A Simple Method for Measuring the Changeable Mechanical Action of Unloader Knee Braces for Osteoarthritis

Purpose

Today's orthotics should be designed to apply the external orthosis moment to the knee joint solely during the stance phase instead of the entire gait cycle. The aim of this study was to validate the reliability of a simple device for measuring forces at the leg–orthosis interface and describe the behavior of an innovating dynamic unloader knee brace built to interrupt its mechanical action during large knee flexion (swing phase of gait).

Methods

A compression testing machine was used to apply known (standard) forces to the device (modeled forces) and the results were compared.

Results

The low absolute mean bias ($～4\text{\%}$), the narrow agreement limits associated with the Bland and Altman analysis as well as the significant linear correlation ($r=0.99$; $p<0.001$) validate the agreement between standard and modeled forces. Likewise, the low standard error of measurement between trials ($～1.3\text{\%}$) and the intraclass correlation coefficient (1.00) reflect high test-retest reliability.

Conclusion

These results demonstrate the validity of the proposed device for measuring constraints induced by the dynamic unloader knee brace. An example of an application is provided through an orthosis moment calculation using kinematic data, which reveal a changeable mechanical action, necessary to improve comfort resulting in potentially better compliance.