A transducer to measure isometric elbow moments

Objective. The purpose of this study was to design and implement a transducer to measure accurately the isometric elbow moments produced by individuals with tetraplegia. Design. The device needed to be insensitive to off-axis moments and proximal joint motions and be capable of being used over a wide range of elbow and shoulder positions in an outpatient clinic setting. Background. Measurement of the smaller isometric moments produced by individuals with tetraplegia is especially sensitive to the errors that can be introduced by inaccurate lever arm determination, off-axis loads, and proximal joint motions. Devices traditionally utilized for quantifying isometric strength are difficult to implement for the spinal cord injured population. Methods. The elbow moment transducer consists of two four-bar parallelogram linkages joined by a lockable pivot. Strain gauges mounted on one beam of the parallelogram produce an output proportional to the elbow moment. Results. Calibration of the device indicates that it accurately quantifies isometric elbow moments over a range that is appropriate for evaluating elbow extension strength in individuals with tetraplegia. Conclusions. A device was developed and implemented that accurately quantifies isometric elbow moments over a range that is appropriate for evaluating elbow extension strength in individuals with tetraplegia. Relevance The ability to quantitatively evaluate elbow strength in persons with tetraplegia is useful for understanding and improving the clinical outcomes of rehabilitative interventions that involve the elbow.