A new anatomic index based on current knowledge for calculating the cumulative percentage of pagetic bone per subject and other parameters.

New data provided by dual-energy X-ray absorptiometry, together with discordances between Howarth's and Coutris' tables for estimating the percentage of bone tissue affected with Paget's disease in a given individual, prompted us to reevaluate the percentage of bone tissue contained in each segment of the skeleton. We weighed each bone in the skeleton of a 30-year-old male, calculated weight ratios from a collection of 48 bones, performed dual-energy X-ray absorptiometry measurements in 22 patients using a Hologic QDR 2000 apparatus, and obtained information from a company that supplies medical schools with human skeletons. We used these data to develop a new anatomic index. The percentage of bone tissue in the skull was 17 in males and 21 in females versus only 11 in Howarth's table; differences were also found at other sites, including the spine (8.5% versus 11%), the femur (9.5% versus 8%), the sacrum (2% versus 3%), and the ribs (5% versus 9%). Our index is useful for calculating the percentage of pagetized bone (i.e., bone in which pagetic lesions develop during follow-up) but underestimates the total percentage of pagetic bone because of the increase in bone mass associated with Paget's disease.