Sesamoid View X-ray vs Weightbearing Computed Tomography in the Measurement of Metatarsal Pronation Angle

Abstract

Category: Bunion; Midfoot/Forefoot Introduction/Purpose: First metatarsal (M1) axial rotation as measured by the metatarsal pronation angle (MPA) has increasingly become recognized as a clinically relevant component of hallux valgus deformity and methods to realign the M1 in 3 dimensions have been developed. Preoperative imaging with weightbearing computed tomography (WBCT) is considered the best way to image and measure the MPA, however WBCT is not available to many foot and ankle surgeons. The aim of this project is to investigate if the MPA measured on sesamoid view weight bearing radiographs is similar to that measured on WBCT. Methods: A retrospective analysis of patient imaging studies was performed. We identified 25 feet with both sesamoid WBR and WBCT images from a consecutive patient database. Included subjects had no trauma or foot and ankle operation between acquisition of the two scans. MPA of the WBCT for each patient was initially measured. After an appropriate washout period, the observer then measured MPA of the WBR for the cohort. Demographic statistics were calculated, a paired t-test was performed to evaluate for any significant difference in angular measurement between the two scans. Results: Patient characteristics: mean age 53 +- 16 years, mean BMI 32 +- 8 kg/m2, 13 right and 12 left feet, 19 females and 6 males. Average time between sesamoid view WBR and WBCT was 5.7 +- 9.5 months. Mean difference in MPA between WBR and WBCT = 0.6 +- 3.9 degrees (p= 0.444, t=0.777). Conclusion: Among the cohort assessed, we found no significant difference present in the measurement of the metatarsal pronation angle as evaluated on sesamoid view weightbearing radiography compared with weightbearing computed tomography (Figure 1). Routine acquisition of a sesamoid view weightbearing radiograph may be considered as an appropriate substitute for weightbearing computed tomography in the preoperative evaluation of M1 rotation in the coronal plane. These findings may benefit physicians who do not have access to weightbearing computed tomography in their clinics.