9 Lumbar Fractures
Abstract
Lumbar spine fractures are among the most common spinal ailments of the aging spine. This is a particularly important problem now, as the elderly population of the United States is rapidly growing. Healthcare costs and hospitalizations for lumbar spine fractures have increased significantly over the past several years. These fractures include compression fractures, burst fractures, chance fractures and, most severely, fracture-dislocation injuries. These fractures are complicated by common comorbidities of the aging spine, such as osteopenia, osteoporosis, diffuse idiopathic skeletal hyperostosis (DISH), and ankylosing spondylitis (AS). Treatment options vary, depending on fracture type and stability, as well as spinal and systemic comorbidities. For stable fractures, conservative management with pain medication, physical therapy, and possibly bracing may be sufficient. More severe fractures may require treatment including kyphoplasty or vertebroplasty, spinal decompression surgeries, percutaneous or open spinal fusions, or even large deformity correction surgeries. Surgery has heightened risks in older adults, but conservative therapy is associated with secondary complications of prolonged immobilization while the injury heals. This chapter will give an overview of common fractures in older adults, as well as treatment modalities and associated risks.
Key Points
Increasing aging population is leading to an increase of lumbar spine pathology requiring specialized treatment.
Osteoporosis is a very common problem that requires nuanced conservative and surgical management.
With age, bone density decreases, leading to compression of the vertebral body, kyphotic changes in the lumbar spine, and higher rates of fracture.
Kyphoplasty and vertebroplasty are minimally invasive ways to improve pain and restore bone height in osteoporotic compression fractures.
When fusion is required, percutaneous pedicle screw placement is often effective and leads to less blood loss, decreased hospital stay, and a trend toward decreased operative time.
9.1 Epidemiology
Lumbar spine fractures are among the most common diagnoses facing spine surgeons as they evaluate and manage today’s increasing aging population in the United States. Over the past 5 years, there has been a 17% increase in hospitalizations for lumbar spine fractures. This has been associated with a 24% increase in spinal fusions for lumbar fractures and a 15% increase in hospital charges. For lumbar spine fractures in 2007 alone, there were an estimated 13,000 kyphoplasty/vertebroplasty procedures associated with a total national bill of $450 million. The health care expenditure associated with lumbar spine fractures in totality that year exceeded $1 billion. Given this common and expensive condition, it is prudent to understand lumbar spine fractures in the aging population. 1
In addition to the economic impact, the recent opioid epidemic has given rise to a new focus on pain management. Most lumbar spine fractures experienced by older adult patients are stable, but they can be quite painful. Finding appropriate pain management options that both respect the medical comorbidities of the patients and decrease the reliance on opioid medications has become increasingly important. There has been a recent increase in minimally invasive management options to treat pain from lumbar spine fractures, which will be highlighted in this chapter.
The goals of treatment for lumbar spine fractures are to reduce pain, prevent further spinal disease and fractures, create stability, and ultimately to increase mobility. This chapter will discuss the biomechanics behind lumbar spine fractures and the treatment options, ranging from medical management to spinal fusions.
