Purpose <p>To determine the efficacy of [¹⁷⁷Lu]Lu-Hydroxyapatite radiosynovectomy (RSV) in patients with refractory chronic inflammatory arthritis of the knee joint.</p> Materials and methods <p>Overall, 24 knees in 22 patients with refractory chronic inflammatory arthritis were enrolled in this prospective study. All patients were assessed clinically for pain, tenderness, range of motion, analgesic intake, Oxford Knee Score, and scintigraphically based on blood pool activity on three-phase bone scan. Various scores were assigned to clinical these parameters. RSV of the knee joint was done using intra-articular injection of [¹⁷⁷Lu]Lu-Hydroxyapatite. Patients were assessed clinically at 1 and 3 months, and scintigraphically at 3 months using blood pool index on three-phase bone scan. Patients were categorised as responders and non-responders on the basis of change in percentage of cumulative scores.</p> Results <p>Out of 24 knees, 18 knees were responders and 6 knees were non-responders at 3 months. There was a significant improvement in clinical scores at 1 month post-RSV, which persisted at 3 months post-RSV (<i>p</i> &lt; 0.05). However, the change in blood pool activity on three-phase bone scan was not significant. Reported adverse effects were mild and not significant.</p> Conclusion <p>This study confirmed the safety and efficacy of [¹⁷⁷Lu]Lu-Hydroxyapatite radiosynovectomy for patients with chronic inflammatory knee joint arthritis refractory to conventional medical treatment.</p>