(A pen or pencil should be utilized to estimate the following relationships.)
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A) Supinated, B) pronated, C) supinated with talar, second metatarsal, and calcaneal axes drawn, and D) pronated with talar, second metatarsal, calcaneal, and cuboid axes drawn.
First, approximate the talar axis by placing a pen or pencil against the film within the talus centrally, parallel to its invisible axis, so that the tip of the pen or pencil extends adjacent to the first metatarsal. The talar axis normally runs alongside the medial aspect of the first metatarsal base and the talar head appears to articulate approximately 75% (3/4) with the navicular (i.e., the medial 25% of the talar head does not appear to articulate). In a pronated foot, the talar axis deviates medially, away from the first metatarsal base (the talocalcaneal angle is increased). Additionally, the talar head will appear to articulate less than 75% with the navicular (greater than 25% of the talar head appears to be non-articular medially), and a "v" like gapping will be seen between the talar head and anterior calcaneus. If the angle is decreased, as in the supinated foot, the talar axis will run through the center of the first metatarsal or lateral to it, and the medial aspect of the talar head will appear to fully articulate with the navicular.
The calcaneal axis is estimated by placing a pen or pencil along the lateral calcaneal surface. A calcaneal axis collinear or parallel to the lateral surface of the cuboid is seen in the rectus and supinated foot. The cuboid's lateral surface will form an obvious angle with the estimated calcaneal axis in the pronated foot.
Place the pen or pencil parallel to the calcaneal axis (as for the cuboid abduction angle, above) so that the tip of the pen or pencil extends to the metatarsophalangeal joints. Normally, the second metatarsal should appear mildly adducted relative to the pen or pencil. If the second metatarsal appears parallel or abducted, pronation exists. If the second metatarsal axis appears grossly adducted, check for metatarsus adductus (see below).
Place a pen or pencil through the second cuneiform parallel to its imaginary long axis. Normally, the second metatarsal appears mildly adducted. Gross adduction relative to the pen or pencil suggests metatarsus adductus deformity.
The longitudinal axes of the first and second metatarsals should normally appear nearly parallel or the first metatarsal will appear slightly adducted relative to the second metatarsal. Gross adduction of the first metatarsal relative to the second metatarsal is associated with pronation.
The longitudinal axes of the first metatarsal and hallux proximal phalanx should normally appear nearly parallel or the hallux proximal phalanx will appear mildly abducted relative to the first metatarsal. Gross abduction of the hallux proximal phalanx relative to the first metatarsal is associated with pronation.
The longitudinal axes of the hallux proximal and distal phalanges should normally appear nearly parallel or the distal phalanx will appear mildly abducted relative to the proximal phalanx. Gross abduction of the hallux distal phalanx relative to the proximal phalanx is considered a deformity.
Place a pen or pencil through the center of the first metatarsal shaft so that the tip of the pen or pencil extends near the posterior margin of the tibial sesamoid. If the tip of the pen or pencil is entirely lateral or medial relative to the tibial sesamoid, its position is considered number 1 or 7, respectively. If the pen or pencil tip just touches the lateral or medial margin of the tibial sesamoid, a position numbered 2 or 6, respectively, is assigned. If the instrument tip bisects the tibial sesamoid into equal halves, this is considered position number 4. Position number 3 or 5 is assigned if the tip of the instrument divides the tibial sesamoid into thirds, such that the larger 2/3 segment is seen medially or laterally, respectively.
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The top two lateral views are of a supinated foot (the right view has the talar, calcaneal, and first metatarsal axes drawn) , the bottom two of a pronated foot. All angles assessed in the lateral view approximate 21 degrees.
The talar axis parallels the middle subtalar joint. Place a pen or pencil collinear through the middle subtalar joint and view its angulation with the plane of support. If the axis forms an angle greater than 21 derees relative to the plane of support, the angle is increased, as is seen in pronation. The angle will be decreased in a supinated foot.
Place the pen or pencil over the first metatarsal so that it appears approximated to its axis. The angle is decreased in a pronated foot, increased in the supinated foot.
Place the pen or pencil along the inferior surface of the calcaneus; this approximates the calcaneal axis. The angle is increased in a supinated foot, decreased in the pronated foot.
© Copyright 1998, Robert A. Christman, D.P.M.
These articles and figures may not be published, reposted, or redistributed without permission from Dr. Christman.
This page was updated May 5, 1998.