9.2 Biomechanical Considerations
The fundamental biomechanics of the spinal column change over the course of a lifetime. Age-related degenerative change, including osteoarthritis, osteoporosis, facet joint arthropathy, and disc dehydration, lead to decreased flexibility, decreased range of motion, and loss of normal physiologic spinal alignment. The accumulation of these changes impacts each region of the spinal column differently. The cervical spine, for example, is most susceptible to uncovertebral joint hypertrophy due to its high degree of mobility. The lumbar spine is more susceptible to compression fractures due to decreased bone mineral density in the setting of increased load bearing from the rostral spine. 2 , 3
Many age-related microscopic changes in cartilage and tendinous attachments increase susceptibility to injury, thus predisposing the elderly population for lumbar spine fractures. Cartilage shock-absorbing capacity decreases due to fewer functional proteoglycans that maintain water binding within the tissue. Age-related cartilage stiffness is further promoted by fibrous protein cross-linking. Furthermore, the intervertebral disk avascular matrix relies on transport metabolites, which decrease with age due to millions of load cycles over the course of a lifetime. 4
The aging population has a high prevalence of low bone mineral density, osteopenia, and osteoporosis. With age comes degeneration of bone density. In the endplates, this causes increased vascularity and subchondral edema, which is seen as Modic type changes on MRI. This causes disruption in the permeability of the intervertebral disks and decreased nutrient transport. The weakening of the endplate leads to concavity, resulting in a more convex shape of the intervertebral disk. The cortex of the bone, however, only carries 10% of the stress of the vertebral body. A larger portion is carried by the inner cancellous bone, which derives its strength from the small bony trabeculae within it. The compressive strength of the vertebral body is exponentially related to the bone mineral density. As a result, small decreases in bone mineral density with age cause a substantial decrease in the vertebral body strength. This is what leads to the degeneration and bony pathology that is so prevalent in the older adults. 3
9.3 Common Injury Types
9.3.1 Compression
Compression fractures are the most common spinal injury in patients with osteoporosis. 1 The degenerating bone mineral density gives a decreased resistance to compressive forces. Because of the applied forces to the spine in an anterior direction, these compression fractures classically cause anterior wedging. Over time, this causes a loss of lordosis, or even kyphosis, in the lumbar spine. 5 Though these injuries are often stable, they can cause significant pain and spinal deformity. Mild compression fractures can be treated with bracing. This can both help pain and prevent further kyphosis. 6 Vertebroplasty and kyphoplasty are also treatment options, and kyphoplasty can even restore some of the vertebral body height. More extensive fusion surgeries are reserved for very severe and unstable cases. These treatment options will be highlighted later in the chapter.
9.3.2 Burst
Burst fractures are compression fractures that extend through both the anterior and posterior endplates. In other words, on the Denis 3-column classification, they disrupt the anterior and middle columns. 7 Like compression fractures, they are caused by axial loading injury. Those that are stable can be treated conservatively with bracing. Unstable injuries with severe compression, deformity, or ligamentous injury, can be treated surgically in a variety of ways. Fusions, usually extending one level above and one level below the injury, can be performed from the anterior, posterior, or combination approach. Percutaneous instrumentation can be a less invasive surgical option. The hardware acts as an internal brace, allowing the fracture to heal and mobility to be maintained. 7 Severe burst fractures may protrude posteriorly and cause compression of the surrounding neural structures. Rarely, this may lead to neurologic deficits. In such cases, a decompression of the spinal canal is required.
Fracture Dislocation/Chance
Fracture dislocations and chance fractures occur from severe flexion events and represent the most severe types of injury to the lumbar spine. Chance fractures were originally described as osseous injuries that involved a horizontal fracture through the spinal column and neural arch at a single level. We now know that they are often associated with ligamentous injury and can in fact involve more than a single level. They are flexion/distraction injuries, and are most commonly found around the thoracolumbar junction. The classically described mechanism is a car accident, where the seatbelt acts as a fulcrum for flexion. According to a study by Chu et al, 30 to 80% of chance fractures involve intra-abdominal injuries, and 25% have associated spinal cord injury. 8 Purely osseous chance fractures may be treated conservatively with a brace in the absence of neurologic deficits, distraction injury, or comminution. When ligamentous injury is involved, operative intervention is required. This can often be achieved with percutaneous fusion to act as an internal brace while the injury heals. 8
Spine fractures with distraction or dislocation are very severe injuries that have high rates of neurologic deficits. The risk of these fractures is higher in patients with ankylosing spondylitis (AS), due to increased lever arm from autofusion. With distraction, the facet joints are disrupted, and may become perched or jumped. For both distraction and dislocation injuries, spinal fusions are required to stabilize the spine. The type of fusion can vary and depends on the location in the spine and the fracture type. The important point regarding these fractures is that they are all inherently unstable and require urgent intervention.
