In this book the author has outhned his philosophy with regard to the pathogenesis and treatment of OA of the hip. The author believes that most cases of OA arise from minor anatomical abnormalities which subsequently lead to the evolution of abnormal forces. Comprehensive study has led to an understanding of these forces and a mechanical means of correcting them. While this may seem simplistic in the extreme, nevertheless the author’s experience with 2500 cases over 19 years suggests that this mechanical theory is at least not far from the truth. Doubtless, in time other facts and other theories will emerge which will lead to modification. Any theory must fit known facts.