Finite element study on whether posterior upper wall fracture is a risk factor for the failure of short-segment pedicle screw fixation in the treatment of L1 burst fracture

Abstract

PurposeTo establish the finite element model of T12 and L2 (T12-L2) pedicle screw fixation for severe L1 burst fracture, and quantitatively simulate and analyze the screw stress and vertebral displacement in different degrees of L1 posterior upper wall fracture (PUWF), and evaluate whether PUWF degree is a risk factor for fixation failure. MethodsThe data of 6 healthy volunteers were used to establish a finite element model of T12-L2 pedicle screw fixation for type A severe burst fractures. The stress and displacement of the conventional and Schanz pedicle screws for the different degrees of PUWF (including the anterior upper wall of the vertebral canal and the bipedicle) were evaluated. ResultsThe maximum stress and L1 displacement of conventional and Schanz pedicle screws were positively correlated with the severity of the PUWF (P<0.05). During anterior flexion, the maximum stress of conventional pedicle screws for 70% type I were 538.3±59.75MPa and the maximum stress of Schanz pedicle screws for 90% type Ⅱ, 90% type Ⅲ and 70% type IV fractures were close to the fatigue threshold. The maximum stress during anterior flexion were significantly higher than those during posterior extension, bending and rotation (P<0.05). ConclusionThe posterior upper wall fracture of vertebral body (VB) of type A burst fracture is not an independent risk factor for the failure of short-segment pedicle screw fixation (SSPSF). Anterior flexion of type A fractures combined with severe PUWF of VB was a risk factor for the failure of SSPSF.