The KP technique is an extension of PV and could alternatively be termed "balloon-assisted vertebroplasty."

The patient is positioned on the fluoroscopic operating table in a prone position. It is important to avoid an antecubital intravenous line. High-resolution C-arm or biplane fluoroscopy is essential when one is performing KP or PV. The patient is positioned so that the spine is located at the isocenter of the C-arm. The fracture is then identified flu-oroscopically. The approach is usually bilateral transpedicular; however, a single posterolateral approach can be used for the large lower lumbar vertebrae (almost always at L5; less commonly at L2 through L4). An extrapedicular approach must be used when the pedicles are too small to accommodate the kyphoplasty instruments (usually in the mid- or upper thoracic regions).

Localization of the pedicles is performed in a manner similar to that used for PV. A posterior approach with slight ipsilateral obliquity of 10 to 25° is preferred. The medial wall of the pedicle must be well visualized.

After sterile preparation and draping of the patients, and after the fluoroscopy equipment has also been covered in sterile fashion, local anesthetic is injected into the patient's skin, subcutaneous tissue, and periosteum of the bone. Typically a 25-gauge needle is used, but a longer spinal needle can be used to reach the periosteum. Most patients require only local anesthesia and conscious sedation. As in PV, the key to local anesthesia is extension of the anesthetic to the periosteum of the pedicle. Patients who cannot lie in a prone position may be candidates for general anesthesia. Prophylactic intravenous antibiotics, typically 1 g of cefazolin, are administered.

The kyphoplasty procedure requires an 11- or 13-gauge (4-6-in.) bone entry needle, a scalpel, a kyphoplasty kit, inflatable balloon tamps, sterile barium sulfate or other opacifier, and bone cement (Figure 18.3). The procedure begins by directing the entry needle into the

Kyphoplasty Technique Guide
Figure 18.2. Sagittal MRI image showing an extreme compression (arrow). There is no room left in this vertebra to insert the balloon for KP.
6in Needle Celiac Plexus Block
Figure 18.3. Some of the materials needed for the kyphoplasty procedure. The inflator and bone cement are not shown (for inflator, see Figure 18.8).

bone under fluoroscopic guidance. For a transpedicular approach, the needle is directed through the pedicle to the posterior aspect of the vertebral body (Figure 18.4). For very small pedicles, an extrapedicular approach can be used. The needle targets a starting point just superior and lateral to the pedicle (Figure 18.5A, B). If a single posterolateral approach is chosen, the trajectory can be established along a postero-lateral path similar to that used for discography. This approach is appropriate for the larger lumbar vertebrae, especially L5. One must be cautious to avoid injuring the exiting nerve roots, and the beginning point must not be so far lateral that puncture of the bowel or kidney results. With the posterolateral approach, the drill should cross the midline of the vertebra on anteroposterior and lateral views. Oblique views should also be used to confirm proper positioning. The advantage of the single posterolateral approach is the time saved by placing one balloon instead of two; the disadvantage is a reduction of the working surface area of the inflatable balloon tamp.

After needle insertions, the trocar is removed. A Kirschner wire (K-wire) is then directed through the cannula and into the bone. The needle cannula is removed, leaving the K-wire in place. A blunt dissector is then fitted over the K-wire and, under fluoroscopic guidance,

Laparoscopic Blunt Dissectors
Figure 18.4. (A) Slight oblique radiograph (from anteroposterior direction) shows the bone introduction needle (white arrow) penetrating the pedicle (small arrows). (B) Lateral image showing the cannula and K-wire tip just at the pedicle-posterior vertebral body junction.

Figure 18.5. (A) Axial drawing demonstrating the trajectory of the needle for a parapedicular approach. The needle follows the junction of the rib and transverse process of the vertebra and enters the vertebral body along the lateral margin of the pedicle. (B) Lateral view of the parapedic-ular approach. Note the needle has a downward angle that allows one to go over the transverse process on the way to the lateral pedicle margin.

