18 Predisposing Factors to Vertebral Fractures
Summary
The risk factors for vertebral compression fractures (VCFs) include infection, trauma, and cancer but the vast majority of vertebral fractures are due to osteoporosis. There are contributing factors to osteoporosis that are modifiable including excessive alcohol and tobacco use, insufficient weight bearing activity, and low body mass. One of the predisposing fractures that is unmodifiable is a person’s genetic predisposition to osteoporosis. There have been at least fifteen genes that have been confirmed as susceptibility genes and the number could be as high as thirty. After vertebral augmentation it appears that the primary risk factor associated with an additional vertebral fracture is the presence of osteoporosis and the treatment of that underlying disorder is important to limit or prevent additional fractures. Pathologic fractures due to metastatic disease may account for up to 25% of the Medicare patients treated for VCFs and the most common metastases to the spine include breast, kidney, prostate, lung, and, thyroid carcinomas. Given the relatively high prevalence of these lesions, a bone biopsy is indicated in focal lesions or with infiltrated bone marrow. Vertebral fractures due to infection should be treated with antibiotics and the infection eradicated before any additional structural support is provided by vertebral augmentation. The majority of vertebral fractures due to trauma happen in younger and healthier patients with a high energy fall being the most common cause. Most traumatic fractures are of the compression variety and involve the thoracolumbar junction. Traumatic fractures are most often not treated with vertebral augmentation but with the development of implant augmentation these fractures may commonly be treated by percutaneous implant augmentation in the future.
18.1 Introduction
Approximately 1.5 million osteoporotic fractures occur each year in the United States, of which more than 50% are VCFs. 1 Osteoporosis is responsible for the vast majority of VCFs; however, trauma, infection, and neoplasm are also predisposing factors to fractures. The risk factors of osteoporotic VCFs are categorized as potentially modifiable and nonmodifiable. Nonmodifiable risk factors include being Caucasian of Northern European descent, female gender, advanced age, susceptibility to fall, presence of dementia, and history of fractures in a first-degree relative. On the other hand, potentially modifiable risk factors include estrogen deficiency, alcohol/tobacco use, frailty, impaired eyesight, insufficient physical activity, and low body weight. Pathologic vertebral fractures are surprisingly prevalent, responsible for up to 25% of the reported Medicare VCF volume. These fractures can be treated with vertebral augmentation especially when radiotherapy is considered. Traumatic vertebral fractures are the most prevalent in patients younger than 50 years. The most common causes of accidents responsible for those fractures are high-energy falls, followed by automobile accidents. Although vertebral augmentation has not been routinely adopted in treatment of traumatic VCFs, preliminary reports have concluded that such interventions could be performed in well-selected cases.
18.2 Current Information Based on Recent Literature and State-of-the-Art Practice
18.2.1 Osteoporosis
The World Health Organization has developed a definition of osteoporosis using dual-energy X-ray absorptiometry as a means of defining bone mass. The bone density is compared to the ideal peak bone mineral density (BMD) of a healthy 30-year-old adult. This comparison results in a T-score. A score of 0 means your BMD is equal to the norm for a healthy young adult. The bones are considered normal or healthy with a bone density from +1 to −1 standard deviation (SD). If the measurement reveals a bone mass between −1 and -2.5 SD, the patient is considered to have low bone mass. Individuals with measurements lower than −2.5 SD are considered osteoporotic. In addition, individuals with a T-score lower than −2.5 SD with an osteoporotic fragility fracture are considered to have severe osteoporosis (▶Table 18.1).
The lifetime risk of all types of skeletal fractures for Caucasian women older than 50 years of age approaches 75%. In fact, the lifetime risk of a symptomatic vertebral fracture is 15.6% in white women and 5.0% in white men. 2 This fracture risk in postmenopausal woman increases sixfold 3 with 25% of additional risk increase in women with a history of prior vertebral fracture in the last 2 years. 4 , 5 Osteoporosis decreases the BMD, disrupts the bone microarchitecture, and alters the contents of noncollagenous proteins in the bone matrix. 6 This structural deterioration leads to fragile bones prone to fractures. It is estimated that approximately 44 million Americans have osteoporosis and an additional 34 million Americans have low bone mass. 7
Genetic predisposition also has an important impact on VCF incidence within a studied population. There is indeed a threefold variation in VCF occurrence in Europe with higher rates seen in Scandinavian countries. 8 Also, at least 15 genes have been confirmed as susceptibility genes (i.e., RANKL, OPG, RANK, SOST, LRP5) and multiple others (at least 30) have been highlighted as promising genes. Those genes are regrouped in three biological pathways: the OPG/RANK/RANKL pathway, the Wnt/β-catenin pathway, and the estrogen, endocrine pathway. 9
The typical risk factors associated with osteoporotic VCFs can be categorized as potentially modifiable and nonmodifiable. Nonmodifiable risk factors include being Caucasian of Northern European descent, female gender, advanced age, susceptibility to fall, presence of dementia, and history of fractures in a first-degree relative. Potentially modifiable risk factors include estrogen deficiency, alcohol/tobacco use, frailty, impaired eyesight, insufficient physical activity, and low body weight. Interestingly, age itself has been found to be a risk factor independent of bone density. 6
The fracture risk is multifactorial but highly dependent on the peak bone mass achieved at 30 years of age. However, the peak bone mass is mainly determined by genetic factors, physical activity, endocrine status, nutrition, and health during growth. Health professionals recommend being active prior to this age to maximize the bone peak mass. Indeed, animal model and human studies suggest stress loading that is of high magnitude and is rapidly applied is effective in increasing bone density prior to 30 years of age along with continued regular exercise afterward. 10 Also, brief high-impact-jump training increases the BMD in premenopausal women.
The trunk muscles provide static equilibrium and appropriate response to changes in loading and displacement perturbations while ensuring stability of the vertebral column. 11 Unfortunately, the current understanding of the muscle/bone interaction in older patients remains limited. Studies report that prevalent VCFs are associated with lower trunk muscle density and/or increased fat accumulation in muscle. 12 It is also known that coactivation of antagonistic muscles can increase muscle stiffness and stability; however, this activation also increases spinal loads 13 , 14 and can contribute to VCFs.
After vertebral augmentation, the only risk factor significantly associated with subsequent compression fracture is the presence of osteoporosis (low T-score). 15 It has been thought and debated for many years that vertebral augmentation might predispose to adjacent-level fractures. However, meta-analyses demonstrated that there is no increase of adjacent-level fracture in patient treated with vertebral augmentation 16 and even a decrease of the incidence of subsequent fractures when comparing the vertebral augmentation arm to the conservative management arm. 17 This decrease in adjacent-level fractures is most likely related to corrected segmental kyphosis and decrease of the flexion moment introduced at the level of the functional spinal unit by the VCF.
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13 Radiation Exposure and Protection: A Conversation Beyond the Inverse Square Law, Thermoluminescent Dosimeters, and Lead Aprons
16 Cost-Effectiveness of Vertebral Augmentation
14 Appropriateness Criteria for Vertebral Augmentation
23 Number of Levels Appropriately Treated with Vertebral Augmentation
30 Vertebral Augmentation in Instrumented Spinal Fusions
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