The congruency of the first MTP joint play important role in the selection of operating method postoperative recurrence in hallux valgus. Studies have shown that the incongruency of the postoperative MTP joint was highly correlated with the recurrence of hallux valgus. Previous literature reported, the evaluation of the congruency of the first MTP joint was only judged by the doctor’s visually assessing whether the arcs of the MTP joint articular surface were parallel, however there was no quantitative indicator. In addition, DMAA was also often used to assess the dislocation of the first MTP joint. For example, for patients with severe hallux valgus accompanied by increased DMAA, Double metatarsal osteotomy (DMO) was a quite effective operating method. But in fact, due to its own complications such as shortening the length of the first metatarsal bone, postoperative avascular necrosis of the metatarsal head, and metastatic metatarsalgia, the application of this technique was limited to a certain extent. Wang's article compares the efficacy of rotating scarf osteotomy and DMO for hallux valgus accompanied by increased DMAA. It was believed that there was no significant difference between the two methods, but the former had a lower incidence of complications. Jeong used the point-connecting method for measuring HVA and IMA, also due to consideration of the MTP joints’ congruency and incongruency, which would affect the assessment of the severity of hallux valgus.
Facts have proved that DMAA is not suitable for evaluating the congruency of the first MTP joint. For the larger metatarsals of DMAA, there will also be two situations where the MTP joints are congruency and incongruency. The statistical results showed that there was an obvious relationship between the patients’ DMAA and the congruency of the first MTP joint for moderate to severe hallux valgus. The DMAA of the congruency group was significantly greater than that of the incongruency group, indicating that the application of DMAA alone to assess whether the first MTP joint was congruency or not was not reliable. We had innovatively proposed two quantitative evaluation indexes for the congruency of the first MTP joint on the weightbearing foot anterior-posterior images, MTPJA and CI, which were quantitatively measured by measuring the angles of the articular surfaces at both ends and the degree of mating of the articular surfaces (Fig. 1). Because of our data were not clinically needed patients and lots of asymptomatic patients were also included, resulting in a larger proportion of patients with mild hallux valgus, most of which were congruency MTP joint. While the proportions of congruency and incongruency patients with moderate hallux valgus can be basically the same. For patients with severe hallux valgus, nearly a quarter of them were congruency with the first MTP joint, which ratio is similar to the data reported by Coughlin. In addition, as the severity of hallux valgus gradually increased, MTPJA gradually increased, and CI gradually decreased, indicating that the contact surface of the first MTP joint surface will gradually decrease.
Compared the difference between congruency and incongruency groups, there was no difference in HVA between the two groups in patients with mild, moderate or severe hallux valgus. But in patients with moderate to severe hallux valgus, the difference between MTPJA and CI was large, the CI of the congruency group was greater than that of the incongruency group, while the MTPJA was smaller than that of the incongruency group, indicating that MTPJA and CI could effectively assess the congruency of the first MTP joint. By drawing ROC curves for MTPJA and CI, the AUC was 0.906 and 0.884 respectively, and both had diagnostic power. The critical value of MTPJA was 10.67 and CI was 0.765. We can define that if the value of MTPJA is greater than 10° or CI is less than 0.765, the first MTP joint is considered as congruency, and the degree of congruency can be measured by the specific value of the two. That is the larger the MTPJA and the smaller the CI, the greater the degree of congruency. In our previous article, 36 patients (38 feet) with moderate to severe hallux valgus were followed up at different times before and after surgery, and their CI recovered from 0.75 before surgery to 0.95 at the last follow-up. Same as HVA, IMA, etc., all of the indicators have been well recovered, which also verifies the effectiveness of this indicator to a certain extent.
In terms of correlation test, DMAA and HVA had a positive correlation in the congruency group, while there was no correlation between the two in the incongruency group. Indicating that if DMAA was used to assess the degree of hallux valgus, it is only limited to the congruency group. In patients with significant dislocation of the first MTP joint, DMAA is less effective in assessing the severity of hallux valgus. Therefore, for more severe hallux valgus surgery, DMAA still needs to be measured in the congruency group, and the value of DMAA will be used to determine whether to perform DMO. In the congruency group, the correlation coefficients between MTPJA, CI and HVA were low, while in the incongruency group, MTPJA and HVA were significantly positively correlated, and CI and HVA were negatively correlated, that is, the more severe the hallux valgus, the more deviated MTPJA and CI normal range. Of course, because the smaller the value of MTPJA and the larger the value of CI, it indicates that the matching relationship of hallux valgus is better. Therefore, whether it is a congruency group or an incongruency group, there is a significant negative correlation between the two.
The present paper also has some limitations that should be taken into consideration. First of all, this study only focuses on the statistical analysis of radiological parameters, and does not apply MTPJA and CI to the comparison of parameters before and after the operation in hallux valgus patients. This is what we need to include in the next step of our research. In addition, the patients included in this study have a certain deviation. The patients with mild hallux valgus are too large, but due to the metatarsophalangeal joint mismatch mostly occurs in patients with moderate to severe hallux valgus, we believe that the data in the study is still reliable.
In summary, different degrees of hallux valgus, especially in patients with moderate to severe hallux valgus, have the first MTP joint of congruency and incongruency. DMAA has poor performance in evaluating matching relationships. The previous imaging indicators are only qualitative evaluations. MTPJA and CI can be quantitative to evaluate the congruency of the first MTP joint, 10° and 0.765 are used as the demarcation points respectively. Clinically, it is necessary to consider the congruency of the first MTP joint in the selection of different degrees of hallux valgus surgery. MTPJA and CI can be used as quantitative evaluation indicators.
This study was approved by the Ethics Committee, and the part number was: (B) KY2021052.