7.1 Epidemiology

The aging population is expected to grow exponentially in industrialized countries. The U.S. population age > 65 years was roughly 15% in 2014; it is expected to double after 6 years and reach 25% of the population by 2030. ^{1 , 2}

One expected rising medical need is skeletal fractures of the aging spine because of the relationship of advanced age to poor bone mineral density and the propensity for falls. Ground level falls (GLF) are particularly high risk in this population and correlate with increased age. The frequency of GLFs increases with age, ranging from an annual incidence of 30% in those over 65 to an incidence of 50% in those over 80 years of age. ³ This age-related GLF risk in combination with the growing aging population contributes to a predicted increase in the annual fracture rate by 50% from 2005 to 2025. ⁴ When compared to their younger counterparts, aging patients suffer a disproportionate number of cervical spine fractures, ⁵ with a high predisposition for C1 and C2 fractures (See Fig. 7‑1). ^{6 , 7} The propensity for cervical fractures in this population may be related to multiple factors, including the more common presentation of a GLF with hyper-extension injury to the head and neck in combination with progressive overall kyphotic spinal alignment.

As aging spine fracture incidence increases, the associated costs of treating these fractures will also grow. At present, the annual cost for fracture treatment in the U.S. for this demographic is reported to be $14 billion. ^{4 , 8} Management of C2 fractures alone resulted in hospital charges in the U.S. of more than $1.5 billion in 2010. ⁹ Due to distinct challenges. such as compounding medical comorbidities, decreased physiological reserve, increased frailty, and unique psychosocial needs, the aging population represents an increasing demand on the health care system. ¹

7.2 Biomechanical Considerations

The most common cause of cervical spine fractures in aging patients is from low-energy GLFs as compared to high-energy injuries seen in younger individuals. ^{6 , 7 , 10} One reason for this difference in injury pattern among demographics may be related to global postural changes that occur with age. ¹ Increasing age is correlated with progressive cranio-pelvic kyphosis, which becomes most significant by the eighth decade of life. ⁶ As degenerative spinal changes lead to multilevel loss of disc height, the spine tends to straighten leading to cervical kyphosis, with an unbalanced shifting of the center of gravity anteriorly. ⁷ This subaxial cervical kyphosis may additionally lead to compensatory mechanisms such as hyperlordotic angulation at the cranio-cervical junction. Additionally, osteoporotic and arthritic changes throughout the vertebral column in aging patients lead to weak bone from decreased bone mineral density and decreased flexibility of the spine from bridging osteophytes that predispose a patient to fractures from low-velocity trauma. ¹⁰ Approximately 40% of patients >65 years old with type II odontoid fractures have positive sagittal malalignment, of which 60% have posterior fracture displacement. ¹¹

Additional risk factors for cervical fracture in this population include progressive poor bone mineral density with age, particularly in postmenopausal women. ¹² Decreased reaction time, increasing impaired balance, ataxia, and gait instability further increase the risk of fall. ¹ The combination of these factors–global kyphosis with an unbalanced center of gravity; hyperlordotic angulation at the cranio-cervical junction; impaired gait, balance and reaction time; and poor bone mineral density–culminate in a high susceptibility for upper cervical spine fractures with GLF.

7.3 Common Injury Types

C1 fractures account for 27% of cervical spine fractures in those > 65 years of age. ¹³ They are classified as those involving a single arch (Type I), those with burst fracture (Type II; aka Jefferson), or lateral mass fractures (Type III). Jefferson fractures generally occur from axial loading, and were classically described as four-point fractures. Now, more commonly Jefferson fractures include two- or three-point fractures as well. C1 fractures may lead to transverse ligament disruption, resulting in atlanto-axial instability.

C2 fractures account for 54% of geriatric cervical spine fractures. ¹³ Hangman’s fractures are defined as bilateral fractures through the pars interarticularis and/or the pedicle of C2. These fractures are often due to hyperextension and axial loading in high-energy mechanisms of injury, and as a result are more commonly observed in younger individuals.

