Background: Knee osteoarthritis (OA) is a degenerative joint disorder that may cause pain, reduced muscle strength, and functional limitations. Physiotherapy interventions, including Transcutaneous Electrical Nerve Stimulation (TENS) and exercise therapy, are used to control pain, improve muscle performance, and support functional activity. Objective: This study aimed to describe changes in pain intensity, muscle strength, and functional ability following a physiotherapy program combining Transcutaneous Electrical Nerve Stimulation (TENS) and exercise therapy in a patient with bilateral knee osteoarthritis. Methods: This study used a case study design involving a patient with bilateral knee osteoarthritis. Data were collected through a series of physiotherapy assessments, intervention sessions, and subsequent evaluations. The physiotherapy program consisted of Transcutaneous Electrical Nerve Stimulation (TENS) and exercise therapy delivered over three treatment sessions. Changes in the patient’s condition were assessed through pain intensity, muscle strength using Manual Muscle Testing, and functional ability using the Jette Scale. Results: Changes were observed in several clinical parameters after three physiotherapy sessions. Pressure pain decreased from a score of 3 to 2, while movement-related pain decreased from 4 to 3. Muscle strength improved from grade 4 to grade 5. Functional ability assessed using the Jette Scale also changed, with the score decreasing from 22 at the initial assessment to 18 at the final evaluation. Conclusion: The physiotherapy program combining Transcutaneous Electrical Nerve Stimulation and exercise therapy was accompanied by improvements in pain intensity, muscle strength, and functional ability in a patient with bilateral knee osteoarthritis. After three treatment sessions, reduced pain was accompanied by improved muscle strength and a lower Jette Scale score, indicating better functional ability.