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Painful Osteoporotic Vertebral Fracture

Pathogenesis, Evaluation, and Roles of Vertebroplasty and Kyphoplasty in Its Management

Investigation performed at the Department of Orthopaedic Surgery, Medical College of Wisconsin, Milwaukee, Wisconsin


Raj D. Rao, MDManoj D. Singrakhia, MD
Department of Orthopaedic Surgery, Medical College of Wisconsin, 9200 West Wisconsin Avenue, Milwaukee, WI 53226

The authors did not receive grants or outside funding in support of their research or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

	Introduction

Top Introduction Pathogenesis of Osteoporotic... Evaluation Consequences of Osteoporotic... General Management of the... Surgical Treatment,... Complications Overview References

 
• Osteoporotic vertebral fractures may be a sentinel sign of failing health in elderly patients and are likely to become an increasing health-care concern as the population continues to age.

• A reduction in the number, thickness, and interconnectivity of vertebral trabeculae in combination with altered load transmission across the degenerated disc predisposes a vertebral body to fracture from minor trauma.

• The clinical course of these fractures is variable; some patients are asymptomatic, many respond to medications and activity modification, and a small subset have debilitating symptoms.

• Good short-term results have been reported following both vertebroplasty and kyphoplasty for the treatment of osteoporotic and metastatic vertebral fractures. The long-term consequences of polymethylmethacrylate injection into the vertebral body are unclear, and discretion must be exercised in the use of these procedures.

• Vertebral body height can be partially restored in some of these fractures by extension positioning of the patient on the table or by inflation of the vertebral body with a bone balloon.

Osteoporotic vertebral compression fractures are a frequently encountered clinical problem, and they are becoming more important as the median age of the population continues to increase. Notwithstanding the potentially devastating consequences, many of these fractures are initially asymptomatic and appear to cause little morbidity other than decreased height and a more forward stooped posture. Only 23% ¹ to 33% ² of these fractures become clinically evident. When such a fracture does cause pain, the patient usually can be managed successfully with a combination of medications, activity modification, and occasionally bracing.

Managing a patient who does not respond to this initial treatment regimen is challenging. The risks of anesthesia and the poor quality of bone in this elderly group make operative intervention such as fusion and application of instrumentation less attractive. Internal splinting of the vertebral body by percutaneously injected methylmethacrylate may provide adequate pain relief that allows the patient to return to his or her previous level of functioning. The aim of this article is to review features of osteoporosis that are pertinent to the pathogenesis of vertebral compression fractures and to discuss the evaluation, natural history, and consequences of these fractures. Two new operative procedures, vertebroplasty and kyphoplasty, will be reviewed, and their role in the management of this condition will be discussed.

	Pathogenesis of Osteoporotic Vertebral Fractures

Top Introduction Pathogenesis of Osteoporotic... Evaluation Consequences of Osteoporotic... General Management of the... Surgical Treatment,... Complications Overview References

 
Bone is composed of a compact cortical compartment and a metabolically active trabecular compartment. The osteoblasts and osteoclasts in trabecular bone participate together in a bone formation/resorption process, which is responsible for the continuous remodeling of bone. Uncoupling of bone remodeling begins when an individual is approximately thirty years old, continues with a steady 3% to 5% loss of bone per decade ³ , and can eventually result in osteoporosis. This manifests as a reduction in the number, thickness, and interconnectivity of the trabeculae ^4,5 . Osteoporotic bone becomes more fragile, which predisposes it to eventual fracture with relatively minor trauma ⁶ .

Trabecular thinning contributes to bone loss with age in both sexes, but trabecular loss occurs to a greater extent in women ⁷ . In women, the loss of bone nearly triples in the ten years following menopause, after which it returns to the premenopausal state of approximately 0.4% per year ⁸ . Alterations in the physiologic turnover of bone occur with age and may be influenced by many hormonal, hereditary, medical, and lifestyle factors ( Fig. 1 ).

View larger version (26K): [in this window] [in a new window]   Fig. 1: Conditions affecting bone turnorver.

View larger version (16K): [in this window] [in a new window]   Fig. 2: Classification of osteoporotic vertebral structure and deformity. a: A normal vertebral body. b: A wedge fracture. c: A biconcave fracture. d: A crush fracture.

Lyritis et al. attempted to determine clinical outcomes on the basis of the initial radiographic appearance of vertebral fractures ¹³ . Patients with an obvious wedge fracture had severe, sharp pain, which gradually decreased within four to eight weeks. Patients with minimal superior end-plate discontinuity tended to have gradual progression to complete collapse of the vertebral body and had dull, less severe, although recurring pain. The authors suggested that patients who have more severe pain initially and a well-defined wedge fracture may do well with acute pain management and early mobilization. Patients who present with an ill-defined fracture pattern initially may require continuing treatment for an eighteen to twenty-four-month period.

Decreased Bone Density
Bone mineral density is perhaps the best indicator currently available for assessment of the risk of osteoporotic fractures. Decreased trabecular bone mass in the vertebrae, hip, wrist, and ribs makes these bones prone to fractures. Lindsay et al. found that, with each standard deviation of decrease in bone mineral density compared with that of a young healthy population, there was a 60% increase in the risk of vertebral fracture ¹ .

