BORDERLINE DYSPLASIA: ARE THESE HIPS ONLY MILDLY UNCOVERED?

Abstract

Background: Controversy surrounds classification and treatment of hips with a lateral center-edge angle (LCEA) between 18° and 25°. It remains undetermined as to whether open or arthroscopic procedures are best used to treat patients with borderline dysplasia. We hypothesized that patients with hip pain and borderline acetabular dysplasia have different features of acetabular morphology as determined by other relevant radiographic measures beyond the LCEA. Methods: A retrospective review of patients undergoing hip preservation surgery between January 2010 and December 2015 with either periacetabular osteotomy(PAO) or hip arthroscopy with a LCEA between 18° and 25° was performed. Anteroposterior, Dunn lateral and false profile radiographs were used to measure LCEA, Tönnis Angle, anterior center edge angle (ACEA), anterior (AWI) and posterior (PWI) wall indexes, the femoral epiphyseal acetabular roof (FEAR) index, joint space width, crossover sign, posterior wall sign, P/A index, and femoral alpha angle. An agglomerative hierarchical clustering analysis was then performed on the continuous radiographic variables to identify different subtypes of hip pathomorphology among this patient cohort. There were sex-specific trends in hip morphology. Therefore, we proceeded to perform separate cluster analyses for each sex. Results: Ninety-nine patients underwent surgery in the study period, 77 (78%) were female, and 81 (82%) of these had complete radiographic images for cluster analysis. Mean age was 22.6 years. Hip arthroscopy was performed in 41% of patients and periacetabular osteotomy was performed in 59% of patients. The ACEA (45%), FEAR Index (34%), and AWI (30%) were the most commonly abnormal radiographic parameters among all patients. In female patients, the ACEA (55%), FEAR Index (42%), and AWI (34%) were the most commonly abnormal radiographic parameters. In male patients, an insufficient PWI (48%) was the most common radiographic abnormality. For females, we identified three clusters representing different patterns of hip morphology: impingement morphology; lateral acetabular deficiency, and anterolateral acetabular deficiency (Table 1A). For males, we identified three clusters: postero-lateral acetabular deficiency with global cam morphology, postero-lateral acetabular deficiency with focal cam morphology, and lateral acetabular deficiency without cam morphology (Table 1B). Conclusions: A comprehensive evaluation of radiographic parameters in patients with LCEA 18-25° identifies sex-specific trends in hip morphology and shows a large proportion of dysplastic features among these patients. A thorough evaluation of all pelvic morphology, not just lateral coverage, should be considered when indicating these patients for hip preservation surgeries. Further studies are needed to investigate the outcomes of patients within each of the identified clusters to determine optimal treatment options for each group. [Table: see text][Table: see text]