Osteoporosis

Osteoporosis is the most common metabolic bone disorder in the world and is a considerable source of morbidity and mortality in the United States. Osteoporosis is defined as a decrease in bone mineral density (BMD) that is 2.5 standard deviations less than the mean peak value in young adults of the same race and sex (World Health Organization). However, a decrease in BMD by only 1 standard deviation increases the risk of vertebral compression fractures (VCFs) by nearly 2-fold. In the United States alone, nearly 700,000 patients are affected with VCFs each year. Patients with symptomatic VCFs suffer a significant amount of back pain and disability. Quality of life is affected, as activities of daily living and ambulation are often gravely affected. Patients with VCFs have an increased likelihood of falls and are 5 times more likely to sustain additional fractures than patients without VCFs. Long-term disability can ensue, as can depression and anxiety. Patients with VCFs have a 6.4 times greater mortality. Economic implications of VCFs are significant. The United States spends nearly $15 million on the treatment of osteoporotic fractures, and VCFs account for more than 150,000 hospital admissions each year.

Pathology

VCFs are a significant cause of back pain. Pain after VCF can be attributed to incomplete healing and progressive collapse of the bone. Incomplete healing causes motion of the fractured vertebral body, which stresses the interosseous and periosteal nerves. The irritated nerves generate substance P, a known factor of nociception. Progressive vertebral collapse can result in spinal deformity, altering individual biomechanics. Kyphotic deformity associated with VCFs shifts the patient’s center of gravity anteriorly, increasing the lever arm and flexion moment at the apex of the kyphosis. The altered biomechanics can lead to progressive kyphosis and future VCFs.

Pathology

VCFs are a significant cause of back pain. Pain after VCF can be attributed to incomplete healing and progressive collapse of the bone. Incomplete healing causes motion of the fractured vertebral body, which stresses the interosseous and periosteal nerves. The irritated nerves generate substance P, a known factor of nociception. Progressive vertebral collapse can result in spinal deformity, altering individual biomechanics. Kyphotic deformity associated with VCFs shifts the patient’s center of gravity anteriorly, increasing the lever arm and flexion moment at the apex of the kyphosis. The altered biomechanics can lead to progressive kyphosis and future VCFs.

Standard treatment of VCFs

Historical treatment options for patients with painful VCFs have been conservative management. Bed rest, acetaminophen, nonsteroidal antiinflammatory drugs, narcotic medications, bracing, and physical therapy have been used to decrease pain and increase functionality. Although seemingly harmless, conservative treatment can be risky for elderly patients suffering VCFs. Bed rest and inactivity can lead to pneumonia, decubital ulcers, deep vein thrombosis, and pulmonary emboli. More recently, injection of polymethylmethacrylate (PMMA) directly into the VCF, or vertebroplasty, has been used to hasten pain relief and return to function.

History of percutaneous vertebroplasty

For many decades, open vertebroplasty has been performed to augment pedicle purchase of surgical instrumentation in spinal fusion cases. Percutaneous vertebroplasty (PV) was first introduced in France in 1984 as an alternative to open vertebroplasty. Galibert and Deramond from the Department of Radiology of the University Hospital of Amiens in France first performed the procedure on a 54-year-old woman with a chief complaint of severe cervical pain with a C2 radiculopathy. Plain radiographs showed a large vertebral hemangioma involving the entire C2 vertebral body, and computerized axial tomographic (CAT) scan confirmed epidural extension. A C2 laminectomy was performed to excise the epidural component of the hemangioma. PMMA was injected percutaneously to obtain reinforcement of the C2 vertebral body. The patient experienced complete pain relief of not only the radicular symptoms but also the axial neck symptoms. The results of the procedure were so impressive that PV was subsequently performed on 6 other patients. In 1987, the first patient with painful VCF was treated with PV, and the procedure was first introduced in the United States in 1988 at the Annual Meeting of the Radiological Society of North America.

Physiology of PV

The exact mechanism of pain relief via vertebroplasty is not understood completely. Initially, pain relief was believed to be secondary to thermal energy. Studies have now shown that in vivo temperatures after vertebroplasty are not high enough to cause thermal necrosis of sensory nerves. Alternatively, pain relief from vertebroplasty likely arises from improved vertebral body strength and stiffness and decreased motion of the vertebral body and periosteal and interosseous nerves. Cadaveric studies have suggested that there is also new bone formation after PV.

Technique

PV is performed under strict sterile conditions using C-arm fluoroscopy or CAT for guidance of needle placement. The C-arm is turned obliquely from the anteroposterior (AP) position to maximize the ovoid appearance of the pedicle, known as “looking down the barrel.” Once this view is achieved, the skin, subcutaneous tissues, and periosteum are anesthetized with a local anesthetic. A small incision is made. A large-bore needle (10–13 gauge) is directed under intermittent fluoroscopic guidance to the midpoint of the pedicle and advanced until the osseum is reached. At this point, lateral fluoroscopy helps to place the tip of the needle at the upper to midpoint of the pedicle. It is imperative that frequent monitoring of the needle position is performed in both planes.

