Elsevier

Clinical Biomechanics

Volume 80, December 2020, 105232
Clinical Biomechanics

Quantifying varus thrust in knee osteoarthritis using wearable inertial sensors: A proof of concept

https://doi.org/10.1016/j.clinbiomech.2020.105232Get rights and content

Highlights

  • Frontal plane gyroscope data were extracted from a single triaxial inertial sensor.

  • Inertial data were associated with optical motion capture varus thrust measures.

  • Mid-thigh inertial sensor data was associated with knee adduction moment.

  • A single mid-thigh inertial sensor may be used to monitor outcomes in large studies.

Abstract

Background

Varus thrust during walking, visualized as excessive frontal plane knee motion during weight acceptance, is a modifiable risk factor for progression of knee osteoarthritis. However, visual assessment does not capture thrust severity and quantification with optical motion capture is often not feasible. Inertial sensors may provide a convenient alternative to optical motion capture. This proof-of-concept study sought to compare wearable inertial sensors to optical motion capture for the quantification of varus thrust.

Methods

Twenty-six participants with medial knee osteoarthritis underwent gait analysis at self-selected and fast speeds. Linear regression with generalized estimating equations assessed associations between peak knee adduction velocity or knee adduction excursion from optical motion capture and peak thigh or shank adduction velocity from two inertial sensors on the lower limb. Relationships between inertial measures and peak external knee adduction moment were assessed as a secondary aim.

Findings

Both thigh and shank inertial sensor measures were associated with the optical motion capture measures for both speeds (P < 0.001 to P = 0.020), with the thigh measures having less variability than the shank. After accounting for age, sex, body mass index, radiographic severity, and limb alignment, thigh adduction velocity was also associated with knee adduction moment at both speeds (both P < 0.001).

Interpretation

An inertial sensor placed on the mid-thigh can quantify varus thrust in people with medial knee osteoarthritis without the need for optical motion capture. This single sensor may be useful for risk screening or evaluating the effects of interventions in large samples.

Introduction

Knee osteoarthritis (OA) is a leading cause of disability among older adults (Guccione et al., 1994) and most commonly affects the medial tibiofemoral compartment of the knee joint (McAlindon et al., 1992). While age, sex, genetics, and other non-modifiable factors have been implicated in OA pathogenesis, gait patterns leading to increased or abnormal biomechanical joint loading also play a role and are frequently targeted in interventions (Felson et al., 2000). A common gait abnormality in people with medial knee OA is varus thrust, an excessive ‘bowing-out’ knee motion in the frontal-plane during ambulation as the limb accepts weight with a return towards a more neutral alignment in late stance and swing (Chang et al., 2004; Wink et al., 2017). Varus thrust has been reported to be present in 12% to 46% of individuals with medial knee OA and has been associated with radiographic disease severity (Chang et al., 2013) and progression (Chang et al., 2004). Cross-sectionally, those with varus thrust have a five-times greater odds for higher pain during walking and standing than those without it7. Individuals with knee OA who exhibit varus thrust also exhibit greater peak external knee adduction moments (EKAM) during gait (Chang et al., 2004), an indication of medial tibiofemoral load (Hurwitz et al., 1998) which has been reported to be a risk factor for future OA progression (Chang et al., 2015). Thus, interventions to reduce varus thrust may lead to reduced pain and slow structural worsening in individuals with medial compartment knee OA.

