Background: Physical modalities have been safely used for decades for pain relief and for reducing physical disability in the conservative treatment of knee osteoarthritis (OA). However, patients’ response to treatment is highly variable, which may be related to certain patient-related factors such as pain catastrophizing and depression. Objectives: This study aimed to evaluate the effects of pain catastrophizing and depression on physical therapy outcomes and to identify the baseline factors predictive of poor outcomes in patients with knee OA. Study Design: This research used a prospective, cohort, observational study design. Setting: The research took place in an outpatient physical therapy unit within a tertiary hospital in Ankara, Turkey. Methods: Eighty-nine patients with knee OA underwent 10 sessions of physical therapy. At baseline, depression and pain catastrophizing were evaluated using the Beck Depression InventoryII (BDI-II) and the Pain Catastrophizing Scale (PCS). The therapeutic efficacy of physical therapy was assessed based on the level of pain and disability using the Visual Analog Scale (VAS) and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Changes in the VAS score and WOMAC were evaluated at 2 and 6 weeks following physical therapy. A multivariate logistic regression analysis was conducted to identify the predictors of poor outcomes. Results: Patients with low pain-catastrophizing and low depression scores tended to demonstrate better improvement at weeks 2 and 6. The results of a multivariate logistic regression analysis showed that the significant outcome predictor for both pain and function at week 6 was the baseline PCS score. The baseline depression score was not an independent predictor of a clinically poor outcome. Limitations: This study is limited owing to the combined use of several physical therapy modalities and short follow-up. Conclusions: This study suggests that the baseline PCS score is a predictive factor of poor response to physical therapy in patients with knee OA. Considering this factor before therapy and taking the necessary precautions may improve the outcomes of physical therapy. Key Words: Catastrophization, central nervous system sensitization, depression, disability evaluation, knee osteoarthritis, pain, physical therapy modalities, transcutaneous electric nerve stimulation.

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