Magnetic resonance imaging (MRI), ultrasound and PET/CT
At present, the most effective imaging methods for arthrofibrosis include magnetic resonance imaging (MRI), ultrasound and PET/CT. X-rays and CT (without a radioactive tracer) are not effective for imaging scar tissue but can detect badly distorted soft tissues, such as patella baja. X-ray and CT may be used to rule out mechanical issues such as a loose prosthesis. However, the usefulness of these methods is limited where a metal prosthesis is present due to imaging artefacts
Sagittal MRI is the most commonly used technique to image fibrosis and inflammation of the IFP . While MRI is helpful, radiologists may lack the necessary training to report on the presence of scar tissue in early arthrofibrosis. Due to image artefacts from metal special methods are required to image joints containing a prosthesis, however, these methods are now widely available in modern imaging centres.
In our experience, where a prosthesis is present ultrasound can be used to image arthrofibrosis, providing the operator is experienced. Imaging tissues in the middle of knees, such as the deep infrapatellar fat pad, is difficult but is often possible.
Positron emission tomography–computed tomography (PET/CT) is a nuclear medicine imaging technique. Using a radioactive tracer for inflammation can accurately image inflammation in a joint. Since inflammation can cause arthrofibrosis this method may be useful. However, the cause of inflammation can’t be determined, and a positive signal can be caused by non-fibrotic conditions, so this method is not diagnostic. A bone scan can also detect regions of active bone remodelling following surgery such as a joint replacement. This may detect regions of active remodelling after healing should be complete, indicating abnormal healing that may arise from arthrofibrosis.
Dragoo, J. L., Johnson, C. & McConnell, J. Evaluation and Treatment of Disorders of the Infrapatellar Fat Pad. Sports Med 42, 51-67, doi:10.2165/11595680-000000000-00000 (2012).
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