpor reconstructions on their faces, including frontal (seven), malar (five), and mandibular (five) regions. A 16-channel multislice computed tomography scanner was used in spiral scanning mode. Sagittal, coronal, and transverse multiplanar reformation and volume-rendered images were reformatted using a PC-based three-dimensional reconstruction program (Extended Brilliance Workspace, Release 1.0.1.1, Philips Medical Systems, Amsterdam, The Netherlands). The three-dimensional images along the course of the implant were additionally reformatted. Window width and level were adjusted for viewing the bone as respective values of 1100 HU and 450 HU in contrast to the values of 800 HU and 200 HU, respectively, for the implant. The detailed contour of the implants could be easily traced on the multidetector computed tomographic images, including either the concave or convex areas. The calcifications and cystic formations around the implants and the spatial relationship between the defects and the implants were also shown. We believe that the present multidetector computed tomographic technique offers direct visualization of the Medpor implant in the body. It has many advantages over the current magnetic resonance imaging techniques that need tissue in growth for visualization.