Elsevier

Journal of Biomechanics

Volume 45, Issue 2, 10 January 2012, Pages 281-288
Journal of Biomechanics

The knee adduction moment measured with an instrumented force shoe in patients with knee osteoarthritis

https://doi.org/10.1016/j.jbiomech.2011.10.027Get rights and content

Abstract

The external knee adduction moment (KAdM) during gait is an important parameter in patients with knee osteoarthritis (OA). KAdM measurement is currently restricted to instruments only available in gait laboratories. However, ambulatory movement analysis technology, including instrumented force shoes (IFS) and inertial and magnetic measurement systems (IMMS), can measure kinetics and kinematics of human gait free of laboratory restrictions.

The objective of this study was a quantitative validation of the accuracy of the KAdM in patients with knee OA, when estimated with an ambulatory-based method (AmbBM) versus a laboratory-based method (LabBM). AmbBM is employing the IFS and a linked-segment model, while LabBM is based on a force plate and optoelectronic marker system. Effects of ground reaction force (GRF), centre of pressure (CoP), and knee joint position measurement are evaluated separately. Twenty patients with knee OA were measured.

The GRFs showed differences up to 0.22 N/kg, the CoPs showed differences up to 4 mm, and the medio-lateral and vertical knee position showed differences to 9 mm, between AmbBM and LabBM. The GRF caused an under-estimation in KAdM in early stance. However, this effect was counteracted by differences in CoP and joint position, resulting in a net 5% over-estimation. In midstance and late stance the accuracy of the KAdM was mainly limited by use of the linked-segment model for joint position estimation, resulting in an under-estimation (midstance 6% and late stance 22%). Further improvements are needed in the estimation of joint position from segment orientation.

Introduction

Osteoarthritis (OA) of the knee is a degenerative joint disease that occurs in a substantial percentage of the elderly population, causing limitations in daily activities. Abnormal or excessive joint loading increases the risk of development and the progression of OA (Andriacchi et al., 2004, Griffin and Guilak, 2005).

The net external knee adduction moment (KAdM) reflects the distribution and magnitude of the load transferred through the medial versus the lateral compartment of the tibiofemoral joint. It is mainly the product of the ground reaction force (GRF) and its lever arm to the knee joint, defined by the centre of pressure (CoP) and the knee joint position. These factors can be influenced by body mass, varus/valgus alignment of the knee joint, foot position, trunk position and walking speed. Patients suffering from medial compartment knee OA have often an increased KAdM during gait, compared to asymptomatic subjects (Foroughi et al., 2009).

The KAdM can be estimated in a gait laboratory, using force plates for three-dimensional (3D) recording of the GRF and CoP, and an optoelectronic marker system for 3D recording of the knee position (Cappozzo et al., 1995, Zatsiorsky, 2002). Despite the increasing interest in measuring the KAdM in knee OA, the clinical use of these laboratory-based systems is limited by the availability of well-equipped gait laboratories, line of sight problems with markers, restricted measurement volume, and constrained foot placement on the force plate (Schepers et al., 2007). Hence, there is a need for new approaches to gait measurements, free of such restrictions.

Instrumented force shoes (IFS) have been introduced for ambulatory assessment of GRF and CoP, as an alternative to force plates (Schepers et al., 2007). An inertial and magnetic measurement system (IMMS) has been used to measure the orientation of body segments from multiple strides when no gait laboratory is available (Luinge and Veltink, 2005, Roetenberg et al., 2007). However, in contrast to an optoelectronic system, direct measurement of segment or joint positions is difficult with the IMMS. When only orientations of body segments are available, positions have to be determined by linking segments to each other, using a linked-segment model based on segment orientation and fixed segment lengths (Faber et al., 2010b).

Although ambulatory movement analysis systems such as IFS and IMMS are promising, little is known about the accuracy of these systems in determination of the KAdM in patients with OA. Therefore, the general goal of this study was to investigate the effects of GRF, CoP and knee joint position measurement on the accuracy of the KAdM, when estimated with an ambulatory-based system in patients with knee OA (AmbBM: in particular the IFS and linked-segment model). This goal was specified in three main objectives: firstly, to study the accuracy of the IFS for measurement of the GRF and CoP during gait in patients with knee OA, in comparison with a force plate. Secondly, to study the accuracy of a linked-segment model based only on segment orientations (using optoelectronic data to simulate IMMS) for measurement of the ankle and knee joint positions, in comparison with direct position measurement via an optoelectronic marker system (actual IMMS were not implemented in this study, in order to restrict validation to the linked-segment model, and to exclude potential technical inaccuracies of the IMMS itself). Finally, to study the overall accuracy of the KAdM estimated with an IFS in combination with a linked-segment model (AmbBM), in comparison to the estimation of KAdM with a force plate and optoelectronic marker system (LabBM).

We hypothesised that the accuracy of the KAdM would mainly be affected by estimation of the knee joint centre when using the linked-segment model.

Section snippets

Subjects

Twenty patients with knee OA participated in the study (four males and sixteen females, age 61±8.8years (mean±standard deviation), body mass 84±16 kg, height 1.67±0.12 m). Patients had medial and/or lateral tibiofemoral radiographic OA, with a Kellgren/Lawrence of at least grade 1 (Altman and Gold, 2007, Kellgren and Lawrence, 1957, Altman et al., 1986), and were recruited from the patient population of the Reade Centre for Rehabilitation and Rheumatology (Amsterdam, the Netherlands). The

Results

Data of 30 legs were included in the analysis. The data of ten legs had to be excluded from analyses, due to unilateral knee OA, limited visibility of the optoelectronic markers, or technical problems with the IFS.

On average, the vertical GRF measured with the IFS was under-estimated by 2% compared to measurement with the force plate (Fig. 2, Table 1, Table 2). Medio-lateral GRF was 10% lower in early stance and 4% lower in midstance. Forward GRF of the IFS was 1–6% higher during the entire

Discussion

The objective of this study was to validate the KAdM using an ambulatory-based method in patients with knee OA. Effects of ground reaction force (GRF), centre of pressure (CoP), and knee joint position measurement are evaluated separately.

Conflict of interest statement

We certify that no party having a direct interest in the results of the research supporting this article has or will confer a benefit on us or on any organisation with which we are associated.

Acknowledgements

This work is part of the FreeMotion project (www.freemotion.tk) funded by the Dutch Ministry of Economic Affairs and Senter Novem. The authors wish to thank all the patients who participated in the study, Tanneke Vogelaar and Kim van Hutten for their assistance with the measurements, and Gert Faber for his advice on data analysis.

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1

Present address: School of Health, Glasgow Caledonian University, Cowcaddens Road, Glasgow G4 0BA, Scotland, UK.

2

Present address: Xsens Technologies B.V., P.O. Box 559, 7500 AN, Enschede. The Netherlands.

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