Vertebral compression fractures after spine irradiation using conventional fractionation in patients with metastatic colorectal cancer

Evaluation of predictive factors of vertebral compression fracture after conventional palliative radiotherapy for spinal metastasis from colorectal cancer

OBJECTIVE Delayed consequences of spinal radiotherapy (RT), including vertebral compression fracture (VCF), are critical complications. However, the predisposing factors that contribute to VCF after conventional RT are unclear. The aim of this study was to assess the incidence of VCF and to determine the predictors of VCF following conventional spinal RT specific to colorectal cancer (CRC). METHODS The authors retrospectively reviewed 237 spinal segments (147 metastatic and 90 nonmetastatic) in 53 patients with CRC who underwent RT with a median total dose of 30 Gy in 10 fractions between January 2007 and December 2014. The primary end point was the development of a VCF following RT, either de novo VCF or the progression of a baseline VCF. VCFs were assessed using the spinal instability neoplastic score (SINS) criteria. RESULTS Among all 237 spinal segments, 22 VCFs (9.3%) were observed following RT, including 13 de novo and 9 progressive fractures, and the median time to VCF was 4 months. All VCFs developed in metastatic spines. Among 147 metastatic spinal segments, 22 fractures were observed, with a 12-month cumulative incidence of VCF of 14.8%. Results of multivariable analysis indicated sex (p = 0.023) and SINS class II/III (p < 0.001) as risk factors related to development of a VCF in metastatic spinal segments. Among the SINS criteria, a lytic tumor and the presence of a baseline VCF were identified as predictors of VCF in metastatic spinal segments. CONCLUSIONS In osteolytic or mixed lesions that were predominant in spinal metastases of CRC, the incidence of VCF was not negligible, even in patients treated with conventional spinal RT. This was especially evident in patients with spinal metastases with a SINS score ≥ 7. Presence of a baseline VCF after spinal RT is a predictor of VCF development and should be observed carefully.

Mechanical assessment of the effects of metastatic lytic defect on the structural response of human thoracolumbar spine

To investigate the effects of a clinical lytic defect on the structural response of human thoracolumbar functional spinal unit. A novel CT-compatible mechanical test system was used to image the deformation of a T12-L1 motion segment and measure the change in strain response under compressive loads ranging from 50 to 750 N. A lytic lesion (LM) with cortex involvement (33% by volume) was introduced to the upper vertebral body and the CT experiments were repeated. Finite element models, established from the CT volumes, were used to investigate the defect's effects on the structural response and the state of principal and shear stresses within the affected and adjacent vertebrae. The lytic lesion resulted in severe loss of the vertebral structural competence, resulting in significant, non-linear, and asymmetric increase in the experimentally measured strains and computed stresses within both vertebrae (p < 0.01). At the cortex, the tensile strains were significantly increased, while compressive strains significantly decreased, (p < 0.05). Both the vertebral bone and cortex regions adjacent to the defect showed significant increase in computed compressive, tensile, and shear stresses (p < 0.01). Changes in stress and strain distribution within the affected and adjacent vertebral bone and the experimentally observed bulging and buckling of the vertebral cortices suggested that initiation of catastrophic vertebral failure may occur under load magnitudes encountered in daily living. Although the effect of LM on the global deformation of the spine was well-predicted, our results show that FE predictions of local strain changes must be carefully assessed for clinical relevance. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1808-1819, 2016.