Vertebral Body Augmentation Research Articles

Kyphoplasty: Chances and limits

Kyphoplasty provides a minimal-invasive surgical technique for the cement augmentation of vertebral bodies following osteoprotic compression fractures or malignant processes. Kyphoplasty has been developed as an advancement of vertebroplasty. Both procedures feature high-success rates in terms of reliable and lasting reduction of pain. Advantages of kyphoplasty over vertebroplasty are to be seen in the possibility of deformity correction as well as in a decreased risk of cement leakage, which represents the most important source for clinical complications. Long-term experiences with the effect of cementing vertebral bodies are sparse. Thus indications and possibilities have to be judged realistically. Conditions, which have to be considered before performing kyphoplasty or vertebroplasty include age of the patient, age of the fracture, degree of deformation and additional degenerative changes of the spine. This article summarizes the present research and literature as well as indications and contraindications and is thought to provide guidelines for the aforementioned decision-making processes.

Bone substitutes in vertebroplasty.

Vertebroplasty--percutaneous cement augmentation of vertebral bodies--is an efficient procedure for the treatment of painful vertebral fractures in osteoporosis. At the present time, polymethylmethacrylate (PMMA) is the only available cement with reports of clinical application and experience. The material is easy to handle, the radiopacity can be adapted by adding contrast dye, and it is mechanically efficient. Composite cements (acrylic cements in conjunction with ceramics) are bioactive, highly radiopaque, and feature excellent mechanical properties. One such cement, Cortoss, is currently undergoing clinical trials for vertebroplasty and has so far been shown to be a potentially valuable alternative to PMMA. Several in vitro studies with injectable calcium phosphate (CaP) cements show their feasibility and mechanical effectiveness. Animal studies confirm their biocompatibility and osteoconductivity. However, handling problems and the limited radiopacity of these cements currently preclude their clinical use.

Experimental vertebroplasty using osteoconductive granular material.

Osteoporotic human cadaveric thoracic vertebral bodies and vertebral bodies from mature sheep were used as model systems to assess coral resorption and new bone formation after injection of coral granules. To evaluate the use of natural coral exoskeleton, an osteoconductive material, for the filling of vertebral bodies. Percutaneous injection of polymethylmetacrylate (PMMA) is often proposed for prophylactically stabilizing osteoporotic vertebral bodies at risk for fracture or augmentation of vertebral bodies that have already fractured. Recently, the possibility of using osteoconductive materials in granular formulation was assessed in pilot studies. As a first step, the possibility of injecting coral granules percutaneously within osteoporotic human cadaveric thoracic vertebral bodies was assessed. As a second step, cavities were drilled into vertebral bodies of 10 mature ewes and were either left empty (control group) or filled with coral alone (CC) or coral supplemented with fibrin sealant (CC+FS). Quantitative evaluation of coral resorption and new bone formation was made 2 months and 4 months after implantation. The distribution of coral granules injected into human cadaveric thoracic vertebral bodies was homogenous as assayed radiographically. In the experimental animal model, osteogenesis was increased in cavities filled with coral in comparison with cavities left empty at both 2 months and 4 months (P < 0.005 and P < 0.02, respectively). Surprisingly, supplementation of coral with a fibrin sealant had no positive influence on osteogenesis (P < 0.0008 at 2 months; P < 0.002 at 4 months). In addition, it led to an increase in coral resorption by as soon as 2 months (P < 0.0008). These results demonstrate the osteoconductivity of coral in granular form for vertebral filling. Interestingly, interconnectivity between adjacent bone trabeculae and newly formed bone was restored; however, its mechanical significance remains to be determined. Further investigations are needed to evaluate the efficacy of coral in osteopenic animals and in relieving pain.

Effect of augmentation on the mechanics of vertebral wedge fractures.

The effect of cement augmentation of wedge-fractured vertebral bodies on spine segment compliance was studied in 16 cadaver specimens. 1) To assess the mechanical effects of cement augmentation of vertebral wedge fractures. 2) To determine whether a new reduction/injection procedure has the same mechanical effects as the established direct injection procedure. Although wedge fractures cause pain and disability in hundreds of thousands of people, few effective treatments are available. Clinical studies have shown that cement augmentation, a new procedure, effectively relieves pain and restores mobility in patients suffering from weak or fractured vertebrae. However, only a few studies have examined the mechanics of vertebral augmentation. A wedge fracture was created in the middle vertebra of 16 three-vertebra cadaver spine segments. Neutral and full-load compliance of each fractured spine segment in flexion/extension and lateral bending were assessed by measuring the relative rotation of the vertebral bodies in response to applied moments. Eight of the fractured vertebral bodies were then augmented using direct injection, while the remaining eight fractured vertebral bodies were augmented using a combined reduction/injection procedure. Compliance of the augmented segments was then assessed. Augmentation significantly reduced the neutral compliance (reduction of 25% +/- 23%) (mean +/- standard deviation) and the full-load compliance (reduction of 23% +/- 20%) in flexion/extension (P < 0.005). Augmentation also significantly reduced the neutral compliance (reduction of 34% +/- 20%) and the full-load compliance (reduction of 26% +/- 17%) in lateral bending (P < 0.0001). No significant difference was found between the two procedures for compliance reduction. Augmentation of wedge fractures using both direct injection and reduction/injection reduces spine segment compliance significantly.

Future directions. Augmentation of osteoporotic vertebral bodies.

Because current medical and surgical treatments of vertebral body fractures are less than adequate, there is a need for interventions that decrease the likelihood of occurrence of these fractures and improve the treatment options once they have occurred. One such broad category of intervention involves the fortification or augmentation of the vertebral bodies. In addition to prophylactically stabilizing osteoporotic vertebral bodies at risk for fracture, augmentation of vertebral bodies that have already fractured may prove to be useful by reducing pain, improving function, and preventing further collapse and deformity. Vertebral body augmentation can also be used as an adjunct to fixation of internal hardware--for example, pedicle screws-in osteoporotic spines. A number of products are now available or are in clinical trials. The most promising products are injectable materials-polymethylmethacrylate or mineral bone cement. The early clinical results using polymethylmethacrylate in percutaneous vertebroplasty for fractured vertebral bodies and the results in vitro using an injectable mineral cement for vertebral body fortification are encouraging. Although the principle of vertebral body augmentation remains encouraging, data to support the widespread use of these techniques remain sparse, and the indications for their use should be more clearly defined.