Mechanical effects of different cast immobilization positions in Colles’ fracture: a finite element analysis investigation

This study investigated the optimal cast immobilization position for conservative treatment of Colles' fracture using finite element analysis (FEA). Ten upper limbs from cadavers were scanned with computed tomography in five palmar-dorsiflexion positions (V30, V15, DV0, D15, and D30) and five radioulnar deviation positions (U20, U10, RU0, R10, and R20). Colles' fracture models with comminuted dorsal cortex and intact volar cortical continuity were developed and subjected to FEA. Each position was assessed for fragment displacement, principal strain at the fracture site, and equivalent stress propagation direction. The minimum fragment displacement was observed at 15° of dorsiflexion and 10° of radial deviation. The differences in distance between dorsal fragments before and after loading in V30, V15, DV0, D15, and D30 were 1.05 ± 0.25, 0.77 ± 0.23, 0.50 ± 0.18, 0.23 ± 0.18, and 0.24 ± 0.11 mm, respectively, with D15 being the smallest. Translation of volar cortical bone in U20, U10, RU0, R10, and R20 was 1.84 ± 1.06, 1.57 ± 0.80, 0.76 ± 0.67, 0.34 ± 0.15, and 0.47 ± 0.24 mm, respectively, with R10 being the smallest. Principal strains at the fracture site were minimal at D15 and R10. Stress propagation analysis revealed that forces were transmitted through the volar cortex at D15 and perpendicular to the fracture line at R10. The FEA demonstrates that cast immobilization at 15° of dorsiflexion and 10° of radial deviation is optimal for conservative treatment of Colles' fracture by minimizing mechanical load at the fracture site.