Procedure and radiometry
To assess longitudinal flatfoot, the radiograph is taken in a lateral projection while the patient stands on one leg, creating a natural axial load. The resulting radiograph must clearly show a 4–5 cm segment of the lower leg.
Image analysis is performed by constructing a triangle. Its vertices are located at the following points:
- The inferior margin of the cuneonavicular articulation.
- The inferior contour of the calcaneal tuberosity.
- The plantar contour of the head of the first metatarsal bone.
The lines formed allow the measurement of two key parameters:
- Longitudinal arch angle: the more severe the flatfoot, the wider this angle.
- Longitudinal arch height: the perpendicular line from the lowest point of the cuneonavicular joint to the support line. In a flattened foot, the height decreases.
Grades of longitudinal flatfoot
The classification of longitudinal flatfoot is based on changes in the arch angle and height according to radiometry results.
| Grade | Arch angle, deg. | Arch height, mm |
|---|---|---|
| Normal | 125 — 130 | 39 — 36 |
| Grade I | 131 — 140 | 35 — 25 |
| Grade II | 141 — 155 | 24 — 17 |
| Grade III | $\ge$ 155 | < 17 |
Diagnosis of transverse flatfoot and hallux valgus
When evaluating transverse flatfoot, which is often accompanied by Hallux valgus (valgus deformity of the great toe), radiologists rely on the angular deviations of the forefoot bones.
To do this, three axes are drawn on the radiograph:
- Axis of the first metatarsal bone.
- Axis of the second metatarsal bone.
- Axis of the proximal phalanx of the great toe.
The degree of deformation is determined by two parameters: the angle between the first and second metatarsals and the deviation angle of the great toe itself. For example, in grade I, the intermetatarsal angle is 10–12°, and the toe deviation is 15–20°. In grade IV, these values exceed 20° and 40°, respectively.
Radiological monitoring in rehabilitation
Radiography plays a crucial role in the postoperative period and during the conservative treatment of foot fractures.
Transitioning from non-weight-bearing crutch walking to partial axial loading is possible only after a control X-ray in two projections is performed to confirm fracture consolidation (healing). Further expansion of the activity regimen also relies on radiographic data. Follow-up radiographs and examinations are recommended at 1–2 months, 6 months, and 1 year after the injury or surgery.
To remember the vertices of the triangle in longitudinal flatfoot: Heel, Toe, Isthmus (calcaneal tuberosity, head of the 1st metatarsal, cuneonavicular joint).
Class and exam questions
How to determine the height of the longitudinal arch on a radiograph?
This is a perpendicular dropped from the lowest point of the cuneonavicular joint to the horizontal support line upon which the foot rests.
What axes need to be drawn to assess transverse flatfoot?
The axes of the first and second metatarsal bones, as well as the axis of the proximal phalanx of the great toe, are drawn.
What else to study on this topic
- Clinical presentation of static flatfoot
- Pathogenesis of complications in hallux valgus
- Organization of rehabilitation after foot injuries and surgeries
- Physical therapy and exercise therapy methods for the foot
Master the entire topic in the "Diagnostic Radiology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Weight-bearing foot radiography" and 2,199 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 10 video lessons on the subject
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.