As indicated by its Greek and Latin roots, chondromalacia patellae (CP) is a condition characterized by abnormal softening of the cartilage along the
undersurface ofthe patella. Common causes include trauma, repeated stress, and patellofemoral instability. Also referred to as ''runner's knee,'' this problem is a cause of anterior knee pain and is often seen in young, otherwise healthy individuals. The disorder affects women more often than men and is thought to be a result of anatomical differences in which more lateral force is applied to the female patella. This results in increased lateral tracking of the patella. With proper therapy, early CP can be reversed; however, if left unchecked its changes become advanced, chronic, and may progress to patellofemoral osteoarthritis.
Multiple imaging modalities and techniques can be used to evaluate the patient with suspected chondromalacia patellae. Conventional radiography, CT arthrography, MR arthrography, and conventional MRI are available options. Conventional radiographs are relatively insensitive in evaluating for cartilage loss, except when it is severe. CT arthrography may demonstrate fissuring and foci of cartilage loss, but this technique is invasive and involves ionizing radiation. MR arthrography has also been shown to be sensitive and specific, but like CT arthrography, it is invasive . Conventional MRI can show focal cartilage surface irregularities, as well as provide excellent soft tissue differentiation and reveal deeper internal cartilaginous derangement . However, some studies have also shown relative insensitivity of conventional MRI in detecting early changes of CP . Although invasive, MR arthrography with spoiled gradient recalled acquisition (SPGR) has demonstrated the high sensitivity for detecting early stage CP in multiple studies [21,22]. The MR findings typically show focal signal abnormalities or focal contour defects along the patellar cartilage on T2WI. These abnormalities can progress to patellofemoral osteoarthritis (PO) if left untreated (Fig. 5). A useful four-level grading scheme for CP based on arthroscopic and MRI appearance is presented in Box 2 and Fig. 5B.
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