Elsevier

Clinical Biomechanics

Volume 27, Issue 5, June 2012, Pages 520-523
Clinical Biomechanics

Brief report
Comparison of peak knee adduction moment and knee adduction moment impulse in distinguishing between severities of knee osteoarthritis

https://doi.org/10.1016/j.clinbiomech.2011.12.007Get rights and content

Abstract

Background

The peak knee adduction moment is a valid proxy for medial knee joint loading. However as it only measures load at one instance of stance, knee adduction moment impulse, a measure that takes into account both the magnitude and duration of the stance phase, may provide more comprehensive information. This study directly compared the abilities of peak knee adduction moment and knee adduction moment impulse to distinguish between knee osteoarthritis severities.

Methods

169 participants with medial knee osteoarthritis completed radiographic and magnetic resonance imaging, the Western Ontario and McMaster Universities Arthritis Index to assess pain and a three-dimensional gait analysis. Participants were classified using four dichotomous classifications: Kellgren–Lawrence grading, alignment, medial tibiofemoral bone marrow lesions, and pain.

Findings

When using Kellgren–Lawrence grade and alignment classifications, the area under the receiver operator curves were significantly greater for knee adduction moment impulse than for peak knee adduction moment. Based on analysis of covariance, knee adduction moment impulse was significantly different between Kellgren–Lawrence grade and alignment groups while peak knee adduction moment was not significantly different. Both peak knee adduction moment and knee adduction moment impulse distinguished between bone marrow lesion severities while neither measure was significantly different between pain severity groups.

Interpretations

Findings suggest knee adduction moment impulse is more sensitive at distinguishing between disease severities and may provide more comprehensive information on medial knee joint loading. Future studies investigating biomechanics of knee osteoarthritis should include knee adduction moment impulse in conjunction with peak knee adduction moment.

Introduction

Evidence suggests that the peak knee adduction moment (KAM) is a valid and reliable proxy for the load on the knee medial compartment (Birmingham et al., 2007, Zhao et al., 2007). It has been shown to be related to radiographic OA severity (Foroughi et al., 2009), some structural OA features (Creaby et al., 2010, Foroughi et al., 2009), and risk of OA disease progression (Miyazaki et al., 2002). Nevertheless, peak KAM only measures the load at one instance of stance and does not take into account the duration of loading, which can be influenced by gait speed (i.e. slower gait speeds longer stance time) .

Individuals with knee OA tend to walk at slower speeds (Al-Zahrani and Bakheit, 2002, Kaufman et al., 2001) and with a longer stance phase (Al-Zahrani and Bakheit, 2002, Astephen et al., 2008) compared to asymptomatic individuals. While peak KAM may be reduced at slower speeds (Robbins and Maly, 2009), the increased duration of stance phase and therefore the time under load can result in an overall increase in joint loading. A measure such as KAM impulse, which takes into account both the magnitude of load and the duration of stance, may provide more comprehensive information about medial knee joint loading. Thorp et al. (2006) first measured the KAM impulse in knee OA and found that while both peak KAM and KAM impulse increased with radiographic disease severity, only KAM impulse was significantly different between those with mild and moderate OA. Similarly, relationships between some OA structural features observed on magnetic resonance imaging (Bennell et al., 2010, Creaby et al., 2010) have been found with KAM impulse but not with peak KAM.

Thus evidence suggests that KAM impulse is a more sensitive measure of mechanical joint loading than peak KAM. However, studies to date have not directly compared the discriminatory ability of the peak KAM and KAM impulse. Given the interest in developing and testing interventions to reduce knee load for managing OA, this information will assist researchers in selecting the most appropriate KAM parameters for biomechanical studies. The purpose of this study was to examine whether KAM impulse during gait can better distinguish between individuals with varying degrees of knee OA severity, based on various measures of clinical and structural disease severity, than peak KAM.

Section snippets

Methods

200 individuals with painful radiographic medial knee OA were recruited for a clinical trial evaluating the efficacy of lateral wedge insoles (Bennell et al., 2011). Inclusion criteria were ≥ 50 years of age, average knee pain during walking > 3 on an 11-point scale (0 = no pain; 10 = maximal pain), pain over the medial knee compartment, medial compartment osteophytes or joint space narrowing on X-ray (Altman et al., 1995) and X-ray anatomical knee alignment ≤ 185o (corresponding to a mechanical axis

Results

Demographic characteristics for groups based on the four classification schemes are provided in Table 1.

When using either KL grade or alignment to classify severity, the AUCs for KAM impulse were significantly greater than the AUCs for peak KAM (P < 0.05) (Fig. 1, Fig. 2, Table 2). There were no differences in the AUCs for KAM impulse and peak KAM when participants were classified using either BMLs or WOMAC pain (Table 2).

Using unadjusted data, there were significant differences in KAM impulse

Discussion

While previous studies have noted differences in peak KAM and KAM impulse between disease severities in knee OA (Mundermann et al., 2005, Sharma et al., 1998, Thorp et al., 2006) our study is the first to statistically compare the discriminatory abilities of peak KAM and KAM impulse. The ROC analysis allows a direct comparison of the discriminatory abilities of these two discrete variables and provides important information on the validity of using these loading variables in knee OA research.

Conclusions

The findings indicate that KAM impulse is better able to distinguish between KL grades and severity of malalignment than peak KAM whereas both parameters were similarly able to distinguish between the presence and absence of BMLs. Neither peak KAM nor KAM impulse distinguished between those with more or less pain. These findings provide evidence of discriminative validity for KAM impulse and suggest that investigating KAM impulse, in addition to peak KAM, may provide more comprehensive

Acknowledgments

This study was supported by a project grant from the National Health and Medical Research Council (NHMRC Project #350297). KB is funded in part by an Australian Research Council Future Fellowship (#FT0991413). We wish to acknowledge the project personnel including Ben Metcalf and Georgina Morrow who assisted with the recruitment and database management.

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