Decision-making in the Borderline Hip.

Borderline acetabular dysplasia represents a "transitional acetabular coverage" pattern between more classic acetabular dysplasia and normal acetabular coverage. Borderline dysplasia is typically defined as a lateral center-edge angle of 20 to 25 degrees. This definition of borderline dysplasia identifies a relatively narrow range of lateral acetabular coverage patterns, but anterior and posterior coverage patterns are highly variable and require careful assessment radiographically, in addition to other patient factors. Treatment decisions between isolated hip arthroscopy (addressing labral pathology, femoroacetabular impingement bony morphology, and capsular laxity) and periacetabular osteotomy (improving osseous joint stability; often combined with hip arthroscopy) remain challenging because the fundamental mechanical diagnosis (instability vs. femoroacetabular impingement) can be difficult to determine clinically. Treatment with either isolated hip arthroscopy or periacetabular osteotomy (with or without arthroscopy) appears to result in improvements in patient-reported outcomes in many patients, but with up to 40% with suboptimal outcomes. A patient-specific approach to decision-making that includes a comprehensive patient and imaging evaluation is likely required to achieve optimal outcomes.