The Use of a Mechanical Model to Describe the Stiffness and Damping Characteristics of the Knee Joint in Healthy Adults

Background and Putpose. Stzmess is a common clinical complaint but is rarely quunttjied by clinicians. The purpose of this study was to determine the reliability of a relaxed oscillation test that yields sttfizess and damping coeficients of the knee. These coeficients describe the knee joint's resistance to bending and the time-dependent nature of that resistance. Suwects and M e t b h. Efects of age, gender, and knee position on these coeficients were messed in 96 healthy volunteers aged 20 to 79 years. Measures were based on the premise that the knee joint can be modeled as a damped spring. Oscillations of the knee were recorded using an electrogoniometer with the knee oscillating through about 45 and 75 degrees of knee flexion. Results. Zntraclm correlation coeficients revealed mod-erate to high reliability in the measurements taken three times In the same test session and on three separate days. Analysis of variance showed signtjicant in-creases in sttjkzess and damping coeficients in the male subjects as compared with the female subjects. Analysis of variance also suggested an age e$ect on stiiess coeficients at the 75-degree test position, with decreasing sttfizess with age. Both sttfizess and damping coeficients were sign@icantly smaller when measured at the 75-degree test position compared with the 45-degree position (Student's t test). C o n c l d n and Discusdon. These results demonstrate a reliable method of measuring knee joint stt@zess, and they correlate well with known morphological dtyerences related to age and gender. This measure may prove to be more use&l in evaluating the function of the knee than more commonly used m e m t s. It may also lead to a better understanding of how the knee functions in such activi-ties as locomotion. [Oatis CA. The use of a mechanical model to describe the stq-ness and damping characteristics of the knee joint in healthy adults. Phys Ther