The first metatarsal pronation leads to increased distal metatarsal articular angle: a self-controlled study

Our study aimed to analyze the relationship between distal metatarsal articular angle (DMAA) and first metatarsal (M1) pronation by measuring the DMAA and first metatarsal rotation angle (MRA) of patients with unilateral hallux valgus (HV) and discussed its significance in the surgery for HV treatment. We performed a retrospective self-controlled study including patients with unilateral HV from January 2015 to December 2018 in our hospital. The affected and contralateral normal feet were divided into HV and normal groups. The hallux valgus angle (HVA), DMAA, the first and second intermetatarsal angle (IMA), first metatarsal rotation angle (MRA), Hardy score in weight-bearing anteroposterior radiographs of the foot, and Yildirim score in tangential radiographs of the sesamoid were measured in the two groups. Statistical analysis was conducted to investigate the difference in all radiographic parameters between the two groups and the correlation between DMAA, Hardy score, and Yildirim score. A total of 20 unilateral HV patients, including 1 man and 19 women (average age 53.35 ± 13.90, range 25–73), were enrolled in this study. The average HVA, DMAA, IMA, Hardy score, and Yildirim score in the HV group (n = 20) were 40.04 ± 8.96°, 29.40 ± 9.73°, 13.34 ± 2.73°, 5.5 ± 0.97, and 2.35 ± 0.65, respectively. The average HVA, DMAA, IMA, Hardy score, and Yildirim score in the normal group (n = 20) were 16.06 ± 2.70°, 16.13 ± 7.77°, 10.02 ± 2.14°, 3.4 ± 1.02, and 0.85 ± 0.73, respectively. There was a significant difference in DMAA between the two groups (P < 0.001). A significant positive correlation was observed between MRA and DMAA (r = 0.617, P = 0.004). However, no significant correlations were found between MRA and the Hardy score (r = 0.028, P = 0.908) or Yildirim score (r = 0.285, P = 0.223). M1 rotation is significantly correlated with DMAA in HV deformity, underscoring the importance of assessing rotational alignment in preoperative planning. Intraoperative correction of rotational deformity may be essential in cases of an inadequately corrected DMAA.