The concept of femoroacetabular impingement: current status and future perspectives

Abstract

Femoroacetabular impingement (FAI) is a recently proposed mechanism causing abnormal contact stresses and potential joint damage around the hip. In the majority of cases, a bony deformity or spatial malorientation of the femoral head or head/neck junction, acetabulum, or both cause FAI. Supraphysiologic motion or high impact might cause FAI even with very mild bony alterations. FAI became of interest to the medical field when (1) evidence began to emerge suggesting that FAI may initiate osteoarthritis of the hip and when (2) adolescents and active adults with groin pain and imaging evidence of FAI were successfully treated addressing the causes of FAI. With an increased recognition and acceptance of FAI as a damage mechanism of the hip, defined standards of assessment and treatment need to be developed and established to provide high accuracy and precision in diagnosis. Early recognition of FAI followed by subsequent behavioral modification (profession, sports, etc) or even surgery may reduce the rate of OA due to FAI.

Fig. 1A–B

A schematic drawing of a socket joint simulates combined FAI in (A) extension and (B) flexion. Pincer FAI (acetabular overcoverage) leads to deformation and fatiguing primarily at the labrum (red labrum) with visible indentation groove at the femoral neck. Cam FAI (femoral head asphericity) leads to shear forces primarily at the adjacent cartilage with disconnection from the subchondral bone (red line within cartilage).

Fig. 2A–D

(A) Acetabular dysplasia with a short and steep acetabular roof and a femoral head that has become unstable, migrating laterally (arrow) out of the acetabular socket. (B) The technique of MR arthrography depicts the intraarticular damage to the labrum with adjacent ganglion formation (arrow) caused by secondary joint incongruity and overload. (C) Femoroacetabular impingement (cam-type) (arrow) with a centered femoral head. (D) Shown is a cam FAI-induced acetabular rim fracture (arrow) and cartilage damage under a resulting intraosseous ganglion formation.

Fig. 3A–B

(A) Preoperative lateral hip radiographs of a 13-year-old girl with a moderate acute-on-chronic SCFE of her left hip. Surgical treatment was by open hip dislocation, subcapital realignment and internal fixation (three fully threaded 3-mm K-wires for subcapital stabilization, two 3.5-mm screws for the greater trochanter). (B) One year later, the patient was asymptomatic with united subcapital osteotomy as evident from the lateral hip radiograph.

Fig. 4A–C

Intraoperative photographs (hip arthroscopy) of a 34-year-old woman suffering from FAI due to mild femoral cam deformity and hypermobility. (A) The chondral/labral junction shows a small tear and fraying at the junction between labrum and cartilage and synovitis at the capsule and labrum as viewed from an anterior portal. (B) Performing peripheral hip arthroscopy, an insufficient femoral offset is present with a small area of central cartilage damage (arrow) treated by (C) femoral osteochondroplasty.

Fig. 5

The number of publications on FAI is almost exponentially increasing during the recent years. Note, however, the high number of review articles (white bars).