In their meta-analysis of eleven separate prospective population cohort studies involving a total of more than 2000 fractures, Marshall et al. reported that every standard deviation of decrease in bone density increases the relative risk of all fractures by 1.5 times and the relative risk of spine and hip fractures by 2.3 and 2.6 times, respectively ¹⁴ . However, even though a decrease in bone density determines fracture risk, the authors pointed out that they could not identify which individuals would actually sustain a fracture. Ross et al. found that a decrease in spinal bone density by two standard deviations was associated with a 5.8-fold increase in vertebral fracture rate ¹⁵ . They reported that prediction of vertebral fractures could be improved by using two factors: bone density and prevalent fractures (fractures that existed at the time of the study), or two bone density measurements. Black et al. found that decreased bone density measurements in the hip, spine, and extremities were equally predictive of increased fracture risk in older women ¹⁶ .

Prevalent Fractures
In a study of postmenopausal Japanese-American women, Ross et al. found a fivefold increase in the risk of a new vertebral fracture when a single vertebral fracture was present at baseline ¹⁷ . This risk increased to twelvefold when there were two or more fractures at baseline. Lindsay et al., in a multicenter study involving 2725 postmenopausal women with a mean age of seventy-four years, found a cumulative incidence of 6.6% new fractures in the first year ¹ . Overall, 19.2% of the women with a confirmed incidental fracture had a second fracture within one year; 11.5% of the women with one previous fracture sustained a second fracture, whereas 24% of the women with two or more prevalent fractures at baseline had a new fracture within a year following the first observed fracture. Age, weight, baseline vitamin-D status, and hormonal therapy had no effect on the risk of new fractures in patients with a prevalent fracture. Bedrest or inactivity as a result of pain from vertebral compression fractures accelerates bone loss, which may increase the risk of additional fractures ^6,18 .

Increased kyphosis from previous fractures also predisposes a patient to recurrent fractures. Black et al. found that prevalent vertebral deformities from previous fractures were associated with a fivefold increase in the risk of new fractures ¹⁹ . The risk was higher as the number of preexisting fractures and the severity of the deformity increased. Prior vertebral compression fractures also increase the risk of sustaining nonspinal fractures ^19,20 , and the presence of multiple and severe vertebral compression fractures was found to be a specific risk factor for sustaining femoral neck fractures ²¹ .

Altered Loading Patterns with Age
Compressive loading of the spinal motion segments helps to maintain the integrity of the trabecular pattern of bone. The reductions in body weight and activity that accompany aging result in decreased loads on the spine and secondarily result in decreased bone mass. In young individuals with healthy discs and uniform trabecular thicknesses and spacing, load transmission at the disc-end plate interface takes place evenly across a large portion of the end plate ²² . As the disc becomes degenerated, loads are transmitted unevenly to the end plates, resulting in possible load concentrations on parts of the end plate ²³ . A fracture results when this load overcomes the resistance of the fragile end plate.

Keller et al. developed a biomechanical model to investigate the height loss and spinal deformity associated with vertebral osteoporosis in older individuals ²⁴ . The bone loss and disc degeneration associated with aging were found to weaken the spinal column, to the extent that postural stresses and gravity alone led to spinal deformity. Forward translation of the cephalad part of the spinal column resulted, causing increased compressive loads at the thoracolumbar junction and making this region more susceptible to compression fractures.

Other Independent Risk Factors
A number of other factors have been reported to contribute to the pathogenesis of vertebral compression fractures. Lack of hormonal replacement therapy, three or more chronic illnesses such as tuberculosis and/or peptic ulcer disease ²⁵ , and smoking ²⁶ are some of these independent factors. Increased vertebral depth, measured from the anterior to the posterior vertebral cortex ²⁷ , in combination with low bone density has also been reported to increase the risk of fracture.

Wilkin suggested that bone density does not contribute greatly to an individual's risk of sustaining a fracture ²⁸ . He noted that antiresorptive agents, which decrease bone turnover, do not greatly increase bone mass but nevertheless substantially decrease fracture incidence. He postulated that it is a state of high bone turnover, combined with the predisposition of elderly individuals for falling, that increases the likelihood of fractures.

	Evaluation

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Patients with a symptomatic vertebral fracture typically present with severe back pain following minor injury. Sometimes, sneezing or vigorous coughing precipitates a fracture in osteoporotic bone. The pain is made worse by standing erect and occasionally even by lying flat. On examination, the patient is often limited to a wheelchair or may stoop forward when standing. The spine shows exaggerated thoracic kyphosis, and the pain is typically reproduced by deep pressure over the spinous process at the involved level. Neurologic deficits are rarely associated with these fractures, but they always must be ruled out ²⁹ .

