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