WBCT of Hallux Valgus Deformity

Abstract

Category: Bunion Introduction/Purpose: Distal metatarsal articular angle (DMAA) is important for the treatment of hallux valgus deformity, because high DMAA is a cause of recurrence and stiffness after surgery. However, the DMAA is not commonly measured on plain radiograph, because of its low reliability. The reliability would be increased, if we clearly understand anatomical structure of the DMAA in hallux valgus deformity. In the WBCT, we found that the DMAA was different between dorsal side and plantar side. The purposes of this study were to compare the degree of the DMAA between dorsal side and plantar side in hallux valgus deformity, to identify which side of the DMAA is more correlated with the hallux valgus deformity, and to define standards for the DMAA measurement on plain radiograph. Methods: We retrospectively evaluated patients who underwent surgery for hallux valgus deformity in our clinic from April, 2017 to July, 2017. All patients underwent WBCT and plain weight-bearing radiograph preoperatively. The WBCT was performed using a cone-beam CT scanner (Planmed, Verity). For measuring the DMAA on axial plane image of the WBCT, we set axial plain parallel to sagittal axis of the 1st metatarsal bone. We determined dorsal and plantar axial WBCT images that located immediately below dorsal cortex and immediately over plantar cortex in the 1st metatarsal bone respectively. (Fig.1-A) We measured the DMAA on these dorsal and plantar axial WBCT images. (Fig.1-B) On the plain weight-bearing foot anteroposterior radiograph, we measured hallux valgus angle (HVA) and the DMAA. For measuring the DMAA on the plain radiograph, we defined the distal articular surface from sagittal groove at medial side to sharp edge at lateral side. (Fig. 1-C) Results: Thirty feet from 30 patients were included in this study. The mean age of patients was 55.6 years (range: 21-77). The mean of HVA was 34.9° (range: 22-52). The mean of the DMAA on the dorsal and the plantar axial WBCT images were 12.5°(0.7- 24.1) and 39.0°(16.7 – 57.6), respectively. Paired t test resulted that the DMAA on the plantar axial image was significantly higher than the DMAA on the dorsal axial image (P=0.000). Correlation analysis resulted that only the DMAA on the plantar coronal image was significantly correlated with the HVA (Pearson correlation coefficient:0.380, P=0.038). The intraclass coefficient indicated that the DMAA on the plain radiograph which defined in this study was highly reliable with the DMAA on the plantar coronal WBCT image.(ICC = 0.811) Conclusion: The present study showed that the plantar side DMAA is 27° higher than the dorsal side DMAA. We believed that this difference made confusion to define the DMAA on plain radiograph and decreased reliability for the measurement of the DMAA on the plain radiograph. Because the plantar side DMAA is more correlated with the HVA than the dorsal side DMAA, it is important to measure the plantar side DMAA on the plain radiograph. The present study proved that our definition of the DMAA on plain radiograph was appropriate for measuring the plantar side DMAA.