TRANSPEDICULAR APPROACH

Under fluoroscopic assessment, a 10- to 15-gauge 10- to 15-cm length needle, preferentially with a beveled cutting tip, is inserted along the selected pedicle (Fig. 31-1).¹ Within the pedicle, the bevel of the needle is oriented medially (the tip of the needle pointing laterally) to avoid the spinal canal. Once within the vertebral body, the bevel is rotated to face laterally (the tip of the needle pointing medially), directing the needle medially, toward the midline. The most desirable position of the needle tip is the anterior third of the vertebral body near the anteroposterior midline (Fig. 31-2). When dealing with a vertebra plana, a more lateral position of the needle is desired. If the underlying pathological condition remains uncertain before the cement injection, a bone biopsy specimen can be obtained using a 15- to 18-gauge biopsy needle placed through the vertebroplasty (VP) needle. Then vertebral venography is performed to evaluate the flow dynamics. When a high-flow, hypervascular pattern is observed, the reposition of the needle tip may be required to perform an embolization of the venous channels, either with alcohol, N-butyl-2-cyanoacrylate (Histoacryl), Gelfoam, plugs, or Avitene powder before cement injection. After the powder and a liquid component are mixed and the desired consistency is reached, the polymethyl methacrylate (PMMA) is injected through the needle. The injection is continued until resistance is met, or the cement reaches the posterior wall of the vertebral body, or a desired result is achieved. The injection should be stopped if epidural, foraminal, or venous leakage is detected.

Fig. 31-1 Entry point of needle insertion in transpedicular approach.

Fig. 31-2 Trajectory of needle insertion in transpedicular vertebroplasty.

VERTEBROPLASTY IN CERVICAL LESIONS

The anterolateral approach for cervical lesions is commonly used, and may be performed under fluoroscopic guidance alone or with the use of computed tomography (CT). The use of a smaller needle (15–18 gauge) for cervical lesions or in vertebrae with extensive destruction of extreme vascularity may decrease the risk of hematoma formation or leakage of acrylic into the needle track.

The entry points are along the anterior margin of the sternocleidomastoid (SCM) muscle. With lateral fluoroscopy, the appropriate level and entry height should be determined. After the entry point is marked, a small skin incision is made. The surgeon pushes the medial structures (trachea and esophagus) to the opposite side with index and middle fingers, then applies a firm pressure in the space between the SCM muscle and the trachea, pointing toward the vertebral surface. The needle is then inserted through the space between the trachea and carotid sheath (Fig. 31-3).

Fig. 31-3 Percutaneous approach to the cervical spine. The needle is inserted through the space between the trachea and carotid sheath.

BIOMECHANICS: VOLUME OF BONE CEMENT

The effective volume of bone cement is estimated to be from 3 to 10cc; however, a study on the effects of bone cement volume and distribution on vertebral stiffness after VP showed that 14% filling or 3.5cc was necessary to restore stiffness of the damaged vertebral body to the pre-damaged value at the lumbar level.² This result suggests that large fill volume may not be the most biomechanically optimal configuration, and an improvement might be achieved by use of a lower cement volume with symmetrical placement. Also, with the unipedicular approach, the stiffness comparable to the intact body can be achieved in cases of symmetrical distribution of bone cement.

COMPLICATIONS

The complication rate in VP for malignant disease is higher than that in osteoporosis: an estimated 10% compared with 1–2% in osteoporosis patients. Hypotension resulting from absorption of the PMMA monomer can be shown. Hence, blood pressure should be monitored during the procedure. Exothermic reaction of adjacent structures can occur theoretically. However, the protective effect of dura and cerebrospinal fluid lessens the significant cord damage caused by thermal injury. The major problems are pulmonary embolism and neurological complication.

Pulmonary Embolism

Pulmonary embolism may occur during the VP. Bone cement leaked from the vertebral body via the venous channel can enter the systemic circulation. It may be filtered in the pulmonary circulation system (Fig. 31-5). Even though pulmonary embolism does occur, most patients may be asymptomatic. If symptomatic, patients complain of tachypnea and respiratory difficulty. Tachycardia is monitored. The incidence of pulmonary embolism is 3–4%.³ Most patients can be treated with anticoagulant therapy and respond favorably.⁴

Fig. 31-5 Pulmonary embolism. Small white dots are seen on the both lung fields.

Neurological Complication (Epidural Leakage)

Epidural leakage may occur at a high incidence, up to 50–70% in osteolytic metastasis or myeloma. Most patients with epidural leakage are asymptomatic; however, few patients may undergo surgery because of radiculopathy. Epidural leakage can occur through the fracture line, cortical destruction, the needle track, or the epidural and paravertebral venous plexus (Fig. 31-6).

Fig. 31-6 Epidural leakage develops through the basivertebral venous plexus.

SPECIAL PROBLEMS OF VERTEBROPLASTY IN CANCER PATIENTS

Venogram

The performance of a venogram in a tumor patient is controversial. Unlike with osteoporosis, venogram performed on tumors may result in substantial leakage of contrast into the canal and paravertebral spaces because of significant cortical destruction and bony erosion (Fig. 31-9).

Fig. 31-9 Dye leakage from the broken posterior cortex.

PARASPINAL TECHNIQUE: LUMBAR SPINE

Entry Point

At the upper lumbar spine (L1 and L2), the entry point is just medial to the 12th rib. The midline and a line bisecting the transverse process and pedicle are identified (Fig. 31-10). The entry point is on the bisecting line and is 5mm medial to the 12th rib. The 12th rib is confirmed with fluoroscopy or palpitation of the rib. At lower lumbar spine (L3–5), a line bisecting the transverse process and pedicle is drawn. The entry point is located on the line, approximately 6–10cm away from the pedicle.

Fig. 31-10 Paraspinal technique in the lumbar spine. The entry point is determined with reference to the 12th rib at L1 and L2 levels. At the L3–5 levels, the entry points are 6–10cm away from the pedicle.