Chapter 19 Unipedicular Approach for Percutaneous Vertebroplasty

Unipedicular vertebroplasty is a percutaneous unipedicular approach [1,2] for introducing polymethylmethacrylate (PMMA) cement into the collapsed vertebral body to provide reinforcement that will relieve pain immediately. There are two distinct approaches for percutaneous vertebroplasty (PVP), the transpedicular approach and the extrapedicular approach (Table 19.1). These approaches are further described in Table 19.2 and Figure 19-1.

Figure 19–1 Imaginary approaching line for safe unipedicular vertebroplasty. To prevent leakage of the cement into the epidural space, the target point has to be at the anterior ¼ to ⅓ and at the midline of the vertebral body. The skin entry point nearest to the midline will be the extension line from the anterior ¼ through the inner pedicle (red). The farthest skin entry point from the midline is the extension line from the anterior ⅓ through the outer pedicle (blue). In most cases, the skin entry point is between 1.5 and 2.5 times the pedicular distance from the midline in the thoracic or lumbar vertebrae. There are three vertical lines parallel to midline of the body, at 1, 2, and 3 pedicular distances (green).

Most patients (88%) who require vertebroplasty for a collapsed vertebral body also suffer from facet joint pain with radicular pain around the affected vertebrae that is difficult to distinguish from the pain caused by the pathology of the vertebral body. Administration of facet joint or medial branch blocks before PVP will relieve the pain that is caused by the facet joints. These blocks can be given to the patient immediately prior to the PVP procedure, in the same session. The patient can then give crucial information to the operator about the specific pain caused by the collapsed vertebral body. Blocks cannot be performed after PVP because on fluoroscopy, the bone cement makes a shadow around the painful facet joints.

The action mechanisms for pain relief from PVP are as follows:

Thermal ablation of sinuvertebral and sympathetic nerves from the heat of the PMMA

Chemical neurolysis from the toxin of the PMMA

Mechanical stabilization from the volume of PMMA

Preoperative prepations

Preoperative Examination and Medications

Physical examination should reveal the following findings:

Palpation on the supraspinous region should elicit intractable pain (essential)

Palpation on the facetal area should elicit radiating pain to the facetal dermatomes (additional)

Imaging diagnosis consists of the following modalities:

Plain radiographs, thoracic or lumbar series

Computed tomography or magnetic resonance imaging should show fracture lines or fatty changes on the vertebrae

Bone scanning should show an active lesion

Bone mineral density (BMD) testing

Medications for PVP are as follows:

Major analgesia agents are a weak opioid (codeine) containing nonsteroidal anti-inflammatory drugs and/or acetaminophen.

Adjuvant analgesia may be achieved with gabapentin for neuropathic pain.

Prevention and treatment for osteoporosis and metastatic osteolysis consists of 70 mg/week of alendronate.

Contraindications

PVP is contraindicated by the following conditions:

Metastatic fracture pain in a patient with life expectancy of less than 1 month

Nonpainful compression fracture

Complications

Possible complications of PVP and their treatment or prevention are as follows:

Subsequent adjacent fractures in adjacent vertebrae due to lower BMD in the patient with osteoporosis or to active lesions in the patient with malignant metastasis; common medications for osteoporotic and metastatic osteolysis can be prescribed to prevent this occurrence.

Transient neuropraxia or spinal cord damage due to damage or contusion from vertebral needle passage; anticonvulsant medications can be prescribed for this rare complication.

Transient hypotension due to sympathetic nerve ablation from polymethylmethacrylate (PMMA) heating and toxin; this complication is rare but preparations should be made for a hypotensive event.

Pulmonary embolism due to leakage of PMMA into the vertebral vein; because of this rare but potentially lethal complication, it is necessary to make preparations for emergency open operation.

Transient or permanent damage of spinal nerve or cord due to mass effect of cement leakage; this complication is rare but requires preparation for emergency open operation.

Infections are rare, and antibiotic medication for osteomyelitis can be given.

Bleeding is rare and can usually be controlled with compression, but it may be necessary to prepare for emergency open operation.

Instrumentation

The equipment and supplies needed for PVP are as follows (Fig. 19-2):

Vertebral needle (11-gauge)

Two-inch, 26-gauge needle for skin and periosteum anesthesia to reach to the pedicle

Marking pencil, ruler, and Kirschner wire for drawing

No.15 scalpel

Bone cement: PMMA with antibiotic is mixed with solvent

Barium for clear visualization under the fluoroscope

Spatula

Injector aid

Hammer

F5-mL syringe

Container to mix PMMA, barium, and solvent

Fluoroscope

Local anesthetic (1% lidocaine)

Agents for conscious sedation, if needed: 50 μg fentanyl, 30 mg ketorolac, and 2-3 mg midazolam

Figure 19–2 Preparation for percutaneous vertebroplasty. 1, Scale; 2, marking pencil; 3, 26-gauge needle for skin infiltration; 4, No. 15 scalpel; 5, 5-mL syringe; 6, injector for cement; 7, Kirschner wire; 8, Kelly clamp to hold the vertebral needle to prevent its passing over the anterior cortex; 9, spatula; 10, 11-gauge, single-bevel vertebral needle; 11, hammer; 12, bone cement including antibiotic; 13, barium powder; 14, solvent for cement; 15, container for mixing cement, barium and solvent; 16, scissors.

