Lower Extremities
Foot
Anatomy
Students should be able to identify the following structures on radiographic images:
Digits, Head, Base, Body or shaft of phalanx.
Proximal Phalanges, Middle Phalanges, Distal Phalanges, Metatarsals, Tarsals, Calcaneous (os calcis), Talus, Cuboid, Navicular, 1st cuneiform, 2nd cuneiform, 3rd cuneiform, Proximal Interphalangeal joints, Distal Interphalangeal joints, Metatarsophalangeal joints, Tarsometatarsal joints
Routine Projections (ARRT Required)
AP / AP Axial Foot
CR Location & Positioning
- SID: 40″
- Patient position: Supine or seated with knee flexed, plantar surface on IR.
- Adjustments: Ensure foot is flat; dorsiflex ankle if possible.
- CR: 10° posterior (toward heel) to base of 3rd metatarsal.
- Pt. Instructions: Remain still.
- Exposure: 60–70 kVp.
Evaluation Criteria
- Coverage: Entire foot including phalanges, metatarsals, and tarsals.
- Rotation checks: Equal concavity of shafts of metatarsals and phalanges; open joint spaces.
- Motion checks: Sharp bone margins.
- Technique checks: Adequate contrast for cortical bone and trabecular detail.
AP Oblique Foot (Medial Rotation)
CR Location & Positioning
- SID: 40″
- Patient position: Supine or seated, knee flexed.
- Adjustments: Medially rotate foot 30–40°.
- CR: Perpendicular to base of 3rd metatarsal.
- Pt. Instructions: Hold still.
- Exposure: 60–70 kVp.
Evaluation Criteria
- Coverage: Entire foot.
- Rotation checks: 3rd–5th metatarsal bases free of superimposition; tuberosity of 5th metatarsal well visualized.
- Motion checks: Trabecular detail sharp.
- Technique checks: Adequate density for both tarsals and metatarsals.
Lateral Foot (Mediolateral)
CR Location & Positioning
- SID: 40″
- Patient position: Lateral recumbent, lateral side of foot against IR.
- Adjustments: Plantar surface perpendicular to IR.
- CR: Perpendicular to base of 3rd metatarsal.
- Pt. Instructions: Hold still.
- Exposure: 60–70 kVp.
Evaluation Criteria
- Coverage: Entire foot and distal tibia/fibula.
- Rotation checks: Superimposed metatarsals and nearly superimposed tibiotalar joint.
- Motion checks: Sharp margins.
- Technique checks: Good contrast and detail.
Supplemental Projections
Weight-Bearing AP Foot
CR Location & Positioning
- SID: 40 inches
- Patient position: Erect, standing with both feet on IR; weight evenly distributed.
- Adjustments: Feet parallel and centered to IR; MSP vertical.
- CR: 10° posteriorly (toward heel) directed between feet at the level of the base of the 3rd metatarsal.
- Pt. Instructions: Stand naturally, hold still.
- Exposure: On suspended respiration.
Evaluation Criteria
- Coverage: Both feet from phalanges through calcanei and distal tib/fib.
- Rotation checks: Bases of metatarsals 2–4 separated, 1 and 2 slightly overlapping.
- Motion checks: Sharp cortical margins and clear trabecular detail.
- Technique checks: Uniform exposure across metatarsal bases and midfoot.
- Clinical aim: Demonstrates alignment of tarsals, metatarsals, and arches under physiological load; evaluates Lisfranc joint integrity and longitudinal arch height.
Weight-Bearing Lateral Foot
CR Location & Positioning
- SID: 40 inches
- Patient position: Erect, standing on IR with affected foot centered.
- Adjustments: Opposite foot slightly behind; weight evenly distributed to avoid lateral tilt.
- CR: Horizontal beam, perpendicular to base of the 3rd metatarsal.
- Pt. Instructions: Remain still, normal breathing.
- Exposure: On suspended respiration.
Evaluation Criteria
- Coverage: Entire foot including calcaneus, distal tibia/fibula, and soft tissues.
- Rotation checks: Metatarsal heads superimposed; talar domes aligned.