Radiographs show the osteopenia characteristic in these patients. The vertebral body shows a fracture with loss of height and wedging and occasionally with retropulsion of osseous fragments into the spinal canal. Fractures commonly occur in the thoracolumbar region, but they may be present anywhere in the spine ^10,30 . Osteoporotic fractures in the upper thoracic spine may be indicative of an underlying malignant tumor, and a thorough search for a possible primary lesion should always be carried out ^31,32 . A white blood-cell count, measurement of the erythrocyte sedimentation rate, and serum protein electrophoresis help to rule out an underlying infectious or malignant etiology.

The age of the fracture cannot be accurately determined from radiographs. Dense sclerotic osteophytes or cortical margins may suggest that the fracture is chronic. A review of any available previous spine or chest radiographs can determine whether the fracture is a new event. Occasionally, the fracture is not visible on initial radiographs but becomes evident on radiographs made two or three weeks later as the osteoporotic bone settles. There is little correlation between the degree of collapse of the vertebral body and the level of pain.

Magnetic resonance imaging of the spine is probably the single most useful test for determining fracture age, ruling out a malignant tumor, and selecting the appropriate treatment. In the acute period following a vertebral fracture, magnetic resonance imaging shows a geographic pattern of low-intensity-signal changes on T1-weighted images and high-intensity-signal changes on T2-weighted images ³³ ( Figs. 3-A and 3-B ). As the fracture becomes chronic, a linear area of low-intensity-signal change replaces the geographic area on T1-weighted images. As healing continues, the linear pattern is replaced by restoration of fatty marrow ³³ . Sagittal short tau inversion recovery (STIR) sequences are helpful; they show high-intensity-signal changes in areas of edema from acute or healing fractures.

View larger version (165K): [in this window] [in a new window]   Fig. 3-A: Figs. 3-A and 3-B An eighty-one-year-old man with an osteoporotic vertebral compression fracture. Fig. 3-A T1-weighted sagittal image showing decreased signal in the vertebral body of T12.

View larger version (169K): [in this window] [in a new window]   Fig. 3-B: Inversion recovery magnetic resonance image showing increased signal through the same region, suggesting a recent fracture.

View larger version (132K): [in this window] [in a new window]   Fig. 4-A: Figs. 4-A and 4-B A seventy-two-year-old man with metastatic colon carcinoma involving the T6 vertebral body. Fig. 4-A T1-weighted sagittal magnetic resonance image showing decreased signal within the vertebral body and posterior elements of T6.

View larger version (138K): [in this window] [in a new window]   Fig. 4-B: Contrast-medium-enhanced T1-weighted sagittal image demonstrating increased signal in the same region. Involvement of the upper thoracic spine and signal changes in the posterior body and pedicle both raise the suspicion of metastatic involvement.

Dual-energy x-ray absorptiometry of the midlumbar spine and proximal part of the femur is quick and safe, and it is the technique of choice for determining bone density. According to World Health Organization criteria, osteoporosis is diagnosed when bone density on a dual-energy x-ray absorptiometry scan measures <2.5 standard deviations below that of young, healthy individuals of the same sex. Individuals with low bone mass and a resultant fracture are diagnosed as having severe osteoporosis ( Table I ) ³ .

	Consequences of Osteoporotic Fractures

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Physiologic Consequences of Fracture
Osteoporotic vertebral fractures with wedging or collapse of the body result in a kyphotic spinal deformity with cosmetic, physiologic, neurologic, and functional effects. Patients with vertebral compression fractures become shorter, both from the vertebral compression and from a flexed posture that they assume because an erect position exacerbates the vertebral pain. An exaggerated thoracic kyphosis (dowager's hump) and a protuberant abdomen develop, and these changes may affect normal functions of the respiratory and gastrointestinal systems. Lung function (forced vital capacity and forced vital capacity in one second) is substantially reduced in patients with thoracic and lumbar fractures ³⁹ . One chronic thoracic vertebral fracture causes a 9% loss of forced vital capacity ⁴⁰ . Thoracolumbar or lumbar fractures result in localized kyphosis and secondary mechanical compression of the abdominal viscera, with early satiety and weight loss ¹⁸ .

Neurologic deficits are infrequently associated with these low-energy injuries, even when there has been retropulsion of osseous fragments into the canal. In one series, neurologic involvement that required surgical decompression was reported in ten of 497 patients with osteoporotic vertebral compression fractures ²⁹ .

The psychological state of the individual may also be altered, with changes in self-esteem, body image, and mood. Patients become more apprehensive and fearful of activity as the potential of more fractures lingers in their minds. Many patients experience severe depression ⁴¹ .

Osteoporotic vertebral fractures may be a sentinel sign of failing health in elderly patients. In one study, a group of women with three or more vertebral fractures had eleven hospitalizations per 100 patient-years, whereas an age and sex-matched group without vertebral fracture had seven hospital admissions per 100 patient-years ⁴² . There is a 35% to 40% increase in cancer deaths, independent of smoking habits, among patients with vertebral compression fractures ⁴³ . Osteoporotic vertebral fractures are associated with an increased mortality rate. In a population-based prospective study involving 9575 women followed for more than eight years, Kado et al. found a 23% to 34% increase in the mortality rate for women with vertebral compression fractures compared with that for women without them ⁴³ . The most common cause of death in that series was pulmonary disease. The five-year survival rate for patients with vertebral compression fractures is 61%, which is substantially worse than the 76% rate for age-matched peers ⁴⁴ . Survival rates following vertebral compression fractures are similar to those following hip fractures in the elderly, but they steadily decline with time. The survival rate following hip fractures returns to baseline in six months ⁴⁴ .

