Stentoplasty, or vertebral body stenting, represents the next step in the evolution of cement spinal augmentation where a stent is placed within the vertebral body followed by infusion of cement. Current available systems include the Osseofix system (Alphatec Spine) and the VBS system (Synthes). Uei Pua writes about the future directions of the procedure.
In the Osseofix system, the stent is expanded using compressive forces while the VBS system is essentially a balloon-mounted stent. In both systems, the approach used is similar to that used in vertebroplasty in which transpedicular and extrapedicular approaches can be used for stent placement. Current indications for stentoplasty include osteoporotic fractures, some traumatic fractures and spinal metastasis (T2–L5 vertebrae).
In stentoplasty, the stent, once it is expanded creates and maintains a cavity within the vertebral body. This allows for cement to be infused into a low pressure environment, reducing the risk of extravasation. In addition, as the stent has high inherent strength, there is less dependence on cement for compressive load-bearing and therefore much less cement is needed, typically around 1cc. The need for low cement volume in turn reduces the risk of cement complications, as this is a function of the volume of cement used. Furthermore, unlike vertebroplasty, stentoplasty has the advantage of deformity correction; that is restoration of compressed vertebral body height and reduction of kyphotic deformity in the context of osteoporotic compression fractures. While balloon kyphoplasty has similar ability for deformity correction, stentoplasty overcomes the problem of acute recompression of the restored height sometimes seen with kyphoplasty following balloon deflation, as the stent maintains the restored height.
Future directions
Unipedicular insertion of a stent into the midline of the vertebral body using combined cone beam CT and fluoroscopic guidance has recently been described, which represents a significant technical improvement. Compared to the traditional bipedicular approach where two paramedian stents are placed, “central stentoplasty” as it is called utilises cone beam CT to place a single mid-line stent. This results in one less stent, one less incision, one less pedicular transgression and also potentially reduces the procedural time and radiation burden compared to the conventional bipedicular approach. This progression is intuitive given that meta-analyses of unipedicular versus bipedicular kyphoplasty have shown non-inferiority of unipedicular kyphoplasty in terms of the clinical endpoints of pain relief and deformity correction. Additionally, with shorter procedure time and less tissue trauma with single stent placement, we are able to perform central stentoplasty using only conscious sedation in most of our patients. This is particularly advantageous in older patients with comorbidities who may not be ideal candidates for general anaesthesia.
Pictured left: Pre- (left) and post- (right) central stentoplasty cone beam CT images of a patient with osteoporotic fracture of T11. Note the height restoration and kyphotic correction after stentoplasty. The patient was discharged the day after the procedure and returned to normal activity within a week.
Can the procedure be cement-free?
Cement-free implantation is another area of interest. This is made possible due to inherent compressive strength of the stents for load-bearing and has been described in small case series. This potentially eliminates the need for cement and its attendant complications. Alternatives such as infusion of allogenic bone graft instead of cement into the stent to promote healing are also a current area of interest.
Besides osteoporosis fractures, the current systems also allow for adjunctive procedures to be performed co-axially prior to stent implantation and cement infusion. Procedures ranging from simple bone biopsies to combination therapy with ablative techniques in the context of metastatic disease are possible.
Uei Pua is an adjunct assistant professor and consultant in Diagnostic Radiology, Tan Tock Seng Hospital, Singapore. He has disclosed that he is a speaker for Alphatec Spine.
