Femoroacetabular Impingement A Cause for Osteoarthritis of the Hip Reinhold Ganz, MD*; Javad Parvizi, MD**; Martin Beck, MD*; Michael Leunig, MD*; Hubert No ¨tzli, MD*; and Klaus A. Siebenrock, MD* A multitude of factors including biochemical, ge- netic, and acquired abnormalities may contribute to osteoarthritis of the hip. Although the patho- mechanism of the degenerative process affecting the dysplastic hip is well understood, the exact pathogenesis for idiopathic osteoarthritis has not been established. Based on clinical experience, with more than 600 surgical dislocations of the hip, allowing in situ inspection of the damage pattern and the dynamic proof of its origin, we propose femoroacetabular impingement as a mechanism for the development of early osteoarthritis for most nondysplastic hips. The concept focuses more on motion than on axial loading of the hip. Distinct clinical, radiographic, and intraoperative parame- ters can be used to confirm the diagnosis of this entity with timely delivery of treatment. Surgical treatment of femoroacetabular impingement focus- es on improving the clearance for hip motion and alleviation of femoral abutment against the acetab- ular rim. It is proposed that early surgical interven- tion for treatment of femoroacetabular impingement, besides providing relief of symptoms, may deceler- ate the progression of the degenerative process for this group of young patients. Osteoarthritis is a disorder of diverse etiologies, which commonly can affect the hip. 5,11,24 A Workshop on Etiopathogenesis of Osteoarthritis (OA) provided a definition and a classification system for OA that includes a category of patients with idiopathic osteoarthritis, for whom no etiologic factors can be determined. 6 The biomechanical principles for develop- ment of OA of the hip generally are based on the calculations of force transmission in that carti- lage degeneration is thought to be initiated by concentric or eccentric overload. 1,22 A malor- iented articular surface with decreased contact area in circumstances such as developmental dysplasia of the hip typically leads to excessive and eccentric loading of the anterosuperior por- tion and subsequently promotes the development of early OA of the hip. 18,19,27 This widely ac- cepted theory implicating axial overload for the onset of OA of the hip fails to provide a sat- isfactory explanation for development of arthritis in groups of often young patients with apparently normal skeletal structures and intraarticular pressures. Based on our clinical experience spanning more than a decade, we have evidence that in many cases of idiopathic arthritis, predisposing factors, in the form of femoroacetabular impinge- ment, are present that are not appreciated readily using the traditional diagnostic modalities. 3,7,12,21 The theory implies that in certain aberrant morphologic features of the hip, abnormal contact CLINICAL ORTHOPAEDICS AND RELATED RESEARCH Number 417, pp. 112–120 B 2003 Lippincott Williams & Wilkins, Inc. 111 From the *Department of Orthopedic Surgery, University of Berne, Inselspital, Berne, Switzerland; **Rothman Institute, Thomas Jefferson University, Philadelphia, PA. Reprint requests to Reinhold Ganz, MD, Department of Orthopedic Surgery, Inselspital, CH-3010 Berne, Switzer- land. Phone: 031 632 2111; Fax: 031 632 3600; E-mail: reinhold.ganz@insel.ch. DOI: 10.1097/01.blo.0000096804.78689.c2 Copyr ight © Lippincott Williams & Wilkins. Unauthor iz ed reproduction of this article is prohibited.