Point vs. traditional method evaluation of hallux valgus: interreader reliability and intermethod performance using X-ray and MRI

Background: The two most widely used measurements for diagnosing and assessing the severity of hallux valgus are the hallux valgus angle (HVA) and the intermetatarsal angle (IMA). Traditionally, these have been measured by using the midaxial lines approximating the axis of each bone. A new simpler point method has been recently suggested for measuring these angles by connecting points along the medial corners of each bone. Interreader reliability of these measurements on X-ray and MRI as well as intermethod and intermodality differences have not been assessed. Methods: A series of 56 consecutive patients between 18 and 100 years old with no history of foot trauma or orthopedic hardware in their feet were included. All had AP and lateral X-rays and MRI performed on the same foot between April 27, 2015 and March 9, 2016. Two readers measured HVA and IMA using both the traditional midaxial and new point methods. ICC correlations were obtained. Results: The interreader reliability for HVA was similar on point method (0.92) and traditional method (0.94). For the IMA, the ICC was 0.77 on point method versus 0.76 on traditional method. The intermodality agreement (between X-ray and MRI) was higher for HVA (ICC = 0.85, 0.88) as compared to IMA (0.58, 0.74), respectively on both methods. The mean difference between the methods was larger on traditional method = 5.5 for HVA and 2.5° for IMA. Conclusions: HVA is more reliable than IMA on both methods and modalities and a significant difference exists between the magnitudes of values obtained using the two methods. Level of Clinical Evidence: 3.