Assessing active thumb palmar and radial abduction in persons with thumb carpometacarpal osteoarthritis via intermetacarpal distance methods: an exploration of validity, reliability, and precision

Caliper and tape-based IMD measurements offer similar reliability, but averaging multiple trials improves precision. RABD-IMD methods demonstrate moderate construct validity, supporting their use in clinical assessment of CMC1 OA. Standardized, repeatable IMD assessments may enhance monitoring and care planning in thumb CMC1 OA. Key Points In persons with carpometacarpal osteoarthritis: • Caliper and tape intermetacarpal distance measures of thumb radial and palmar abduction demonstrate excellent test-rest reliability and acceptable precision. • Averaging two or three intermetacarpal distance measurements is recommended over a single measure due to superior precision. • Radial abduction (via the intermetacarpal distance) is strongly associated with self-reported disability and may be more clinically meaningful than palmar abduction.