Introduction

The incidence of osteoporosis and osteoporotic vertebral compression fractures (VCFs) increases with advancing age with an estimated incidence of more than 50% in women over the age of 80 years.¹ Adverse anatomical and biomechanical consequences of osteoporotic VCFs contribute substantially to the chronic morbidity and economic impact of osteoporosis.¹ With increasing demand for improved quality of life, immediate pain relief, early mobilization, and preservation of function have become the goals for the management of osteoporotic VCFs.²

A single vertebral body compression fracture results in a sagittal plane deformity and greater flexion bending moment around the fractured vertebral body, thereby decreasing the force required to cause further increase in degree and number of additional VCFs with a corresponding increase in kyphosis.¹ Spinal deformity resulting from the loss of vertebral body height also leads to loss of pulmonary capacity, malnutrition, decreased mobility, and depression.³ Kyphosis secondary to osteoporotic vertebral compression fractures is associated with a two to three times greater incidence of death due to pulmonary causes.³ Moreover, the pain associated with acute VCFs may be incapacitating and may become chronic in a significant number of cases.⁴ Interventions that restore fractured vertebral height and stabilize the fractured segment are presumed to improve spinal biomechanics and thereby mitigate these consequences.^5,6

Vertebroplasty and kyphoplasty are effective treatment alternatives for osteoporotic VCFs. Disadvantages of vertebroplasty include high injection pressures, inability to correct deformity, and cement extrusion. Similarly, poor directional reduction control, propagation of burst fractures, and cement extrusion are insufficiencies of kyphoplasty. The OsseoFix (Alphtatec Spine, San Diego, CA USA) technique and implant permit a hybrid technique that we term structural osteoplasty. Structural osteoplasty is the controlled directional reduction and bone augmentation of VCFs. OsseoFix is a stent-like titanium device that is inserted percutaneously into the fractured vertebral body and is intended to stabilize and restore the height of vertebral compression fractures before the insertion of polymethylmethacrylate (PMMA) cement in a controlled and predictable manner. This implant is designed to overcome the disadvantages associated with vertebroplasty and kyphoplasty.

Clinical Indications and Contraindications

The clinical indications for the OsseoFix device include symptomatic and unhealed osteoporotic VCFs in the thoracic and lumbar spine from T6 to L5. Additional potential indications include its use in tumor and traumatic fractures. Before proceeding with this procedure, it is important to clarify whether the fracture is actually caused by the fractured vertebral body by use of clinical examination and radiographic analysis, which should include radiographs and magnetic resonance imaging (MRI) with short tau inversion recovery (STIR) images. MRI would also confirm any cord or cauda compression necessitating a decompression procedure. It is prudent to obtain a CT scan if a break in the posterior cortex of the involved vertebral body is expected, especially when a traumatic genesis is suspected.

Contraindications to this procedure include titanium allergies, chronic healed fractures, vertebra plana, unstable burst fractures, fractures in the cervical spine, local or systemic infections, elevated white blood cell count, fever, obesity, pregnancy, mental illness, or any other medical condition that would prohibit beneficial surgical outcome apart from general contraindications, such as coagulation disorder, unsuitability for general or local anesthesia, or the inability to lie prone.

Description of the Osseofix Device

The OsseoFix device is a titanium implant composed of surgical grade titanium alloy (Ti-6Al-4V, ASTM F 136) and commercially pure titanium (Ti-CP2, ASTM F 67) with an electrolytic conversion coating. It is a cylindrical-shaped capsule, which expands in the middle after deployment and helps reduce the vertebral fracture and maintains the vertebral body height. Cement is then injected into the deployed implant. The implant is available in various sizes to provide versatility for individual anatomical dimension needs (Figure 37-1; Table 1).

FIGURE 37-1 OsseoFix titanium implants.

