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,

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