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

BACKGROUND

Thumb carpometacarpal osteoarthritis (CMC1 OA) is a prevalent and disabling rheumatological condition. One impairment commonly described in the context of CMC1 OA is a loss of radial (RABD) and palmar (PABD) thumb abduction. Traditional goniometric measures are unreliable and poorly correlated with functional limitations. The intermetacarpal distance (IMD) method, using digital calipers, shows promise for better reliability, but its validity and the feasibility of using tape measures remain untested.

OBJECTIVE

To evaluate the construct validity, test-retest reliability, and precision of IMD-based thumb abduction measurements using calipers and tape in individuals with non-operative, radiographically confirmed CMC1 OA.

METHODS

Forty participants underwent standardized IMD assessments using both caliper and tape methods across two sessions, 2 weeks apart. Three trials were recorded per session. Reliability (ICC2,3), precision (SEM, MDC, MDC%), and construct validity (correlation with Michigan Hand Questionnaire [MHQ]) were analyzed.

RESULTS

Reliability (ICC2,3) ranged from 0.90 (PABD-tape, 1 trial) to 0.97 (RABD-caliper, 2-3 trials). All methods had acceptable precision (MDC% < 22); PABD-caliper (3 trials) showed excellent precision (MDC% = 9.1). RABD-caliper and RABD-tape showed strong, significant correlations with MHQ ADL scores (r = .38, p < .05; r = .40, p < .01). PABD methods showed weak or non-significant associations.

CONCLUSION

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.