The clinical and radiographic findings of 194 patients with rheumatoid arthritis and atlantoaxial (C1-C2) subluxation and/or atlantoaxial impaction (AAI) were reviewed. The condition of most patients with C1-C2 alignment abnormalities remained unchanged or became worse with time (i.e., the misalignment became fixed, subluxation increased, or AAI developed). The chance of developing upper cervical cord compression was not related to worsening per se, but to the degree of deformity. Upper spinal cord compression developed more often in men; when C1-C2 subluxation was greater than 9 mm; and in the presence of atlantoaxial impaction. The presence of lateral C1-C2 subluxation probably also contributes to the development of upper spinal cord compression. Settling of the skull and C1 onto C2 (AAI) were considered to be present when the anterior arch of C1 was abnormally low in relation to C2.

Objective. Chondrocalcinosis, which can promote joint inflammation and cartilage degeneration, is highly prevalent in elderly white subjects. Data on its prevalence are scarce in other ethnic populations. This study was undertaken to compare the prevalence of chondrocalcinosis in Chinese subjects with that in white subjects.Methods. We recruited a random sample of Beijing residents ages >60 years. Participants underwent standard weight-bearing anteroposterior knee radiography and posteroanterior hand radiography using the protocols developed in the Framingham Osteoarthritis Study. Radiographic chondrocalcinosis was defined as present in a knee or wrist when there was evidence of definite linear cartilage calcification. We compared the prevalence of chondrocalcinosis in Chinese subjects with that in white subjects using age-standardized prevalence ratios. We used identical methods to collect samples of tap water from 2 cities and measured their levels of calcium, magnesium, and phosphate in the same laboratory.Results. Chinese subjects had a much lower prevalence of knee chondrocalcinosis (1.8% in men, 2.7% in women) than did white subjects (6.2% in men, 7.7% in women), with the age-standardized prevalence ratio Calcium pyrophosphate dihydrate (CPPD) crystal deposition in articular fibrocartilage and hyaline cartilage, termed "chondrocalcinosis," is a common radiographic and pathologic finding associated with both aging and osteoarthritis (OA) (1). Most subjects with chondrocalcinosis are asymptomatic, but CPPD crystal deposition can promote articular cartilage degeneration (pseudo-OA), and traffic of the crystals from articular cartilage into the joint space can stimulate acute syno-

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The radiographs of 268 patients with knee trauma were retrospectively reviewed. In 15 patients with intraarticular fracture, the images demonstrated fat-fluid levels. In 28 other patients with intraarticular fracture, only joint effusion without a fat-fluid level was depicted. The presence of a fat-fluid level in the knee indicated fracture in all patients in whom it was seen. The absence of such a level, however, did not exclude intraarticular fracture.

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