"This 6-month randomized, placebo-controlled, double blind trial will compare a single intra-articular (IA) injection of 100 units of Botulinum Toxin A (BoNT/A) to placebo for improvement in pain, function and quality of life (QOL), and safety in patients with painful total knee arthroplasty (TKA). Patients will be recruited at the Minneapolis VA Medical Center. Patients will be eligible if they are over age 18, have TKA, have pain ≥6/10 on 0-10 numeric rating scale (NRS) and are not candidates for revision surgery.

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.

At visit #1, after informed consent and screening for inclusion/exclusion criteria, patients will undergo: index joint X-ray, laboratory tests; history, physical examination, index joint pain history, comorbidity and medication history; patient pain assessments, WOMAC and SF-36; and blinded index joint, neurological examination, TST and TUG tests. 50 patients will be randomized to receive either IA BoNT/A 100 units or sterile saline in the index joint. FU phone interviews at 2 and 4-weeks will include pain assessments, WOMAC, patients' global assessment and adverse effects. Interim visits at 2, 3 and 4-months will be identical to visit #1, but will also include patients' and physicians' global assessment and there will be no joint injection. End of study visit at 6 months will be identical to interim visits with the addition of index joint X-ray and laboratory tests.

Main analyses will include patients with unilateral TKAs. Sensitivity analyses will be done by including patients with bilateral knees, accounting for correlatedness of observations. Multiple analysis of variance, mixed model regression analyses and/or generalized estimating equations will be used for analysis of continuous and categorical outcomes respectively. Chi-square tests will be used to compare frequency of adverse events. Analysis will be intention-to-treat.