C2 odontoid process (dens) fractures are the most common upper cervical spine fracture in adults > 70 years of age (~89% of cervical fractures, see Fig. 7‑1). ^{14 , 15} Hyperflexion is the most common mechanism of injury, with subsequent anterior atlanto-axial displacement. Anderson and D’Alonzi classified these fractures through the apical portion (Type I), through the base of the neck (Type II), and through the body of C2 (Type III). ¹⁶ Shallow Type III fractures can be further differentiated from Type II fractures by determining whether the fracture line involves the C2 superior facets. ¹⁷ Grauer et al proposed a subtyping of Type II fractures into nondisplaced/horizontal (IIA), antero-superior to postero-inferior/anteriorly displaced (IIB), and antero-inferior to postero-superior/posteriorly displaced (IIC) fractures, which can be utilized in surgical planning. ¹⁷ Type II fractures are most common; they increase in frequency with age and additionally have been increasing in proportion each year. ¹⁵ Type II fractures generally demonstrate poor healing rates with conservative management, ^{15 , 17} whereas, Type I and Type III fractures can often be successfully treated with nonoperative immobilization. One caveat to that generalization is Type I fractures which significantly disrupt the apical and/or alar ligamentous attachment to the occiput may result in atlanto-occipital instability. ¹⁸ Fig. 7‑2 shows the Grauer classification of odontoid fractures. A cervical CT demonstrating a displaced Type II odontoid fracture is depicted inFig. 7‑3. Fig. 7‑2 lists the general guidelines for management of each type.

Isolated subaxial (C3-C7) cervical fractures without a concomitant C1 or C2 fracture account for only 19% of geriatric cervical spine fractures. ¹³ These injuries include simple axial loading burst or compression fractures or more complex fracture and/or facet dislocations. Less common injury patterns include clay-shoveler’s fracture (avulsion of a spinous process) and teardrop fractures (severe hyperflexion with antero-inferior vertebral body fracture and posterior ligamentous disruption).

7.4 Treatment options

A complete review of the breadth of treatment options of cervical fractures is beyond the scope of this chapter. We will limit the described options to general principles of treatment and those specific to odontoid fractures, which represent the most common injury type. Conservative management includes a variety of external immobilization devices, including cervical collars and the halo vest. Cervical collars can be soft or rigid and strap around the neck to facilitate application and removal. Typically, soft collars do not immobilize the cervical spine, while rigid collars generally are best at stabilizing the lower cervical spine. The halo-vest externally immobilizes the cervical spine by external pin fixation of the skull connected by four rod posts to a rigid torso vest. The halo-vest is best at immobilizing the upper and lower cervical spine. It can be used to reduce flexion, extension, bending, and rotation; however, it is unable to provide distraction once the patient is upright. For certain fractures with significant displacement or angulation, closed reduction with traction may be necessary prior to immobilization. ¹⁹

Surgical treatment provides the potential benefit of enhanced immediate fracture immobilization by applying internal fixation directly to the spinal elements, via screw–rod, screw–plate, or wiring techniques. Additionally, spinal fixation devices and graft materials can be used to provide intraoperative reduction maneuvers for improved spinal alignment and bony healing. When necessary, spinal cord decompression can also be performed at the time of surgical stabilization via either anterior and/or posterior approaches (e.g., laminectomy, discectomy/corpectomy).

Odontoid fractures represent the most common cervical injury type in the elderly population, and typically result in atlanto-axial instability with abnormal translational motion through the fractured portion of the dens. Types I and III odontoid fractures demonstrate high fracture healing rates with nonoperative external immobilization, whereas Type II fractures are associated with significant failure rates with the same approach. ^{9 , 15} Therefore, there is extensive clinical experience describing various surgical treatment options for specifically Type II odontoid fractures.

In general, surgical fixation of odontoid fractures is via either a posterior or an anterior approach. Posterior spinal fixation with C1–C2 fusion is performed by either C1–C2 wiring, C1–C2 transarticular screw fixation, or by a C1–C2 screw–rod construct. There have been several previously described posterior wiring methods. The Brooks method uses a double-wire loop passed from cranial to caudal beneath the lamina of C1 and C2, which is used to secure a structural iliac crest graft. ²⁰ The Gallie method uses an “H” graft that fits over the posterior arches of C1 and C2 with a wire passed underneath the lamina of C1, over the spinous process of C2, and tightened to secure the graft in place. ²⁰ The Sonntag method is similar to the Gallie in that the wire is passed underneath only the C1 lamina and is looped around the C2 spinous process. Both the Gallie and the Sonntag approaches only require passing the wire underneath the C1 lamina, as opposed to the Brooks technique, which involves passing the wire under the lamina of both C1 and C2. Posterior wiring fixation alone is associated with a relatively high nonunion rate and has since been supplanted by C1–C2 transarticular screw and C1–C2 screw–rod construct techniques. Posterior wiring, however, remains an important approach, as it provides added supplemental rigidity to primary posterior screw fixation and is an effective method for incorporating structural bone graft into the fusion construct.

