A method to calculate the centre of the ankle joint: a comparison with the Vicon Plug-in-Gait model.
BACKGROUND
In gait analysis, calculation of the ankle joint centre is a difficult task. The conventional way to calculate the ankle joint centre is using the Vicon Plug-in-Gait model. The present study proposes a new model, which calculates the joint centre from two markers positioned over the medial and lateral malleoli (i.e. Two-marker-model).


METHODS
In order to compare the proposed model with Plug-in-Gait model, gait data from healthy and patient subjects were captured using a motion capture system. The ankle joint centres were calculated by the two models. A test-retest experiment was carried out to check reliability and repeatability for Two-marker-model.


RESULTS
Two ankle joint centres produced by two models were significantly different. The distances between two ankle joint centres were approximately 16.8 (mm), and the differences in the posterior-anterior, medial-lateral and inferior-superior directions were approximately 6.3, 7.7 and 8.2 (mm). Further error analysis highlighted that the probability of producing errors in Two-marker-model is lower than that in Plug-in-Gait model due to the Two-marker-model's simple and reliable marker positioning. The reliability and repeatability coefficients for the new model were greater than 0.9.


CONCLUSIONS
In principle, the Plug-in-Gait model is more likely to produce errors than the Two-marker-model, because the former employs multiple markers from the pelvis to calf to define the ankle joint centre with marker positions being very user-dependent. The results suggest that the Two-marker-model can be considered an alternative to Plug-in-Gait model for calculating ankle joint centre.
Nair
Syam Prabhakaran
SP
Institute of Motion Analysis and Research, Department of Orthopaedic and Trauma Surgery, TORT Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee, United Kingdom.
Gibbs
Sheila
S
Arnold
Graham
G
Abboud
Rami
R
Wang
Weijie
W
D000293:Adolescent; D000328:Adult; D000465:Algorithms; D000843:Ankle Joint / Q000033:anatomy & histology / Q000502:physiology*; D000886:Anthropometry; D001696:Biomechanical Phenomena; D002648:Child; D005260:Female; D005684:Gait; D006801:Humans; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D015203:Reproducibility of Results