Copyright 983 by The Journal of Bone and Joint Surgery, Incorporated 768 THE JOURNAL OF BONE AND JOINT SURGERY Terminology and Measurement

In 1975 a classification ofspondylolisthesis according to etiology was publishedta. This internationally accepted system of categorization has clarified the definitions of the several lesions that are grouped under the term. It is the purpose of this article to present a system of terminology and measurement for spondylolisthesis. The terminology and methods of measurement have been considered by the Committee on the Spine of The American Academy of Or-thopaedic Surgeons, and while most of the items are ac-ceptable to the Committee, there are some that may not be consistent with their preferences, which are not yet in final form. Spondylolisthesis, from the Greek roots spondvl (spine) and olisthesis (to slip), refers to displacement of a vertebral body on the one below (most commonly the low