Methods: Case-series of five patients with six refractory painful TKAs (failed all conservative options including oral analgesics/anti-inflammatory medications) with pain duration >12-months received 100-units of IA-BoNT/A followed by re-injection of 200-units 8-12 weeks later for non-responders. Infection, prosthetic loosening and other surgically correctable causes of pain were ruled out. Data was collected prospectively: pain severity on 0-10 numeric rating scale (NRS), onset and duration of pain relief, patients' global assessment of change (7-point scale ranging from very much improvedvery much worse) and adverse effects.

Results: 5/6 painful TKAs had ³30% and 3/6 had ³50% reduction in Daytime pain (Table). 4/5 painful TKAs had ³30% and 3/5 had ³50% reduction in Night-time pain. 5/6 painful TKAs had “much improvement” on global assessment. Pain relief lasted 3-40 weeks. No increase in joint inflammation, periarticular muscle weakness, fever/fatigue, or other complications were noted.

Table. Pre- and Post-injection (IA-BoNT/A) pain on 0-10 Numeric Rating Scale

	Pre→ Post-injection Daytime Pain (% improvement)	Pre→ Post-injection Nighttime Pain (% improvement)	Onset of Pain Relief
Pt. 1: 73 M-R*‡	5 →3.5 (30%)	5 →1 (80%)	7 days
Pt. 1: 73 M-L	6 →3.5 (42%)	10 →1 (90%)	7 days
Pt. 2: 56 F-R	5 →2 (60%)	5 →2 (60%)	7 days
Pt. 3: 81 M-R‡	8 →7.5 (6%)	2.5 →2 (20%)	No relief
Pt. 4: 65 M-R	7.5 →3 (60%)	3 →2 (33%)	11 days
Pt. 5: 56 M-L	7 →1 (86%)	0 →0 (N/A)	6 days

*Patient 1 had bilateral knee injection;‡Patients who received the second injection; R, right; L, left; M, male; F, female.

Conclusion: I/A BoNT/A significantly decreased refractory prosthetic joint pain and appeared to be safe.