Inter-rater and intra-rater reliability of the fluid goniometer for measuring active knee flexion in painful knees; correlations do not mean agreement.
Wilton Remigio, Nancy Tsai, Leonivic Layos and 1 others
PMID 28626305WHAT IT FOUND
Fluid goniometer knee flexion measurements were highly consistent between raters, but agreement was poor: two raters could differ by 36.8 degrees.
A change must exceed 18 degrees to be real when therapists differ.
Key findings
01Intra- and inter-rater ICCs for fluid goniometer knee flexion were both 0.97.
02The SEM was 6.6°, and 95% limits of agreement spanned +19.3° to -17.5° (range 36.8°).
03The smallest detectable difference was 18°, so measurements by different therapists were not interchangeable.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The study used 25 patients and 35 knees, so the agreement estimates are based on a small sample. The raters had no previous experience with the fluid goniometer, although they practiced for two days. There was no comparison with the universal goniometer or with pain-free knees, so the error cannot be separated from the instrument or the painful knee. Measurements were only of active knee flexion in the prone position, with the lower leg free to oscillate.
The easy way to misread this
Do not conclude that a 0.97 ICC means the fluid goniometer is interchangeable between therapists or that small changes are real. The limits of agreement were +19.3° to -17.5°, and the smallest detectable difference was 18°.