The congruency of the first MTP joint plays an important role in the selection of the surgical method for postoperative recurrence in hallux valgus. Studies have shown that incongruency of the postoperative MTP joint was highly correlated with the recurrence of hallux valgus. Previous literature reported that the congruency of the first MTP joint has been evaluated only by a doctor’s visual assessment of whether the arcs of the MTP joint articular surface were parallel; however, there is no quantitative indicator. In addition, the DMAA is often used to assess dislocation of the first MTP joint. For example, for patients with severe hallux valgus accompanied by an increased DMAA, double metatarsal osteotomy (DMO) is an effective surgical method. However, due to the related 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 has been limited to a certain extent. Wang's study compared the efficacy of rotating scarf osteotomy and DMO for hallux valgus accompanied by an 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 to measure the HVA and intermetatarsal angle (IMA), also considering the congruency and incongruency of the MTP joints, which would affect the assessment of the severity of hallux valgus. supported
Evidence has supported that the DMAA is not suitable for use in evaluating the congruency of the first MTP joint. For the larger metatarsals of the DMAA, there will also be two situations where the MTP joints are congruent and incongruent. 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 larger than that of the incongruency group, indicating that the application of the DMAA alone to assess whether the first MTP joint was congruent was not reliable. We innovatively proposed two quantitative evaluation indexes for congruency of the first MTP joint on weightbearing foot anterior-posterior images, the MTPJA and CI, which were quantitatively assessed by measuring the angles of the articular surfaces at both ends and the degree of bonding of the articular surfaces (Fig. 1). Because our data were not clinically necessary, many asymptomatic patients were also included, resulting in a larger proportion of patients with mild hallux valgus, most of whom had congruent MTP joints. The proportions of patients with congruency and incongruency with moderate hallux valgus was basically the same. For patients with severe hallux valgus, nearly a quarter of them had congruency of the first MTP joint, which is similar to the data reported by Coughlin. In addition, as the severity of hallux valgus gradually increased, the MTPJA gradually increased, and the CI gradually decreased, indicating that the contact surface of the first MTP joint surface will gradually decrease.
In comparing the difference between the congruency and incongruency groups, there was no difference in the HVA between the two groups of patients with mild, moderate or severe hallux valgus. However, among patients with moderate to severe hallux valgus, the difference between the MTPJA and CI was large; moreover, the CI of the congruency group was greater than that of the incongruency group, and the MTPJA of the congruency group was smaller than that of the incongruency group, indicating that the MTPJA and CI could be used to effectively assess the congruency of the first MTP joint. ROC curves of the MTPJA and CI showed that the AUCs were 0.906 and 0.884, respectively, and that both had diagnostic power. The critical value of the MTPJA was 10.67, and that of the CI was 0.765. We can thus define the first MTP joint as incongruent if the value of MTPJA is greater than 10° or CI is less than 0.765, and the degree of incongruency 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 is. 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. Similar to the HVA, IMA, etc., all of the indicators recovered well, which also verifies the effectiveness of this indicator to a certain extent.
In terms of the correlation test, the DMAA and HVA were positively correlated in the congruency group, while there was no correlation between the two in the incongruency group. This indicates that if the DMAA is to be used to assess the degree of hallux valgus, it is limited to the congruency group. In patients with significant dislocation of the first MTP joint, the DMAA is less effective in assessing the severity of hallux valgus. Therefore, for more severe hallux valgus surgery, the DMAA still needs to be measured in the congruency group, and the value of the DMAA will be used to determine whether to perform DMO. In the congruency group, the correlation coefficients between the MTPJA, CI and HVA were low, while in the incongruency group, the MTPJA and HVA were significantly positively correlated and the CI and HVA were negatively correlated; that is, the more severe the hallux valgus is, the more deviated the normal ranges of the MTPJA and CI are. Of course, the smaller the value of the MTPJA and the larger the value of the CI, the better the matching relationship of hallux valgus is. Therefore, whether in the congruency group or incongruency group, there was a significant negative correlation between the two.
The present paper also has some limitations that should be taken into consideration. First, this study focused only on the statistical analysis of radiological parameters and did not apply the MTPJA and CI to the comparison of parameters before and after the operation in hallux valgus patients. Nor did it classify the magnitude of the two parameters relative to the clinical symptoms. This is what we need to include in the next step of our research. In addition, the patients included in this study had a certain deviation. The number of patients with mild hallux valgus was too large, but because metatarsophalangeal joint mismatch mostly occurs in patients with moderate to severe hallux valgus, we believe that the data in the study are still reliable.
In summary, in hallux valgus of different degrees, especially in patients with moderate to severe hallux valgus, the first MTP joint is either congruent or incongruent. The DMAA has poor performance in evaluating matching relationships, and the previously used imaging indicators are only qualitative evaluations. The MTPJA and CI can be used to quantitatively evaluate the congruency of the first MTP joint, and 10° and 0.765 are used as the demarcation points. Clinically, it is necessary to consider the congruency of the first MTP joint in the selection of different degrees of hallux valgus surgery. The MTPJA and CI can be used as quantitative evaluation indicators. That is, for patients with small MTPJA or large CI, Scarf or Chevron osteotomy can be performed alone. For patients with MTPJA far greater than 10° or CI far less than 0.765, it is necessary to consider whether to perform double metatarsal osteotomy to correct DMAA.