Osteoporotic Spinal Fractures

Introduction

Osteoporosis is a common disease that is characterized by structural deterioration of bone architecture and manifests as fragility fractures occurring at multiple skeletal sites, most commonly involving the spine, hip, or wrist. It is increasingly recognized that osteoporosis is an important health problem because of the large affected population and the devastating impact of osteoporotic fractures on patient morbidity and mortality, as well as on societal costs. The purpose of this chapter is to highlight the clinical and socioeconomic concerns of osteoporotic spine fractures and give an overview of nonoperative and operative treatment for patients who sustain these injuries.

Epidemiology

The prevalence of osteoporosis in the United States is estimated to increase from approximately 10 million to more than 14 million people in 2020. Using the World Health Organization's definition of osteoporosis, a bone mineral density (BMD) more than 2.5 standard deviations below the mean in young, normal people, approximately 30% of postmenopausal white women in the United States have osteoporosis. However, low BMD only explains about half of fragility fractures, and thus several recent guidelines have included the presence of a major fragility fracture, including spine fractures, as a diagnostic criterion for osteoporosis. Prevalence rates are lower when bone density is assessed at a single skeletal site, and it is estimated that 16% to 20% of this population has osteoporosis of the lumbar spine. Historically, fragility spine fractures in men were thought to be uncommon. However, recent population-based studies show an unexpectedly high frequency of vertebral fractures in men. It is now estimated that men account for more than 25% of the burden of osteoporosis-related fractures in the United States.

Cooper and colleagues reported the overall age- and sex-adjusted incidence of vertebral fractures to be 117 per 100,000 and that, all together, 25% of women 50 years of age or older have one or more vertebral fractures. This rate is consistent with the 20% reported in an Australian population, the 21% reported in a random sample of 70-year-old Danish women, and the 24% documented among elderly white women from other longitudinal studies. The US population 50 years of age and older is predicted to increase by 60% between 2000 and 2025, eventually reaching 120 million people, which will undoubtedly cause a rise in the number of people affected by osteoporotic fractures.

Unlike fractures of the hip and forearm, spine fragility fractures are often not associated with a fall or trauma. It is estimated that only 30% of osteoporotic vertebral fractures come to clinical attention, and many are found incidentally on routine imaging studies. Unfortunately, many patients present with back pain that often causes significant morbidity. Even if the acute pain of a spinal fragility fracture subsides, many patients develop irreversible spinal deformity, usually an increase in kyphosis, that is associated with significant health consequences, including decreased physical functioning (sarcopenia) and health-related quality of life (HRQOL), chronic back pain, impaired balance, and increased subsequent falls. Another concerning finding is that patients who have one or more vertebral fracture at baseline are five times more likely to develop another spinal fragility fracture compared with patients without prevalent vertebral fracture at baseline.

For most patients, pain and its effect on physical function are the leading cause of morbidity associated with these fractures. A recent prospective observational study showed that radiographically detected vertebral fractures were associated with long-term substantial increases in back pain and back-related disability compared with before fracture. After adjustments for covariates, women with a fracture had a 2.4-times-higher risk for increased back pain compared with women without a fracture during the 4-year follow-up period. Furthermore, the annual rate of days of bed rest was nine times higher in women with a first-incident fracture, and the rate of limited activity days was approximately twice as high compared with the control group. Based on their data, the authors estimated an additional 10 days per year of limited activity because of back pain in the fragility fracture group. This is comparable to the days of limited activity for patients with diabetes (15 days), ischemic heart disease (15 days), and arthritis and rheumatism (7 days).

Osteoporotic fractures have a significant impact on HRQOL. Hallberg and colleagues found that HRQOL was significantly lower for all domains, physical and mental, at the 3- and 24-month follow-up after osteoporotic fractures in women 55 to 75 years of age. Moreover, vertebral fractures have a considerably greater and more prolonged impact on HRQOL than hip, forearm, and humerus fractures.

Osteoporotic spine fractures are also associated with an increased risk of death. Lau and colleagues reviewed Medicare claims from 1997 through 2004 and found that the overall mortality rate after a vertebral fracture was twice that of the matched control participants. The survival rates after a fracture diagnosis, as estimated with the Kaplan-Meier method, were 53.9%, 30.9%, and 10.5% at 3, 5, and 7 years, respectively, and were significantly lower compared with control participants. The mortality risk was greater for men than women, and the overall difference in mortality was greatest when the patients were younger at the time of fracture. Kado and colleagues showed that women with at least one new fracture have an age-adjusted 32% increased risk of death compared with those without incident vertebral fracture. They concluded that this increased risk of death is explained in large part by associated weight loss and markers of decreased physical function. The mortality risk is 25% greater after spine fracture than hip fracture.

