Effect of Third-Generation Minimally Invasive Bunionectomy on First-Ray Pronation

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Category: Bunion; Midfoot/Forefoot Introduction/Purpose: Hallux valgus(HV) is a triplanar deformity that includes the pronation of the first ray. Although there is little data regarding the effect of pronation on clinical outcomes, the rotational component of HV may play an important role. One study suggested that the modified Lapidus technique effectively decreased the pronation of the first ray. However, there is no evidence for alternative procedures such as minimally invasive(MIS) bunionectomy. This study sought to assess if MIS bunionectomy can effectively correct the first ray's pronation and determine the correlation with improved PROMIS scores. In addition, the association between postoperative first-ray pronation and the sesamoid station was investigated. We hypothesized a significant decrease in first-ray pronation after MIS bunionectomy, which would be associated with improved PROMIS scores. Methods: Sixty-three consecutive patients who underwent MIS bunionectomy with available pre- and at least 5-month postoperative WBCT-scans were included. Pre- and postoperative measurements of HV deformity, including the intermetatarsal angle(IMA) and hallux valgus angle (HVA) on plain radiographs, and triplanar pronation angle (TAP – a measure of first ray pronation) and sesamoid station from WBCTs, were performed as previously described. The TAP was referenced to the dorsal aspect of the second metatarsal base. Pre- and 1-year postoperative PROMIS scores were reviewed. Sample t-tests were used to compare pre- and postoperative values. The Kruskal-Wallis test assessed statistical differences between postoperative sesamoid station groups regarding postoperative TAP or IMA. Spearman rank (rho) was used to assess correlations between pre- to postoperative change in TAP with PROMIS scores in the physical function (PF), pain interference (PIF), and pain intensity (PI) domains. Scatterplots were simultaneously presented to visualize potential trends between TAP and PROMIS scores. Results: The mean TAP significantly decreased by 8.21º(95%CI -9.62,-6.8) after MIS bunionectomy (p< 0.05). Mean(SD) pre- and postoperative TAP values were 31.57º(8.3) and 23.36º(7.6), respectively. Similarly, mean HVA and IMA values decreased by 21.98º and 11.41º, respectively. Mean preoperative sesamoid station was 1.84, which decreased to 0.95 after surgery. Forty-four patients reduced their sesamoid position by one station. There was a statistically significant difference in TAP between postoperative sesamoid station groups (p=0.038). Mean(SD) postoperative TAP according to sesamoid station was 25.93º(6.2) for group 1, 23.83º(7.9) for group 2, and 18.75º(6.6) for group 3. No significant differences between groups were observed regarding IMA (p=0.25). There was a modest correlation between TAP change and PROMIS PF (rho = 0.046), PIF ( rho = -0.30), and PI (rho = -0.03). Conclusion: Our study suggests that MIS bunionectomy is an effective tool for reducing first-ray pronation in patients with HV. Although there was a statistically significant correlation between first-ray pronation and sesamoid station, our results showed that patients with higher first-ray pronation had less reduced sesamoids. Therefore, these should be considered separate deformities, and the sesamoid station shouldn’t be used as a guide for pronation correction. It appears that correction of the first-ray pronation is poorly associated with 1-year PROMIS scores. Consequently, future studies assessing mid-to-long-term effects of first-ray pronation on clinical outcomes, such as recurrence, are still warranted.