Relative Position of the First Ray and Patient Reported Outcome Measures Following the Modified Lapidus Procedure: a Weightbearing CT Study

Abstract

Category: Bunion; Midfoot/Forefoot Introduction/Purpose: Hallux valgus is a complex three-dimensional deformity, and the modified Lapidus is a commonly used procedure to correct moderate to severe deformities. Shortening and elevation of the first ray are two potential factors that may predispose to increased pressure on the lesser metatarsal heads. However, there is currently no consensus regarding optimal position of the first ray following the modified Lapidus. The purpose of this study is to evaluate the impact of the position of the first ray on patient reported outcome measures. Methods: This retrospective study identified 68 patients (72 feet) from a prospectively collected foot and ankle registry who underwent the modified Lapidus bunionectomy over a 4-year period at a single institution with an average follow-up of 20.3 months (Table 1). Patients were included if they were over 18 years of age, had pre and post-operative weightbearing CTs (WBCT), and pre- and minimum 1-year post-operative PROMIS scores. PROMIS scores from 6 domains including Physical Function, Pain Interference, Pain Intensity, Global Physical Health, Global Mental Health, and Depression were evaluated and compared pre- and post-operatively. Radiographic parameters including 1st metatarsal declination angle (MDA), relative metatarsal length (RML), sesamoid position, metatarsus primus elevatus (MPE), hallux valgus angle (HVA), Intermetarsal angle (IMA), and distance from the metatarsal head and sesamoid from the floor were measured and compared before and after surgery. Paired t- tests were employed to evaluate the significance of pre- to post-operative changes. Results: PROMIS physical function, pain interference, pain intensity, and global physical health improved significantly following the modified Lapidus (all p<.001), however, scores did not show significant correlation with shortening of the first ray. The length of the 1st metatarsal relative to the 2nd decreased by an average of 2.7mm following the procedure when measured on WBCT (p <.001), and 2.6mm when measured on plain radiographs (p <.001). There was no significant change in elevation of the first metatarsal (MPE) relative to the 2nd (3.5mm to 3.47, p>=.9). The distance from the sesamoid to floor increased significantly by 1.42mm and the metatarsal to floor distance increased by 2.22mm (both p<.001). The MDA increased from 20.22 to 21.89 (p <.001). Symptoms of transfer metatarsalgia were noted in 5/72 feet (6.9%). Conclusion: This study revealed that the Lapidus bunionectomy resulted in significantly improved PROMIS scores, however, the scores did not correlate strongly with radiographic parameters for first ray shortening or elevation. The relative shortening of the first ray that occurs with the modified Lapidus procedure is minimal (2.7mm) and does not appear to have a significant adverse impact on patient reported outcome measures. Reduction of the sesamoids under the metatarsal head increased the distance from the metatarsal to floor, but did not result in any significant increase in MPE.