9.3.3 Comorbidities – DISH, Ankylosing Spondylitis
AS is the most common spondyloarthropathy seen by spine surgeons. The disease is characterized by an inflammatory process that leads to progressive autofusion of the spine. This causes stiffening and angulation, and manifests in patients with progressive back pain and disability as the disease progresses. The classic “bamboo spine” appearance on imaging refers to the fusion process that takes place in the anterior and posterior endplates. It is also common to have fusion within the posterior column of the spine. The segments of autofusion within the spine lead to a long lever arm that predisposes these patients to fractures from even minor trauma. The disease affects 0.1 to 0.2% of the U.S. population and is more common in men than women, with a ratio of 3:1. Patients with the disease are more than twice as likely to be on disability than the general population. They are also more likely not to have been married or to be divorced, and women with the disease are more likely to not have children. 9
Diffuse idiopathic skeletal hyperostosis (DISH) is a noninflammatory process of ossification of the spinal ligaments. This affects the anterior longitudinal ligament most profoundly, and while AS begins with the sacroiliac (SI) joint, DISH generally does not involve the SI joint. DISH was considered a relatively benign disease in the past, but with further studies, the disease is associated with many complications, which will be discussed later in the chapter. 10
9.4 Treatment Options
Generally, conservative therapy should be pursued in those patients who have stable injuries and are neurologically intact. Conservative therapy involves medication for pain relief, physical therapy, bracing, and calcium supplementation. Instability and neurologic deficits from compression of nerve roots, conus medullaris, or cauda equina need to be dealt with surgically. 11 For the aging population, invasive treatment modalities—such as vertebral augmentation, decompressive surgery, or fusions—come with increased operative risks. This population generally has medical comorbidities that can pose potential problems to the patient undergoing general anesthesia. The standard concerns of neurologic deficits, hardware failure, bleeding, and infection also come with these procedures. For the elderly, it can be more difficult to recover from these complications. Osteoporosis also poses an increased concern of hardware failure due to a lack of quality bone to provide hardware purchase. Because of these issues, conservative therapy is preferred in patients who get adequate pain relief with these measures.
9.4.1 Conservative Therapy
Pain Relief
Pain in the setting of an acute compression fracture is typically managed with narcotic medication. In the aging population, it is very important to closely manage the dosing and duration of such medication. Epidural steroid injections can be considered if the pain is still not well controlled with medication.
Another source of pain in patients with compression fractures is radicular pain from pressure on the exiting nerve root. This will follow a typical dermatomal distribution. It is treated initially with antiinflammatory medication and narcotics, if necessary. If the pain is still not well controlled, then a selective transforaminal epidural steroid injection can be considered. 12
Chronic pain can be treated with anticonvulsant or antidepressant medication. Tricyclic antidepressants are the most studied of these medications. They act by blocking the reuptake of norepinephrine and serotonin. Gabapentin and pregabalin are also very effective medicines for neuropathic pain.
9.4.2 Physical Therapy
Physical therapy has been shown to help people with osteoporotic compression fractures in a number of ways. It can improve posture, help maintain bone mineral density, train the patient to avoid painful triggers, and decrease the risk of further falls. Core exercise is an integral part of physical therapy and helps to strengthen the back extensor muscles. In patients with kyphotic deformity from wedge compression fractures, posture and sagittal alignment is improved and pain is decreased. 12
Bracing
Braces are a common treatment modality for patients with osteoporotic compression fractures. They function to limit flexion and decrease the load on the anterior column. In creating stability for the spine, they also promote healing and decrease pain. A thoracolumbosacral orthosis, or TLSO brace, is very commonly used for the treatment of stable fractures, particularly osteoporotic compression fractures. There is also literature to support their use in stable burst fractures (those with less than 30° kyphosis, less than 50% loss of vertebral height, and less than 50% canal narrowing from retropulsion). 6 These braces should have at least three points of fixation and put the patient into a small amount of relative extension. Many advocate for obtaining X-rays every 4 to 6 weeks during the healing process to monitor. The braces are generally worn for 8 to 12 weeks, depending on how rapidly the fracture has healed.
