 The primary outcome is: 1 proportion with clinically meaningful change in pain severity on 0-10 scale 2 months after IA injection. The choice of 2-month for primary end-point is based on previous observations from open-label case series in painful TKA. Secondary outcomes will be assessed at each efficacy follow-up FU visit. The duration of the trial is 6-months to capture the duration of pain relief. Based on other trials of Botulinum toxin, we expect the peak effect between 2-8 weeks and expect the effect to wear off between 2-4 months. Therefore, for all analyses except duration of pain relief, the efficacy time-points 2 wk, 4 wk, 2 month and possibly 3- or 4-month depending on duration of pain relief will be used. Secondary outcomes include: 1 clinically meaningful pain relief 2-point or 30 decrease in pain severity 0-10 scale; 2 change in pain severity at 2 months and at all efficacy time-points; 3 percent with Minimal Clinically Important Improvement on Western Ontario MacMaster Arthritis Index WOMAC pain and function sub-scales at 2 months and at all efficacy time-points; 4 amount and duration of pain relief; 5 patient and physician global assessment of response at 2 months and at all efficacy time-points; 6 QOL assessed by WOMAC and Short-form 36 SF-36 scores at 2 months and at all efficacy time-points; 7 change in function by Timed Stands Test TST and Timed-up-and-go TUG tests at 2 months and at all efficacy time-points; 8 change in dose of analgesics during the study. We will determine time to onset of and duration of pain relief and time to improvement in function. Safety will be assessed by structured interview form for adverse effects, sensory and manual muscle strength testing, and index joint examination for swelling, erythema and tenderness. 