C1-C2 transarticular screw fixation results in superior biomechanical immobilization and is associated with high bony healing rates. ¹⁸ In this procedure, bilateral posterior screws are placed through the isthmus of C2, crossing the C1-C2 articulation, and into the lateral mass of C1. ¹⁷ While this technique provides immediate rigid fixation of C1 and C2, it is associated with a potentially significant risk of injury to the vertebral artery, as it courses adjacent to the C2 foramen transversarium. In the presence of a high-riding, torturous or hyperplastic vertebral artery, modified trajectories may be necessary, or may simply not be technically feasible. ¹⁹ Preoperative planning with multiplanar CT reformatted images is necessary to assess an adequate screw path before considering C1–C2 transarticular screw fixation. Additionally, intraoperative navigation is a potentially useful adjunct for particularly challenging screw trajectories.

C1–C2 screw–rod fixation is an alternate approach for posterior spinal stabilization with equivalent biomechanical immobilization as C1–C2 transarticular screws (Fig. 7‑4). ¹⁹ C1 lateral mass screws can be combined with C2 pedicle, pars or intralaminar screws via a connecting rod to provide internal fixation. C2 pedicle screws cross the C2 pedicle into the vertebral body, providing rigid fixation of C2 via a long bicortical screw. Because C2 pedicle screws traverse the isthmus, they are subject to the same potential risk of vertebral artery injury as C1–C2 transarticular screws. Alternatively, C2 pars screws enter the C2 isthmus; however, they do not pass the transverse foramen, thereby obviating the risk of potential vertebral artery violation. C2 intralaminar screws involve placement of crossing screws directly through the cancellous channel of the lamina. Intralaminar screws decrease the risk of vertebral artery injury; however, they require an intact C2 lamina (i.e., cannot be performed in the setting of a laminectomy for decompression).

Posterior surgical treatment of odontoid fractures requires stabilization across the C1–C2 motion segment, which ultimately results in significant loss of axial head rotation. An alternative anterior approach allows for direct surgical fixation across the odontoid fracture line, thereby preserving C1–C2 motion. ¹⁹ In this approach, a pilot hole is drilled through C2 and coaxially through the dens to its apex. The hole is then tapped and a lag screw is placed to secure the fragment to the body (Fig. 7‑5). ¹⁸ A second adjacent screw may be placed to prevent rotation around the single screw, which may be increasingly considered for the elderly population. ^{18 , 21} The anterior odontoid screw approach relies on eventual bony healing across the fracture line, and, as such, chronic fractures > 6 months after injury may fail secondary to the formation of fibrous nonunion across the fracture gap. Additionally, anterior odontoid screw fixation requires a nondisplaced, well-aligned fracture with specific anatomic limitations with respect to fracture morphology and patient thoracic chest size. Finally, osteoporotic patients have an additional risk of poor bone healing and screw purchase. Therefore, careful preoperative patient assessment is necessary before considering potential anterior odontoid screw fixation.

7.5 Benefits and Risks

In aging patients, halo vest immobilization is associated with impaired swallowing, respiratory function, and mobilization due to restriction of normal thoracic chest-wall motion. Complications from halo-vests include aspiration, pneumonia, cranial pin-site infection, dural violation, pressure sores, and, rarely, intracranial abscess. ^{9 , 22} These risks are countered by the perceived benefit of achieving better rigid upper cervical immobilization compared to cervical collars. Additionally, a halo vest may be preferred in patients suspected of poor compliance with removable or adjustable cervical collars. These risks may be reduced by close interval follow-up of patients in a halo vest to avoid common complications. Cervical collars also carry risk of complications, albeit less than observed with halo vests. Primarily, cervical collars without diligent hygiene and routine surveillance of pressure points can lead to skin breakdown and ulcers.

Surgical treatment carries general risk of bleeding, infection, anesthetic complications, neural or vascular injury, spinal implant malfunction (e.g. screw breakage or loosening), and pseudo-arthrosis. Various surgical approaches carry additional specific risks unique to aspects of the technique. Passing sublaminar wires may injure neural elements, particularly in the setting of spinal canal narrowing (e.g., posteriorly displaced dens fracture). ¹⁸ As previously mentioned, C1-C2 transarticular screws can cause vertebral artery injury, with a small incidence of potentially devastating brainstem stroke. ^{18 , 19} Excessively long or misplaced lateral mass or pedicle screws risk injury to the internal carotid or vertebral arteries, hypoglossal nerve, and spinal cord. With anterior odontoid screw fixation, esophageal or pharyngeal perforation and/or airway complications are potential risks from the surgical exposure. ²¹ In addition, elderly patients are at increased risk of dysphagia and aspiration pneumonia from anterior neck dissection and soft tissue retraction. ²¹ The surgical risk profile for a given patient should take into account– such individual factors as medical comorbidities, baseline frailty, and functional status–and should be weighed against the benefit of immediate fracture stabilization and neural decompression.