Abstract
Femoroacetabular impingement (FAI) refers to a condition characterized by impingement of the femoral head–neck junction against the acetabular rim, often due to underlying osseous and/or soft tissue morphological abnormalities. It is a common cause of hip pain and limited range of motion in young and middle-aged adults. Hip preservation surgery aims to correct the morphological variants seen in FAI, thereby relieving pain and improving function, and potentially preventing early osteoarthritis. The purpose of this article is to review the mechanisms of chondral and labral injury in FAI to facilitate an understanding of patterns of chondrolabral injury seen on MRI. Preoperative MRI evaluation of FAI should include assessment of osseous morphologic abnormalities, labral tears, cartilage status, and other associated compensatory injuries of the pelvis. As advanced chondral wear is the major relative contraindication for hip preservation surgery, MRI is useful in the selection of patients likely to benefit from surgery.Teaching points • The most common anatomical osseous abnormalities predisposing to FAI include cam and pincer lesions.• Morphological abnormalities, labral lesions, and cartilage status should be assessed.• In cam impingement, chondral wear most commonly occurs anterosuperiorly.• Pre-existing advanced osteoarthritis is the strongest predictor of poor outcomes after FAI surgery.• Injury to muscles and tendons or other pelvic structures can coexist with FAI.
Highlights
Femoroacetabular impingement (FAI) refers to pathological contact between an abnormally shaped femoral head and acetabulum, which can result in early labral and chondral damage
Symptomatic FAI requiring surgery is more prevalent in high-level athletes than in individuals who participate in recreational sports activity [1]
Knowledge of the mechanisms of injury in FAI can facilitate an understanding of patterns of chondrolabral injury seen on MRI
Summary
Femoroacetabular impingement (FAI) refers to pathological contact between an abnormally shaped femoral head and acetabulum, which can result in early labral and chondral damage. Cam morphology appears on MRI as insufficient offset between the femoral head and neck, with a focal osseous bump or protuberance at the femoral head–neck junction, which can be assessed on axial or coronal images (Fig. 4) This is often associated with fibrocystic change at the femoral neck anterosuperiorly from chronic impingement, which can be seen on MRI as small cysts varying in diameter [36]. - Superior acetabular retroversion - True acetabular retroversion - Global acetabular overcoverage: coxa profunda or protrusio Mixed cam/pincer deformity Chondrolabral separation Labral tear or degeneration Intralabral ossification Chondral delamination Chondral loss Other signs of osteoarthritis: subchondral cysts, sclerosis, osteophytes Alpha angle Femoral anteversion Pubic symphysis stress reaction Adductor aponeurosis injury Tendinopathy and tendon tears: hip flexors, abductors, and hamstrings. This is seen on MRI as narrowing of the space between the lesser trochanter and ischial tuberosity, with edema, tear, or fatty atrophy of the quadratus femoris muscle [61]
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