Vertebroplasty ExtrapedicularVertebral Body

into the bone to be situated at the level of the K-wire. In a transpedic-ular approach, the K-wires and blunt dissector are directed to the posterior third of the vertebral body. One should manipulate the K-wire with the same caution that one would use for a guide wire in the vascular system. The operating physician should always have control of the proximal end of the K-wire because the sharp tip could easily penetrate soft bone and breach the anterior vertebral cortex.

A skin incision is then made to accommodate the working cannula, which is advanced through the soft tissues over the blunt dissector and through the pedicle to rest along the posterior aspect of the vertebral body. A plastic handle can be placed on the hub of the cannula to advance it manually into the vertebral body, or a mallet can be used to tap the plastic handle, driving the cannula into the vertebral body. If there is considerable resistance to placing the working cannula, the can-nula's handle can be rotated in an alternating clockwise, counterclockwise (screwing) motion to help breach the cortex and facilitate advancement. If using the mallet, one must be careful to direct the blows onto the handle; inadvertently striking the K-wire or blunt dissector might drive the object deeper into the vertebra.

Next, the K-wire and blunt dissector are removed, leaving the working cannula in place. A 3 mm drill is advanced through the cannula, and multiplanar fluoroscopy is used to recheck the orientation of the working cannula. Then the drill is directed ideally along a slightly pos-terolateral to anteromedial trajectory into the vertebra until the tip of the drill is 3 to 4 mm posterior to the anterior margin of the vertebral body, or at least within the anterior third of the vertebral body (Figure 18.6). If the fracture involves the superior aspect of the vertebral body, the drill must be directed somewhat inferiorly to the midline of the vertebral body. If the fracture is along the inferior aspect of the vertebra, the drill must be directed superiorly to the midline of the vertebra. Extreme caution should be used to avoid breaching the anterior cortex of the vertebral body with the drill. For bilateral transpedicular or extrapedicular approaches, the sequence of events is repeated on the contralateral side.

The inflatable balloon tamp is available in different sizes. Each balloon has markers to delineate its distal and proximal extents (Figure 18.7). These markers are also radiopaque and easily visualized under fluoroscopy. The bone tamps are then prepared for inflation. Air is purged from the balloons, and the reservoir of an angioplasty injection

Air Vertebral Body
Figure 18.6. The bone drill (arrow) in the vertebral body (introduced through the bone cannula).

Figure 18.7. Lateral radiograph, with black markers pointing to the distal and proximal markers of the balloon (bone tamp).

Air Vertebral Body

device (incorporating a pressure monitor) is filled with 10 mL of diluted iodine contrast material (Figure 18.8). If the patient has an allergy to iodine, gadolinium can be substituted. The drill is then removed. (If there is a question of underlying malignancy, a biopsy can be performed by pushing the drill bit back and forth in the cavity to collect bone fragments before the drill is removed from the working cannula.)

The uninflated balloon tamps are inserted through the working can-nulas under fluoroscopy and directed to the most anterior extent of the vertebral body. If the clinician feels resistance in the passageway of the drilled hole, perhaps secondary to small shards of bone, the drill or bone filler device can be inserted and withdrawn once or twice along the path to clear it of debris, whereupon the balloon tamp can be inserted without difficulty.

Balloon inflation should be performed slowly. Inflation via the injection device is begun under continuous fluoroscopy, increasing balloon pressure to approximately 50 psi to secure the balloon in position. The stiffening wire is withdrawn from the shaft of the bone tamps, and the volume of contrast media in the reservoir is recorded. The balloons

Vertebrae Bone Decay
Figure 18.8. The inflator, which is connected to the bone tamp by high-pressure tubing.

are progressively inflated by half-milliliter increments (Figure 18.9), with frequent pauses to check for pressure decay, which occurs as the adjacent cancellous bone yields and compacts. If the bone is osteoporotic, pressure decay may be immediate. If the bone is quite dense, there may be little or no pressure decay, even at pressures up to 180 psi. The balloon system is rated to 180 psi, with a practical maximum of 220 psi. Even with slow inflation, pressures higher than 220 psi have been achieved in dense bone.14 If a balloon ruptures, it is simply withdrawn through the working cannula and replaced.

