The main objective of this study will be to compare the effects of 2 intra-articular injections of onabotulinumtoxinA with those of 1 intra-articular injection of onabotulinumtoxinA and 1 of normal saline and those of 2 intra-articular injections of normal saline on base-of-thumb pain at 6 months after the first injection.

The base of the thumb is a frequent location of osteoarthritis. Base-of-thumb osteoarthritis affects middle-aged and older individuals and results in base-of-thumb pain and limitations in hand-specific activities. For the medium and long term, evidence suggests that splinting could reduce pain and improve hand function. For the short term, a combination of conservative treatments is recommended, with small-to-moderate treatment effect. However, use of intra-articular treatments (e.g., glucocorticoids and hyaluronan) for the short and medium term is currently debated. Use of intra-articular botulinum toxin A injection as a pain modulator in joint diseases has recently raised interest. Botulinum toxin A is a neurotoxin produced by Clostridium botulinum that inhibits acetylcholine release into the synaptic cleft in cholinergic nerve terminals. Additionally, treatment with botulinum toxin A showed intrinsic antinociceptive effects in various animal models of joint diseases.

In a pilot single-centred randomized controlled trial of 60 participants with painful base-of-thumb osteoarthritis, the investigators compared the effects of a single intra-articular injection of onabotulinumtoxinA (Botox® ) with those of a single intra-articular injection of normal saline on base-of-thumb pain, and found a significant reduction in pain.

Several perspectives raised from this pilot study. Like in the treatment of spasticity, repeated courses of intra-articular injections onabotulinumtoxinA may be necessary to obtain sustained analgesic effects over time. A replication of these findings in a multicentred setting, analysis of cost-effectiveness and description of safety at longer term are also needed before the official recommendation of this treatment. In RHIBOT II, the investigators hypothesize that 2 ultrasound-guided intra-articular injections of onabotulinumtoxinA, as an add-on therapy to custom-made rigid splinting, could reduce base-of-thumb pain at 6 months after the first injection.

Inclusion Criteria:

• • Individuals aged at least 18 years;

  • Pain intensity of at least 30 on a self-administered 11-point pain numeric rating scale (0: no pain to 100: maximal pain);
  • Pain involving the base of the thumb;
  • X-ray evidence of trapezometacarpial osteoarthritis with at least two of the following items involving the trapezometacarpial joint: osteophytes, joint space narrowing, subchondral bone sclerosis, or subchondral cysts;
  • 1990 ACR classification criteria for hand osteoarthritis adapted to trapezometacarpial osteoarthritis.
  • Patient able to give written informed consent prior to participation in the study
  • Affiliation with a mode of social security (profit or being entitled).
  • Negative pregnancy test in women of childbearing potential

Exclusion Criteria:

• • Secondary osteoarthritis;

  • History of thumb surgery, inflammatory or crystal-associated rheumatic disease, or epilepsy;
  • Uncontrolled dysphagia, pneumonia, cardiovascular diseases, or clinical or subclinical signs of neuromuscular transmission disorders;
  • Contra-indication to onabotulinumtoxinA;
  • Neurological disorders involving the hands other than carpal tunnel syndrome;
  • Collagen disorders involving the hands;
  • Osteoarthritis predominating at the scaphotrapezial joint on x-ray;
  • Bilateral trapezometacarpial osteoarthritis without a predominant painful side;
  • Hand or wrist trauma for up to 2 months;
  • Intra-articular treatments for up to 2 months;
  • Use of IM, IV or oral corticosteroids for up to 2 months.
  • Protected adults (including individual under guardianship by court order)
  • Pregnant women and lactation; lack of contraception for women of childbearing potential
  • Patient participating in another investigational therapeutic study
  • Patient unable to speak and read french