A new bilateral closed chain assessment technique: methods and error analysis

The purpose of this paper is to present the Omnikinetic methodology for clinical evaluation of lower extremity function, to characterize its sensitivity to errors, and to present typical data for an assessment protocol.

A 5-bar, 2-degree of freedom linkage was used to model the geometry of the crank, pedal, and lower extremity. Two-degree force transducers at the pedal were used to calculate center of pressure and force applied at the foot. A Newton-Euler inverse dynamic model was used to calculate net joint torques and powers bilaterally of the ankle, knee, and hip. Ten subjects performed a high velocity evaluation protocol which served as the control. Error sensitivity was determined by adding instrumental error, hip translation, and segmental length errors to the collected data and comparing the outcome to the control.

All variables associated with instrumental error had mean errors under 4%. Mean errors associated with violations of the fixed hip assumption were under 15% for all variables. Mean errors associated with anthropometric measures were divided into two types: relative error (overall length unchanged, ratios of segments changed) and absolute (overall length changed, ratios of segment lengths unchanged). Relative anthropometric mean errors were under 5%. Absolute anthropometric mean errors were under 12%.

The Omnikinetic is a new tool for bilateral lower extremity evaluation that enables the whole lower extremity to be evaluated at the joint level. Instrumental accuracy was excellent. The instrument was most sensitive to violations of the fixed hip position assumption over the last 20 degrees of knee extension.