Pain from Vertebral Fractures
Symptomatic vertebral fractures usually present as acute thoracic or lumbar back pain. Most symptomatic fractures are adequately managed with a short period of rest or activity modification, narcotic analgesics, and a brace. However, approximately 150,000 vertebral compression fractures every year in the United States are refractory to these measures and require hospitalization, with prolonged periods of bed rest and intravenous analgesics ³⁷ . The bed rest probably aggravates the bone loss in these patients ⁴⁵ : studies have shown a 0.25% loss in bone mineral density per week in normal individuals treated with bed rest for seventeen weeks ⁴⁶ and a 1% loss per week in individuals with herniated intervertebral disc disease treated with bed rest ⁴⁷ .

The intensity and duration of pain from symptomatic fractures varies from patient to patient. In an attempt to link radiographic fracture types with clinical presentation, Lyritis et al. studied 210 postmenopausal women who had acute pain and radiographic evidence of spinal fracture ¹³ . All patients had initial pain of >5 as indicated on a visual analogue scale ranging from 0 to 10. All were followed with repeat radiographs and dual-energy x-ray absorptiometry scans of the lumbar spine every six months, or immediately if a second episode of acute pain developed. At the end of eighteen months, two different groups of patients could be identified: the first had a mean age of sixty-seven years, lower bone density, and radiographic evidence of a completely collapsed vertebra, and the second had a mean age of sixty years and either no obvious fracture or mild depression of the superior end plate of the vertebra. The women in the first group had only a single acute episode of pain, which persisted for a short duration of 6 ± 1.8 weeks. The number of subsequent attacks of acute pain (3 ± 1.05) was higher in the second group, and it took more than forty-nine weeks on the average for them to finally present with a complete collapse fracture. The acute pain in the first group was severe, whereas it was milder in the second group and usually those patients did not have subsequent attacks of pain requiring follow-up visits with a physician. In the first group, the complete deformity developed after the first episode of pain, whereas the deformity developed gradually in the second group. The authors concluded that older patients with acute pain and early radiographic evidence of a collapsed vertebra should be treated promptly with early mobilization, whereas the patients in the second group should be treated intensely with hormones and calcium for a longer period to prevent complete collapse fractures.

Many patients have chronic pain from these fractures ¹⁸ ; in some, the pain may recur after an asymptomatic period that lasts for a variable period of time. The etiology of chronic pain from vertebral compression fractures is unclear, but there are probably multiple sources, including: (1) back muscle fatigue from localized fracture kyphosis, (2) back muscle fatigue from forward shift of the upper part of the trunk, (3) secondary facet joint arthrosis, (4) recurring trabecular microfractures, (5) neural irritation, or (6) the rib cage descending and impinging on the pelvis. The risk of chronic pain increases with the number of vertebral levels fractured ^48,49 .

Economic Impact
Many patients who have osteoporotic fractures have concomitant medical comorbidities common to this age-group. Immobility or pain from the fractures may aggravate underlying medical conditions. Thus, it may be difficult to assess the economic impact of these fractures separately from that of other problems experienced by the elderly. The Michigan Department of Community Health nevertheless estimated the direct expenditures resulting from osteoporotic fractures in the United States in 1995 to be greater than $13.8 billion, or $38 million per day. These costs are likely to escalate as the population continues to age. The projected direct costs for the year 2030 exceed $60 billion, or $164 million per day ⁵⁰ . Indirect costs of these fractures resulting from lost productivity and earlier transition to residential facilities for the elderly may add to the overall economic impact of these fractures.

	General Management of the Osteoporotic Patient

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Prophylaxis against osteoporosis is best carried out by obtaining optimal peak bone mass before early adulthood and preserving bone mass thereafter. Exercise and an active lifestyle in combination with appropriate nutrition, including calcium and vitamin D, are adequate prevention measures for most individuals. Lack of exercise, poor nutrition, and tobacco or alcohol abuse may contribute to loss of bone in adult life. Close monitoring of bone health is necessary in individuals with conditions associated with secondary osteoporosis. The indications for the use of hormone replacement therapy in menopausal women are very limited, as the benefits in terms of bone mass are outweighed by the risks of cardiovascular problems and breast cancer ⁵¹ .

Nonmedical interventions may play a role in preventing fragility fractures in elderly patients. Fall prevention strategies include light weight-bearing exercise and proprioceptive training with gentle stretching. Tai chi chuan or other balance training programs have been associated with a 40% reduction in the risk of falls ⁵² . Simple modifications of the environment and appropriate use of assistive devices and footwear may make a large difference in the overall health of elderly patients.

