Fig. 5
From: Finite element analysis after rod fracture of the spinal hybrid elastic rod system
The von Mises stress distribution on the pedicle screw, outer PCU shell (PS) and inner nitinol stick (NS) during flexion. The PS stress of the fractured nitinol stick (Ns-F) was higher than that of intact nitinol stick (Ns-I). In contrast, the screw stress and NS stress were lower in Ns-F group. The outer PS stress was shielded by the inner NS when the NS was intact. Once the inner NS was broken, the screw and NS lost attachment in the Ns-F, and the PS took over the stress. Hence, the NS stress and screw stress decreased, and the PS stress increased