A finite element study of the effect of cross-link stabilisation in a lumbar spine tumour model.

Spinal metastases can increase the risks of vertebral fracture due to bony destruction and instability in the spine. There are concerns that cross-links may impair adjuvant treatments, such as radiotherapy and proton beam therapy. The aim of this study was to assess the biomechanical effects of cross-link stabilisation for a growing tumour in order to provide recommendations on the use and placement of the cross-link. A finite element (FE) model of a fixation device was developed. The device was inserted virtually into a FE model of the lumbar spine (L1-S1) between L2 and L4. Tumour deposit of either 1.3%, 10.1%, 38.3%, 71.5% and 92.1% of the vertebral body was simulated. A 1000 N compressive, a 10° lateral bending and a 7.5 Nm torsional load were simulated on the top of L1. Results indicate that the stabilisation is capable of reducing the stress of the L3 lumbar spine under torsion with a growing tumour. However, compressive loading is concentrated in the L3 anterior vertebra when the tumour volume was greater than 10.1% of the vertebra volume. The cross-link stabilisation reduced the stress of the posterior body within the stabilised segments (L2-L4), especially under torsion. The position of the cross-link does affect the ability of stabilisation to reduce concentrated stress of both vertebrae and screws, which indicates that the position of the cross-link should be considered in clinical surgery to refine the stress concentration, spinal stability and structural stiffness, without compromising adjuvant treatments.