Procedure

1. The patient’s written informed consent is obtained.

2. Basic monitoring systems are set up, including those for blood pressure, pulse rate, and respiration rate, pulse oximeter, and electrocardiogram.

3. Sedative analgesia with fentanyl, ketorolac, and midazolam is given if needed.

4. The skin is marked with a marking pencil under the fluoroscope (Fig. 19-3).

5. If necessary, facet joint blocks are performed prior to the vertebroplasty (shading of the facet joints due to the cement makes blocks impossible after PVP) (Fig. 19-4).

6. Local anesthesia with 1% lidocaine is infiltrated into the skin and periosteum of the pedicle.

7. A small skin incision is made with a No. 15 scalpel along the skin crease (Fig. 19-5).

8. The vertebral needle is anchored on the outer upper quadrant of the pedicle (Fig. 19-6).

9. Under guidance of a lateral fluoroscopic view, the vertebral needle is advanced and rotated until it passes the pedicle, with the bevel up to avoid damage to the spinal nerve root (see Fig. 19-6).

10. After passing the pedicle, the vertebral needle is pressed, rotated, and punched with the bevel down (see Fig. 19-6).

11. The vertebral needle reaches the vertebral body between its anterior ¼ and anterior ⅓, as seen on the lateral view, and to the midline of the vertebral body as seen on the AP view (see Fig. 19-6).

12. Contrast medium is injected to test for leakage into the venous system or epidural space (Fig. 19-7).

13. If leakage is found, it is corrected with gelatin sponge embolization (Fig. 19-8).

14. The cement and barium powder are mixed with solvent and made into a mixture that is toothpaste-like in consistency (Fig. 19-9).

15. Cement is insertion into the 5-mL syringe, which is then inserted into the injection aid (Fig. 19-10).

16. The cement is injected into the vertebral body, from posterior to anterior—pedicle, posterior, mid-, and anterior body—and the inflow is monitored at each level (see Fig. 19-10).

17. The injection of cement is discontinued when the pos-terior body is being filled.

18. The vertebral needle is removed with rotation.

19. An adhesive bandage with a piroxicam patch for analgesia is applied (Fig. 19-11).

Figure 19–3 Drawing with a marking pencil on the skin under the fluoroscope.

Figure 19–4 The medial branch of posterior ramus near the L2-L3 facet joint. The white silk elevates the medial branch of posterior ramus, and the needle is inserted into the L2-L3 facet joint.

Figure 19–5 Small skin incision with No. 15 scalpel along the skin crease. A skin incision made along the skin crease can produce a smaller scar after operation than a vertical incision or no incision.

Figure 19–6 Anchoring the vertebral needle on the outer upper quadrant of the pedicle on schematic drawings (A, B and C) and on fluoroscopic AP (D) and lateral view (E). Pressing and rotating the vertebral needle until it passes the pedicle on the lateral view with the bevel up, to avoid damaging the spinal nerve root seen on flouoroscopic AP (F) and lateral view (G). The target point is the midline of the body on the fluoroscopic AP view (H) and the body between the anterior ¼ and ⅓ on the lateral view (I).

Figure 19–7 Test with contrast media for leakage into the venous system and epidural space. Before injection of cement, check the leakage out into the venous system (A and the red line in B) or into the epidural space (B and C) on the lateral view. (D) Schematic drawing of possible cement leakage if test procedure is omitted.

Figure 19–8 Preparing the gelatin sponge for embolization if leakage is found.

Figure 19–9 Mixing of bone cement and barium powder with solvent to form a mixture of toothpaste-like consistency.

Figure 19–10 Insertion of cement into the 5-mL syringe and injection with the injector aid while the inflow of the cement into the body seen on intraoperative photography (A) and lateral fluoroscopic view (B). Monitoring the cement filling from posterior to anterior—pedicle, posterior, mid, and anterior body through fluoroscopic AP view (C) and lateral view (D).

Figure 19–11 Application of a piroxicam patch for analgesia.

Related anatomy and physiology

The following aspects of anatomy and physiology are important for PVP:

The venous plexus in the vertebral body (Fig. 19-12)

The nervous system in the vertebral body (Fig. 19-13)

Classification of fractures of the vertebral body (Fig. 19-14)

Figure 19–12 The venous plexus in the vertebral body.

Figure 19–13 The nervous system in the vertebral body.

Figure 19–14 Normal vertebra and types of vertebral fracture.

Postoperative care and follow-up

Absolute bed rest is required for 2 hours after the procedure for fixation of PMMA and to check vital signs.

Follow-up is needed after 1 week for the following procedures:

Removal of adhesive dressing and examination of the wound

Removal of opioid medication and/or nonsteroidal anti-inflammatory drugs and/or acetaminophen

BMD testing and administration of medications for osteoporotic and metastatic osteolysis as needed

Key points

The introduction of a 20% solution of bone cement by volume results in a significant increase in the compressive strength of the vertebral body.

Cement leakage is frequently noted with the 20% cement solution, especially in patients with higher BMD.

Unipedicular vertebroplasty and kyphoplasty are comparable to bipedicular techniques in restoring vertebral body strength, stiffness, and height.

The advantages of the unipedicular approach are decreases in risk of vertebral pedicle cannulation, operative time, radiation exposure, and cost.

It is essential to perform any necessary facet joint blocks prior to percutaneous vertebroplasty because the cement could shade the facet joints in fluoroscopy after the procedure, thus preventing the blocks.