Normal Intermetatarsal Angle Size on Radiography
The intermetatarsal angle (IMA) is the angle formed between the long axes of adjacent metatarsal bones, most commonly measured between the 1st and 2nd or 4th and 5th metatarsals on weight-bearing anteroposterior foot radiographs. Accurate measurement of this angle is essential for evaluating forefoot deformities, guiding surgical planning, and monitoring treatment outcomes in conditions such as hallux valgus and tailor's bunion.
Normal Reference Values
| Orientation | Location | Measurement |
|---|---|---|
| Anteroposterior | 1St Metatarsal - 2Nd Metatarsal | <9¡ |
| Anteroposterior | 4Th Metatarsal - 5Th Metatarsal | <8¡ |
Clinical Significance
The 1st–2nd intermetatarsal angle is a cornerstone measurement in hallux valgus assessment. A normal value of <9° is expected; values ≥9° indicate metatarsus primus varus, a key contributor to hallux valgus deformity. Surgical correction (e.g., distal or proximal metatarsal osteotomy) is often planned based on the degree of IMA elevation, with moderate deformity typically defined as 9–13° and severe deformity as ≥14°.
The 4th–5th intermetatarsal angle, normally <8°, is the primary metric for evaluating tailor's bunion (bunionette deformity). An angle ≥8° suggests lateral splaying of the 5th metatarsal and may warrant conservative or operative intervention depending on symptom severity.
- Hallux valgus (elevated 1st–2nd IMA)
- Metatarsus primus varus (isolated widening of 1st–2nd IMA)
- Tailor's bunion / bunionette (elevated 4th–5th IMA)
- Splay foot (generalized forefoot widening)
- Post-operative recurrence following metatarsal osteotomy
Reference: Harris GF, Smith PA. Foot and Ankle Motion Analysis, Clinical Treatment and Technology. CRC Press. (2010).
Imaging Notes
Intermetatarsal angles should be measured on weight-bearing anteroposterior (AP) radiographs of the foot to reflect true functional alignment; non-weight-bearing views may underestimate deformity. The angle is constructed by drawing lines through the central axes of the respective metatarsal shafts and measuring their intersection. Consistent shaft axis selection — using the midpoints of the proximal and distal shaft diaphyses — reduces inter-observer variability. Rotation and patient positioning must be standardized, as oblique projections can artificially alter the measured angle.