Brief reportComparison of peak knee adduction moment and knee adduction moment impulse in distinguishing between severities of knee osteoarthritis
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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2022, Journal of BiomechanicsCitation Excerpt :There is a strong body of literature linking the KAM peak to medial knee osteoarthritis outcomes, but the KAM peak may not be the optimal mechanical target for disease-modifying interventions. The KAM impulse provides information about cumulative loading, and some studies report that it is a better predictor of osteoarthritis severity and progression (Bennell et al., 2011; Kean et al., 2012) than the KAM peak. Additionally, the KAM does not capture changes in muscle force that occur from kinematic and coordination changes (Charlton et al., 2018; Richards et al., 2018; Uhlrich et al., 2018; Walter et al., 2010) that often accompany FPA modifications; increases in the force generated by knee-crossing muscles induced by gait modifications counteract the medial-compartment-offloading effect of reducing the KAM.