Vertebral augmentation using expandable intravertebral implants

Introduction

Osteoporotic vertebral compression fracture (OVCF) is one of the most common manifestations of osteoporosis. OVCFs occur in approximately 20% of individuals over 70 years of age. The fractures can cause persistent pain and result in an overall decrease in quality of life. Treatment goals of OVCF include reduction of pain and stabilization of the vertebrae. Conservative treatment includes rest, activity modification, analgesics, and bracing. However, conservative treatment can be ineffective for some patients and surgical intervention can prove to be helpful in those with significant vertebral instability or neurological compromise.

Vertebroplasty and kyphoplasty are the standard methods for minimally invasive treatment of vertebral compression fractures. Vertebroplasty involves the percutaneous injection of polymethylmethacrylate (PMMA) bone cement directly into the fractured vertebral body to stabilize the OVCF. Balloon kyphoplasty (BKP) addresses the kyphotic deformity as well as the fracture pain. The procedure involves insertion of an inflatable bone tamp to elevate end plates. This restores the vertebral body back to its original height and creates a cavity to be filled with a bone cement. There is potential for intraprocedural loss of vertebral height as the balloon deflates. Several clinical and biomechanical studies have shown that there is a height loss after deploying the balloons. ^,

Newer intravertebral reduction devices improve anatomical restoration of the end plates of the vertebral body. The SpineJack (SJ) system (Stryker Corporation, Kalamazoo, MI) is an expandable metal implant (titanium alloy) mounted on an expander, two of which are inserted bilaterally into the vertebral body and simultaneously expanded. The SJ was designed to restore vertebral shape and stabilize the fractured vertebra. The expandable implant is inserted before the injection of the bone cement in order to prevent secondary loss of vertebral body height, which can be observed in BKP. In biomechanical studies, the device has been shown to be superior to BKP in terms of sagittal height restoration and height maintenance. ^, Furthermore, the SAKOS trial was a prospective, multicenter, randomized study that successfully demonstrated noninferiority of the SJ system to BKP with an excellent risk–benefit profile over 12 months. Adjacent-level fractures are the most commonly cited procedure-related adverse event in various single-center studies of SJ outcomes. SAKOS demonstrated radiographic superiority of the SJ over BKP with freedom from adjacent-level fractures and minor superiority for midline vertebral body height restoration at 6 and 12 months.

Anatomy

OVCF often occur at the midthoracic (T7–T8) spine and the thoracolumbar junction (T12–L1). The 12 thoracic vertebrae are intermediate in size between the cervical and lumbar vertebrae ( Fig. 7.1 ). The thoracic spine maintains a slight kyphosis and each vertebral body articulates with the rib cage. The thoracolumbar junction is susceptible to injury and instability because the spinal column progresses from the stable thoracic spine to the more mobile lumbar spine at this level.

Diagnosis

Initial imaging for an OVCF should include anteroposterior (AP), lateral, and oblique views of the entire thoracolumbar spine because many patients have fractures at more than one level. Anterior and posterior vertebral body heights are compared to determine severity of vertebral fractures and are staged as follows.

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Grade 1: 20% to 25% height deformity
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Grade 2: 25% to 40% height deformity
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Grade 3: greater than 40% height deformity

A loss of more than 50% of the original height is indicative of instability ( Fig. 7.2 ).

On the AP view, the interpedicular distance, which is the distance measured between the pedicles, can be appreciated. The pedicles appear as ring-like structures on either side of the vertebral body. When compared with adjacent vertebrae, a widening of the space between each of the pedicles by more than 3 mm indicates a fracture of the vertebral body ( Fig. 7.3 ). Oblique views can help determine alignment of the superior and inferior facets. The facet joints should be tightly apposed, symmetrical, and paired.