The bulk of pharmacologic agents used in the treatment of osteoporosis work by preventing bone resorption. The most commonly used bisphosphonates, alendronate and risedronate, bind to the hydroxyapatite crystals on bone surfaces and inhibit resorption. Both are safe and generally well tolerated, and they are now available in once-weekly doses ^53,54 . Raloxifene is a selective estrogen-receptor modulator that inhibits bone resorption and may be particularly indicated in women at increased risk for breast cancer or coronary artery disease. Calcitonin prevents osteoclast-mediated bone resorption and may also have an analgesic effect. It is administered as a nasal spray and is used most commonly by patients who are unable to tolerate the oral bisphosphonates and by those with acute fractures because of the analgesia that it offers. The most recently approved drug for the treatment of osteoporosis is teriparatide, the first thirty-four amino acids of human parathyroid hormone. Unlike its predecessors, teriparatide works by stimulation of bone formation. It is administered by daily subcutaneous injection.

All of the above pharmacologic agents have been shown to increase bone mineral density. The incidence of vertebral fractures decreases by approximately 60% after one year of treatment with any of these drugs ^55-57 . It is likely that this protective effect against fractures begins as early as six months after initiation of therapy with the antiresorptive drugs and lasts for at least the first three to four years of treatment. Additional placebo-controlled studies may help to determine whether the decreased incidence of vertebral fractures persists over the long term.

	Surgical Treatment, Vertebroplasty, and Kyphoplasty

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Operative intervention is necessary in a very small subset of patients with vertebral compression fractures in whom a progressive neurologic deficit or intractable pain develops from the fracture deformity. These operations are extensive, involving prolonged duration of anesthesia, blood transfusion, and associated complications ^58,59 . Frequently, the osteoporotic bone results in inadequate purchase of pedicle screws, wires cutting through bone, construct failure, and possibly even worsening of the deformity.

A number of measures can be taken to optimize the results of conventional surgery in this challenging group of patients. Hu et al. called attention to the fact that nutritionally depleted patients have higher mortality rates and decreased healing potentials, and they recommended optimizing the nutritional status of patients prior to any operative intervention ⁶⁰ . During operative treatment, longer constructs with multiple segmental points of fixation are often necessary to preserve fixation. The lamina consists primarily of cortical bone, and sublaminar wires are used when possible ⁶¹ . The use of larger pedicle screws and augmentation of pedicle screws with methylmethacrylate or bone graft may allow for more secure purchase ^62,63 .

Percutaneous cement augmentation of the vertebral body was introduced to treat a subset of patients with vertebral compression fractures who do not need operative decompression of the neural elements but nevertheless have intractable pain. Both vertebroplasty and kyphoplasty refer to an essentially percutaneous injection of methylmethacrylate into the vertebral body, which splints the fracture internally and provides pain relief. Vertebroplasty was initially described by Galibert et al., in 1987, to treat symptomatic hemangiomas of the vertebral body ⁶⁴ , but it is now more frequently used in the management of painful osteoporotic vertebral compression fractures ( Fig. 5 ). Kyphoplasty, developed by Reileyin 1998 ⁶⁵ , refers to the insertion of a balloon tamp into the vertebral body prior to cement injection. The balloon is expanded within the compressed vertebral fracture in an attempt to increase vertebral body height and correct the kyphotic deformity. Cement is injected into the void left behind after the balloon is withdrawn ( Fig. 6 ).

View larger version (24K): [in this window] [in a new window]   Fig. 5: Restoration of vertebral height during vertebroplasty. a: A fractured vertebral body with an intravertebral mobile cleft. b: Extension positioning opens the cleft within the vertebral body, allowing some restoration of vertebral body height. c: Methylmethacrylate injection stabilizes the fracture in this position.

View larger version (23K): [in this window] [in a new window]   Fig. 6: Restoration of vertebral height during kyphoplasty. a: A fractured vertebra displaying loss of height. b: An inflated bone balloon displaces vertebral trabeculae and elevates the superior end plate, allowing some restoration of the height of the vertebral body. c: Removal of the balloon is followed by injection of methylmethacrylate into the void space.

The cement is mixed with barium sulfate to increase radiopacity. Antibiotics can be added for prophylaxis against infection. Using cold cement allows a slight increase in the working time before the cement becomes too viscous to allow injection through the cannula system.

Pain Relief
Short-term pain relief is very good following vertebroplasty and kyphoplasty for the treatment of osteoporotic compression fractures. Studies of the results of vertebroplasties demonstrated moderate or complete pain relief in 90% (twenty-six of twenty-nine) to 95% (thirty-six of thirty-eight) of patients with osteoporotic compression fractures ^66,67 and in 72% (twenty-three of thirty-two) to 75% (twelve of sixteen) of patients with vertebral metastases or multiple myeloma ^68,69 . In a short-term follow-up study, Garfin et al. reported that 90% of 340 patients had a decrease in symptoms after kyphoplasty ⁷⁰ . In a study using the Short Form-36 questionnaire to assess outcomes, Lieberman et al. also found substantial improvement ⁶⁵ . Katzman compared vertebroplasty and kyphoplasty in two dissimilar groups: vertebroplasty was carried out for fractures that were more than three months old, and kyphoplasty was carried out for more acute fractures ⁷¹ . Results were excellent in both groups, without a significant difference between them. Factors that may predispose to a successful outcome with either procedure include (1) localized pain over the fracture site, (2) evidence of a recent fracture on magnetic resonance imaging or bone-scanning, and (3) severe pain ⁷² .

