Correlation of First Metatarsal Sagittal Alignment with Clinical and Functional Outcomes Following the Lapidus Procedure

CATEGORY: Bunion; Midfoot/Forefoot INTRODUCTION/PURPOSE: Lapidus procedure (LP) for hallux valgus (HV) requires an adequate control of first metatarsal (M1) sagittal alignment to avoid dorsiflexion. Otherwise, clinical and functional impairment, including transfer metatarsalgia may occur. This study aimed to evaluate the effects of pre- and postoperative measurements of M1 sagittal alignment on clinical and functional outcomes, and whether these variations would lead to transfer metatarsalgia or not. METHODS: 29 patients (36 feet) with a mean follow-up of 20 months after LP were reviewed. Clinical and functional data were assessed with the VAS for pain, AOFAS, LEFS and SF-12. SF-12 comprises physical and mental health scales (PCS-12 and MCS-12, respectively). Transfer metatarsalgia diagnosis was based on the clinical exam. M1 sagittal alignment analysis was based on the first metatarsal declination angle (FMDA) and Meary Angle (MA). Decrease of FMDA means that the M1 dorsiflected (Figure 1). Intermetatarsal angle (IMA) and hallux valgus angle (HVA) were assessed. Radiographic, clinical and functional measurements were compared. Intraclass Correlation Coefficients (ICC) were calculated for FMDA and MA. Linear regression was used to assess the association of Δ-FMDA and Δ-MA with clinical and functional questionnaires. Based on that, we assessed our sample at different cut-off points to evaluate whether a given Δ-FMDA and/or Δ-MA measurement was significantly related to the Δ-Questionnaires. RESULTS: Pre- and postoperative ICC of FMDA was 0.90 and 0.91 and MA was 0.94 and 0.88, respectively. FMDA showed significant variation after the LP, but MA did not. IMA and HVA improved significantly. Significant clinical and functional improvement were observed, except in MCS-12. No patient developed transfer metatarsalgia. A direct correlation was found between ΔFMDA with Δ-PCS-12 and Δ-LEFS (p=.028 and p=.02, respectively), meaning that excessive dorsiflexion of M1 as measured by FMDA led to a decrease in PCS-12 and LEFS. We found that at the cut-off point of quartile 50%, in which our sample was divided equally, patients with Δ-FMDA below 3.2 degrees of dorsiflexion had significantly improved results on Δ-PCS-12 compared to those with greater values (p=.029) (Figure 2). CONCLUSION: The present study showed that excessive dorsiflexion of M1 led to decreased outcome scores as measured by PCS- 12 and LEFS. It supports that M1 dorsiflexion should be avoided after the LP. However, slight dorsal deviation can occur and, even so, satisfactory outcomes can be obtained. Further prospective and comparative studies with larger populations are required to evaluate the effects of M1 inclination on clinical and functional outcomes.