Chapman, Reagan S.

Abstract Background: Prior studies have evaluated the efficacy of subchondroplasty for the management of subchondral cysts of the knee, yet few studies to date evaluate minimum 2-year outcomes following subchondroplasty of the acetabulum. Purpose: The purpose of this study was to evaluate minimum two-year outcomes following arthroscopic subchondroplasty for the treatment of acetabular subchondral cysts and to identify variables associated with total hip arthroplasty (THA) conversion following subchondroplasty. Study Design: Cases Series, Level of Evidence IV. Methods: A retrospective review of prospectively maintained data was performed on patients who underwent primary hip arthroscopy May 2019 to September 2021 by a single surgeon. Consecutive patients who underwent subchondroplasty for acetabular subchondral cysts with minimum two-year follow-up were identified. Demographics, magnetic resonance imaging (MRI), intraoperative findings, and clinical outcomes were evaluated. Cross-sectional area of the subchondral cysts was measured on MRI. Clinical outcomes included Hip Outcome Score–Activities of Daily Living (HOS-ADL), HOS–Sports Subscale (HOS-SS), international Hip Outcome Score-12 (iHOT-12), and visual analog scale for pain (VAS-Pain). Conversion to THA was recorded. The patients who converted to THA were compared to those who did not. Continuous variables associated with THA conversion were analyzed with receiver operating characteristic (ROC) curves to identify thresholds associated with THA conversion. Results: Twenty-nine patients underwent subchondroplasty for acetabular subchondral cysts with minimum two-year follow up (age: 48.2±11.1 years, body mass index: 29.9±6.6kg/m2, 52.0% female). The THA-free survivorship rate was 62.1%. Patients who achieved THA-free survivorship had smaller subchondral cysts (88.5±59.2 mm2 vs. 147.1±54.8, P=0.013) and a lower prevalence of high-grade femoral head chondral defects (16.7% vs. 54.5%, P=0.048) compared to patients who converted to THA. ROC analysis identified patients with a subchondral cyst <133 mm2 were 21.3 times more likely to achieve THA-free survivorship (P=0.001). The THA-free survivors demonstrated significant improvements across all measured PROs (P≤0.015). Conclusions: Subchondroplasty for acetabular subchondral cysts demonstrated a 62.1% THA-free survivorship at minimum 2-year follow-up, with survivors demonstrating significantly improved PROs. Patients with cysts <133 mm2 were 21.3 times more likely to achieve THA-free survivorship than patients with larger cysts. Keywords: Hip, Acetabulum, Subchondral Cysts, Subchondroplasty