The long-term outcome of cement injection into the vertebral body is less clear. In a study of thirteen patients followed for five years after vertebroplasty, Perez-Higueras et al. reported that twelve patients stated that they would have the procedure done again under similar circumstances ⁷³ . Pain scores on a visual analog scale decreased significantly (p < 0.001) from 9.07 prior to the procedure to 2.07 three days after the procedure and remained steady at 2.15 five years later. In a study of twenty-five patients with either primary or secondary osteoporosis who underwent vertebroplasty, Grados et al. found that the pain relief provided by the procedure continued through the four-year follow-up period ⁷⁴ . Yeom et al. reported on thirty-eight patients who had significant (p < 0.001) pain relief following vertebroplasty ⁷⁵ . However, the pain relief was less satisfactory after more than two years of follow-up, with eleven of the thirty-eight patients having recurrent pain that was moderate or severe. The cause of the pain was either recollapse at the level of the injection or fracture of adjacent vertebrae. We are not aware of any long-term independent studies of the kyphoplasty procedure.

	Complications

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Complications are infrequent after vertebroplasty and kyphoplasty, and those that occur are usually transient. Transient local pain, radiculopathy, or fever that resolves in two to four days may occur as a result of inflammation or infection at the site of injection or as a result of exothermic effects of the cement ⁷⁶ . Unreacted monomer from the cement can have systemic cardiopulmonary effects resulting in hypoxia and embolism ⁷⁷ . Rib fractures may occur from positioning or pressure on the rib cage in these elderly patients ⁶⁶ . In a group of 274 patients who underwent vertebroplasty, the complication rate was 1.3% for those with osteoporotic vertebral fractures and as high as 10% for those with metastatic fractures ⁷⁸ . We are not aware of any reports of adverse events associated with the use of the balloon tamp in kyphoplasty. In general, both procedures are relatively safe, and complications from either procedure appear to be primarily caused by improper needle placement or inattention to fluoroscopic patterns of cement flow during the injection process.

Leakage of cement into the epidural or paravertebral areas has been reported in 30% to 70% of vertebroplasties, but usually it has been minor and has not resulted in adverse events ^68,69,73 . In a group of thirty patients who underwent kyphoplasty, Lieberman et al. reported cement leakage into the epidural space in one patient, into a disc space on two occasions, and into the paraspinal tissues in three patients ⁶⁵ . The incidence of cement leakage following either procedure may be higher than that seen on radiographs. Yeom et al. found that computerized tomography revealed cement leakage 1.5 times more frequently than did radiographs ⁷⁹ . Only 7% (two) of twenty-eight leaks into the spinal canal were correctly diagnosed with radiographs, and leakage of cement into the basivertebral vein or segmental vein was commonly missed or underestimated on routine lateral radiographs. Phillips et al. evaluated whether the creation of a bone void during kyphoplasty reduced the risk of cement leakage ⁸⁰ . Under fluoroscopic control, they injected radiopaque contrast material into the vertebral body prior to and following the creation of a void within the vertebra. There was less extravertebral leakage of the contrast material into the epidural vessels, inferior vena cava, and transcortically following the creation of the cavity, suggesting that cement leakage may be less likely following kyphoplasty.

Methylmethacrylate leakage causing neurologic injury has been reported with both vertebroplasty and kyphoplasty. Cement can extrude through a cortical defect into the spinal canal or foramen and result in a neurologic deficit. In a study of 274 vertebroplasties, Chiras et al. reported post-vertebroplasty radicular pain in 3.7% of patients and spinal cord injury in one ⁷⁸ . Lee et al. reported total paraplegia below T11 in a sixty-six-year-old woman who had undergone a three-level vertebroplasty with 7 mL of methylmethacrylate at each level ⁸¹ . Computed tomography scanning showed extravasation of methylmethacrylate into the anterior and posterior epidural veins and longitudinal venous sinuses leading to spinal cord compression. Harrington reported claudication symptoms developing as a result of circumferential constriction by extravasated methylmethacrylate of the thecal sac at the T10-L2 levels following vertebroplasty ⁸² . Garfin et al. reported on two patients with spinal cord injury following kyphoplasty ⁷⁰ . One patient had partial motor loss in the lower extremities as a result of improper placement of the insertion tools and subsequent injection of cement into the spinal canal through the tract. In another patient, with a fracture at the junction of the body and pedicle, an anterior cord syndrome developed following performance of the kyphoplasty through an inferior extrapedicular approach.

