Sesamoids Tangential, Lewis Method is a radiography positioning projection of the Lower Extremity. Patient prone, toe flexed back on IR. CR perpendicular and tangential. SID 40". The centering point is located plantar surface of the first metatarsal head (sesamoid area).. The central ray is perpendicular and tangential to the plantar surface of the first metatarsal head.. Image-quality criteria include medial and lateral sesamoids of the first metatarsal head visible., sesamoids separated and demonstrated in their entirety.. Standard exposure ranges from 55 to 65 kVp, 2 to 4 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Medial sesamoid of the first metatarsal head.
- Lateral sesamoid of the first metatarsal head.
- Plantar surface of the first metatarsal head.
- Articulation of sesamoids with metatarsal head.
- Interphalangeal joint of the great toe.
Patient preparation
- Verify patient identity using two identifiers.
- Remove footwear, socks, and any radiopaque foot jewelry.
- Position the patient prone at the table with the foot off the edge.
- Extend the ankle fully with the forefoot and toes hanging off the table.
- Flex the great toe backward until the ball of the foot is perpendicular to IR.
Position & centering point
Plantar surface of the first metatarsal head (sesamoid area).
Central ray
Perpendicular and tangential to the plantar surface of the first metatarsal head.
Exposure / technique
- kVp
- 55–65
- mAs
- 2–4
- SID
- 40" (102 cm)
- Notes
- Lewis method requires the great toe to be dorsiflexed and the ball of the foot perpendicular to IR.
Image-quality criteria
- Medial and lateral sesamoids of the first metatarsal head visible.
- Sesamoids separated and demonstrated in their entirety.
- Plantar surface of the first metatarsal head clearly shown.
- No superimposition of other tarsal structures.
- Bone trabeculae sharp, no motion artifact.
- Tight collimation, 1-2 inches on all sides of the sesamoid area.
Common errors / ARRT traps
- 1 Inadequate dorsiflexion of the great toe closes the view of sesamoids.
- 2 Ball of foot not perpendicular to IR obscures sesamoid anatomy.
- 3 Off-centered CR clips the sesamoid region.
- 4 Incomplete ankle extension superimposes metatarsal structures.
Clinical indications
- Suspected sesamoid fracture or osteonecrosis.
- Evaluation of sesamoiditis or plantar pain syndrome.
- Assessment of sesamoid morphology or deformity.
Aligned to the 2025 ARRT Content Specifications.