A 52-year-old woman with a 10-year history of osteoarthritis of the right knee presents with progressive pain, morning stiffness lasting 30 minutes, and functional limitation affecting her daily activities. She has failed conservative management including NSAIDs, physiotherapy, and intra-articular corticosteroid injections over the past 2 years. On examination, there is crepitus, restricted range of motion, and varus deformity. X-rays show Kellgren–Lawrence grade 3 changes. What is the most appropriate next step in management?