The criteria for FAI from the Japanese hip societyAs a consequence of recent developments in hip arthroscopy, there has been a focus onintra-articular pathology of the hip, which has resulted in an increased number of reports onfemoroacetabular impingement (FAI). FAI has been promoted since 2008 in the annualmeetings of the Japanese hip society. However, the criteria for FAI, including physicalexaminations and radiographical findings, have remained unclear. Consequently, confusionregarding FAI diagnosis and treatment still prevails among Japanese hip surgeons andarthroscopists. Therefore, the Japanese hip society has proposed some FAI indicatorguidelines.
FAI was first discussed systematically by Ganz et al in 2003, when it was put forward as aprimary cause of osteoarthritis. Moreover, emphasis was placed on the pathology being acause of sports injuries, the concept of which was then rapidly developed globally. Thepathology of FAI consists of repetitive impingement on hip movement with bone abnormalityat the acetabulum or proximal femur and sequential labrum and/or cartilage damage.
Therefore, the distinctive findings of the acetabulum and proximal femur tend to be a focusfor the diagnosis of FAI. In overseas articles on FAI, the cross-over sign and α angle havebeen used most frequently for FAI diagnosis, but no consensus has been achieved regardingwhich FAI-related findings should be used. Such diagnostic findings based on observationsmay be employed in a variety of hip disorders with positive readings, leading to possiblemisdiagnoses. Ganz also mentioned that other hip disorders, which may cause cartilagedamage or secondary bone abnormality, should be excluded before considering FAI diagnosis.
The center-edge angle (CE angle) by Wiberg is described as being a selection criterion of FAIpatients. Patients with CE angle of less than 25 degrees are excluded. Moreover a CE angleof more than 40 degrees, or a CE angle of more than 30 degrees with acetabular roof obliquityof less than 0 degree, are indicators of pincer impingement. Some reports include an MRIlabrum evaluation as an additional indicator of FAI. However, labrum abnormality is oftendetected in the normal population, and is reported as a degenerative tear caused by aging.
Therefore, a labrum tear is unsuitable as a specific indicator of FAI.
In our country, owing to the high prevalence of acetabular dysplasia, the cause of groinpain may be correlated with many factors other than FAI. On treating hip disorders withJapanese-specific pelvic morphology, FAI should be carefully diagnosed. Otherwise, a facilediagnosis could induce inappropriate treatment and may cause hip instability to progressdue to underlying hip dysplasia.
Based on these considerations, the Japanese hip society recommends inclusion andexclusion criteria for primary FAI without secondary bone abnormality subsequent toobvious hip disorders.The criteria for primary FAIRadiographical findings・CE angle ≥ 25 degrees・The indicators for pincer impingement①CE angle ≥ 40 degrees②CE angle ≥ 30 degrees and ARO ≤ 0 degree③CE angle ≥ 25 degrees and positive cross-over sign*Accurate AP view of radiograph is necessary for evaluation.
・The indicators for cam impingementPrincipal indicator：α angle (≥55 degrees)Accessory indicator：Head-neck offset (< 8mm), Pistol grip deformity, Herniation pit（2 indicators including the principal indicator are necessary at least）*Plain radiograph, CT, and MRI are available.
Physical examination (Reference)・Positive impingement test・Positive Patrick’ sign (FABER test)・Decreased range of motion in flexion and internal rotationExclusion criteria・Previous hip disordersInflammatory diseases (Rheumatoid arthritis, Ankylosing spondylitis, Reiter’s syndrome, orLupus), Calcium pyrophosphate disease, Diffuse idiopathic skeletal hyperostosis, Bone tumor,Gout, Hemochromatosis, Osteonecrosis, Fractures around the hip (Fracture of theacetabulum, femoral head,or femoral neck). Damage to the cartilage from infection orresulting from penetration of a fixation device into the intraarticular space), Osteoarthritiswith obvious narrowing of joint space, Hip disorders from developmental or acquireddeformities that occurred in infancy or childhood (Developmental dyplasia, Slipped capitalfemoral epiphysis, Legg-Calve-Perthes disease, Epiphysial dysplasia, etc)・Previous hip surgeryDecision of diagnosisPrimary FAI is strongly suspected in patients with preceding radiographical findings,continuous clinical symptom, and referential information of physical examinations.