Inter- and Intra-observer Agreement of Visual Estimation, Goniometric and Radiographic Measurement of Passive Thumb Metacarpophalangeal Joint Hyperextension

Background: Reliable methods for measuring range of motion is important for hand therapists. Currently, there is no gold standard for the measurement of thumb metacarpophalangeal joint (MCPJ) hyperextension. We hypothesised that visual and goniometric measurements of thumb MCPJ hyperextension vary greater than 10 degrees from radiographic measurements, and between observers.Methods: Twenty-six fresh-frozen hands were measured by a senior orthopaedic resident and fellowship trained hand surgeon. Passive thumb MCPJ hyperextension was measured by visual estimation, goniometry and axis measurement on a lateral thumb radiograph. Raters were blinded to each other's and their own prior measurements. Descriptive statistics were recorded for measurement type and inter-observer agreement using a two-way intra-class correlation coefficient (ICC). Intra-observer agreement was calculated using concordance correlation coefficient (CCC). Bland-Altman plots identified trends, systemic differences or potential outliers.Results: Mean measurements for both raters were similar for visual estimation and radiographic measurements. Mean goniometric measurements were twice as high for Rater B, and closer to radiographic measurements. For both raters, mean radiographic measurements were 10 degrees greater than the other two methods. For inter-rater agreement, measurements were within 10 degrees most frequently with radiographic measurement, then visual estimates, and least by goniometer measurements. Rater B had better agreement comparing visual and goniometric to radiographic measurements.Conclusions: Radiographic measurement has the best inter-observer agreement and precision for evaluating passive thumb MCPJ hyperextension, especially considering adjunct corrective procedures when performing a soft-tissue basal joint arthroplasty. Rater experience improves precision, but there is still poor agreement between visual estimates and goniometer measurements compared to radiographic measurements, as the former two underestimate hyperextension by 10 degrees. Development of a standard method of clinical measurement is needed to improve reliability.