The goal of this clinical trial is to compare the efficacy of hip arthroscopy versus individualized conservative treatment in patients with borderline developmental dysplasia of the hip (BDDH), defined by a lateral center-edge angle (LCEA) of 18-25°. The main question it aims to answer is: which treatment approach, surgical or conservative, provides superior pain relief, functional recovery, and quality of life improvement at 12 and 24 months post randomization? Participants will be randomly assigned (1:1) to either standardized hip arthroscopy, comprising capsular management, acetabular rim limited trimming, labral repair, and Cam deformity correction when indicated; or a 3-month individualized conservative protocol including patient education, nonsteroidal anti-inflammatory drugs (NSAIDs) for 2-4 weeks, chondroprotective supplementation for 8 weeks, and supervised progressive exercise training. All participants will undergo follow-up assessments at baseline, 12, and 24 months. The primary outcome is the modified Harris Hip Score (mHHS). Secondary outcomes include patient-reported outcome measures (VAS pain, iHOT-12, SF-12, and patient satisfaction), clinical assessments, and safety monitoring.