Intra-articular botulinum toxin A injection for painful base-of-thumb osteoarthritis: a double-blind, randomised, controlled, phase 3 trial (RHIBOT).

Background: Intra-articular botulinum toxin A injection might have analgesic effects in patients with joint diseases. We aimed to compare the effects of intra-articular botulinum toxin A injection with those of intra-articular saline injection for patients with painful base-of-thumb osteoarthritis.

Methods: RHIBOT was a double-blind, randomised, controlled, phase 3 trial conducted at Cochin Hospital, Paris, France. We recruited adult patients with x-ray evidence of trapeziometacarpal osteoarthritis who fulfilled the 1990 American College of Rheumatology criteria for hand osteoarthritis and reported a pain intensity score of at least 30 on an 11-point numeric rating scale (0: no pain to 100: maximal pain). Participants were randomly assigned (1:1), using a computer-generated randomisation list with permuted blocks of variable size (4 or 6), to receive an ultrasound-guided injection of either botulinum toxin A (50 Allergan units) in 1 mL of saline (experimental group) or 1 mL of saline alone (control group) in the trapeziometacarpal joint, in addition to custom-made rigid splinting. The primary outcome was the mean change from baseline in base-of-thumb pain in the previous 48 h on a numeric rating scale at 3 months after injection, analysed by intention to treat. This study is registered with ClinicalTrials.gov, NCT03187626.

Findings: Between Nov 2, 2018, and Nov 3, 2020, we assessed 370 individuals for eligibility and recruited 60 (16%) participants (mean age 64·9 years [SD 9·4], 47 [78%] women and 13 [22%] men), of whom 30 (50%) participants were randomly assigned to the experimental group and 30 (50%) to the control group. At baseline, base-of-thumb pain score was 60·0 of 100·0 (SD 15·9). At 3 months, the mean reduction in base-of-thumb pain was -25·7 (95% CI -35·5 to -15·8) in the experimental group and -9·7 (-17·1 to -2·2) in the control group (absolute difference -16·0 [-28·1 to -3·9]; p=0·043). Overall, 51 adverse events were reported in both groups: 27 (53%) in the experimental group and 24 (47%) in the control group. During follow-up, 14 (47%) participants in the experimental group and two (7%) participants in the control group reported mild transient motor deficit of the thenar muscle. No serious adverse events were reported.

Interpretation: Botulinum toxin A could be considered as a fast-acting, intra-articular therapy targeting chronic pain in individuals with base-of-thumb osteoarthritis. Future studies are needed to investigate the potential mechanism of the effects observed in this trial, to replicate our findings, and to assess the effects of repeated injections over time and their clinical effectiveness, including an analysis of cost-effectiveness.

Funding: Assistance Publique-Hôpitaux de Paris.