Loading of the knee joint during activities of daily living measured in vivo in five subjects

Abstract

Detailed knowledge about loading of the knee joint is essential for preclinical testing of implants, validation of musculoskeletal models and biomechanical understanding of the knee joint. The contact forces and moments acting on the tibial component were therefore measured in 5 subjects in vivo by an instrumented knee implant during various activities of daily living.

Average peak resultant forces, in percent of body weight, were highest during stair descending (346% BW), followed by stair ascending (316% BW), level walking (261% BW), one legged stance (259% BW), knee bending (253% BW), standing up (246% BW), sitting down (225% BW) and two legged stance (107% BW). Peak shear forces were about 10–20 times smaller than the axial force. Resultant forces acted almost vertically on the tibial plateau even during high flexion. Highest moments acted in the frontal plane with a typical peak to peak range −2.91% BWm (adduction moment) to 1.61% BWm (abduction moment) throughout all activities. Peak flexion/extension moments ranged between −0.44% BWm (extension moment) and 3.16% BWm (flexion moment). Peak external/internal torques lay between −1.1% BWm (internal torque) and 0.53% BWm (external torque).

The knee joint is highly loaded during daily life. In general, resultant contact forces during dynamic activities were lower than the ones predicted by many mathematical models, but lay in a similar range as measured in vivo by others. Some of the observed load components were much higher than those currently applied when testing knee implants.

Introduction

The knee joint is loaded by external forces (ground reaction force, masses and acceleration forces of foot and shank). Their sum is counterbalanced by the forces acting across the joint, i.e. the tibio-femoral contact forces, muscle forces and forces in soft tissue structures. The ‘net moment’, caused by the external forces, is additionally counterbalanced by the moments exerted by muscles, soft tissues, contact forces and frictional forces. Muscle and joint contact forces can be analysed using gait data together with musculoskeletal modelling techniques e.g. inverse dynamics and static optimization. However, large variations of reported loading exist. Using gait analysis and a mathematical model, Morrison calculated joint forces of 200–400% BW (percent of body weight) during level walking (Morrison, 1970). Whilst more recently forces of approximately 310% BW were reported using a similar computational approach (Taylor et al., 2004), other studies calculated contact forces of up to 710% BW during level walking and even 800% BW for downhill walking (Costigan et al., 2002, Kuster et al., 1997, Seireg and Arvikar, 1975).

To overcome uncertainties of mathematical models, telemetrized implants were developed to measure the joint contact forces in vivo. Taylor and co-workers measured loads in the shaft of a distal femoral replacement (Taylor et al., 1998). The estimated forces in the knee joint of 220–250% BW during level walking were smaller than those determined analytically. Recently, load data measured by instrumented total knee replacements during activities of daily living in vivo became available (D'Lima et al., 2005, D'Lima et al., 2006, D'Lima et al., 2007; Mündermann et al., 2008). One year post-operatively peak tibial forces were 280% BW (level walking), 290% BW (stair ascending), 330% BW (stair descending) and 264% BW (chair rise). Most data is restricted, however, to total compressive forces measured in one subject. Complete six component load data during walking and stair climbing, measured in two subjects in vivo, was only published by Heinlein et al. (Heinlein et al., 2009). Peak axial forces of 208–276% BW (level walking) and 327–352% BW (descending stairs) were reported.

The aim of this study was to examine the tibio-femoral contact forces and moments in the knee joint during daily life in vivo in a more representative cohort of 5 subjects and to examine inter-individual differences. All six load components (3 forces, 3 moments) acting on an instrumented tibial tray were measured.