To study the availability of the radiological classification for incongruent hallux valgus deformities, which has been used as the key to the algorithm for selecting surgical options.

To determine radiological severity, 257 cases of incongruent hallux valgus deformities were studied. The hallux valgus angle (HVA) and the 1/2 intermetatarsal angle (IMA) were measured in each case. Following Mann's radiological classification system, the HVA and IMA were compared to determine any similarity in severity. The distal metatarsal articular angle (DMAA) was also measured to observe the extent of its effect on the incongruent deformity.

The HVA was 36.1° on average (range, 16-60°) and the 1/2 IMA was 15.8° on average (range, 5-30°). In 126 cases (49.1%), the severity between the 1/2 IMA and HVA coincided with the index classification, whereas. 131 cases (50.9%) did not correspond. Overall, the severity of approximately half the cases, could not be graded. The DMAA was 15.6° on average (range, 0-40°) and 133 cases (51.8%) demonstrated a value above normal value (>15°).

The radiological classification system used as a guide for surgical decision-making needs to be revised, due to the overt limits of correspondence between the severity of the 1/2 IMA and HVA. Because the HVA would be influenced by both the lateral subluxation and bony deformity around the first metatarsophalangeal joint, it is reasonable to consider these factors on the HVA as elements to be corrected individually, instead of the HVA alone.