Biomechanical Studies

The OsseoFix implant has undergone intense in vitro biomechanical testing in terms of stiffness, yield load, and ultimate load after insertion into a fractured vertebral body.^7,8 These studies have evaluated the biomechanical stability of vertebral compression fractures repaired using kyphoplasty type repair techniques compared to several methods of using the OsseoFix repair technique.^7,8

In the first reported in vitro biomechanical study evaluating the OsseoFix implant, four male human cadaveric (age 68 ± 9 yrs) spines from T2 to L5 were scanned for bone mineral density (BMD) using a 3-D computed tomography (CT) BMD measurement system (average BMD across spines and all levels = 119 ± 44 mg/ml). Individual vertebral bodies were sectioned from each spine and measured for anterior vertebral body height. Once measured, the intact vertebral bodies were mechanically tested using established techniques.^5,6

To summarize these techniques, the intact vertebral bodies were placed within a test frame with custom fixtures and epoxy resin that conformed to the upper and lower vertebral body endplates (Figure 37-2). Vertebral bodies were then compressed by 25% of the measured intact anterior vertebral body height (30-mm height × 25% = 7.5 mm compression). Following intact testing, data for stiffness (N/mm), yield load (N), and ultimate load (N) were calculated.

FIGURE 37-2 Testing configuration setup to compress anterior column by 25% of intact height.

Fractured vertebral bodies were then randomly assigned to one of two repair groups: those using standard kyphoplasty or those using the smallest possible OsseoFix device (4.5 mm) (Figures 37-3 and 37-4). Both groups were injected with PMMA cement. Following repair, anterior column heights were remeasured to once again compress the vertebral bodies by 25% of the anterior column heights. The same data were calculated for the repair groups. Data between intact and repaired vertebral bodies as well as data between types of repairs were evaluated using a two-way ANOVA (p < .05). In addition, the volume of cement injected and the height maintained following testing of the repaired vertebral bodies were evaluated with a one-way ANOVA (p < .05).

FIGURE 37-3 OsseoFix implant inserted (A, B) and following cement injection (C).

FIGURE 37-4 Kyphoplasty repair A, Coronal radiograph with a deployed Ossefix device with cement. B, Lateral radiograph with a deployed Ossefix device with cement.

Results – Study 1

Data from this initial study found no differences in anterior column height between repair techniques in the intact or repaired phases. However, there was a statistically greater amount of height maintained following mechanical compression of the repaired vertebral bodies for the OsseoFix group compared to the kyphoplasty group (Figure 37-5). In addition, it was found that statistically less cement was injected (1 ml less) for the OsseoFix group compared to the kyphoplasty group.

FIGURE 37-5 Collapse of repaired vertebral bodies following testing.

There were no differences found in any of the mechanical variables between OsseoFix or kyphoplasty repair groups. These data were then normalized to the intact data to evaluate the ability of each repair technique to restore the vertebral body to its intact mechanical strength (Figure 37-6). The normalized data were not statistically different between repair groups. The yield load and ultimate load were restored to intact values, but the stiffness did not reach intact values. This result is similar to data previously reported for vertebroplasty or kyphoplasty biomechanical restoration of fractured vertebral bodies.^5,6

FIGURE 37-6 Ability of repair to return to intact data.

Results – Study 2

Because of the strength provided by the smallest possible implant with the lower injected cement volumes, a second biomechanical study was conducted to evaluate the inherent strength provided by the implant alone when compared to kyphoplasty and OsseoFix implants with cement.⁸ This study followed identical specimen preparation as the previous biomechanical study.⁷ However, in the second study, the OsseoFix implant repairs were selected based on pedicle width and height and the desired amount of repair height. In addition, the mechanical data were normalized to the BMD of individual vertebral bodies to understand how fractures may be stabilized by eliminating the effect of the inherent bone density.

This study found no mechanical difference for any of the mechanical variables among the kyphoplasty type repair, the OsseoFix with cement repair, and the OsseoFix repair without cement (Table 37-2). Thus an OsseoFix implant alone (without cement) provides biomechanical strength that is equivalent to the other repair techniques evaluated. Whereas the definitive explanation remains unclear, it may be related to the compliance or elasticity of the commercially pure titanium expandable region deforming beneath the superior endplate when loaded. When using the cement, the bolus underneath the superior endplate may not be as elastic and thus causes more directed loading to the endplate and lower stability. Further visualization studies are needed to understand the deformation of the implant in real-time while being loaded. It also may be possible to use alternative injectable materials within the OsseoFix implant, because the implant provides stability and structural support that is not required from the injectable material. Again, further studies are warranted to understand the fracture stabilization provided in this scenario.

