OBJECTIVES: The aim of this study was to assess the diagnostic value of pre-treatment inflammatory markers, including neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and lymphocyte-to-monocyte ratio (LMR), in distinguishing frozen shoulder (idiopathic stiff shoulder) from secondary stiff shoulder caused by shoulder pathologies. PATIENTS AND METHODS: Between February 2008 and August 2021, a total of 176 patients (64 males, 112 females
mean age: 54.0±9.9 years
range, 24 to 82 years) were retrospectively analyzed. The patients underwent analysis of surgical video recordings. Seventy-one patients with rotator cuff pathology were classified as having secondary stiff shoulders, while 105 patients without a history of trauma or cuff pathology were classified as having frozen shoulder (primary stiff shoulder). Demographic and preoperative laboratory data, including white blood cell count (WBC), C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), neutrophil, lymphocyte, monocyte, platelet counts, along with NLR, PLR, and LMR values, were evaluated. RESULTS: Significantly higher levels of WBC, neutrophils, and NLR were observed in patients with secondary stiff shoulder (p<
0.002 for all). In contrast, LMR (p=0.013) and platelet values (p=0.046) were found to be significantly higher in the frozen shoulder group. No statistically significant differences were observed between the groups regarding CRP, ESR, lymphocyte count, monocyte count, or PLR (p>
0.05). CONCLUSION: The NLR and LMR values have diagnostic utility in differentiating primary and secondary stiff shoulder. Elevated NLR values are associated with more acute inflammatory responses typical of secondary stiff shoulder, while higher LMR and platelet levels are linked to chronic and fibrotic processes observed in frozen shoulder.