1. How is the CR directed for this AP (dorsoplantar) foot?
Foot
The foot has 26 bones: 7 tarsals, 5 metatarsals and 14 phalanges. A routine foot is an AP (dorsoplantar), a medial oblique and a lateral.
Overview
Bones
Tarsals (7)
- Calcaneus
- Talus
- Navicular
- Cuboid
- Medial cuneiform
- Intermediate cuneiform
- Lateral cuneiform
Metatarsals (5)
- 1st (great toe)
- 2nd
- 3rd
- 4th
- 5th
Phalanges (14)
- Great toe: proximal and distal
- Toes 2–5: proximal, middle and distal
Seven tarsals: calcaneus, talus, navicular, cuboid and three cuneiforms (medial, intermediate, lateral). The talus sits on the calcaneus; the cuboid is lateral, the navicular medial.
Registry must-knows
- AP foot: CR 10° toward the heel (perpendicular to the metatarsals), centered to the base of the 3rd metatarsal.
- Medial oblique (30–40°) best shows the cuboid, the base of the 5th metatarsal and the sinus tarsi.
- Jones fracture: the proximal shaft of the 5th metatarsal; avulsion fractures happen at its tuberosity.
- Weight-bearing AP and lateral feet show the longitudinal arches (flat foot).
Show 2 more
- Toes: center to the MTP joint of the toe of interest; the great toe has two phalanges, the others have three.
- Calcaneus: an axial (plantodorsal, CR 40° cephalad) and a lateral. Falls from a height cause calcaneal fractures; check the spine too.
3D model
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Radiographs 9
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Projections 8
Tap a projection for positioning, central ray and image criteria. See every exam in the Positioning Guide ›
AP (dorsoplantar) foot
CR: 10° toward the heel (perpendicular to the metatarsals)
- Position
- Supine or seated, knee flexed, plantar surface flat on the IR.
- Central ray
- 10° toward the heel (perpendicular to the metatarsals)
- Centering
- Base of the 3rd metatarsal
- Typical technique
- 55–65 kVp · 2–4 mAs · 40" SID
Image criteria
- Entire foot, toes through the tarsals, included.
- Equal spaces between the 2nd–4th metatarsals; no rotation.
- Tarsometatarsal joints of the medial side open.
AP oblique, medial rotation
CR: Perpendicular
- Position
- From the AP, rotate the foot 30–40° medially so the plantar surface is at that angle to the IR.
- Central ray
- Perpendicular
- Centering
- Base of the 3rd metatarsal
- Typical technique
- 55–65 kVp · 2–4 mAs · 40" SID
- Best shows
- Cuboid, base of the 5th metatarsal and the sinus tarsi
Image criteria
- 3rd–5th metatarsals free of superimposition.
- Cuboid and its joints open.
- Tuberosity of the 5th metatarsal in profile.
Lateral foot (mediolateral)
CR: Perpendicular
- Position
- Lateral recumbent on the affected side, plantar surface perpendicular to the IR.
- Central ray
- Perpendicular
- Centering
- Medial cuneiform (base of the 3rd metatarsal)
- Typical technique
- 60–65 kVp · 3–4 mAs · 40" SID
Image criteria
- Metatarsals superimposed.
- Fibula over the posterior half of the tibia.
- Tibiotalar joint open.
AP toes
CR: 10–15° toward the calcaneus (or perpendicular with a wedge)
- Position
- Plantar surface on the IR, toes extended.
- Central ray
- 10–15° toward the calcaneus (or perpendicular with a wedge)
- Centering
- MTP joint of the affected toe
- Typical technique
- 50–55 kVp · 1–2 mAs · 40" SID
Image criteria
- Toes and distal metatarsals included.
- IP and MTP joints open.
- No rotation: equal concavity of the phalangeal shafts.
AP oblique toes, medial rotation
CR: Perpendicular
- Position
- From the AP, rotate the leg and foot 30–45° medially.
- Central ray
- Perpendicular
- Centering
- MTP joint of the affected toe
- Typical technique
- 50–55 kVp · 1–2 mAs · 40" SID
Image criteria
- Phalanges and distal metatarsals included.
- IP and MTP joints open.
- More concavity on one side of the phalangeal shafts.
Lateral toe (great toe shown)
CR: Perpendicular
- Position
- Great toe: medial side of the foot to the IR (lateromedial). 3rd–5th toes: lateral side to the IR. Tape the other toes into flexion so the toe of interest is free of superimposition.
- Central ray
- Perpendicular
- Centering
- IP joint of the great toe (PIP joint for the 2nd–5th toes)
- Typical technique
- 50–55 kVp · 1–2 mAs · 40" SID
- Best shows
- The phalanges in a true lateral and the IP and MTP joints
Image criteria
- Toe of interest in a true lateral, free of the other toes.
- IP and MTP joints open.
- Great toe: sesamoids under the 1st metatarsal head in profile.
Axial calcaneus (plantodorsal)
CR: 40° cephalad to the long axis of the foot
- Position
- Supine or seated, leg extended. Foot dorsiflexed so the plantar surface is near perpendicular to the IR (a strap around the forefoot helps).
- Central ray
- 40° cephalad to the long axis of the foot
- Centering
- Base of the 3rd metatarsal, so the CR exits through the heel
- Typical technique
- 65–75 kVp · 5–8 mAs · 40" SID
- Best shows
- Calcaneal body, tuberosity and sustentaculum tali; fractures widening the heel
Image criteria
- Entire calcaneus from the tuberosity to the talocalcaneal joint seen.
- Calcaneus not foreshortened (too little angle) or elongated (too much).
- Sustentaculum tali in profile on the medial side; no rotation.
Lateral calcaneus (mediolateral)
CR: Perpendicular
- Position
- Lateral recumbent on the affected side, foot dorsiflexed so the plantar surface is perpendicular to the IR.
- Central ray
- Perpendicular
- Centering
- About 1 inch (2.5 cm) distal to the medial malleolus
- Typical technique
- 60–65 kVp · 3–5 mAs · 40" SID
- Best shows
- Calcaneus in profile, the subtalar joint and Böhler's angle (flattened in calcaneal fractures)
Image criteria
- Calcaneus seen in lateral profile with the ankle joint and the talus above it.
- Sinus tarsi and the cuboid–calcaneal joint open.
- No rotation: lateral malleolus over the posterior tibia.
Technique values are typical starting points; follow your department's technique chart.
Labeled diagrams
Quick check
2. For bilateral weight-bearing lateral feet to evaluate the longitudinal arches, how is the CR directed?
3. The side-view diagram shows the setup for a plantodorsal axial calcaneus: the patient is supine with the foot dorsiflexed so its long axis is vertical. The CR will be angled 40 degrees cephalad to the long axis of the foot. At which labeled point should the CR enter?
4. An AP foot is taken on a 24 x 30 cm field at 100 cm SID. To use the anode heel effect, which part of the foot should be placed toward the cathode end of the tube?
5. This lateral view of the great toe shows a small bone fragment pulled off the dorsal base of the distal phalanx. How is a lateral great toe positioned?
