Kyphoplasty and Vertebroplasty

Sergey Mlyavykh

Andrey Bokov

Vertebroplasty and kyphoplasty are minimally invasive procedures that are based on the injection of polymethylmethacrylate (PMMA) into the vertebral body through a biopsy needle. Vertebroplasty was described first in 1987 and now has been broadly introduced into clinical practice to treat patients with low energy fractures and tumor and tumor-like lesions of vertebra body. Kyphoplasty is a more recent modification of vertebroplasty that involves inflation of balloon within the collapsed vertebral body, theoretically enhancing vertebral body height restoration and providing a cavity for the introduction of PMMA cement. With kyphoplasty, bone cement can be injected under a lower pressure due to the cavity in the vertebral body which may reduce the risk of cement leakage.

The plausible mechanisms of the clinical effects of kyphoplasty and vertebroplasty include the restoration of load-bearing capacity of vertebra body after PMMA injection and chemical and thermal denervation of local tissues. Unpolymerized methylmethacrylate has been shown to be a strong cytotoxic agent and may inhibit neoplastic proliferation following vertebroplasty or kyphoplasty.¹

The indications for a vertebroplasty/kyphoplasty procedure include the treatment of osteolytic lesions associated with multiple myeloma, lymphoma, osteolytic metastases and low energy vertebra fractures associated with osteoporosis. In case of low energy fractures, vertebroplasty or kyphoplasty is indicated to treat patients with intractable pain resistant to conservative treatment of at least 1 month’s duration.¹,²

A primary benefit of cement augmentation technology is the minimally invasive nature of the procedures. Compared to open surgery, these procedures generally have a shorter duration of hospitalization and a lower risk of mortality and morbidity, especially in elderly patients. In addition, vertebroplasty and kyphoplasty do not require general anesthesia, even in cases with multifocal vertebral lesions.³

The contraindications to vertebroplasty and kyphoplasty include active infection, cement allergy, coagulation disorders, and fractures with the disruption of posterior elements. Relative contraindications include fractures where there is a high risk of cement leakage (e.g., fractures with posterior cortical disruption). In cases with severe vertebral collapse (80% of height loss and more) and with osteoblastic metastasis vertebroplasty may not be appropriate. Patients with symptomatic spinal cord and nerve root impingement due to epidural extension of metastases are also generally poor candidates for vertebroplasty and kyphoplasty.¹

VERTEBROPLASTY TECHNIQUE

Patients should have a normal coagulation profile at the time of kyphoplasty or vertebroplasty. Vertebroplasty and kyphoplasty are performed under sterile conditions in an operation room or fluoroscopy suite. Fluoroscopic guidance during the procedure is mandatory. Patients may be treated under local anesthesia with conscious sedation or general anesthesia depending on patient and physician preferences.

The patient is positioned prone on soft pads, with the arms extended forward or at shoulder level. Prophylactic antibiotics are administered prior to the procedure.¹

The entry points for a biopsy needle are verified using fluoroscopy anteroposterior (AP) view and should be 1.5 to 3 cm laterally to the lateral boarder of the pedicle. Local anesthesia is utilized to anesthetize the skin and periosteum at the entry point of pedicle. A beveled- or trocar-tipped needle is used to perform vertebroplasty and kyphoplasty procedures. The common needle sizes are 8G to 10G needles in the lumbar spine and 10G to 13G needles at
thoracic levels. Various approaches can be used to introduce needle into the vertebral body including the transpedicular, parapedicular, or costovertebral approach. The safest and most frequently used approach is transpedicular. With this approach, the cortical bone of a pedicle is not violated. Using AP view, the vertebroplasty needle is docked at the lateral margin of the cortical bone shadow. Then using a sterile mallet or hand pressure, the needle is gently inserted to the mid-pedicle shadow on the AP view. The lateral view is checked to ensure that the needle tip is near to the junction of the pedicle and vertebral body. The needle tip must be safely in the vertebral body on the lateral view before it reaches the medical cortex of the pedicle on the AP view, as seen on Figure 22.1. If increased resistance is encountered when passing the needle through the pedicle, additional images should be performed to make sure that needle tip is not hitting the cortical bone of the medical pedicle wall. After traversing the pedicle, the vertebroplasty needle is introduced into the anterior third of the vertebra body. Depending on the nature of the lesion being treated, either a unipedicular and bipedicular approach may be utilized. Because the goal of the procedure is to augment the region of the vertebral body involved with a tumor lesion or pathologic fracture, alternative approaches are sometimes required. It is therefore useful for the physician to be familiar with the parapedicular approach where the needle is introduced along the lateral margin of the pedicle into the vertebra body. Another useful approach for certain thoracic level cases is the costovertebral approach where the needle is introduced along the posterior surface of the rib to enter the vertebral body at the costovertebral junction. These approaches are sometime useful in cases where the pedicle is too thin to allow a transpedicular approach. The paravertebral approach is considered the most risky due to the potential for the needle tip to damage a segmental vessel or other adjacent structures.

Figure 22.1 The true position of needles in Th12 pedicles—the tip of the needle does not cross the medial cortex (red ovals) of the pedicle on AP fluoroscopic view (A) and entered the posterior part (red line) of a vertebra body on lateral fluoroscopic view (B).

After placement of the needle into the vertebral body, some authors recommend venospondylography where a contrast agent is injected to visualize the venous drainage of the region to try and predict the potential for cement to migrate along the venous tributaries.¹,⁴ In cases where a high risk of cement migration is established, the surgeon would have the option of needle repositioning or to inject a very small volume of cement and then wait to allow this to set prior to proceeding with additional injection.

With the needle or needles in position, the PMMA components (radiopaque powder and liquid methylmethacrylate) are mixed. Most authors recommend that the cement should be injected when it has reached dough-like consistency. Some manufactures provide high viscosity cements along with high-pressure syringes, special injectors or hydraulic delivery systems to allow the cement to be injected in a very viscous state when it would be less prone to extravasation.²,⁵,⁶ The PMMA should be injected slowly, using fluoroscopic control to ensure safe localization of the cement into the vertebral body (see Fig. 22.2).