INTRODUCTION

Pathologic vertebral compression fractures (VCFs) are a leading cause of disability and morbidity in patients with osteoporosis, multiple myeloma, and bone metastases.^1–4 The consequences of these fractures include pain and often progressive vertebral collapse with resultant spinal kyphosis. Osteoporotic VCFs have been shown to adversely affect quality of life, physical function, mental health, and survival.^4–6 These effects are related to the severity of the spinal deformity and are, in part, independent of pain.^4,5 In recent years, researchers have highlighted the reduced quality of life, functional limitations, and impaired pulmonary function associated with spinal kyphotic deformity from osteoporotic VCFs.^3,4,7–9 Kyphosis can lead to reduced abdominal space with poor appetite and resultant nutritional problems.^4,10 By shifting the patient’s center of gravity forward, kyphotic deformity not only increases the risk of additional fractures,¹¹ but also may lead to poor balance which potentially increases the risk of accidental falls.^12,13

The ideal surgical treatment of VCFs should address both the fracture-related pain and the kyphotic deformity. It should be accomplished in a minimally invasive fashion without subjecting the patient to inordinate risks or excessive surgical trauma. Over the past decade, percutaneous vertebroplasty, involving the injection of polymethylmethacrylate (PMMA) into a fractured vertebral body, has been popularized. Substantial alleviation of pain has been reported in a majority of patients treated with vertebroplasty for osteopenic VCF.^14–22 Although effective at relieving vertebral fracture pain, vertebroplasty is not designed to address the associated sagittal plane deformity.

Kyphoplasty involves the penetration of the vertebral body with a trochar followed by insertion of an inflatable balloon tamp (IBT). Inflation of the balloon tamp restores the vertebral body back towards its original height, while creating a cavity to be filled with bone void filler. This technique was first performed in 1998. Early results of kyphoplasty suggest significant pain relief as well as the ability to improve the collapsed vertebral body’s height.^23–29

The kyphoplasty procedure was designed to address vertebroplasty’s shortcomings such as high rates of cement leakage, although they rarely manifest with symptoms, and inability to correct fracture deformity. As the balloon tamp is inflated in the fractured vertebral body, the vertebral endplates are pushed apart reducing the fracture, and cancellous bone is pushed away from the balloon creating a cavity surrounded by compacted cancellous bone.^30–32 The creation of an intravertebral cavity may decrease the potential for cement leakage by allowing for low-pressure, controlled placement of ‘doughy’ cement into the cavity and by creating a dam effect by densely compacting bone around the cavity.

PMMA has been the most common bone void filler used in both vertebroplasty and kyphoplasty. This acrylic cement has a long history of clinical use for the fixation of metal and plastic joint replacements and for the fixation of pathological fractures.^33,34 When used to treat vertebral compression fractures, PMMA is usually modified (for example, addition of more barium sulfate, addition of antibiotics, alteration of monomer to powder ratio), in part to attain a viscosity that allows percutaneous insertion into vertebrae while minimizing risk of extravertebral leaks. In April, 2004, the United States FDA approved a formulation of PMMA for use in kyphoplasty procedures.

KYPHOPLASTY PATIENT SELECTION

SURGICAL ANATOMY

Understanding the anatomy of the spinal column and correlating spinal anatomy with intraoperative fluoroscopic images is essential to performing kyphoplasty. The mediolateral pedicle diameter is significantly smaller than the superior–inferior diameter. In the thoracic spine, the pedicle diameters are smallest in the midthoracic region especially at T5–7. The pedicle size appears to decrease as one descends from the upper thoracic segment to the middle segment and later increases in the lower segments. In the lumbar spine, the pedicle diameter increases gradually in the caudal segments. Also, in the majority of patients, the L1 pedicle diameter is smaller than the T11 or T12 pedicle diameter.

The orientation of the pedicle is important in planning an appropriate trajectory for kyphoplasty. The medial inclination in the transverse plane appears to be greatest in the upper thoracic segments (T1–3), and becomes a straight anterior trajectory in the middle to lower thoracic spinal segments (Fig. 33.1). In the lumbar spine, the medial orientation of the pedicles increases slightly from L1 to L5. In the thoracic spine, the attachment of the ribs to the corresponding vertebral body (i.e. costovertebral joint) protects the lateral side of the pedicle allowing cannulation through an extrapedicular approach. Despite the smaller size of the thoracic pedicle, the costovertebral attachment results in a much larger effective pedicle size (Fig. 33.2)

Fig. 33.1 In the thoracic spine, the pedicles have less of a medial inclination (arrows), so that an extrapedicular approach will allow for better medialization of the IBTs.

Fig. 33.2 The costovertebral attachment results in a much larger effective pedicle size in thoracic vertebrae.

KYPHOPLASTY SURGICAL TECHNIQUE

Fluoroscopic imaging

The authors have found simultaneous biplanar fluoroscopy to be advantageous by allowing orthogonal visualization without having to move the C-arm. The ability to visualize the pedicles in both anteroposterior (AP) and lateral views is essential to performing the procedure. Fluoroscopic images confirming the patient’s anatomy must be obtained prior to initiating vertebral cannulation. In the AP view, the superior and inferior endplates are parallel to the fluoroscopic beam and are each visualized as a single cortical shadow, the spinous process is centered in the vertebral body, and the pedicles are symmetric and positioned in the upper half of the vertebral body (Fig. 33.3A). In the lateral view, the endplates are also parallel and the pedicles are superimposed (Fig. 33.3B), Alternatively, the fluoroscope can be rotated 10–20° for a pedicle en-face view, the view down the path of the pedicle (Fig. 33.3C) In this position, the pedicle is visualized directly and can be cannulated by paralleling the pathway of the X-ray beam.

Fig. 33.3 (A) In a centered AP view, each endplate is visualized as a single cortical shadow, the spinous process is centered in the vertebral body, and the pedicles are symmetrical and positioned in the upper half of the vertebral body. (B) In a centered lateral view, the endplates are parallel, and the pedicles are superimposed. (C) When the fluoroscope is rotated 10–20°, a pedicle en-face view, the view down the path of the pedicle, is visualized.

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