To Örebro University

Introduction: The Assessment of Capacity for Myoelectric Control (ACMC) is an observation-based tool that evaluates ability to control a myoelectric prosthetic hand [1]. Validity evidence led to ACMC version 2.0, but test - retest reliability and minimal detectable change (MDC) of ACMC have never been evaluated. For instruments that have an evaluative purpose, such as ACMC, the MDC is a useful clinical value to suggest whether a change is due to measurement error or true change. Investigation of rater agreements in this version was also needed because it has new definitions in certain rating categories and items.

Methods: Upper limb prosthesis users (n=25, 13/12 male/female, 15/10 congenital/acquired; mean age 27.5, range 7-72, years) performed one standardized activity twice, 2–5 weeks apart. Activity performances were video-recorded and assessed by two ACMC raters. The item raw scores were converted to Rasch interval ability measures. Ordinal data were analyzed by weighted κ; interval data were analyzed by intraclass correlation coefficient (ICC) and Bland–Altman limit of agreement (LOA) method.

Results: For test–retest reliability, ICC2,1 was 0.94. Average weighted κ was 0.76 and percentage agreement (PA) was 85%. In individual items, weighted κ agreements were fair to excellent (0.52・1.00) and PAs were ≥6・100%. MDC95 was ≤.55 logits (1 rater) and 0.69 logits (2 raters). All MDC95 values were ≤5% of the total ability logit range. In the Bland-Altman plot the upper and lower LOA were 0.86 and -0.88 respectively. All except one participant were within the 95% LOA. For inter-rater reliability, weighted κ agreements were fair to excellent in both sessions (0.44–1.00), and ICC2,1 was 0.95 (test) and 0.92 (retest). Intra-rater agreement (rater 1) was excellent (ICC3,1 0.98). The weighted κ values of the test session were all >0.80 and the PAs for each item were ≥6%.

Conclusion: The results of the present study demonstrate different aspects of the reliability of ACMC 2.0. Based on these results, we can recommend ACMC as a tool to follow the progress of users in controlling their myoelectric prostheses. The MDC is clinically useful for ACMC raters as a guideline when following the client’s changes over time.