title: Femoro-acetabular impingement: the diagnosis-a review.
abstract: BACKGROUND
  The recognition of the importance of femoral acetabular impingement (FAI) as a potential cause of hip pain has been stimulated by major efforts to salvage hip joints by reconstruction in order to prevent or delay the need for replacement. The purpose of this review is to define the nature of FAI, the various types, and how to make the diagnosis.
  
  
  METHODS
  The review describes the characteristics of the hip that cause FAI and emphasizes understanding that the femoral and acetabular components normally function as a unit, complementing each other.
  
  
  CONCLUSIONS
  The methods of making the diagnosis of FAI and their limitations are described. If the acetabulum and femur are considered to be independent of each other, conflict may occur, hindering function, and not be apparent. The increasing frequency of making this diagnosis based on abnormal anatomy on one side of the joint, often in face of unclear physical findings, can bring the diagnosis into question. FAI seen in Perthes disease and acetabular dysplasia is explained. Knowing how to analyze the hip, being aware of the limitations of various available clinical and diagnostic studies, and recognizing the continued and ever-changing extensive body of literature is important and challenging. This primer is just the beginning.
authors: Department of Orthopaedic Surgery, NYU School of Medicine, NYU Hospital for Joint Diseases, 301 East 17th Street, New York, NY 10003 USA.
authors: Alfred D
authors: AD
authors: Grant
authors: Debra A
authors: DA
authors: Sala
authors: Ran
authors: R
authors: Schwarzkopf
keywords: Acetabular retroversion; Cam impingement; Crossover sign; Femoro-acetabular impingement; Ischial spine sign; Pincer impingement; Posterior wall sign