The significance of enthesopathy as a skeletal phenomenon.

Enthesophytes and enthesopathy, while easy to define, represent a phenomenon of unclear clinical significance. As the high frequency in skeletal populations suggests that enthesopathy may not be disease-specific, the nature of the reaction was assessed in 872 individuals from a representative skeletal population, subdivided into groups characterized by the presence or absence of rheumatoid arthritis, spondyloarthropathy, calcium pyrophosphate deposition disease and diffuse idiopathic skeletal hyperostosis (DISH). Achilles, plantar fascia, patellar and iliac crest entheses were examined for evidence of calcific overgrowth or "erosions." Enthesophytes were found to be a phenomenon of aging in individuals, and unrelated to the presence of inflammatory arthritis or DISH. The frequency increased with age, independent of sex or the site examined, plateauing in frequency after age 60. Enthesophytes in individuals under age 60 were usually unrelated to any underlying disorder. The absence of effect of underlying forms of arthritis on the frequency of enthesophytes at the patellar, Achilles and plantar sites suggests that mechanical factors outweigh the "enthesis calcifying" impact of such disorders as spondyloarthropathy, calcium pyrophosphate deposition disease and DISH. Individuals with rheumatoid arthritis, however, manifested a less severe iliac crest enthesial reaction, in keeping with the minimal reactive new bone formation characteristic of its erosions. Analysis of Achilles, plantar, and patellar enthesial reactions as a function of underlying inflammatory arthritis or DISH also revealed no significant variation with the underlying process. Cortical discontinuity at enthesial sites was a relatively infrequent phenomenon. While calcaneal discontinuities were originally thought to be erosive in nature, these observations suggest the possibility of tendon avulsion injuries.