- Motion checks: Sharp cortical detail; no blur from sway or breathing.
- Technique checks: Penetration sufficient to visualize arches and subtalar joint.
- Clinical aim: Demonstrates longitudinal arch collapse, flatfoot deformities, and alignment of tarsals during full weight bearing.
Hows & Whys of Foot Radiography
Anatomy
- Why is the 5th metatarsal base a critical landmark?
It helps confirm correct centering and identifies common avulsion or Jones fractures. - Why are weight-bearing views useful?
They demonstrate alignment, joint spacing, and arch integrity under physiological load. - Why does the longitudinal arch matter clinically?
Its collapse (pes planus) alters gait mechanics and can cause chronic pain or deformity. - What type of joints are the tarsometatarsal (TMT) joints?
Diarthrodial, gliding type. - What type of joints are the metatarsophalangeal (MTP) joints?
Diarthrodial, condyloid type. - What type of joints are the interphalangeal joints?
Diarthrodial, hinge type.
Positioning
- Why is the CR angled 10° posterior for the AP foot?
To open joint spaces of the midfoot and reduce foreshortening of metatarsals. - Why is the foot rotated medially 30–40° for the oblique projection?
This opens the intertarsal joints, especially between the cuboid and calcaneus, and demonstrates the sinus tarsi. - Why is the lateral foot performed with the medial side down?
It provides a more natural position, ensuring the foot’s longitudinal arch is better demonstrated. - Why should the toes be kept parallel to the IR in AP and oblique foot projections?
To prevent foreshortening of the phalanges and to open the joint spaces. - Why is a weight-bearing AP foot sometimes performed?
To evaluate arches, alignment, and joint spacing under normal load-bearing conditions. - Why is the plantar surface kept flat on the IR for AP projections?
To prevent rotation and ensure equal concavity of shafts of phalanges and metatarsals.
Technique & Image Evaluation
- How do you know an AP foot was not rotated?
Equal concavity of metatarsal and phalangeal shafts on both sides. - What indicates correct CR angulation on an AP axial foot?
Open TMT joint spaces and visualization of metatarsal bases without excessive overlap. - What error is indicated if the tarso-metatarsal joint spaces are not open on an AP foot?
Insufficient CR angle was used or the plantar surface was not flat against the IR. - How do you know the oblique foot was rotated the correct 30°–40°?
The cuboid is demonstrated in profile, the 3rd–5th metatarsal bases are free of superimposition, and the sinus tarsi is well visualized. - What error is indicated if the sinus tarsi is not visible on an oblique foot?
The foot was under-rotated. - What error is indicated if the bases of the 1st and 2nd metatarsals are superimposed on the oblique projection?
The foot was over-rotated. - What error is indicated if the 5th metatarsal tuberosity is not well demonstrated on an oblique foot?
The foot was under-rotated. - How do you confirm correct positioning on a lateral foot?
The tibiotalar joint is open, the distal fibula is superimposed over the posterior half of the tibia, and the metatarsals are nearly superimposed. - What error is indicated if the distal fibula is too far posterior on a lateral foot?
The foot was rotated externally. - What error is indicated if the distal fibula is too far anterior on a lateral foot?
The foot was rotated internally. - What error is indicated if the distal metatarsals are separated rather than superimposed on a lateral?
The foot was not in a true lateral position. - How can you confirm patient cooperation and exposure timing on foot projections?
Sharp cortical bone and trabecular markings should be visible, with no evidence of motion blur. - How do you know the arch is well demonstrated on a lateral weight-bearing foot?
The longitudinal arch is visible with clear joint spacing, showing arch integrity.
Clinical Applications
- Why is the oblique foot important in trauma imaging?
It demonstrates the 5th metatarsal base, a common site of avulsion fractures. - Why are weight-bearing projections often ordered?
They reveal deformities (flatfoot, hallux valgus), fractures, or misalignments not visible in non–weight-bearing studies. - Why are non-weight-bearing projections still essential?
They provide controlled positioning for fracture detection and routine evaluation. - Why might bilateral weight-bearing feet be obtained?
For comparison of arches and joint alignment between the affected and unaffected sides.