The impact of lunate type on scapho-trapezio-trapezoid arthritis in trapeziometacarpal osteoarthritis patients.

Background: Type II lunate has an extra facet with the hamate. This difference alters the biomechanics of the midcarpal joint, influencing the development of scapho-trapezio-trapezoid (STT) arthritis. We aimed to investigate whether, in patients with trapeziometacarpal (TMC) osteoarthritis (OA), involvement of the STT joint is associated with the lunate type.

Methods: A retrospective review was performed on 121 patients (mean age of 69 years) diagnosed with TMC OA. The lunate type was classified based on the presence of the facet detected on computed tomography images. The incidence of STT OA between patients with type I and II lunates was compared. A multivariate analysis was performed on factors associated with STT OA, such as age, sex, TMC OA severity, TMC joint stability, and the lunate type.

Results: 40.5% (n = 49) of wrists had type I lunate, and 59.5% (n = 72) had type II lunate. STT joint involvement was more common in type I lunate than type II lunate (26.5% vs. 8.3%, p = 0.007). Multivariate analysis indicated that age, stable TMC joint, and type I lunate were independently associated with OA involvement of the STT joint.

Conclusion: In patients with TMC OA, STT joint involvement was more common in type I lunate, contrary to the general population, where type II lunate is more common. Since STT OA is a source of pain after debridement, partial and complete trapeziectomy, implant arthroplasty, or arthrodesis, identifying the risk of STT OA can be important. Further studies are necessary to confirm our findings and to identify factors associated with the progression of pantrapezial disease in patients with TMC OA.