Decreased Synovial Fluid Ghrelin Level Is Associated With Acute Cartilage Injury in Patients With Anterior Cruciate Ligament Tear

BACKGROUND: Ghrelin, an amino acid hormone secreted primarily from the stomach, can regulate bone metabolism, regulate inflammation via suppressing proinflammatory cytokines, and suppress expression of matrix metalloproteinases (MMPs). PURPOSE: To measure synovial fluid levels of ghrelin in young patients with anterior cruciate ligament (ACL) tear to assess the role of ghrelin as a potential biomarker for cartilage injury. STUDY DESIGN: Controlled laboratory study. METHODS: This study included 120 patients who underwent ACL reconstructionbetween January 1, 2016, and May 31, 2021. We categorized 60 patients with acute cartilage injury (International Cartilage Regeneration & Joint Preservation Society grade 2 or 3) as the acute group and 60 patients with no acute cartilage injury as the nonacute group, with the healthy contralateral knee of each patient acting as the control group (n = 120). Synovial fluid samples were collected from the knees in the operating room before ACL reconstruction. We assessed the inflammatory biomarkers interleukin (IL)-6, MMP-1, MMP-9, and MMP-13, as well as serum ghrelin level and Mankin score, and results were compared between the 3 study groups with the Mann-Whitney U test. RESULTS: Lower serum ghrelin levels in the synovial fluid were found in the acute group compared with the nonacute group and healthy controls (232.4 vs 434.4 vs 421.5 pg/mL, respectively; P < .001). Ghrelin level in the synovial fluid was significantly and positively correlated with IL-6 (r = 0.4223; P < .0001), MMP-13 (r = 0.3402; P < .0001), and Mankin score (r = 0.1453; P = .0244). CONCLUSION: In patients with ACL injury, ghrelin synovial fluid was significantly differently expressed in patients with cartilage injury and no cartilage injury. CLINICAL RELEVANCE: Ghrelin synovial fluid has the potential to be a biomarker to predict acute cartilage injury in patients with ACL injury.