Accuracy and reliability of a smartphone application for measuring the knee joint angle.
Keisuke Ishii, Hiroyuki Oka, Yuji Honda and 10 others
PMID 34083881WHAT IT FOUND
A Japanese smartphone photo app measured mannequin knee angles as closely as a standard goniometer.
It was repeatable across examiners and over three days, but this was tested only on fixed mannequin knees, not on patients.
Key findings
01The app and the standard goniometer gave closely matching knee angle measurements, and the Bland-Altman plot showed no bias either above or below the standard line.
02Different examiners using the app produced almost perfect agreement on single and averaged mannequin knee measurements.
03The same examiners using the app produced almost perfect agreement when remeasuring the same fixed knee joints three days later.
STILL TO COME
How it was doneWhat they foundWhat it means for PTsWhat it means for OTs
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What it does not show
No human participants were measured, so it did not test whether the same accuracy and reliability would occur in humans. The mannequin knee angles were fixed at 0 to 100 degrees, so deep flexion beyond 100 degrees was not shown. Only hinge knee joints were tested, so ball joints such as the shoulder and hip were not shown to be measurable with the app. The mannequin lower extremity did not have an axis corresponding to either the femur or tibia, so the basic axis and movement axis were measured based on appearance. The app will only be accurate if the photo is taken perpendicularly to the plane containing the joint's movement axis, and inaccurate if the three points are not accurately determined. The examiners had never used the app before the study and received instructions just before measurement.
Declared interests
Keisuke Ishii receives grants from Naradewa Inc, which is named with the app in the paper. The remaining authors declare no conflict of interest.
The easy way to misread this
Do not conclude that the app is accurate for measuring a patient's knee angle. It was tested only on fixed mannequin knees, and the authors say human testing is still needed.