Thumb Proprioception in Trapeziometacarpal Osteoarthritis

Inclusion Criteria (TMC OA group): * Voluntary participation * Radiographic Eaton-Littler stage I-IV confirmed by an orthopedic specialist * Symptom duration ≥6 months * Age 25-75 years * Pain intensity ≥4/10 on the Visual Analog Scale (VAS) during daily activities at assessment * Ability to actively perform ≥40° palmar abduction * Adequate cognitive capacity to understand and perform study procedures (for participants aged ≥65 years: Montreal Cognitive Assessment \[MoCA\] score ≥21) Inclusion Criteria (Control group): * Voluntary participation * No thumb pain * Age 25-75 years * No clinical signs of TMC OA * Negative provocation tests * Adequate cognitive capacity to understand and perform study procedures (for participants aged ≥65 years: MoCA score ≥21) Exclusion Criteria (TMC OA group): * Inability to abduct the thumb beyond 40° due to severe pain/deformity (especially advanced stage III-IV) * Acute trauma or prior surgery of the hand/wrist * Conservative treatment for hand/thumb pain in the same extremity within the previous 6 months * Current use of anti-inflammatory medication * Peripheral nerve disorders affecting proprioception (e.g., carpal tunnel syndrome, dorsal radial nerve irritation, cervical radiculopathy, double crush syndrome) * Concomitant upper-extremity musculoskeletal disorders (e.g., trigger finger, De Quervain's disease) * Generalized joint hypermobility (Beighton score ≥4) * Neuromuscular, systemic peripheral neuropathic, autoimmune, rheumatic, or infectious diseases * Active malignancy * Neurological conditions affecting pain perception * Visual impairment * Pregnancy Exclusion Criteria (Control group): -Exclusion criteria identical to the TMC OA group