BACKGROUND: Osteoarthritis (OA) is a frequent cause of pain and disability, affecting half of the world’s population aged 65 years or older. Due to experienced pain and limitations, OA patients generally spend most of their waking hours sedentary and fail to adhere to physical activity (PA) recommendations. As a result of living together with OA patients, their partners might adopt a sedentary lifestyle. This study investigates the change in habitual PA and sedentary behavior (SB) in patients and their partners one year after the patients’ total joint replacement (arthroplasty) and inpatient rehabilitation. METHODS: This is a follow-up of a prospective cohort study including 24 older couples (69.3± 7.8 years, gender ratio 11:13) consisting of OA patients (17 hip OA, 7 knee OA) and their partners. The participants’ habitual PA and SB were assessed by means of synchronous accelerometry (16h per day, 4– 7 days) and additional self-report. RESULTS: Although the partners (∼ 6300 steps per day) were significantly more active than the patients (∼ 4800 steps per day) before arthroplasty, their lifestyle was still classified “low active”. Irrespective of the method used, the PA and SB parameters of patients and partners were significantly correlated before arthroplasty (accelerometry: r≥ 0.333, p≤ 0.001; self-report: r≥ 0.569, p≤ 0.004). Following the patients’ arthroplasty, no improvement in PA or SB was observed either in the patients or their partners. A detailed evaluation of accelerometric data on hourly basis revealed no change in behavior for both groups. Furthermore, their everyday activities remained correlated (accelerometry: r≥ 0.418, p≤ 0.001; questionnaire: r≥ 0.554, p≤ 0.005). CONCLUSION: One year post-arthroplasty and inpatient rehabilitation neither the OA patients nor their partners had changed their PA or SB. Their everyday physical activity was still strongly intertwined. Further research is needed to determine why behavior change does not occur even though the prerequisites are in place.