Positive FABER distance test is associated with higher alpha angle in symptomatic patients

Abstract

Purpose: The purpose of this study was to determine the diagnostic value of the flexion abduction external rotation (FABER) distance test (FDT) for the diagnosis of cam-type femoroacetabular impingement (FAI) as defined by alpha angle.

Methods: For this study, 603 patients with symptomatic, unilateral femoroacetabular impingement were included. Patients with symptoms of hip instability, bilateral symptoms, bilateral surgery, or bilateral alpha angles over 55 were excluded from the analysis. A positive FDT was defined as a difference of 4 cm or more between hips. A pathological cam was defined as an alpha angle of 78° or greater.

Results: The average age was 36.4 ± 12 years, with 344 males and 259 females. Faber distance of the injured hip was correlated with age at surgery (rho = 0.148; p < 0.001). Alpha angle on the injured hip was positively correlated with injured hip FABER distance (rho = 0.276; p < 0.001). The average alpha angle in patients with a positive FABER distance test was 74° (SD = 11°) compared to 68° (SD = 8°) in patients with a negative distance test (p = 0.001). The sensitivity of the FDT to diagnose pathological cam was 0.848 (0.79-0.89) with a negative predictive value of 86% (81-90%).

Conclusion: This study demonstrated that the FABER distance test is correlated with the alpha angle and is a good diagnostic exam for pathological cam-type FAI as defined by and alpha angle equal to or greater than 78°.

Clinical relevance: FABER distance test is a simple test that can be used as a screening test to decide if FAI should be suspected and further testing is needed.

Level of evidence: III.

Keywords: Alpha angle; Diagnosis; FABER; Femoroacetabular impingement.