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Centre of Rotation of the Human Subtalar Joint Using Weight-Bearing Clinical Computed Tomography - PubMed

  • ️Wed Jan 01 2020

Centre of Rotation of the Human Subtalar Joint Using Weight-Bearing Clinical Computed Tomography

Marta Peña Fernández et al. Sci Rep. 2020.

Abstract

Accurate in vivo quantification of subtalar joint kinematics can provide important information for the clinical evaluation of subtalar joint function; the analysis of outcome of surgical procedures of the hindfoot; and the design of a replacement subtalar joint prosthesis. The objective of the current study was to explore the potential of full weight-bearing clinical computed tomography (CT) to evaluate the helical axis and centre of rotation of the subtalar joint during inversion and eversion motion. A subject specific methodology was proposed for the definition of the subtalar joint motion combining three-dimensional (3D) weight-bearing imaging at different joint positions with digital volume correlation (DVC). The computed subtalar joint helical axis parameters showed consistency across all healthy subjects and in line with previous data under simulated loads. A sphere fitting approach was introduced for the computation of subtalar joint centre of rotation, which allows to demonstrate that this centre of rotation is located in the middle facet of the subtalar joint. Some translation along the helical axis was also observed, reflecting the elasticity of the soft-tissue restraints. This study showed a novel technique for non-invasive quantitative analysis of bone-to-bone motion under full weight-bearing of the hindfoot. Identifying different joint kinematics in patients with ligamentous laxity and instability, or in the presence of stiffness and arthritis, could help clinicians to define optimal patient-specific treatments.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1

An illustration of the subtalar joint. The ligaments on the outside of the joint have been divided and the talus (B) has been reflected. The calcaneus (A) is visible from above. The three articular facets of the subtalar joint are illustrated, the posterior facet (green); the middle facet (pink) and the anterior facet (blue). The head of the talus articulates with the navicular bone (D) anteriorly at the talonavicular joint (C). The soft tissue ligamentous restraints are labelled. Image by Catherine Sulzmann, Medical Artist.

Figure 2
Figure 2

3D rendering of the subtalar joint in inverted, neutral and everted positions in the left foot of one subject from a (a) lateral, (b) superior and (c) posterior view. The calcaneus is shown fixed to demonstrate the relative motion of the talus in the three configurations. Lateral opening and closing of the sinus tarsi can be observed in inversion and eversion relative to neutral position, respectively (red arrows). The lateral tubercle in the talus rotates towards the sustentaculum tali from inversion to eversion (yellow arrows), whereas the lateral malleolar surface approaches the sinus tarsi (blue arrows).

Figure 3
Figure 3

Local 3D displacements in talus and calcaneus from neutral to inversion and neutral to eversion position in the left foot of one subject from an (a) lateral, (b) superior and (c) anterior view as computed using DVC. Higher displacements in the talus can be observed in the inverted foot compared to the everted one.

Figure 4
Figure 4

Boxplot distribution of the mean displacements over the entire bones for both (a) calcaneus and (b) talus from neutral-inversion (N-I) and neutral-eversion (N-E) positions. p-values from two-sided Wilcoxon signed-rank test are reported in each plot.

Figure 5
Figure 5

Graphic representation of the helical axis for subtalar motion from inversion to eversion in the (a) left and (b) right feet of the eight healthy subjects. To highlight the differences in axis orientation, all helical axes are grouped by overlaying a representative talus-based XYZ-coordinate system of the subjects and passing through the centre of mass of the talus (origin of the XYZ-coordinate system). (c) Boxplot distribution of helical axis parameters (inclination angle, deviation angle, rotation and translation) for the subtalar joint motion from inversion to eversion in both left (L) and right (R) feet. Data outliers (above/below the whiskers) do not belong to the same subject. p-values from two-sided Wilcoxon signed-rank test are reported in each plot.

Figure 6
Figure 6

Graphic representation of the centres of rotation for subtalar motion from inversion to eversion in the (a,c) left and (b,d) right feet of the eight healthy subjects. (a,b) To highlight the differences in the centres of rotation location, these are grouped by overlaying a representative talus-based XYZ-coordinate system with the calculated centres for all subjects. (c,d) Superior view of the calcaneus with overlaying centres of rotation. (e) Boxplot distribution of centre of rotation location (anterior, medial and distal) for the subtalar joint motion from inversion to eversion in both left (L) and right (R) feet. Data outliers marked with × belong to the same subject, and it is identified in (d) (white arrow). p-values from two-sided Wilcoxon signed-rank test are reported in each plot.

Figure 7
Figure 7

Boxplot distribution of the shift of the centre of rotation, total range of talus displacement and percentage shift motion in both left (L) and right (R) feet. Data outliers marked with × belong to the same subject. p-values from two-sided Wilcoxon signed-rank test are reported in each plot.

Figure 8
Figure 8

Bilateral weight-bearing PedCAT-CT. An X-ray source and a flat-panel detector on opposite sides rotates horizontally around the foot. (a) Subject positioned in bipedal standing position in pedCAT during scan. (b) Wedges placed in pedCAT platform to allow for eversion and inversion position of the feet. (c) Subject standing on the wedges with right foot in eversion and left foot in inversion configuration.

Figure 9
Figure 9

Workflow of the image post-processing. (1) Weight-bearing clinical CT images of the entire foot in inversion, neutral and eversion positions. (2) Semi-automatic active contour segmentation of the individual bone in the subtalar joint. (3) The calcaneus in the rotated positions (inversion/eversion) was rigidly register with the corresponding calcaneus in the neutral position. (4) Subtalar joint after rigid registration of the calcaneus. Pink represents inversion and green eversion positions. When pixels of the three configurations match, they displayed the colour grey. After registration, the calcaneus of the three images is perfectly aligned and the relative talus motion can be assessed.

Figure 10
Figure 10

Schematic representation for the calculation of the centre of rotation and its translation on the helical axis. The centre of mass of the talus in (a) neutral, (b) inversion and (c) eversion positions was computed based on the grey-intensity value of the PedCAT images. (d) A sphere-fitting approach was used to define the parameters of a sphere (purple) with centre on the helical axis (dashed line) and with the centre of mass of the talus in the rotated configurations (orange and yellow dots) on its surface. The centre of rotation of the talus relative to the calcaneus was determined as the centre of such sphere (purple dot). (e) The distances from the centre of rotation (CoR) to the centre of mass of the talus in neutral (Rn), inversion (Ri) and eversion (Re = Ri) positions were computed. (f) The translation of the centre of rotation (i.e. shift) was defined as the difference between such distances (Shift = Rn − Rn′).

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