Advanced Principles of Minimally Invasive Vertebral Body Stabilization in Severe Benign and Malignant Fractures: Stent-Screw Assisted Internal Fixation

The anterior and middle columns of the spine supports about 80% of the overall load across the spine. After vertebral augmentation the repaired vertebrae may refracture around the stabilizing cement or the refracture can involve the middle column of the vertebral body by fracturing posterior to the bone cement previously used in the augmentation procedure. The importance of the middle column has traditionally been underemphasized but is important to consider to maintain vertebral body stability given its weight bearing role and the fact that this area is typically not augmented with bone cement during most vertebral augmentation procedures. Osteolysis of the weight bearing portions of the vertebral bodies may be seen with osteolytic metastases. Although pedicle screw and rod fixation of the spine is commonly used in cases where the metastatic disease has compromised the stability of the spine, stand-alone vertebral augmentation may be another viable option to provide pain relief and stability to the spine. The technique of screw-assisted internal fixation (SAIF) was developed to address the limitations of stand-alone vertebral augmentation and is performed with a combination of vertebral body stents and percutaneous cannulated and fenestrated transpedicular screws. The vertebral body stent has advantages over balloon kyphoplasty in that the stent preserves the vertebral body height after the balloon that was used to expand it has been removed and the metallic mesh of the stent helps to control and confine the cement injection thereby making the stent more optimal for use in cases of severe fracturing or prominent osteolysis. In cases where additional support is necessary, such as with middle column fractures or fractures of the pedicles, the stents can be joined to screws placed using a transpedicular technique and cemented in place by injecting bone cement through the cannulated and fenestrated screw. The SAIF technique represents an image guided 360° fusion of the incident fracture level that is much less invasive and has even biomechanical stability than a traditional spanning pedicle screw and rod construct. The SAIF technique has also been shown to reduce the fracture risk of the superior endplate and the posterior vertebral body wall as compared to vertebral augmentation alone. The SAIF technique can be performed as a stand-alone construct or along with traditional spanning spine instrumentation and can be used to obviate or reduce the need for more invasive surgical techniques.