Calcium pyrophosphate dihydrate crystal deposition in and around the atlantoaxial joint: Association with type 2 odontoid fractures in nine patients

PURPOSE: To investigate the histopathologic anatomy of calcium pyrophosphat e dihydrate (CPPD) crystal deposition in and around the atlantoaxial joint and the association between CPPD crystal deposition and subchondral cysts, erosions, and fracture involving the odontoid process of the axis. MATERIALS AND METHODS: One adult cadaver demonstrating calcification in the retro-odontoid area at computed tomography (CT) was selected for further r adiography, CT, and magnetic resonance (MR) imaging at the C1-2 level. Anat omic sectioning and histologic evaluations were performed in the specimen. For clinical study, radiographs (n = 5), CT scans (n = 8), and MR images (n = 6) in nine patients (mean age, 74.4 years) with odontoid process fractur es and CPPD crystal deposits in and around the atlantoaxial joint were revi ewed. RESULTS: In the cadaveric specimen, radiography and CT demonstrated calcifi cations in the transverse ligament; histologic evaluation confirmed that th ese calcifications were CPPD crystal deposits. In all nine patients, radiog raphy (n = 5) and CT (n = 8) also showed calcification in areas adjacent to the odontoid process, which included the transverse ligament. T1 and T2-we ighted MR imaging showed a retro-odontoid mass of low signal intensity that compressed the cervical cord in six patients. CT, MR imaging, or both demo nstrated subchondral cysts, osseous erosions, or a type 2 odontoid fracture in all patients. CONCLUSION: CPPD crystal deposition disease involving the C1-C2 articulatio n can be a clinically important entity that may place affected patients at increased risk of pathologic fracture of the odontoid process.