Three-Dimensional Weightbearing Assessment of the First Ray in Hallux Valgus: A Case-Control Study

CATEGORY: Bunion INTRODUCTION/PURPOSE: Coronal plane rotational deformity of the first ray has been implicated with the developmental pathologic process of hallux valgus (HV). Weight Bearing CT (WBCT) is an imaging technology that can support the assessment of this complex three-dimensional (3D) deformity. The objective of the study was to analyze the 3D architecture of the first ray in patients with HV when compared to controls using WBCT images and a 3D biometric algorithm analyzing the deformity in all three planes. We hypothesized that WBCT would confirm the rotational deformity in HV patients, and that the 3D algorithm would demonstrate increased specificity and sensitivity for the pathology when compared to traditional two-dimensional (2D) HV measurements such as the 1-2 intermetatarsal angle. METHODS: Retrospective case-control study, ethics committee approved. Twenty-one feet of patients with clinically symptomatic HV and 20 feet of asymptomatic controls were included. Exclusion criteria applied were previous trauma or surgery affecting first ray or forefoot morphology. All patients were assessed using WBCT. First ray 3D coordinates (x, y, z) were harvested including: center-points of the heads and bases of the first and second metatarsals, center-point of the medial and lateral sesamoids, distal condyles of the proximal phalanx (PP) of the first toe, as well as the medial and lateral borders of the first metatarsal head and diaphysis. The 2D measurements (dorsoplantar 1-2 intermetatarsal (IMA) and metatarsophalangeal (MPA) angles) were obtained using digitally reconstructed radiographs (DRR). The Sesamoid Rotation Angle (SRA) was measured in the coronal plane. Using these coordinates, all 2D, 3D axes, distances, angulations and 3D biometric for HV (HV-3DB) could be calculated. RESULTS: Mean ages were respectively 62.2y in the HV group and 48.8y in the control group (p<0.05). In 2D, the mean IMA and MPA for HV/controls were respectively 14.9/9.3 (p<0.001) and 30.1/13.1 (p<0.001). The SRA were respectively 29.1/7.1 (p<0.001). We found an almost perfect positive correlation between P1 rotation and sesamoid rotation, good correlation between IMA, MPA and SRA angles. There was poor correlation between pronation angles of the 1st phalanx and the 1st metatarsal. The 3D biometric algorithm combining IMA, MPA and SRA had a sensitivity of 95% and a specificity of 95.2% for the diagnosis of HV, compared to 90%/85.6% for the IMA and 90%/90.5% for the SRA. CONCLUSION: This original study confirmed our hypotheses. Weight Bearing CT efficiently analyzed the 3D architecture of the 1st ray in HV patients compared to asymptomatic controls. We concur with previous findings described in the literature concerning increased pronation of the 1st ray in HV. A novel biometric for HV using a specific multidimensional algorithm which combined IMA, HVA and SRA in a single 3D measurement, demonstrated increased sensitivity and specificity compared to the conventional 2D 1-2 intermetatarsal angle for the diagnosis of HV.