Investigation performed at The Hospital for Special Surgery, New York City.(*) No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.(**) Department of Orthopaedic Surgery, University of Rochester, 601 Elmwood Avenue, Box 665, Rochester, New York 14642. Please address requests for reprints to Dr. Rubery.(***) Minnesota Spine Center, Suite 602, 606 24th Avenue South, Minneapolis, Minnesota 55454.(****) The Hospital for Special Surgery, 535 East 70th Street, New York, N.Y. 10021.(*****) The New York Hospital-Cornell University Medical Center, 525 East 68th Street, New York, N.Y. 10021.