In the current work, we used an isotopically labeled high resolution LC MS/MS-based proteomics approach to analyze the protein profile of synovial fluid at 6 and 12 months after ACL transection in untreated and repaired porcine knees. Our primary aim was to determine how the synovial fluid proteome differs between the two groups in an effort to identify candidate proteins that may be associated with the development of posttraumatic OA. We hypothesized that the development of macroscopic cartilage damage following surgical ACL transection would be accompanied by differential changes in synovial fluid proteome in untreated knees compared to repaired joints.