We present the results of a 5 year prospective follow-up study on the functional outcome after total replacement of the trapeziometacarpal joint with the Ivory prosthesis (Memometal, Stryker Corporate, Kalamazoo, Michigan, USA) in 22 patients. The female to male ratio was 21:1 and the mean age was 66 (range 54-78) years. The mean follow-up period was 67 (range 60-77) months after operation. Patient satisfaction was high. The mobility of the operated thumb was restored to a range of motion comparable to the contralateral thumb. Key pinch and grip strength improved by 13% and 31%, respectively. Overall function, according to Quick Disabilities of the Arm, Shoulder and Hand (QuickDASH) score, improved by 59%. Pain decreased by 85% according to the numerical rating scale. Radiological evaluation revealed no loosening of the implant after 5 years except in one patient who required revision due to polythene wear with secondary joint instability. Another patient had asymptomatic polythene wear that required no revision but remains in follow-up. The 5 year overall survival of the prosthesis was 95%. These medium-term results suggest that the Ivory arthroplasty is a reliable option for treating advanced trapeziometacarpal arthritis, because it appears to give a very good functional outcome and has the potential for long-term survival rates.

II.

Osteoarthritis at the base of the thumb can cause severe pain, weakness, and deformity and can result in marked disability. Shear stress forces, due to weakening of the palmar beak ligament, can cause damage to the articular cartilage that can progress to degenerative osteoarthritis. 1 Initially, osteoarthritis of the trapeziometacarpal (TMC) joint should be treated conservatively. Surgery has been suggested in cases of pain that hampers the activities of daily life. In one study, patients treated conservatively had subjectively worse results than patients who underwent surgery. 2 Keywords ► trapeziometacarpal ► ball-and-socket prosthesis ► lengthening ► de Quervain AbstractBackground One of the surgical treatment options for trapeziometacarpal (TMC) joint arthritis is a prosthetic ball-and-socket replacement. One of the complications in the postoperative setting is de Quervain tendinopathy. Purposes Although this complication has been reported following a resection athroplasty, we questioned whether lengthening of the thumb following the Ivory (Memometal, Stryker Corporate, Kalamazoo, MI, USA) ball-and-socket arthroplasty could be a causal factor. Methods In a prospective study regarding the overall outcome of the Ivory prosthesis, we analyzed 96 cases (83 patients; 69 female, 12 male, 8 bilateral) of primary implanted Ivory prosthesis and the incidence of de Quervain disease during the first year following surgery. We found a particularly high incidence (17%) of de Quervain tendinopathy the first year following this ball-and-socket arthroplasty. We measured the lengthening of the thumb radiographically in the group presenting de Quervain and the asymptomatic group and compared this measure between the two groups. Results We did not find any measurable or statistically significant difference between the groups regarding lengthening. Discussion These findings suggest that lengthening of the thumb following ball-andsocket arthroplasty is not a causal factor in the development of de Quervain tendinopathy within one year after surgery.