The possible end points of inflation are (1) restoration of the vertebral body height to normal, (2) flattening of the balloon against an endplate without accompanying height restoration, (3) contact with a lateral cortical margin, (4) inflation without further pressure decay, and (5) reaching the maximum volume of the balloon or maximum pressure. The operating physician must maintain both visual and manual control throughout the entire inflation process and should record the amount of fluid used to inflate the balloon when the end point has been achieved. This volume indicates the size of the cavity that has been created, and it will serve as an estimate of the amount of cement to be delivered. If substantial height restoration has not been achieved, careful repositioning of the bone tamps and reinflation may be helpful.

Once adequate inflation has been achieved, the cement is mixed in a manner similar to that for PV. The cement mixture is transferred to a 10 mL syringe that is used to fill a series of 1.5 mL bone filler devices. The volume of cement for injection is approximately 1 mL more than the volume of the cavity created by each inflatable balloon tamp.15 If a quantity of cement is equal to or less than the volume of the cavity, the vertebra will not be reinforced and will recollapse quickly.

Once the bone cement has undergone transition from a liquid to a cohesive, doughy consistency (about 3-4 minutes after mixing), the

Kyphoplasty Technique

Figure 18.9. (A) Anteroposterior image reveals two inflated balloons (arrows) during kyphoplasty. (B) Lateral image shows the two inflated balloons (arrows).

Figure 18.9. (A) Anteroposterior image reveals two inflated balloons (arrows) during kyphoplasty. (B) Lateral image shows the two inflated balloons (arrows).

bone filler devices are passed through the working cannula and into the anterior aspect of the vertebral cavities. The cavity is then filled with cement, proceeding from the anterior to the posterior aspect of the vertebra. Continuous fluoroscopic monitoring is maintained to identify leakage of cement into the spinal canal, paraspinous veins, inferior vena cava, or disc space. One hypothetical advantage of KP over PV is that the former affords a low-pressure cement delivery into the cavity created by the inflatable balloon tamp. However, there are no reports of measurements of intravertebral pressure during cement injection. Recent pressure measurements taken in our laboratory during cement injection in ex vivo vertebral bodies suggest that the pressure increase is minimal and not likely to be of clinical consequence (unpublished data). Some operating physicians prefer to fill one cavity first, leaving the contralateral balloon inflated as a supporting strut. This maneuver may be effective at maintaining any height elevation that has been achieved.

When cement filling of the cavity has been confirmed fluoroscopi-cally from both lateral (Figure 18.10A) and anteroposterior views, the bone filler devices are withdrawn partially to allow complete filling of the cavity; then they are used to tamp the bone cement in place before being withdrawn completely. The cannulas are then rotated (so they are not cemented in the bone) and removed, and hemostasis is obtained at the incision site by using manual pressure. Steri-Strips are usually sufficient for wound closure. The patient remains prone on the table and is not moved until the remaining cement in the mixing bowl has hardened completely. The usual time frame for KP is 35 to 45 minutes, which compares favorably with the 20 to 25 minutes per level required

Leak Fracture
Figure 18.10. (A) Lateral radiograph shows the pretreatment appearance of the compression fracture. (B) Postkyphoplasty image. A small cement leak occurred anteriorly but was asymptomic. There is mild height restoration of between 3 and 4 mm.

for PV. In denser bone, the balloons may take longer to respond to small incremental increases in pressure.

The follow-up and postoperative procedures for KP are identical to those for PV. At some institutions, KP and PV are performed on an outpatient basis unless the patient is extremely frail, or unless the procedure is performed at the end of the day and staffing issues make it easier to keep the patient overnight for discharge the next morning. Outpatients are observed for 3 to 4 hours after the procedure.

Kyphoplasty is a technically demanding procedure. Safe performance requires a high level of skill and high-quality imaging equipment. One should not perform this procedure without being an expert in clinical and radiographic spinal anatomy, without having completed a kyphoplasty course with expert instructors, and without imaging equipment that is capable of clearly delineating key bony landmarks, particularly the pedicles, the cortices, and the spinous processes.

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