Editorial Commentary: Forty, Female, 15° (Tönnis Angle), and the Terrible Triad of Hip Instability Are Among the Predominant Predictors of Poor Outcomes After Hip Arthroscopy in Patients With Borderline Dysplasia.

Borderline hip dysplasia (BHD) remains challenging to treat, with conflicting outcomes reported for hip arthroscopy (HA) alone and periacetabular osteotomy. This may be in part because of heterogeneity in the definitions for BHD with respect to measurements such as the lateral center-edge angle, Tönnis angle, and anterior wall index. Recent research analyzing predictors of poor outcomes after HA alone for patients with BHD has shown that the predominant predictors of poor outcomes after HA included Tönnis angle of 15° or greater, age at surgery greater than 40 to 42 years, female sex, preoperative clinical arthritis, grade 3 or 4 articular cartilage changes to the femoral head or acetabulum, anterior wall index lower than 0.35, and labral debridement. In addition, we have investigated other predictors of failure of HA in the treatment of BHD and coined the term "the terrible triad of hip instability." This triad of risk factors includes (1) lateral center-edge angle lower than 25°, (2) presence of joint hypermobility (Beighton score > 4), and (3) presence of a hypertrophic labrum (labral width > 8 mm on magnetic resonance imaging).