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Background and purpose — Anterior knee pain is common after tibial nailing. Its origin is poorly understood. Injury of the infrapatellar nerve is a possible cause. In this randomized controlled trial we compared changes in knee pain after an infrapatellar nerve block with lidocaine or placebo in patients with persistent knee pain after tibial nailing. Patients and methods — Patients with chronic knee pain after tibial nailing were randomized to an infrapatellar nerve block with 5 ml 2% lidocaine or placebo (sodium chloride 0.9%), after which they performed 8 daily activities. Before and after these activities, pain was recorded using a numeric rating scale (NRS; 0–10). Primary endpoint was the change in pain during kneeling after the infrapatellar nerve block. Secondary outcomes were changes in pain after the nerve block during the other activities. Results — 34 patients (age 18–62 years) were equally randomized. A significant reduction of the NRS for kneeling pain with an infrapatellar nerve block with lidocaine was found compared with placebo (–4.5 [range –10 to –1] versus –1 [–9 to 2]; p = 0.002). There were no differences between the treatments for the NRS values for pain during other activities. Interpretation — Compared with placebo, an infrapatellar nerve block with lidocaine was more effective in reducing pain during kneeling in patients with chronic knee pain after tibial nailing. Our findings support the contention that kneeling pain after tibial nailing is a peripheral nerve-related problem.