Rotator cuff tears are one of the most common shoulder disorders and can lead to pain, weakness, and limited mobility. Although the clinical condition has been widely studied, its molecular mechanisms are still not fully understood. In this study, we analyzed the proteomic profile of synovial fluid in patients with full-thickness rotator cuff tears and compared the results to those from a control group. Proteomic analysis was performed on synovial fluid samples from seven patients with full-thickness tears and three patients with partial-thickness tears, who served as the control group. Label-free quantification using the MaxQuant platform identified 284 proteins at 1% FDR. Among them, CLEC3B (tetranectin) showed the most significant difference, with a fold change of approximately 40 and a p-value of 2.6 × 10⁻³. Gene ontology enrichment analysis revealed biological processes related to extracellular matrix remodeling, fibrinolysis, and inflammation. Given its known roles in extracellular matrix remodeling, tetranectin identified as a candidate for full-thickness rotator cuff tears, providing insight into pathological processes such as tendon degeneration and fatty infiltration.