Calcium Supplementation
There are multiple modalities of calcium augmentation. Nasal calcitonin is a commonly used supplement. In addition to its antiresorptive effect, it also has an analgesic effect. 1 Medications such as alendronate and risedronate function to prevent calcium resorption. Teriparatide is a newer medication that functions to promote bone formation through direct stimulation of osteoblasts. Park et al studied the use of teriparatide vs. antiresorptive medications in women with single level osteoporotic compression fractures. They found that the compression fractures in both groups of the study progressed with collapse of the injured vertebral body. The degree of collapse, however, was significantly less in the group treated with teriparatide. These patients had less height loss in the anterior and middle columns and also had significantly less kyphosis and lower wedge angle than the group treated with antiresorptive medications. 13
Vertebroplasty and Kyphoplasty for Osteoporotic Compression Fractures
Vertebroplasty and kyphoplasty are two methods for bone augmentation for patients with vertebral compression fractures (VCF). In the past, treatment for VCFs consisted of open surgery or conservative treatment. The development of both vertebroplasty and kyphoplasty offered an alternative option that was percutaneous and less morbid than surgery. The rates of both procedures increased significantly after their inception in the early 1990s.
Vertebroplasty is the injection of cement into the fracture percutaneously without any attempt to restore height of the vertebral body. Kyphoplasty involves the inflation of a balloon in the fracture to create a cavity. The balloon is then withdrawn and cement is injected into the cavity. Some of the arguments in favor of vertebroplasty are that it is less expensive and may cause less alteration of pressure on adjacent levels, and hence less risk of adjacent level disease. Arguments in favor of kyphoplasty are that it poses less risk of cement embolism (as the cement is contained inside a cavity), and it also gives the ability for some degree of height restoration (Fig. 9‑1,Fig. 9‑2).
For both procedures, fluoroscopic guidance is used to pass a large bore needle (typically 11–13-gauge) through the pedicle into the affected vertebral body. In the case of vertebroplasty, barium-opacified polymethylmethacrylate (PMMA) is injected into the fracture until it fills the fracture to oppose the endplates anteriorly and posteriorly.
9.5 Surgical Management
In some cases of lumbar spine fractures, such as those that are unstable or those causing neurologic compromise, surgical spinal fusion is indicated. Patients requiring operative intervention are generally those with fractures resulting in greater than 30° local kyphosis, greater than 50% loss of vertebral body height, or those in which greater than three contiguous levels are involved. 6 Denis’s 3-column model is often used to assess for instability. In this model there are three vertical columns within the spine. The anterior column consists of the anterior longitudinal ligament, anterior annulus fibrosis, and the anterior two-thirds of the vertebral body. The middle column consists of the posterior longitudinal ligament, the posterior annulus fibrosis, and the posterior one-third of the vertebral body. The posterior column consists of the pedicles, facet joints, lamina, spinous processes, and posterior ligaments. If at least two of the three columns of the spine are injured, that segment of the spine is considered unstable. 14 These patients generally require surgical intervention.
