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01.12.2014 | Research | Ausgabe 1/2014 Open Access

Journal of Foot and Ankle Research 1/2014

Reliability and concurrent validity of a novel method allowing for in-shoe measurement of navicular drop

Journal of Foot and Ankle Research > Ausgabe 1/2014
Birgitte H Christensen, Kathrine S Andersen, Kristina S Pedersen, Britt S Bengtsen, Ole Simonsen, Simon L Kappel, Michael S Rathleff
Wichtige Hinweise

Electronic supplementary material

The online version of this article (doi:10.​1186/​1757-1146-7-12) contains supplementary material, which is available to authorized users.

Competing interests

MSR, OHS and SK were part of the group who invented the stretch-sensor used in the current study. The patent is owned by their employers, Aalborg University Hospital and Aarhus University and neither of the authors own any rights to the patent or technology. A patent application for the technology has been submitted under the application number PCT/DK2012/050341.

Authors’ contributions

All authors participated in planning of the study. BHC, KSA, KSP and BSB were responsible for study design and data collection. All authors participated in data analysis and dissemination. BHC, KSA and MSR drafted the manuscript while KSP, BSB, OS and SLK all helped finalize the manuscript. All authors read and approved the final manuscript.



Increased navicular drop is associated with increased risk of lower extremity overuse injuries and foot orthoses are often prescribed to reduce navicular drop. For laboratory studies, transparent shoes may be used to monitor the effect of orthoses but no clinically feasible methods exist. We have developed a stretch-sensor that allows for in-shoe measurement of navicular drop but the reliability and validity is unknown. The purpose of this study was to investigate: 1) the reliability of the stretch-sensor for measuring navicular drop, and 2) the concurrent validity of the stretch-sensor compared to the static navicular drop test.


Intra- and inter-rater reliability was tested on 27 participants walking on a treadmill on two separate days. The stretch-sensor was positioned 20 mm posterior to the tip of the medial malleolus and 20 mm posterior to the navicular tuberosity. The participants walked six minutes on the treadmill before navicular drop was measured. Reliability was quantified by the Intraclass Correlation Coefficient (ICC 2.1) and agreement was quantified by Limits of Agreement (LOA). To assess concurrent validity, static navicular drop was measured with the stretch-sensor and compared with static navicular drop measured with a ruler on 27 new participants. Linear regression was used to measure concurrent validity.


The reliability of the stretch-sensor was acceptable for barefoot measurement (intra- and inter-rater ICC: 0.76-0.84) but lower for in-shoe measurement (ICC: 0.65). There was a significant association between static navicular drop measured with the stretch-sensor compared with a ruler (r = 0.745, p < 0.001).


This study suggests that the stretch-sensor has acceptable reliability for dynamic barefoot measurement of navicular drop. Furthermore, the stretch-sensor shows concurrent validity compared with the static navicular drop test as performed by Brody. This new simple method may hold promise for both clinical assessment and research but more work is needed before the method can be recommended.
Authors’ original file for figure 1
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