Eichelberger P.1,2, Blasimann A.1, Woodtli S.I.1, McEvoy J.C.1, Bohnenblust M.1, Kaufmann E.1, Pohl J.1, Krause F.3, Baur H.1
1Bern University of Applied Sciences, Health, Physiotherapy, Bern, Switzerland, 2Graduate School for Cellular and Biomedical Sciences, University of Bern, Bern, Switzerland, 3University Hospital Bern, Inselspital, Department of Orthopaedic Surgery, Bern, Switzerland
Background: Although multi-segment foot models offer dedicated approaches to detect intrinsic foot kinematics, they lack of clinical applicability due to complexity, preparation time and cost-intensive instrumentation. We therefore propose to measure intuitive parameters to assess dynamic foot function: navicular drop (NDrop, difference between the minimum navicular height (NH) during stance and NH at heel strike), navicular rise (NRise, difference between NH at toe off and minimum NH during stance), navicular drift (NDrift, maximum medial navicular deviation during stance), as well as foot lengthening (FLen) and shortening (FShort).
Purpose: The study aimed to explore reliability and movement coupling of vertical navicular motion, with the medial navicular drift and foot length change during stance.
Methods: A set of four reflective spherical markers (1st and 5th metatarsal heads, heel, navicular tuberosity) was applied bilaterally on twenty healthy subjects. Ten trials were averaged to calculate representative stance phase time series from which NDrop, NRise, NDrift, FLen and FShort were extracted. The test session was repeated on the same day and one week apart to assess intra- and interday reliability, respectively. The reliability was evaluated with the Bland-Altman method and the parameter relationship was explored by linear regression.
Results: The relative intra- and interday bias was similar and did not exceed 6%. Relative repeatability of NDrop, FShort and NRise was between 12% and 18% for intraday and between 37% and 38% for interday. Relative repeatability of NDrift and FLen was 27% for intraday and 72% and 75% respectively for interday. Significant relationship was found between NRise and NDrop and between FLen and NDrop (p 0.05), possible relationship was uncovered between NDrift and NDrop and weak relationship was found between FShort and NRise. R2 values were below 0.32.
Conclusion(s): We assessed reliability and relationship of several intrinsic foot motion parameters based on healthy subjects during level walking. Bias was generally low and was not considered relevant for judging reliability. Relative repeatability was the discriminating reliability parameter and allowed comparison. It quantifies the minimal detectable change relative to the expected amplitude of the respective parameter. Repeatability reached larger values for the interday compared with the intraday condition. Medial navicular drift and foot lengthening were found to be less reliable parameters than navicular drop, navicular rise and foot shortening. The limited number of subjects and the fact that the status healthy could have bounded the range of values, may be explanations for the relatively poor fit of the linear model.
Implications: The regression analysis supports the common notion of foot kinematics during stance: the foot pronates and lengthens while the arch flattens under loading followed by supination and arch rise during push-off. Contrary, a relationship between foot shortening and arch rise during push-off could not have been detected. To decide whether the reliability is sufficient or not, effect sizes must be considered. Minimal changes in navicular drop, foot shortening and arch rise must overcome 20% on the same day and 40% between days in order that the effects are measurable in the evaluated setting.
Funding acknowledgements: This work was founded by the Swiss National Science Foundation (Project number 140928).
Topic: Human movement analysis
Ethics approval: The study was approved by the ethics committee of the canton of Bern.
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