As previously mentioned, the medical comorbidities that aging patients have may preclude them from open surgery. Minimally invasive approaches may help decrease blood loss, hospital stay, postoperative pain, and complication rates. 15 , 16 Minimally invasive techniques involve the percutaneous placement of pedicle screws with the aid of intraoperative imaging and fluoroscopy or stereotactic guidance, as shown in Fig. 9‑3. This allows for smaller incisions and less muscle dissection than open procedures. 17 Studies have shown no statistical difference in neurologic outcomes between the minimally invasive and open approaches. Minimally invasive instrumentation functions as an internal brace to give the fracture time to heal on its own. It is therefore generally reserved for bony fractures that will likely heal with time. 15 Using this form of internal fixation, as opposed to orthotic braces and conservative management, allows the patient to mobilize sooner. This can prevent deconditioning and deep venous thrombosis related to bed rest. It may also decrease the amount of postoperative opioids required. 16
Kyphotic deformities often result from compression fractures. When this causes intractable pain, severe disability, pulmonary function impairment, or progressive neurologic deficits, open surgical correction with fusion may be required (Fig. 9‑4). In elderly patients, this is generally done from a posterior-only approach, if possible, with pedicle screws and rods. This allows for less blood loss and less operative time than a combined anterior-posterior approach. The fusion construct encompasses the area of hyperkyphosis. The upper end of the construct for these deformities will be in the thoracic spine. The region of T5–8, which is the natural kyphotic apex, is avoided because ending a fusion at the apex results in high rates of proximal junctional kyphosis. Because of this, the upper limit of the construct is usually below T10 or, in higher deformities, between T2 and T5. The lower limit of the fusion has been described by Smith et al as being the sagittal stable vertebra (SSV). This is the vertebral body that first encounters a vertical line drawn from the posterior superior point of the sacrum. 18
9.6 Benefits and Risks
9.6.1 Conservative
Pain Medication
This population is even more susceptible than younger patients to the cognitive effects of opioid medications, which could lead to further falls and resulting injury, not to mention the usual risks of addiction, nausea, constipation, and respiratory depression. 12 Inflammatory processes causing pain are not typically well controlled by narcotic medication; non-steroidal antiinflammatory medications typically work better for this type of pain. These also come with side effects, most typically being nausea, gastritis, and resulting ulcers.
Gabapentin and amitriptyline come with the side effect of drowsiness and should be titrated up and down when starting and stopping.
Bracing
Keeping patients in braces for too long can also have a negative impact. They can create pressure sores and resultant infection, and dependence on them can lead to weakening of the axial musculature. The rigidity around the abdomen can lead to decreased lung capacity. There is also an inherent risk of noncompliance and worsening of the fracture, as the braces can be taken off and on. 6
Older adults are very susceptible to both osteoporotic compression fractures and burst fractures. There is a large amount of literature regarding the treatment of burst fractures, particularly with TLSO. Many advocate for stable burst fractures (AO class A3 and better) to be treated with TLSO braces. As 10 to 20% of all thoracolumbar fractures are burst fractures, the ability to undergo conservative treatment as opposed to surgical treatment can pose a large economic benefit. Wood et al, in a randomized prospective study that controlled for fracture severity and patient disability, found that those patients with burst fractures treated with bracing had a shorter hospital stay and had a cost nearly 4.4 times less than those treated surgically. 11
Vertebral Augmentation
In the past decade, there has been increasing concern over vertebral augmentation-related complications, including venous embolization, pulmonary cement embolism, cement compression of neurological structures, and adjacent segment fractures. Despite these complications, vertebroplasty, and more often kyphoplasty, are frequent modes of treatment for osteoporotic compression fractures. As previously mentioned, there is less associated blood loss, shorter hospital stay, positive pain reduction, and less anesthetic risk than in open procedures. 1
Surgical Intervention
Surgical intervention for fractures can prevent worsening or new neurological injuries and also prevent further vertebral body collapse and associated deformity. Patients with unstable fractures have a high risk of neurologic deficit without operative intervention to stabilize their area of injury. In these cases, the benefit of preventing neurologic deterioration generally outweighs the risk of associated medical comorbidities with surgery. Patients with severe compression fractures are slightly more of a grey area in terms of medical decision-making. Without intervention, these patients may develop further collapse of their vertebrae and even kyphotic deformity of the lumbar spine. These patients may benefit from a minimally invasive vertebral augmentation procedure. 1
Surgical intervention in the aging population comes with risks of complications due to medical comorbidities, and also has a higher cost than nonoperative management. Many of these patients have cardiac and respiratory comorbidities that put them at an increased risk for anesthesia. In terms of the surgical outcomes themselves, there are also risks. Osteoporosis makes fusion more difficult, as there is less bone surface area for screw purchase and thus a higher rate of screw loosening, fractures related to hardware placement, and adjacent segment disease. 19 The cost associated with surgery, as well as vertebroplasty and kyphoplasty, is higher than that of nonoperative management. Goldstein et al found that patients in their study who underwent vertebral augmentation had an overall cost of $26,074, and those who underwent conservative management without augmentation had an average cost of $15,507. 1
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