Subchondral Phosphate Injection During Hip Arthroscopy Safely Treats Acetabular Bone Marrow Lesions in Early Osteoarthritis

<b>Introduction</b>: Arthroscopy for femoroacetabular impingement (FAI) yields inferior outcomes when subchondral edema and cystic degeneration are present. Subchondroplasty (SCP), which involves injecting osteoconductive calcium phosphate into Bone Marrow Lesions (BMLs), may enhance subchondral structural support and can be performed alongside hip arthroscopy. <b>Materials and Methods</b>: This single-center retrospective study included patients who underwent SCP for acetabular BMLs during primary hip arthroscopy for FAI from March 2019 to March 2023. Clinical and radiographic outcomes were recorded at ≥2-year follow-up. Survivorship with treatment failure as the endpoint was assessed using Kaplan-Meier analysis. <b>Results</b>: Thirty-four patients were evaluated at a mean 3.1-year follow-up. No perioperative, early, or late complications or adverse events occurred. No bone substitute migration or intra-articular extravasation was seen. Four patients (11.8%) showed osteoarthritis progression and required conversion to total hip arthroplasty; no intraoperative issues with acetabular preparation were encountered. All clinical scores improved significantly (<i>p</i> < 0.001), and 82.4% returned to sport. <b>Conclusions</b>: SCP performed during hip arthroscopy appears safe in selected patients with early hip osteoarthritis and BMLs. Calcium phosphate injection may help restore subchondral integrity and load distribution, though the independent contribution of SCP beyond standard arthroscopic management remains uncertain.