Thumb carpometacarpal (CMC) osteoarthritis (OA) is common, seen frequently in middle-aged and elderly women. While a variety of surgical treatments have been described with none superior to any other, there is no consensus on the optimal duration of postoperative immobilization. Immobilization following surgery is critical for wound healing, pain control, and aid with activities of daily living in the early recovery period, though the duration of this must be weighed against the negative impacts of immobilization, such as stiffness, contracture, and delay in return to full function. The information gained in this study may allow hand surgeons to use an evidence-based postoperative rehabilitation protocol. Thus, our goal is to compare varying durations of postoperative immobilization after thumb CMC arthroplasty in a randomized trial design. Subjects will be randomized to treatment with non-removable thumb spica plaster postoperative splint immobilization for 2 weeks or non-removable thumb spica plaster splint transitioned to cast for a total of 6 weeks immobilization following base of thumb arthroplasty. Patient-reported outcome measures (PROs) and objective metrics will be tracked in the follow-up period.