Author & Illustrator: Tiffany Ni | Medical Student at University of Toronto, Temerty Faculty of Medicine
Editor: Rohan Patil | Medical Student at The George Washington University SMHS
In 1979, a 54-year-old woman presented to the hospital complaining of severe cervical pain for years. On plain radiographs of her cervical spine, everything appeared normal. Five years later, she presented again – this time with unbearable pain associated with severe radiculopathy localized to the C2 nerve root and plain radiographs showing a large vertebral hemangioma involving the entire C2 vertebral level. An epidural extension of the disease was seen on axial computerized tomography, and a C2 laminectomy was promptly performed. To stabilize the vertebra and provide structural reinforcement, Pierre Galibert and Hervé Deramond, two interventional radiologists from Amiens, France, decided to inject 3 mL of cement into the vertebral body percutaneously using a 15-gauge needle1. Surprisingly, the patient experienced complete pain relief. Given such a miraculous outcome, the physicians subsequently performed this procedure in six other patients and published the first report on the percutaneous vertebroplasty shortly after in 19871.
Originating from the Greek word “plastos,” the English suffix “plasty” means to change, remodel, or form. The vertebroplasty procedure, therefore, means rebuilding the vertebrae. Performed under fluoroscopic guidance, percutaneous vertebroplasty (PV) is a minimally invasive procedure that has since become widely used for treating vertebral fractures caused by osteoporosis, malignancies, and trauma2. Bone fragments at the fracture site are stabilized with polymethylmethacrylate (PMMA), commonly referred to as bone cement (Figure 1).
Figure 1: Percutaneous vertebroplasty. A) Vertebral compression fracture at T12 vertebra. B) Transpedicular injection of PMMA bone cement through the cannula under fluoroscopic guidance.
Unlike actual cement used on construction sites to bond two bricks together, PMMA acts as a filler to create a tight space in the fracture site3. Thus, it may be more accurately termed “bone grout.” Ultimately, it aids in maintaining spinal alignment and prevention of future spinal-related events, specifically, progressive collapse of the vertebral body and neurological complications1,4. The two main indications currently for PV in spinal metastasis are pain management and vertebral column stabilization5. Although vertebroplasty is an effective and safe procedure, the technique has some complications. Previous reports have reported cement leakage in 30-65% of patients with osteoporotic vertebral collapse and 38-72.5% of patients with malignant collapse6–8. While most patients are clinically asymptomatic, cement extravasation can lead to serious side effects, including neurological deficits, new vertebral compression fractures, and pulmonary embolism7.
Building upon the vertebroplasty procedure is balloon kyphoplasty. Also used for treating vertebral fractures, balloon kyphoplasty is performed by first sending a bone tamp into the vertebral body with a balloon at the tip9 (Figure 2).
Figure 2: Balloon kyphoplasty. A) Vertebral compression fracture at T12 vertebra. B) Transpedicular insertion and inflation of balloon under fluoroscopic guidance. C) Balloon is removed and PMMA bone cement is injected.
Inflation of the balloon with a radiopaque contrast medium subsequently creates a cavity inside the vertebral body while restoring the height10. After collapsing and removing the balloon, the space left behind allows the injection of more viscous cement at a lower pressure – reducing the downstream risk of cement leakage through the vertebral body wall into the spinal canal9,10. However, restoration of the vertebral body height may be temporary as there is often a partial vertebral body collapse following deflation of the balloon11. Moreover, the added advantage of height restoration in kyphoplasty is still debated in the literature and studies have shown that additional factors such as the amount of cement injected or the cement viscosity may also play an important role on pain relief and risk of cement extravasation, respectively7,12. There exists a great need for large-scale randomized controlled trials to better delineate and mitigate the risks associated with vertebroplasty and balloon kyphoplasty procedures.
In the years since, many third-generation vertebroplasty technologies have aimed to remedy this temporary height restoration problem. Designed like a literal car jack, the SpineJack implant system (Stryker, Kalamazoo, MI) is a small device for mechanical kyphoplasty recently approved by the FDA to treat vertebral compression fractures13 (Figure 3).
Figure 3: SpineJack implant system. A) Vertebral compression fracture at T12 vertebra. B) Symmetrical transpedicular insertion and deployment of the SpineJack device (second SpineJack device not shown in diagram). C) PMMA bone cement is injected.
Made of titanium alloy, this implant restores the height of the vertebral body by using the transpedicular approach to insert two symmetrically positioned implant devices, allowing for the homogenous spreading of the PMMA13,14. A randomized controlled trial in Europe compared the SpineJack to balloon kyphoplasty and demonstrated noninferiority of the SpineJack system, with significantly more pain relief in the SpineJack group at one month and six months following surgery15. Other widely used third-generation vertebroplasty augmentation devices include the Vertebral Body Stenting System and the OsseoFix Spinal Fracture Reduction System (Alphatec Spine Inc., Carlsbad, CA)16. Although similar in function, these devices bear different technical features and are therefore indicated for different patient demographics, fracture characteristics, and morphologies16.
Remarkably simple and elegant, the first vertebroplasty procedure showed great promise in providing immediate pain relief for patients with debilitating spinal pathologies. While complications have been documented in the years since, clever innovations using devices such as balloons or spine jacks continue to pave the way in optimizing and improving this procedure.