INTRODUCTION: Arthrofibrosis, which occurs in a substantial portion of the population, is a pathologic accumulation of scar tissue that presents in patients as a painful decrease in joint range of motion. Since an individual’s quality of life can be significantly impacted by arthrofibrosis and because there are limitations in current treatments, this thesis focuses on examining the use of the hormone relaxin to alleviate shoulder arthrofibrosis. METHODS: A set of 20 Sprague Dawley rats were given secondary shoulder contractures and separated into groups to examine the efficacy of relaxin using intravenous delivery, intra-articular delivery, and different treatment frequencies. The differences across groups were examined through mechanical range of motion testing as well as histologic sampling. RESULTS: Multiple doses of intra-articular injections of relaxin showed a complete return to the normal range of motion (P < 0.01) when compared with the surgical control, whereas other delivery methods and frequencies failed to show meaningful improvements. This was further confirmed in histologic analysis through the lack of fibrotic adhesions within the capsular space after multiple intra-articular relaxin treatments when compared with the surgical control. DISCUSSION: Although significant improvements to range of motion were seen after multiple doses of intra-articular relaxin, potential tissue degradation was also observed within the joint space after histologic examination. Further research is necessary to fully understand the proper dosing needed to avoid potential negative side effects caused by excess use of relaxin.