Three-Dimensional MRI-Based Statistical Shape Analysis of Knee Bone Morphology in Individuals with Generalized Joint Hypermobility

Abstract

Background: Generalized joint hypermobility (GJH) is associated with ligamentous and capsular laxity and an increased risk of knee injury. Whether GJH is associated with three-dimensional knee bone morphology remains unclear. This study compared femoral, tibial, and patellar morphology between young adults with GJH and healthy controls using magnetic resonance imaging (MRI)-based statistical shape modeling (SSM). Methods: This cross-sectional study included 80 participants aged 18–25 years, comprising 40 individuals with GJH (Beighton score ≥ 6) and 40 healthy controls (Beighton score ≤ 2). One right knee per participant was analyzed. High-resolution 3.0-T MRI was used to segment and model the femur, tibia, and patella separately in ShapeWorks. The primary SSMs were scale-normalized using Procrustes alignment to remove global isotropic scale differences. Principal components (PCs) accounting for at least 95% of cumulative shape variance were retained. Overall group differences were assessed using permutational multivariate analysis of variance (PERMANOVA), with multivariate dispersion assessed using PERMDISP. Individual PCs were compared with Benjamini–Hochberg false discovery rate (FDR) correction. Results: Significant overall scale-normalized shape differences were observed between the GJH and healthy control groups for the femur (pseudo-F = 8.14, R2 = 0.0945, p = 0.0009), tibia (pseudo-F = 9.13, R2 = 0.1048, p = 0.0006), and patella (pseudo-F = 2.00, R2 = 0.0250, p = 0.0255), with no significant between-group differences in multivariate dispersion. After FDR correction, femoral PC1 (Hedges’ g = 0.765, q = 0.0171) and tibial PC1 (g = 0.841, q = 0.00621) differed significantly between groups, whereas no individual patellar PC remained significant. Descriptive surface maps showed visually larger group-mean surface displacements in periarticular osseous contours than across the major articular contact surfaces. Conclusions: Significant three-dimensional differences in femoral, tibial, and patellar morphology remained detectable between individuals with GJH and healthy controls after removal of global isotropic scale. Femoral and tibial differences were primarily reflected in PC1, whereas the patella showed an overall multivariate difference without an individual FDR-significant PC. After global isotropic scale was removed, between-group shape differences persisted, indicating that they were not solely attributable to overall bone size.