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Validation of a one degree-of-freedom spherical model for kinematics analysis of the human ankle joint


During passive motion, the human tibiotalar (ankle) joint behaves as a single degree-of-freedom (1DOF) system [1, 2]. In these conditions, fibres within the ligaments remain nearly isometric throughout the flexion arc and articular surfaces nearly rigid. Relevant theoretical models are showing that the ligaments and the articular surfaces act together as mechanisms to control the passive joint kinematics [35]. Kinematic measurements and corresponding model predictions also revealed that the instantaneous screw axes of passive motion pass near to a single point, hereinafter called pivot point [5]. The present study investigates the extent to which this motion is spherical-like.

Materials and methods

A 1DOF Spherical Parallel Mechanism is analyzed, based both on joint anatomy and kinematics: the calcaneal-fibular and tibio-calcaneal ligaments are modelled as binary links of constant length, and relevant bones are connected by a spherical pair centred at the pivot point [5]. Geometrical data and reference motion were obtained from experiments in 5 amputated lower limbs, free from anatomical defects. Anatomical landmarks, articular surfaces and ligament origins and insertions were digitized. Passive dorsi-/plantar-flexion cycles were performed and relevant bone motion was recorded by a standard stereo-photogrammetric device. The pivot point was obtained by searching the point with the least mean squared distance from the instantaneous screw axes of passive motion. The closure equations were solved to obtain the simulated motion of the joints, to compare it with the original experimental motion.


In all specimens, the model replicated passive motion with a very good precision (Figure 1).

Figure 1
figure 1

The three displacements of a typical specimen, obtained from experiments (black), a previous model (red) and the spherical one (blue).


The passive motion of the ankle joints can be approximated well by a 1DOF spherical mechanism, despite the simple structure of this model. Replication of the original experimental motion can be a little worse than using previous mechanisms [4] (Figure 1), but computational costs, mechanical complexity and numerical instabilities are significantly reduced.


  1. O'Connor JJ, et al: Review: Diarthrodial Joints-Kinematic Pairs, Mechanisms or Flexible Structures?. Comput Methods Biomech Biomed Engin. 1998, 1: 123-150.

    Article  PubMed  Google Scholar 

  2. Leardini A, et al: Kinematics of the human ankle complex in passive flexion; a single degree of freedom system. J Biomech. 1999, 32: 111-118. 10.1016/S0021-9290(98)00157-2.

    Article  CAS  PubMed  Google Scholar 

  3. Leardini A, et al: A geometric model of the human ankle joint. J Biomech. 1999, 32: 585-591. 10.1016/S0021-9290(99)00022-6.

    Article  CAS  PubMed  Google Scholar 

  4. Franci R, et al: A new one-DOF fully parallel mechanism for modelling passive motion at the human tibiotalar joint. J Biomech. 2009, 42: 1403-1408. 10.1016/j.jbiomech.2009.04.024.

    Article  CAS  PubMed  Google Scholar 

  5. Franci R, Parenti-Castelli V: A one-degree-of-freedom spherical wrist for the modelling of passive motion of the human ankle joint. IAK 2008. 2008, Lima, 1-13.

    Google Scholar 

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Correspondence to Alberto Leardini.

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Open Access This article is published under license to BioMed Central Ltd. This is an Open Access article is distributed under the terms of the Creative Commons Attribution License ( ), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Sancisi, N., Parenti-Castelli, V., Baldisserri, B. et al. Validation of a one degree-of-freedom spherical model for kinematics analysis of the human ankle joint. J Foot Ankle Res 5 (Suppl 1), P13 (2012).

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