TABLE 37-2 Normalized Biomechanical Data for Each Treatment Group

Conclusion

Several in vitro biomechanical investigations have found that the OsseoFix implant provides equivalent biomechanical strength compared to standard kyphoplasty type of technique. However, greater height maintenance and lower cement injection volumes were key results in the initial study. The subsequent study found that a stand-alone OsseoFix implant provided strength equivalent to the other repair techniques. From these investigations it can be concluded that the OsseoFix repair technique provides a viable biomechanical alternative to the standard kyphoplasty repair techniques.

Clinical Data

The first case of vertebral compression fracture reduction and internal fixation using OsseoFix fracture reduction system was done by Dr. Rudolf Bertagnoli on July 21, 2008, at Bogen center in Germany. Several hundred patients have received this treatment since then. The first patient was suffering from acute T12 vertebral compression fracture (Figure 37-7). The surgeon was able to achieve considerable height (Figure 37-8). The patient got immediate pain relief and did not require any external bracing or support. Two such cases have been done to date with good clinical outcomes, and no complications have been reported so far.

FIGURE 37-7 Osteoporotic vertebral compression fracture of the T12 vertebral body.

FIGURE 37-8 Reduction and internal fixation of T12 osteoporotic VCF using the OsseoFix fracture reduction system.

Operative Technique

Step 1: Positioning

The patient is carefully placed prone on a Jackson table with all the bony prominences well padded. Fluoroscopic views are taken in the anteroposterior (AP) and lateral projections such that vertebral bodies are clearly visualized. The spinous process should be equidistant from the medial pedicle edges on AP view. The endplates should be superimposed on lateral view. The level of surgical interest is identified and marked.

Step 2: Creating an access channel into the vertebral body (Figure 37-9)

The transpedicular approach is currently the most commonly used technique to access the vertebral body and is easy to master. An extrapedicular approach may be preferable in the upper and mid thoracic regions, where the size of the pedicle may limit the size of the OsseoFix device that can be used via transpedicular approach.

FIGURE 37-9 An access channel is created into the vertebral body. A, Extrapedicular approach. B, Transpedicular approach.

A 1-cm incision is then made over the bony prominences at the marked level. A targeting Jamshedi cannula with trocar is then placed into the vertebral body via transpedicular or extrapedicular approach. The trocar is then replaced with a guide wire through the Jamshedi cannula. The position of the guide wire must be verified using fluoroscopy at this stage. The Jamshedi cannula is then removed and replaced with a drill sleeve. A pathway is created into the anterior one third of the vertebral body by drilling over the guide wire through the drill sleeve (Figure 37-10). The pathway should end a few mm posterior to the anterior cortex. Position is reconfirmed with fluoroscopy, and the drill is removed, keeping the guide wire in place.

FIGURE 37-10 Creating the pathway in the pedicle and the vertebral body by drilling over the guide wire.

Step 3: Insertion and deployment of the implant (Figure 37-11)

The chosen implant size comes preassembled on the inserter. Make sure that the implant is not torqued onto the shaft. The actuator is then positioned perpendicular to and on top of the implant inserter handle. Rotate the fluted metal shaft of the actuator clockwise until a click is heard, indicating locking of the actuator onto the implant inserter handle. If the red band on the top of the actuator is exposed, turn the actuator counterclockwise until it is no longer visible. The color-matched actuation rod is then advanced through the actuator into the implant inserter and is rotated until the end is firmly threaded into the implant. The outer knob of the actuation rod is depressed into the key feature of the actuator and is rotated clockwise until a positive lock is achieved. The tip of the actuation rod should be seen protruding through the distal end of the implant.

FIGURE 37-11 A, Rotating the metal shaft of the actuator for the deployment of the device. B, Fluoroscopic image showing implant insertion in the anterior one third of the vertebral body. C, Fluoroscopic images showing deployment of the implant.

The assembled implant inserter instrument with the actuator setup is then inserted over the guide wire. The position of the implant is confirmed with AP and lateral fluoroscopy. The guide wire is then removed, and initial deployment of the implant is performed by rotating the actuator clockwise under direct visualization using fluoroscopy. If the surgeon is satisfied with the initial deployment of the implant and reduction of the endplates, final deployment of the implant is performed. There is a stop mechanism in the actuator to prevent overdeployment of the implant. The actuator can be turned 3.5 times before the stop mechanism is engaged. After satisfactory deployment of the implant, the implant inserter assembly is disassembled and the actuator rod is removed. The insertion cannula is left behind in the vertebral body. The second implant can be placed in the same vertebral body through the other pedicle, if clinically indicated.

