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Pinhole Scintigraphic Sign of Chondromalacia Patellae in Older Subjects: A Prospective Assessment with Differential Diagnosis

Department of Radiology and Nuclear Medicine, Kangnam St. Mary's Hospital, Catholic University Medical College, Seoul, Korea

Correspondence: For correspondence and reprints contact: Yong Whee Bahk, MD, Department of Radiology and Nuclear Medicine, Kangnam St Mary's Hospital, Catholic University Medical College, Seoul 137, Korea

ABSTRACT

Chondromalacia patellae (CP) is an important cause of anterior knee pain. Two clinical types are known: one that typically affects young subjects and the one that affects older patients. The primary diagnostic approach is radiography reinforced with arthrography. A ^99mTc-MDP bone scan is invaluable in the study of bone diseases especially when augmented with pinhole scintigraphy (PS). In this study previously unknown, specific sign of CP demonstrated by PS in six middle-aged and elderly patients is described. Methods: Noting an increased patellar uptake in a planar spot view, a medial PS scan of the patella was taken to detail the uptake pattern using a 3-mm or 4-mm aperture pinhole collimator. The uptake pattern was analyzed in terms of location, definition, mode, grade and other associated changes, and correlated with radiographic and CT scan alterations. Results: The planar views showed patellar uptake to be diffuse and nonlocalizing in five patients and ill-defined and spotty in the remaining patient in contrast PS revealed small, spotty uptake well localized in the central retropatellar facet in all but one patient in whom uptake was segmental. A control PS study of 16 patients with their patellas involved by osteoarthritis (n = 6), rheumatic arthritis (n = 5) and Reiter's syndrome (n = 5) also revealed retropatellar uptake with or without anterior patellar uptake in every patient. The CP with localized osteolysis or osteopenia accumulated tracer intensely, whereas those without showed mild to moderate uptake. Conclusion: Spotty tracer uptake occurring exclusively in the central retropatellar facet without other knee joint alteration appears pathognomonic of CP in older patients.

Key Words: chondromalacia patellae • patella • bone scan • pinhole scintigraphy