The intermetatarsal angle is measured on a weight-bearing anteroposterior foot X-ray. Lines are drawn along the central axes of the first and second metatarsals, and the angle between them is recorded. As a bunion develops, the first metatarsal may drift medially while the big toe moves laterally, increasing this angle.
This measurement matters because bunion correction is not simply the removal of a prominence. In an appropriate operation, the position of the first metatarsal and big toe must be addressed while preserving or restoring joint alignment. The degree and pattern of metatarsal displacement influence how much correction may be required.
An Austin or Chevron osteotomy is commonly used for selected mild-to-moderate deformities with a suitable joint and anatomy. It allows the metatarsal head to be shifted laterally and stabilised. More substantial, unstable, arthritic or recurrent deformities may require a different strategy. The angle is therefore one factor in selection, not a stand-alone rule.
Measurement error is possible, and foot rotation during the X-ray can affect apparent alignment. The clinician should therefore review the actual images rather than rely only on the radiology report. Other features—including sesamoid position, first-metatarsal rotation, joint congruity and the patient’s clinical flexibility—also matter.
Explaining these measurements can help patients understand why simply shaving the bump is usually not considered a complete structural correction. The underlying relationship of the bones needs to be evaluated if symptoms justify surgery.