Radiographic evaluation of the congruency of the first metatarsophalangeal joint in hallux valgus

Abstract

Background The congruency of the first metatarsophalangeal (MTP) joint was extremely important for the selection of operating methods and prognosis, while its radiographic evaluation method was relatively lacking. The purpose of this article was to explore the radiographic indicators for evaluating the congruency of the first MTP joint. Methods The patients who had X-ray of weightbearing in the outpatient system were selected, excluding patients with trauma, deformity, and history of operation. 183 patients with 245 feet were included. The hallux valgus angle (HVA), distal metatarsal articular angle (DMAA), metatarsophalangeal joint angle (MTPJA), congruency index (CI) and tibial sesamoid position (TSP) were measured and do statistical analysis. Results The higher the degree of hallux valgus, the higher the proportion of incongruency of the first MTP joint. Significant differences were found in DMAA, MTPJA and CI between the congruency and incongruency groups of patients with moderate to severe hallux valgus (P < 0.05). The area under curve (AUC) of the receiver operating characteristic(ROC) curve for MTPJA and CI was 0.906 and 0.884, the sensitivity and specificity reached 0.791 and 0.862, 0.949 and 0.644, and the critical values were 10.67 and 0.765 respectively. The correlation test indicated that in the congruency group, DMAA and HVA had positive correlation, but MTPJA, CI and HVA had low correlation coefficients. DMAA and HVA were not correlated in the incongruency group, while MTPJA and HVA were significantly positively correlated, and CI and HVA showed a negative correlation (P < 0.05). Conclusion MTPJA and CI are indicators that can quantitatively evaluate the congruency of the first MTP joint, taking 10° and 0.765 as the demarcation points respectively. Clinically, the congruency of MTP joint should be considered when choosing operating methods for different degrees of hallux valgus, MTPJA and CI can be used as quantitative evaluation indicators.