51 patients between the ages of 35 and 70 years with chronic frozen shoulder (FS) were included in this retrospective, double blind trial in which patients were randomly allotted to undergo prolotherapy (PT; n=19) or normal saline injections (NS; n=20). The primary outcomes of interest was the change in the ratio of matrix metalloproteinase-1 (MMP-1) and tissue inhibitor of matrix metalloproteinase-1 (TIMP-1). The secondary outcomes of interest included the change in pain, assessed by numeric rating scale (NRS), and function, assessed by range of motion (ROM) and the disability of the arm, shoulder, and hand (DASH) score. All outcomes were measured at baseline and at 6 and 12 weeks. Results reveal a significant improvement in the MMP-1/TIMP-1 ratio in the PT group at 6 and 12 weeks. No significant between-group differences were found in terms of NRS or DASH scores at 6 and 12 weeks. No significant difference was observed between groups with regards to ROM.