AAOS: FABER distance test can be a simple screen for femoroacetabular impingement

FABER distance test can be a simple screen for femoroacetabular impingement (AAOS)

INTRODUCTION:   FABER (Flexion Abduction External Rotation) test is a clinical exam used to screen patients for sacroiliac joint and hip joint pathology. This test is widely used by orthopaedic surgeons, with good sensitivity but low specificity for detection of intra-articular pathologies. The FABER distance test (FDT) has been used as a diagnostic test for CAM impingement. The purpose of this study was to determine the correlation between the FABER distance test and other clinical test associated with CAM impingement.
METHODS: A prospective data registry was queried for patients with unilateral hip pain with complete physical exam and hip arthroscopy between 2007 and 2014. For FDT, the patient in the supine position, the leg was flexed and the heel of the affected leg is placed on the contra-lateral knee, just above the patella. The distance from the lateral femoral epicondyle of the knee to the exam table was measured while stabilizing the pelvis (FABER distance), on both legs. A positive test was defined as greater than 3cm difference between the sides. Alpha angle was measured on MRI. Range of motion was measured on both limbs prior to arthroscopy. Patients with bilateral symptoms, bilateral surgery, or bilateral alpha angles over 55 were excluded from the analysis. This study was IRB approved.
RESULTS: A total of 648 patients met the inclusion criteria. The average age was 36.1 (range 18 to 71). The average alpha angle was 69.8 (range 30 to 110), and the average FD difference was 5.9 (range -11 to 26)cm on the injured hip. The average flexion was 116 (SD=14), abduction was 46 (SD=12), adduction was 22 (SD=9), internal rotation was 31 (SD=15), and external rotation was 42 (SD=13) on the injured hip. Alpha angle was positively correlated with FD (r=0.292;p<0.01). The alpha angle in patients with a positive FDT test was 72.4 (SD=12) compared to 64.6 (SD=11) in patients with a negative distance test (p=0.001). The diagnostic odds ratio of the FDT was 3.1 times more likely to have an alpha angle 55 degrees or greater compared to those with a negative test [95CI:1.8 to 5.3]. The FDT had a positive predictive value of 93% [95%CI: 91% to 95%].
DISCUSSION AND CONCLUSION: This study presents a variation of the classic FABER test, the FABER distance test (FDT). In this cohort of patients, a patient with a positive test is three times more likely to have an alpha angle greater than 55 degrees. The FDT and range of motion measured in young athletes that practice vigorous sporting activities, provide a simple screening program to detect abnormal morphologies of the hip in a preclinical phase of FAI, without exposing patients to unnecessary imaging tests, avoiding the cumulative radiation doses and spending on other costly exams like MRI. Patients with positive tests could follow prevention programs avoiding “dangerous” positions such as squatting or not doing extreme movements in their respective sports. In conclusion, this study demonstrated that the FABER distance test is associated with the alpha angle. It can predict an alpha angle over 55 degrees, which defines FAI. The use of the FABER distance in screening programs can predict higher alpha angles without the use of expensive diagnostic imaging or radiation from radiographs.