Vertebral Compression Fractures and Minimally Invasive Spine Surgery

Article submitted by Ghassan K. Bejjani, MD, Clinical Assistant Professor Department of Neurosurgery University of Pittsburgh School of Medicine.

Introduction
Vertebral compression fractures (VCF) are a common problem, especially among the elderly and are secondary to excessive or even normal loads on a weakened vertebral body. The vertebral body is usually weakened by osteoporosis, which is by far the most common etiology, or an infiltrative process, usually tumoral or infectious. Traditional surgical management consists of major decompressive and reconstructive procedures, reserving it for the minority of cases with neurologic deficits (0.05%). Conservative management has been the mainstay for treatment, particularly in cases of osteoporotic VCF. However, conservative treatment is not always successful and does not prevent the long-term complications of VCF. Minimally invasive surgical techniques, which have a low morbidity, are slowly shifting the VCF management paradigm.

The Myth About VCF
Although VCF are thought by some to be benign, the literature suggests that these fractures have serious consequences on the mental and physical health of patients.

VCF affect the patient's health most noticeably in reduced pulmonary function-a 9 percent loss of forced vital capacity. The degree of kyphosis is significantly related to the risk of pulmonary death in patients with VCF (p=0.005). The mortality rate after VCF is worse than expected and comparable to that of hip fractures (8.64 and 6.68, respectively).

Studies also indicate that psychosocial sequelae result from VCF. Initially, patients exhibit substantial anxiety about the possibility of future fractures and physical deformity. As osteoporosis progresses, profound depression may result as the condition's disabling and disfiguring aspects affect social roles and interpersonal relationships.

Medical Treatment of VCF
The conservative management of VCF traditionally consists of bed rest, analgesics for pain, and bracing for chronic pain. While this management has its advantages, it also has its limitations:

• The pain may not resolve even with a prolonged period of expectant management
• Prolonged bed rest will worsen osteoporosis.
• Conservative management does not prevent further VCF.

VCF predisposes to further VCF in a downward spiral. As the vertebral body collapses, its anterior border takes most of the compression deformity, increasing kyphosis and shifting the center of gravity forward. This forward shift increases the length of the lever arm of the body weight on the spine, creating a large bending movement and increasing the compressive stresses on the osteoporotic anterior spine. The result is further VCF. After an initial VCF, the risk of subsequent fractures is increased five times. And after two or more VCF, the risk increases 12 times. To prevent further VCF requires correcting the kyphosis, or at least preventing it from worsening, as well as treating the underlying osteoporosis. However, traditional surgical means for achieving this goal are extremely invasive.

Surgical Treatment of VCF: Past and Present
Traditional open surgical management of vertebral compression fracture includes major surgical interventions with corpectomy and reconstruction. The approach entails a thoracotomy or transabdominal exposure in an elderly and medically frail population, followed by decompression of the neural elements, with instrumentation and fusion of an already osteoporotic bone.

The present shift toward minimally invasive surgical techniques has benefited the surgical management of VCF. Using percutaneously inserted needles, artificial bone cement is injected into the body of the involved vertebrae to increase its compressive strength reducing the microfractures and eliminating pain. There are two technical variations kyphoplasty and vertebroplasty.

In the kyphoplasty variant, a balloon is introduced first into the vertebral body and inflated to attempt to restore body height, creating a cavity within the body itself. After the balloon is deflated and removed, cement is injected within the newly created cavity under low pressure. In the vertebroplasty variant, the cement is injected under pressure to fill the interstices of the osteoporotic vertebral body. Both techniques can be done under local anesthetic. Fortunately, the published incidence of clinically relevant leaks is low, from 0 to 2-3 percent.

Tumoral VCF
Painful tumoral VCF also respond to kyphoplasty or vertebroplasty. IN these cases, the pain is bifactorial: caused by tumoral invasion and irritation of the sensitive structures, and the VCF itself.
Radiotherapy and/or chemotherapy will address the first element, while kyphoplasty will adequately address the second one. These surgical procedures are usually used for osteolytic metastasis and multiple myeloma.

Future Treatment of VCF
While minimally invasive spine surgery increasingly is being used to treat VCF, some questions remain to be answered. When should a patient be surgically treated? And what is the ideal bone cement?

Earlier treatment would lead to a better correction of the deformity and better pain resolution, but would it be exposing some patients to surgery whose condition might otherwise have been managed conservatively? The history of VCF points to a progressive course with subsequent kyphosis is left untreated; however, a more definitive answer to the first questions awaits a well conducted study.

The ideal bone cement is another area for future investigations. Is the artificial cement that is currently used effective or should bone-regenerating substances be used? And how will these fare in the osteoporotic environment where they will be used?

Conclusion
Minimally invasive surgical techniques have simplified the surgical management of VCF and widened its indications. How far these indications will go is a question that remains to be answered.