Abstract
Vertebral compression fractures are one of the most relevant clinical consequences caused by osteoporosis: one of the most common treatment for such fractures is vertebral augmentation through minimally invasive approaches (vertebroplasty or balloon-kyphoplasty). Unfortunately, these techniques still present drawbacks, such as re-fractures of the treated vertebral body with subsidence of the non-augmented portions or re-fracture of the non-augmented middle column at the junction with the augmented anterior column. A novel minimally-invasive augmentation technique, called Stent-Screw Assisted Internal Fixation, has been recently proposed for the treatment of severe osteoporotic and neoplastic fractures: this technique uses two vertebral body stents and percutaneous cannulated and fenestrated pedicular screws, through which cement is injected inside the expanded stents to achieve optimal stents' and vertebral body's filling. The role of the pedicle screws is to anchor the stents-cement complex to the posterior column, acting as a bridge across the middle column and preserving its integrity from possible collapse. In order to evaluate the potential of the new technique in restoring the load bearing capacity of the anterior and middle spinal columns and in reducing bone strains, a Finite Element model of an osteoporotic lumbar spine has been developed. Both standard vertebroplasty and Stent-Screw Assisted Internal Fixation have been simulated: simulations have been run taking into account everyday activities (standing and flexion) and comparison between the two techniques, in terms of strain distribution on vertebral endplates and posterior and anterior wall, was performed. Results show that Stent-Screw Assisted Internal Fixation significantly decrease the strain distribution on the superior EP and the cortical wall compared to vertebroplasty, possibly reducing the re-fracture risk of the middle-column at the treated level.
Highlights
Osteoporosis, defined as “a systemic skeletal disease characterized by low bone mass and micro-architectural deterioration of bone tissue with a resultant increase in fragility and risk of fracture,” is a major clinical issue worldwide (Lippuner, 2003)
The median values obtained on the anterior column demonstrate that both Screw Assisted Internal Fixation (SAIF) and Vertebral augmentation (VA) techniques reduced the principal strains in the treated vertebra compared to the OP case (Table 2)
Following VA, the strains significantly decrease on the middle column, due to the higher load shared by the anterior column filled with stiff cement; in the middle column, the median strains significantly decrease of 15% (p = 0.03, Figure 5) on the superior EP and of 48% (p < 0.01, Figure 5) on the posterior wall, compared to OP condition
Summary
Osteoporosis, defined as “a systemic skeletal disease characterized by low bone mass and micro-architectural deterioration of bone tissue with a resultant increase in fragility and risk of fracture,” is a major clinical issue worldwide (Lippuner, 2003). Vertebral compression fractures (VCFs) is one of the most relevant clinical consequences, potentially causing acute and chronic pain, and reduced quality of life (Du et al, 2014), with an impact on mortality (Edidin et al, 2015). Vertebral augmentation (VA), performed with vertebroplasty or balloon-kyphoplasty, implies percutaneous image-guided injection of bone cement in the anterior two thirds of the VB (i.e., the anterior column), and it is widely used to treat fragility fractures, to arrest fracture progression, to palliate pain and to restore the load-bearing capability of the VB (Wardlaw et al, 2009; Klazen et al, 2010; Firanescu et al, 2011; Clark et al, 2016; Filippiadis et al, 2017). The injection of cement in the VB aims at a homogeneous trabecular filling, but it is stopped for safety reasons, when the cement approaches the posterior third of the VB, to avoid leakage in the central canal
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