Osteoporosis, and in particular osteoporotic spine fractures, has a great socioeconomic impact and therefore has become an important public health problem and concern. In 2005, fragility fractures in the United States resulted in 2.5 million medical office visits, 430,000 hospital admissions, and 180,000 nursing home admissions. Their direct cost was $17 billion. The projected increase in the elderly US population will likely cause this economic burden to significantly increase over the next several decades. Therefore healthcare professionals need to focus on identifying patients at risk for osteoporosis and use evidence-based treatment strategies to prevent fractures in an ultimate effort to decrease the morbidity and mortality associated with these fractures. In select patients who fail nonoperative treatment, surgical intervention may be indicated.

Evaluation

Patients who sustain osteoporotic spine fractures often present to their primary care doctors or emergency departments complaining of acute-onset back pain. A thorough spine and neurologic examination should be performed, and the entire spinal column should be palpated and inspected for areas of tenderness to palpation and focal abnormalities (i.e., palpable step-offs between the spinous processes). A detailed motor and sensory examination should be documented, and the presence of any pathologic reflexes should be elicited (hyperreflexia, clonus, Babinski sign, etc.). It is rare for these patients to sustain a neurologic injury, but in such cases, an accurate motor and sensory level and degree of injury (American Spinal Injury Association [ASIA] grades A to E) needs to be clearly defined. Height measurement is a simple test that is infrequently performed but is reliable in detecting fractures and indicating who needs further diagnostic testing. An acute 2-cm loss or a 4-cm lifetime loss indicates a high likelihood of an osteoporotic-related fracture.

Diagnosis and Classification

Upright biplanar plain radiographs of the spine should be the first imaging modality used to evaluate patients with a suspected osteoporotic spine fracture. An anterior-posterior (AP) and lateral radiograph should be taken of the suspected area of injury based on the physical examination. If a fracture is present, the degree of vertebral body collapse and presence of focal or global deformity should be noted. A computed tomography (CT) scan should be used if the radiographs are equivocal or more detail is needed to help determine treatment. CT is much more sensitive and specific in detecting spinal column injuries compared with plain radiographs. If CT has been performed, an estimation of BMD can be made by determination of Hounsfield units (HU), which can easily be measured using the CT software. Thresholds to estimate osteoporosis using HU of the L1 vertebral body have been established. An L1 HU greater than 150 rules out osteoporosis, HU less than 110 rules in osteoporosis, and values less than 135 suggest likely osteoporosis. Finally, magnetic resonance imaging (MRI) is used to determine, if necessary, the acuity of the fracture or the presence of neurologic compression.

Osteoporotic spine fractures are typically axial-loading injuries, and therefore endplate compression fractures or burst fractures are the most commonly seen injury morphologies. Classically these fractures were classified using Genant criteria. This was useful for identifying fractures in clinical trials but is not helpful to trauma surgeons in management decisions. Sugita et al. described five types of osteoporotic spine fractures (swelled-front type, bow-shaped type, projecting type, concave type, and dented type) and investigated the relationship between initial radiographs (fracture type) and clinical outcomes. Of the five types, swelled-front type, bow-shaped type, and projecting type fractures had a poor prognosis with late collapse and often showed a vacuum cleft. On the other hand, concave type and dented type had a good prognosis and rarely required surgical intervention. Although this fracture classification system does not help guide treatment, it does provide some data on the clinical prognosis of these fractures based on injury morphology. The Arbeitsgemeinschaft für Osteosynthesefragen (AO) Classification system (type A, compression; type B, distraction; type C, translation), although not specifically designed for osteoporotic spine fractures, continues to be the most comprehensive fracture classification system and can be used to help guide the management of these injuries.

Management

The majority of patients having osteoporotic spine fractures are initially treated nonsurgically, with the use of analgesics, activity modification, initiation of osteoporosis medication, bracing, and physical therapy. Bracing is controversial. In fact, a recent randomized controlled study showed no difference in clinical and radiographic outcomes from orthosis compared with no orthosis in osteoporotic fractures. It is important to mobilize these patients as quickly as possible and limit opioid medication use. In a select group of patients, cement augmentation procedures or more invasive surgical interventions may be warranted.