The AP view should demonstrate that the needle is proceeding parallel to the x-ray beam as in a hub view. Lateral projections show the needle moving either parallel to or slightly downwards to the superior and inferior edges of the pedicle.

As the needle tip enters the soft bone marrow, less pressure is required to advance the needle. Frequent AP and lateral views are required to monitor needle positioning and ensure that the needle does not breech either the anterior vertebral wall or vertebral end plates. The needle is advanced until the stylet tip is located near the junction of the anterior and middle thirds of the vertebral body.

Venography can be performed before injection of the cement. For immunocompromised patients, gentamicin or tobramycin can be added to the PMMA mixture. Commercially available PMMA must be mixed with a radiopaque substance before injection. Injection is then completed under continuous lateral fluoroscopy to confirm that the cement does not extravasate during the procedure into the epidural space or inferior vena cava. The amount of pressure required to inject the cement increases as the vertebral body is filled and settling of the PMMA cement occurs. If venous uptake occurs, the injection is halted until the cement thickens. End points include holovertebral filling, hemivertebral filling, extravasation of PMMA into either veins or disk space, or until no more cement can be injected.

After the procedure is completed, the patient should remain supine for several hours to ensure curing of the PMMA before axial loading.

Efficacy

Current standard of care for VCFs without neurologic compromise is nonoperative. Treatment includes rest, analgesic medications, physical therapy, and bracing. However, this treatment modality is not without risk. Prolonged bed rest and immobility can lead to further compression fractures, decubital ulcers, pneumonia, deep venous thrombosis, and pulmonary emboli.

Many retrospective studies have found that PV gives immediate and long-term pain relief to patients suffering from VCFs. Decreased analgesic use has been reported. Improvement in the quality of life, activities of daily living, and mobility has also been demonstrated after PV. Although patients with VCFs as old as 24 months have been shown to have improvement in pain scores, subacute VCFs seem to be associated with the best outcomes and least adverse outcomes.

Similar results have been found in prospective case series. Decreased pain, improved function and mobility, decreased usage of pain medications, and improved quality of life have all been demonstrated. In addition, PV has been shown to stabilize VCFs and prevent further vertebral body collapse.

For 2 years, Diamond and colleagues prospectively studied 88 patients who underwent PV and 38 patients who were treated with conservative therapy. Lower pain scores were found in the PV group at 6 weeks, but at 6 to 12 months and 2 years, there was no statistical difference in pain scores between the 2 treatment groups. Favorable natural history of VCFs and possible regression to the mean of PV are possible reasons that no long-term clinical or statistical difference was present between the 2 groups.

In addition to osteoporotic compression fractures, PV has also been shown to be efficacious for the treatment of pathologic compression fractures. Both primary and metastatic lesions of the spine can cause substantial pain, instability, and kyphotic deformity in the spine. PV has been shown to decrease pain, stabilize the vertebral body, and improve the quality of life in patients with lesions of the vertebral body.

PV was first used for the treatment of painful hemangioma. Several studies have also demonstrated efficacy of PV in decreasing pain caused by hemangioma.

Although the studies mentioned earlier have documented that vertebroplasty is often associated with an immediate dramatic pain reduction in patients with VCFs, recent randomized controlled trials (RCTs) have failed to show any difference in the outcomes of patients treated with PV versus sham procedure or conservative care. Voormolen and colleagues initiated an RCT, the VERTOS study, comparing PV with optimized pain medication (OPM). Patients were randomized to a treatment group of PV or OPM, and at 2 weeks, the patients randomized to the OPM group were allowed to cross over to PV. Most patients in the OPM group elected to undergo PV after only 2 weeks, and the study was terminated early. The primary clinical outcome was measured using the visual analog scale (VAS). Follow-up occurred at 1 day and 2 weeks after initiation of either PV or OPM treatment. Intention-to-treat analysis was used. On day 1, both groups were found to have a statistically significant decrease in VAS and analgesic use. Two weeks after the initiation of treatment, the difference on the VAS between PV and OPM groups was not statistically significant.

Kallmes and colleagues studied PV versus a simulated noncemented procedure in 131 patients. At 1 month, although there was a trend toward a higher rate of clinically meaningful improvement in pain (30% decrease from baseline), there was no statistical difference between the treatment and control groups in regard to pain scores, quality of life, and physical disability related to back pain.

Buchbinder and colleagues failed to find any significant difference in patients treated with PV versus sham procedure. Seventy-eight patients with 1- or 2-level VCFs were randomized into treatment and sham groups and followed up for 6 months. After the procedure, both groups had a significant decrease in pain and use of narcotics, with no difference between groups at 1 week, 1 month, 3 months, and 6 months.