Thumb carpometacarpal palmar and radial abduction in adults with thumb carpometacarpal joint pain: Inter-rater reliability and precision of the inter-metacarpal distance method

Study Design: Psychometric study of inter-rater reliability. Introduction: Functional use of the thumb can be limited in individuals with thumb carpometacarpal (CMC) osteoarthritis(OA), especially in the presence of a thumb adduction contracture. Goniometry is a common method of assessing palmar and radial abduction of the thumb base and can be used as a method of determining effectiveness of an intervention for adduction contracture. However, goniometry for the assessment of these motions has been shown to have low to moderate reliability. The intermetacarpal distance (IMD) measurement method has been shown to be the most reliable for measuring CMC palmar abduction in individuals with healthy hands but has not been studied in persons with thumb CMC OA. Purposes: The purpose of this study was to determine the inter-rater reliability and precision of the inter-metacarpal distance method for measuring palmar and radial abduction in persons with symptoms of thumb CMC OA. Methods: Two trained hand therapists utilized the IMD method to measure palmar and radial abduction in the affected hands of 22 subjects (28 thumbs) with a physician-confirmed diagnosis or positive provocative test consistent with a diagnosis of thumb CMC OA. The intraclass correlation coefficient (ICC_2,2) was used to assess inter-rater reliability of the IMD method. To determine the precision of the measurements, the standard error of measurement (SEM), minimal detectable change (MDC), and MDC percent were calculated. Findings were supplemented with descriptive data on the IMD values as well as descriptive data on the sample. Results: Intraclass correlation coefficients for both radial and palmar abduction were found to be >.75, indicating excellent reliability. The precision of the IMD measurements were acceptable-to-excellent as evidenced by MDC% values of <30% and <10% for radial and palmar abduction respectively. Conclusions: We present a new method for measuring thumb radial abduction. The inter-metacarpal distance method has excellent inter-rater reliability and acceptable-to-excellent precision when measuring palmar and radial abduction in individuals with or suspected to have thumb CMC OA. Currently, it is the most reliable tool for measuring thumb abduction.