Restoration of Vertebral Height
The concept of kyphoplasty has brought to the forefront the issue of restoration of vertebral height in osteoporotic vertebral compression fractures. Residual vertebral deformities have been reported to be associated with a fivefold increase in the risk of progression of the deformity, with the risk of new fractures depending on the number of levels involved and the severity of the deformity ¹⁹ . Restoration of vertebral body height and reduction of postfracture kyphosis has the theoretical benefits of correcting sagittal deformity, restoring lost height, improving cosmetic appearance, improving pulmonary and gastrointestinal function, and reducing the risk of a neurologic deficit being caused by progression of the deformity.

Garfin et al. reported that kyphoplasty can restore height and reduce kyphosis if it is performed within three months after the occurrence of the fracture ⁷⁰ . They reported that predicted anterior vertebral body height increased from an average 83% before treatment to 99% after kyphoplasty. Lieberman et al. reported that kyphoplasties carried out at a mean of 5.9 months after seventy vertebral fractures restored an average of 35% of the lost height ⁶⁵ . In another series, 34% of the lost height was restored in vertebral fractures resulting from multiple myeloma ⁸³ . Katzman reported that nineteen of eighty-two patients had correction of vertebral body height after kyphoplasty and that there was a 57.6% chance of correction if the procedure was done within two weeks after the fracture71.

McKiernan et al. reported that the wedging of the vertebral body in many compression fractures is not fixed ⁸⁴ . So-called mobile fractures show an intravertebral radiolucent cleft, and a reversal of kyphosis may be seen on extension radiographs. Substantial recovery of lost height can be achieved during vertebroplasty with careful patient positioning alone. McKiernan et al. reported on sixty-five vertebral compression fractures in forty-one patients who underwent vertebroplasty at an average of eighty-nine days following fracture; 44% of these patients showed dynamic mobility of the fracture ⁸⁴ . In these mobile fractures, anterior vertebral height increased from an average of 42% to 70% of normal, with an average increase of 106% of the diminished height of the vertebral body after the fracture, as a result of postural height restoration followed by a vertebroplasty. The patients with fixed fractures in that series had no appreciable restoration of vertebral height. Another recent study demonstrated an average 2.5-mm increase in anterior vertebral body height following vertebroplasty in which no attempt was made to posturally reduce the fracture ⁸⁵ . The authors postulated that the restoration of height resulted from the injection of high-viscosity bone cement under pressure.

We are not aware of any studies providing a direct comparison of height restoration with vertebroplasty and kyphoplasty. Assessment of height restoration has varied widely among the different studies, making it difficult to draw meaningful comparisons.

Secondary Vertebral Fractures
In a study that included twenty-five patients with severe primary (mean T-score, -3.1) and secondary osteoporosis evaluated four years after vertebroplasty, Grados et al. found that at least one vertebral fracture developed in the vicinity of the cemented vertebra in thirteen patients (52%) ⁷⁴ . In another study, 23% (three) of thirteen patients who had undergone vertebroplasty sustained additional vertebral fractures over a five-year period, with the fractures in two of these patients being adjacent to a treated vertebra ⁷³ . In a study of 115 patients who underwent kyphoplasty, Harrop et al. reported that 19% (twenty-two) had new compression fractures within ten months after the index procedure ⁸⁶ . Within this group, 9% (seven) of eighty patients with primary osteoporosis and 43% (fifteen) of thirty-five patients with osteoporosis secondary to long-term steroid use had new fractures in the follow-up period. Hyde et al. reported a 30% prevalence (twenty of sixty-six) of new fractures in a nine-month period following kyphoplasty ⁸⁷ . New fractures were more likely in patients who had had more than a single fracture previously. Katzman found fractures at adjacent levels in 5% (two) of forty-two patients who had undergone vertebroplasty and 5% (four) of eighty-two patients who had undergone kyphoplasty ⁷¹ . Neither procedure had an adverse effect on the refracture rate when compared with the rate in a control group.

The natural history of osteoporotic vertebral compression fractures suggests that 11.5% of women with a single prevalent vertebral fracture and 24% of women with more than two prevalent vertebral fractures are likely to sustain a new vertebral fracture within a year ¹ . Up to 23% of these fractures may be symptomatic ¹ . It is unclear whether the injection of cement and the abnormal stiffness of the vertebral body resulting from either vertebroplasty or kyphoplasty increase the likelihood of fractures at adjacent levels. Because of the lack of long-term follow-up and the small numbers of patients in most series, it is not possible to determine whether either procedure has an advantage over the other in this regard.

Biomechanics of Vertebral Augmentation
With the recent surge in interest in osteoporotic fractures, many authors have explored the biomechanical effects of cement augmentation in these fractures. The limiting factor in all of these studies is insufficient knowledge about the optimal strength and stiffness required in the clinical management of these fractures. The long-term effects of varying cement volumes or patterns of fill, in terms of both relief of pain and the effects on the adjacent segments, are still unclear.

Early vertebral augmentation procedures focused on maximal fill of the vertebral body, but it is now evident that smaller volumes may more appropriately restore biomechanical properties of the vertebral body. The volume of cement injected into the vertebral body is directly related to the stiffness and strength that is achieved ⁸⁸ . A small amount—approximately 15% volume fraction—may be adequate to restore the stiffness of the vertebral body to its prefracture level. Use of a large volume of cement in an attempt to maximally fill the vertebral body increases the stiffness of the vertebra and potentially leads to fractures of adjacent, nonaugmented vertebrae ⁸⁹ . A large fill volume also makes the vertebral body more sensitive to cement placement. Asymmetric distribution of the cement promotes single-sided load transfer and potential toggle ⁸⁸ .

