This is a randomized controlled trial comparing the Pyrocardan® implant (intervention group) with the standard ligament reconstruction and tendon interposition (LRTI) (control group). All Danish citizens with osteoarthritis of the thumb carpometacarpal joint referred to the orthopedic department at Copenhagen University Hospital in Herlev/Gentofte will be considered for participation in the trial. The following exclude from participation in the study: Below 40 years of age; cognitive or linguistic impairment; osteoarthritis of other carpal bones; previous surgery in the carpometacarpal joint; patients with rheumatoid arthritis. A total of 64 patients will be included. The primary outcome is the patient reported outcomes questionnaire; Quick-DASH. The secondary outcomes are patient-reported outcomes, functional outcomes, radiographic outcomes, readmission, complications, revisions. The patients are examined before surgery and 3, 6, 12 and 24 months after the operation. The patients are also contacted after 5 and 10 years.