Step 4: Cement delivery

The cement powder is mixed with the liquid monomer in the mixing chamber at room temperature. The delivery gun is then loaded with the desired amount of cement. A bone biopsy cannula is inserted through the implant inserter into the most distal portion of the implant. The cement delivery gun is connected to the extension tube. The desired amount of cement is then injected through the bone biopsy cannula into the vertebral body under live AP and lateral fluoroscopy. The cement should never be inserted directly through the implant inserter tube. The cement injection is stopped when a sufficient amount has been placed to stabilize the fracture, if cement reaches cortex or an endplate, or leakage is noted. The bone biopsy and the insertion cannula are removed after the cement delivery has been completed. Final fluoroscopic images are taken and the skin is closed.

Pitfalls and Complications of the Procedure

Besides the usual anesthetic complications that can occur with any procedure, there are certain procedural complications that can occur with OsseoFix. The preoperative radiographs, MRI, and CT scans should be carefully examined for any retropulsed fragments and break in the posterior cortex. The retropulsed fragments may be pushed back into the canal during deployment of the device and can cause adverse neurological outcomes, which may include radiculopathy, paresis, or paralysis. Cement may leak out of the fracture or fissure in the posterior cortex and cause neurological damage. Embolism of fat, thrombus, or other materials can occur during reduction of fracture or delivery of cement and can cause catastrophic clinical sequelae. It is possible, though highly unlikely, that the implant may break, dislocate or get infected and may require revision surgery. Proper patient selection, good fluoroscopic guidance with good quality images, patient compliance, proper surgical training, good understanding of the spinal anatomy to avoid the spinal cord and nerves at all times during insertion of instruments, proper postoperative care and physiotherapy, and treatment of osteoporosis all help to improve the surgical outcome.

Treatment Alternatives

Vertebroplasty, or augmentation of the vertebral body with cement, was first used in the 1980s for the management of vertebral hemangioma, and later its use was extended to the management of painful osteoporotic VCFs and osteolytic metastasis of spine. The success rate of vertebroplasty for relief of pain is very high as reported in various studies.⁹ Cement interdigitates with the trabecular bone of vertebra and thus strengthens the vertebra. However, vertebroplasty does not correct the sagittal alignment, which is important for better biomechanics and to prevent the progression of kyphosis.¹⁰ Moreover, some studies have reported cement leakage and embolism with vertebroplasty, possibly a result of cement injection under high pressure.¹¹

Kyphoplasty is a minimally invasive procedure involving the insertion of a bone tamp “pump” via a small cortical window, allowing the low-pressure injection of bone cement (PMMA) into a compression fracture to restore vertebral body height. Kyphoplasty is supposed to correct the vertebral deformity and thus improve the sagittal alignment of spine. It is also argued that cement is injected under low pressure in kyphoplasty, because a cavity is usually created with the bone tamp before the cement is injected. Recent studies have shown that injection pressures depend on the size of the cannula and rate of injection rather than creation of intravertebral cavity. One of the problems with kyphoplasty is that some of the restored height is lost on removal of the balloon tamp before insertion of cement. Also, because the cement bolus does not interdigitate with the cancellous bone in kyphoplasty, it compresses the adjacent cancellous bone with progressive loading and leads to some loss of regained height.

Bed rest, analgesics, bracing, and treatment of osteoporosis remain the mainstay of treatment for stable VCFs. Open decompression, reduction, and fixation by anterior, posterior, or combined approach is warranted whenever there is mechanical compression of the spinal cord or cauda equina with or without neurological deficit.

Discussion and Conclusion

Early clinical and biomechanical results indicate that the OsseoFix device is successfully able to correct the vertebral deformity and restore the spinal alignment, provide rapid pain relief with dramatic improvement in the quality of life, and also prevent subsequent fractures and progressive kyphosis. Unlike kyphoplasty, OsseoFix allows interdigitation of the cement with the cancellous bone and thus has load-bearing properties. It also uses less cement than kyphoplasty. Moreover, it allows for controlled deployment of the device and reduction of vertebral fracture before injection of cement, delivering predictable and reproducible results. Therefore, positive patient outcomes, improved clinical results, and fewer complications may be expected when using the OsseoFix implant in properly selected patients.