Reliability and Measurement Error of Instrument-Based Methods to Assess Ankle Evertor Strength: A Systematic Review

Accurate assessment of ankle evertor strength is essential for guiding rehabilitation and return-to-sport decisions after lateral ankle sprain, yet the reliability and measurement error of commonly used assessment instruments remain unclear.

To synthesize the literature evaluating the reliability and measurement error of instruments used to assess ankle evertor strength.

A systematic search was conducted in MEDLINE, Embase, Scopus, and DiTA without date restrictions. Studies assessing voluntary instrument-measured ankle evertor strength were included and evaluated using the COSMIN risk of bias tool. Two reviewers independently screened articles and extracted data on reliability (intraclass correlation coefficient or Pearson r) and measurement error (minimal detectable change, limit of agreement, or coefficient of variation). Sufficient reliability was defined as intraclass correlation coefficient or r ≥ .70, and sufficient measurement error was define as minimal detectable change, limit of agreement, or coefficient of variation ≤20%. Key protocol characteristics, including contraction velocity, knee position, stabilization methods, visual feedback, and verbal encouragement, were extracted.

From 4047 records, 23 studies were included. Instruments used were isokinetic dynamometers, hand-held dynamometers, vertical pulley, and custom instruments. Most participants were healthy (90%), while 10% had lateral ankle sprain. Methodological quality was rated adequate (35%), doubtful (39%), or inadequate (26%). Reliability was sufficient in 83% of extracted values, whereas measurement error was sufficient in 34%. Protocol parameters did not significantly influence test-retest reliability; however, contraction velocity, knee position, and verbal encouragement influenced test-retest measurement error, and knee position and stabilization influenced interrater reliability.

Isokinetic dynamometry, especially in isometric testing, demonstrated the most consistent reliability and the lowest measurement error. When unavailable, hand-held dynamometers offers a reliable field alternative for isometric testing. One-repetition maximum methods may be used for dynamic strength evaluation, despite higher measurement error. Protocol parameters influencing measurement error and interrater reliability should be standardized to improve measurement reproducibility.