Association of First Metatarsal Pronation with Patient-Reported Outcomes and Recurrence Rates in Hallux Valgus

Abstract

Category: Bunion Introduction/Purpose: Hallux valgus (HV) is a triplanar deformity of the first metatarsal in which the first metatarsal adducts, dorsiflexes, and pronates with an average increase in pronation between 2° and 8° compared with normal patients (Kimura JBJS, Campbell FAI). Despite these radiographic changes of the first metatarsal in patients with HV, no correlation between postoperative two-dimensional radiographic parameters and patient-reported outcomes has been reported (Thordarson FAI). The purpose of this study was to determine if a postoperative decrease in first metatarsal pronation (1MTPronation) was associated with changes in patient-reported outcomes as measured by the PROMIS physical function, pain interference, and pain intensity domains or recurrence rates in patients with HV who undergo a first tarsometatarsal fusion (modified Lapidus procedure). Methods: This study included thirty-nine consecutive HV patients who underwent a modified Lapidus procedure, had preoperative and >=2-year postoperative PROMIS scores, and had 1MTPronation measured using the previously described triplanar angle of pronation (FAI, in press) on preoperative and at least 5-month postoperative weightbearing CT scans. Multivariable regression analyses were used to investigate differences in the change in PROMIS domains preoperatively and 2-years postoperatively between patients with 'no change/increased 1MTPronation' and 'decreased 1MTPronation.' No differences in preoperative radiographic parameters or patient characteristics found between two groups. A secondary analysis using multivariable regression modeling was performed to determine if patients with a decrease in 1MTPronation between 2°-8° ('moderate pronation change') had greater improvements in PROMIS scores compared with 'minimal pronation change' (8°) groups. A log-binomal regression analysis was performed to identify if a decrease in 1MTPronation was associated with recurrence of the HV deformity (postoperative HVA>=20° Results: The decreased 1MTPronation group (n=26) had a statistically significant greater improvement in the PROMIS physical function scale by 7.2 points (95% confidence interval (CI) 2.1-12.3, P=0.007) compared to the no change/increased 1MTPronation group (n=13). There were no statistically significant differences in PROMIS pain interference (P=0.380) or pain intensity (P=0.443) scores between the two groups. The secondary analysis found that patients in the moderate pronation change group (n=15) had significantly better improvements in the PROMIS physical function and pain intensity domains than the minimal pronation change group (n=14) (Table 1). The moderate pronation change group also had greater improvements in the PROMIS pain interference and pain intensity domains than the substantial pronation (n=10) change group (Table 1). Recurrence rates were significantly lower in the decreased 1MTPronation pronation group when compared to the no change/increased 1MTPronation group (11.5% and 46.2%, respectively; risk ratio 0.25, 95% CI 0.07-0.84, P=0.025). Conclusion: In patients undergoing a modified Lapidus procedure for correction of their HV deformity, a postoperative decrease in pronation of the first metatarsal, especially between 2° and 8°, was associated with improvement in PROMIS scores at two- years postoperatively and a lower recurrence rate. These results suggest that the rotational component of the hallux valgus deformity may play an important role in outcomes following surgery, and consequently, surgeons should consider addressing but not overcorrecting the first metatarsal pronation deformity when performing a surgical procedure for the treatment of hallux valgus.