Is There Any Difference Between Conical and Hemispherical Cups in Dual Mobility TMC Prostheses? A Prospective Clinical and Radiographic Study With a 5-Year Follow-Up

BACKGROUND: Dual mobility trapeziometacarpal arthroplasty was developed to address the limitations of trapeziectomy-based procedures and earlier prosthetic designs by preserving thumb motion while improving implant stability. Although hemispherical and conical trapezial cups are currently available, the influence of cup geometry on fixation reliability and implant survivorship remains uncertain. This study compared the clinical and radiographic outcomes of hemispherical and conical cups in patients with comparable trapezial anatomy. METHODS: A prospective observational study included 176 patients (192 hands) with Eaton-Littler stage II-III trapeziometacarpal osteoarthritis treated with dual mobility arthroplasty. Outcomes included pain (visual analog scale [VAS]), function (QuickDASH), grip and pinch strength, thumb range of motion, radiographic findings, complications, and implant survivorship over a maximum follow-up of 5 years. RESULTS: Both cup geometries produced significant improvements in pain, function, strength, and range of motion, with no significant differences in clinical or radiographic outcomes between groups. However, revision surgery due to cup mobilization occurred only in the hemispherical cup group, whereas no revisions were observed in the conical cup group during follow-up. CONCLUSIONS: Dual mobility trapeziometacarpal arthroplasty provides reliable mid-term outcomes regardless of cup geometry. Although functional and radiographic results were comparable, conical cups demonstrated a more consistent fixation profile and may represent a more reliable option for achieving durable implant stability, even in patients with adequate trapezial bone stock. LEVEL OF EVIDENCE: Level II, prospective comparative study.