RecruitingDrug trialEfficacy of Two Ultrasound-guided Intra-articular Injections of Botox® Combined With Custom-made Rigid Splinting in Painful Base-of-thumb Osteoarthritis.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.