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| Subtalar joint motion (pronation or supination) occurs around a single, oblique axis (pictured here for the left foot). |
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Because the joint's axis is oblique, we observe a component of subtalar motion no matter which of the three reference planes (sagittal, frontal, or transverse) that we use as our point of view.
| The arrows in this transverse plane (cross-sectional) view of the right foot illustrate the three components of open chain movement in the right subtalar joint. The line represents the subtalar joint axis. | ||||||||||
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| Plane of movement | PRONATIONSUPINATION
FRONTALabduction adduction
SAGITTALdorsiflexion plantar flexion
TRANSVERSE | inversion | |||||||||
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| The figures supply the mean values for the angulation of the subtalar joint axis in two planes. |
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Investigators first located the axis empirically by examining cadaver specimens. The axis may be a line that connects the points at which the talus contacts the navicular anteriorly and the calcaneus inferiorly. Similarly, biomechanists identify the radioulnar joint axis as a line that connects the two points at which the radius and ulna contact one another. Kendall (1993) use the same reasoning to define the hip joint's mechanical axis as a line that connects the femur's points of articulation with the pelvis and tibia.