Center edge (CE) angle could not predict poor clinical outcomes after hip arthroscopy for older 30 year-old and under 30 degrees of CE angle patients. Narrow medial joint space, large femoral neck shaft angle and small vertical center anterior angle negatively predicted outcomes preoperatively.
Borderline hip dysplasia (BD) is typically defined as center edge (CE) angle measuring between 20 and 25 degrees. Nonetheless, a challenging clinical scenario is to determine whether a patient belongs to BD or not when the CE angle of a patient is near the 25 degrees.
To determine the predictors of worsen clinical outcomes after hip arthroscopy for patients older 30 year-old and with CE angle of less than 30 degrees.
Even between 25 and 30 degrees of CE angle, there is a possible risk of BD or of poor clinical outcome after hip arthroscopy.
From August 2010 to December 2012, 30 year-old and older patients who underwent hip arthroscopy by an experienced hip arthroscopist were enrolled in this study. We excluded patients younger than 30 year-old, with CE angle more than 30 degrees, with follow-up of less than 2 years and revision surgeries. Finally, forty patients were included. Modified Harris Hip Score (MHHS), Hip Outcome Score (HOS) for activities of daily living (ADL), HOS for sports and Vail hip score (VHS) were collected at the final follow-up. Patients who were converted to total hip replacement (THR) or with modified Harris Hip Score (MHHS) less than 60 points at the final follow-up were identified as failures.
At a mean of 3.5-years follow-up (range, 2.0 – 6.0), four hips (10%) were converted to THR, and the final MHHS were less than 60 points in 5 hips (13%). The outcome scores improved significantly in 31 hips (median, Wilcoxon signed-rank test, MHHS, 63 to 85, p < 0.005, HOS-ADL, 68 to 92, p < 0.001, HOS-sport, 37 to 76, p < 0.001, VHS, 40 to 75, p < 0.001). Comparing the failure group (9 hips, 23%) to the success group, there was a significant difference regarding preoperative medial joint space (failure group v success group, 3.0 mm v 3.6 mm, p < 0.05, Mann-Whitney U-test). No significant difference was found between failure and success group regarding age, CE angle, Sharp angle, weight bearing surface angle, presence of broken Shenton line, lateral or foveal joint space, alpha angle and prevalence of acetabular bone marrow edema or cyst in preoperative magnetic resonance imaging. Medial joint space narrowing (< 3.15 mm, odds ratio 8.3, p < 0.01, chi-square test), larger femoral neck shaft (FNS) angle (> 137.6 degrees, odds ratio 5.8, p < 0.03) and smaller vertical center anterior (VCA) angle in false profile view (< 16.6 degrees, odds ratio 5.4, p < 0.04) were identified as preoperative risk factors of poor clinical outcomes.
CE angle could not predict poor clinical outcomes after hip arthroscopy for older 30 year-old and under 30 degrees of CE angle patients. Narrow medial joint space, large FNS angle and small VCA angle negatively predicted outcomes preoperatively. These findings indicate that medial joint space, FNS angle and VCA angle are possible factors associated with poor clinical results in patients with CE angle between 25 and 30 degrees.