To aid in the development of effective interventions, it is important to accurately and reliably identify the presence of varus thrust. Typically, varus thrust is assessed through a subjective, visual evaluation of walking (Chang et al., 2004; Chang et al., 2010; Chang et al., 2013; Fukutani et al., 2016; Iijima et al., 2015; Iijima et al., 2017; Lo et al., 2012; Sharma et al., 2017). While these assessments are used clinically, they only provide a dichotomous categorization (present/absent) without any indication of severity. To overcome this limitation, optical motion capture has been used to objectively quantify biomechanical parameters as surrogate measures of varus thrust (Brown et al., 2018; Chang et al., 2004; Chang et al., 2013; Fukaya et al., 2015; Hunt et al., 2011; Kakihana et al., 2007; Kuroyanagi et al., 2012; Mahmoudian et al., 2016; Sosdian et al., 2016), including knee adduction velocity (Chang et al., 2013) and knee adduction angular excursion (Kuroyanagi et al., 2012). However, while optical motion capture provides detailed information on joint kinematics and kinetics, these systems require expensive equipment, time-consuming data collections run by skilled technicians, and a large calibrated measurement volume, making their clinical use infeasible. Additionally, analyses conducted in a laboratory environment do not always reflect typical walking in real-world settings (Brodie et al., 2016). In contrast, small, low-cost wearable inertial sensors have become increasingly popular for collecting biomechanical data in free-living conditions and may provide a convenient alternative to optical motion capture systems for quantifying varus thrust (Tao et al., 2012).

The primary aim of this study was to compare data from a single wearable inertial sensor to surrogate measures of varus thrust captured using optical motion capture technology during self-selected and fast speed walking in individuals with medial compartment knee osteoarthritis. We hypothesized that measures of frontal plane segment velocity from single inertial sensors placed on the thigh or shank would be significantly associated with measures from optical motion capture based on previously reported agreement between inertial sensor and optical motion capture kinematic and kinetic measures (Konrath et al., 2019; Zügner et al., 2019). For a secondary aim, we hypothesized that the inertial sensor measures would be associated with EKAM after adjusting for confounders.

Section snippets

Participants

Participants were recruited using advertisements online and in local newspapers from October 2017 to May 2019. Inclusion criteria were age between 45 and 80 years, body mass index (BMI) ≤ 40 kg/m2, and at least one knee meeting the American College of Rheumatology clinical or radiographic criteria for knee OA (Altman et al., 1986) with primarily medial tibiofemoral compartment involvement (medial joint space narrowing identified from weight bearing knee radiographs). Exclusion criteria were

Results

One hundred and sixty-three individuals underwent telephone screening, 82 passed the initial screening process, 59 underwent a radiographic screening visit, and 26 individuals (16 female) were deemed eligible for this study (Fig. 3, Table 1). The number of knees across analyses differed depending on useable data available for each inertial sensor (Fig. 3). Average values for each inertial and optical motion capture measure are reported in Table 2.

Both mid-thigh and mid-shank adduction velocity

Discussion

This proof-of-concept study showed that the measures from single inertial sensors were associated with surrogate measures of varus thrust obtained using optical motion capture. Furthermore, supporting our secondary hypothesis, mid-thigh adduction velocity was significantly associated with peak EKAM after adjusting for confounders. These results suggest that inertial sensors should be further investigated as a tool to objectively quantify varus thrust in clinical settings where optical motion

Conclusions

In this proof-of-concept study, we demonstrated a significant association between increases in thigh angular velocity derived from the gyroscope signal of a single inertial sensor and increases in surrogate varus thrust measures derived from an optical motion capture system. Furthermore, increased thigh angular velocity from this single inertial sensor was associated with increased peak EKAM after adjusting for confounders. These results highlight the potential of inertial sensors for

Declaration of Competing Interest

Ali Guermazi is Shareholder of BICL, LLC and Consultant to AstraZeneca, MerckSerono, TissueGene, Pfizer, Roche and Galapagos. Other authors declare no conflict of interest.

Acknowledgments

We would like to acknowledge the staff and students of the Movement & Applied Imaging Laboratory for their contributions to data collection and processing. We would also like to thank the participants for their contributions to this study and ASICS for donating the shoes used in this study.

Research reported in this publication was supported by the National Institutes of Health, under award numbers K01AR069720 and T32AR007598. The content is solely the responsibility of the authors and does not

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