The new millennium and right on schedule comes thefourth edition of Diagnosis of Bone and Joint orders.This, then, is the third time I have revised this text sinceits initial publication in 1981, more than 2 decades ago.Each time I have begun work on a new edition, I be-lieved incorrectly that my job would be easier because,I thought, how much information could possibly havebeen introduced in the 5 or 6 years that had elapsedsince the previous edition? And each time, without ex-ception, I have been surprised by the progress that hasoccurred with regard to the further understanding andimproved diagnostic assessment of the many diseasesthat affect the musculoskeletal system. So now, 7 yearsafter the publication of the third edition, the fourthedition is offered as clear evidence that much has beenlearned, new concepts have emerged, and "old facts"have been modified or eliminated altogether.

I am often asked at the time of publication of a newedition precisely how much of the material is appearingfor the first time. This is a difficult question to answerquantitatively. My educated guess is that 30 per cent ofthe information is new or has been modified significantlyfrom that contained in the third edition, that the number of references has been expanded by 25 to 35 per cent (with emphasis given to pertinent recent publications), and that new illustrations represent 25 to 30 per cent of the total number appearing in this edition. With regard to the illustrative material, the new figures underscore the increasing importance of MR imaging as a vehicle for investigation of these diseases.

The size of the fourth edition does not differ signifi- cantly from that of the last edition, although the number of volumes has been decreased by one. (You will note that each is somewhat heavier than in the past!) To be certain that this multivolume book did not become too large, I consulted extensively with the following changes.