Ikeuchi et al. investigated cement distribution within the vertebral body ⁹⁰ . They found that cement that was injected into only the caudad half of the vertebral body provided the same stiffness, strength, and mechanical gradient with adjacent vertebrae as did cement injected into the entire vertebral body. A bipedicular approach is sometimes indicated when the cement does not symmetrically infiltrate the collapsed vertebra, as in patients with a severe long-standing osteoporotic wedge or biconcave fracture. Liebschner et al., in their finite element study, found that unipedicular distribution led to a mediolateral bending movement toward the untreated side during compressive loading ⁸⁸ .

In an attempt to study the loading patterns on the anterior column following vertebroplasty and kyphoplasty, Ananthakrishnan et al. recently simulated an osteoporotic fracture in a human cadaver model ⁹¹ . Hydrostatic pressures in adjacent discs were increased following either vertebroplasty or kyphoplasty, but there was no significant difference in these pressures between the two procedures.

Alternative Materials for Vertebral Augmentation
Polymethylmethacrylate has been used successfully, and almost exclusively, for vertebroplasty and kyphoplasty. The advantages are that (1) orthopaedic surgeons are familiar with it, (2) it is easy to handle, (3) radiopaque materials can be added to it, (4) it provides the necessary strength and stiffness, and (5) it is inexpensive. Its disadvantages are (1) it has no osteoconductive or inductive properties, (2) high polymerization temperatures can result in damage to surrounding tissues, (3) unreacted monomer has systemic cardiopulmonary side effects, (4) excessive inherent stiffness can have a mechanical effect on adjacent vertebrae, and (5) it is not remodeled by creeping substitution over time.

Several investigators have reported promising results of vertebral augmentation with the use of biodegradable products such as calcium phosphate, hydroxyapatite, or coral granules in vitro ^92-94 . Injectable mineral cements harden within metaphyseal bone without producing much heat. It is presumed that new bone is laid down in apposition to, and eventually replaces, the bone cement. At this time, it is unknown whether this process of remodeling will occur in osteoporotic vertebrae. Current problems with mineral cements are (1) high viscosity, which prevents interstitial diffusion within the vertebral body, (2) handling characteristics that differ from those of polymethylmethacrylate, (3) the fact that the in vivo resorption properties have not yet been defined, and (4) high cost.

Takemasa and Yamamoto reported preliminary results in a study of thirty-eight patients who had undergone stabilization of osteoporotic vertebral compression fractures with bioactive calcium phosphate cement ⁹⁵ . All patients had substantial pain relief, and radiographs made three months after treatment showed no progression of vertebral collapse and no radiolucent zone around the injected cement.

	Overview

Top Introduction Pathogenesis of Osteoporotic... Evaluation Consequences of Osteoporotic... General Management of the... Surgical Treatment,... Complications Overview References

 
Osteoporotic vertebral fractures are likely to become an even greater health-care concern as our population continues to age. These fractures are a clinical indicator of decreased bone mineral density, and they occur in an older age group that often has underlying medical problems. Fortunately, the majority of these fractures are asymptomatic and require minimal or no treatment. The management of patients who have painful fractures can be challenging. Rest, bracing, and medications help to some degree, and operative stabilization is generally reserved for patients with an impending or actual neurologic deficit.

Newer techniques—i.e., vertebroplasty and kyphoplasty—internally splint the vertebral body with methylmethacrylate, which helps to relieve the pain caused by these fractures. Complications from these procedures can be avoided by the use of proper technique and appropriate use of fluoroscopy. The reported pain relief provided by these procedures is generally excellent in the short term, but the long-term efficacy is as yet unclear. We are not aware of any studies that have determined whether the pain relief over the long term is superior to the natural history of the vertebral fractures. Restoration of the height of the fractured vertebral body to decrease the secondary morbidity from these fractures is an attractive concept. The height is restored by positioning the patient in extension and/or by using an inflatable balloon. The degree to which either of these treatments contributes to height restoration is unclear, but it is more certain that the likelihood of height restoration decreases with the time after the injury. More information is needed to determine whether either of these procedures helps to diminish morbidity or mortality in the long term and the effect of the chronicity of the fracture on the outcome.

The injection of methylmethacrylate alters the mechanical properties of the vertebral body, and larger volumes of methylmethacrylate may alter these properties even more. It is possible that injected cement may increase the stresses at adjacent levels and thus increase the likelihood of fractures at those levels. The eventual development of bone cements with mechanical properties that are similar to those of bone and that demonstrate long-term biocompatibility may be a better solution.

	References

Top Introduction Pathogenesis of Osteoporotic... Evaluation Consequences of Osteoporotic... General Management of the... Surgical Treatment,... Complications Overview References

 

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