Cervical Spine Trauma in Patients with Congenital Spinal Stenosis

h1 class=”calibre8″>17 Cervical Spine Trauma in Patients with Congenital Spinal Stenosis

Colin T. Dunn, Kelley E. Banagan, and Steven C. Ludwig

Abstract

Congenital cervical spinal stenosis is a bony narrowing of the spinal canal that most often presents as cervical myelopathy resulting from degenerative lesions in an already narrowed cervical spinal canal. Several radiographic criteria have traditionally been used to define congenital stenosis, such as midsagittal canal diameter and canal-to-body ratio, but magnetic resonance imaging has emerged as the preferred imaging modality. Patients with congenital stenosis, especially those participating in contact sports, are at elevated risk of neurological injury after cervical spine trauma. Congenital narrowing of the cervical spinal canal is associated with a number of such injuries, including cervical cord neurapraxia, brachial plexus neurapraxia, and central cord syndrome.

Congenital stenosis has implications for return-to-play decisions after cervical spine trauma. Although such decisions should be made on a case-by-case basis, several criteria have been proposed regarding the role congenital stenosis should play in making decisions to permit return to contact activities. Management of cervical spine trauma differs little in patients with congenital spinal stenosis, but there have been questions surrounding the value of prophylactic surgery in patients with congenital stenosis at risk of cervical trauma and how surgical management of stenosis should affect return-to-play decisions.

Keywords: congenital spinal stenosis, cervical spine trauma, Torg ratio, cervical cord neurapraxia, stingers, central cord syndrome

17.1 Introduction

Cervical spinal stenosis can either be degenerative or congenital in origin. Degenerative spinal stenosis generally presents at a later age with myelopathic symptoms resulting from spondylotic encroachment into the cervical spinal canal. In certain patients, symptomatic relief is achieved with decompressive surgery to relieve pressure on the spinal cord.

Congenital spinal stenosis is present from an early age and is generally of unknown etiology. Understanding of the factors that contribute to a congenitally narrow spinal canal is poor, but roles have been proposed for premature closure of ossification centers and neurohormone-mediated negative chemotaxis acting on chondroblasts. ¹^,² Most patients with congenital stenosis are asymptotic in the absence of trauma or degenerative changes.

17.2 Congenital Spinal Stenosis

17.2.1 Anatomic Changes in Congenital Spinal Stenosis

Congenital spinal stenosis is characterized by decreased spinal canal areas at multiple levels in the absence of degenerative changes (▶ Fig. 17.1). Patients with congenital spinal stenosis exhibit significantly smaller lateral masses, lamina lengths, and lamina-pedicle angles with larger lamina-disc angles, resulting in a shortened midsagittal canal diameter. ³ Congenital cervical stenosis is strongly associated with decreased sagittal canal diameter and interpedicular distance, but not decreased pedicle length. ⁴ Congenital stenosis is found in association with a number of syndromic presentations, including achondroplasia, hypochondroplasia, Klippel–Feil syndrome, chondrodysplasia punctata, and brachytelephalangic chondrodysplasia. ¹

Fig. 17.1 (a) Axial T2-weighted image showing uncovertebral osteophytes causing neural foraminal narrowing, more prominent on the right side and disc bulge causing central canal stenosis. (b) Sagittal T2-weighted image showing cervical canal stenosis at multiple levels. Spinal cord is compressed and deformed but shows no signal changes.

17.2.2 Epidemiology

The absence of universally accepted criteria for defining congenital cervical stenosis has complicated the efforts to determine its true prevalence. In one study of skeletal specimens, the prevalence of cervical stenosis in the adult population was estimated at 4.9%. ⁵ Nakashima et al ⁶ found narrow cervical canals (< 14 mm anteroposterior diameter on radiograph) in 10.2% of asymptomatic study participants, with greater prevalence in female and older patients. Estimates of the prevalence of congenital cervical spinal stenosis among football players, a population at particular risk of cervical trauma, have varied. Using a Torg ratio < 0.8 at one or more level from C3–C6 to define stenosis, the prevalence of cervical spinal stenosis among professional football players was estimated to be 34%. ⁷ Another study of college and high school players found congenital cervical stenosis in 7.6% of cases. ⁸

17.2.3 Diagnosis

A number of radiological criteria have been proposed for the assessment of congenital cervical stenosis using various imaging techniques. Lateral view radiography of the cervical spine permits assessment of the bony diameter of the spinal canal to identify patients with congenital stenosis. The average values for this measurement range from 17 mm in lower cervical segments to 23 mm at C1. Values below 14 mm at any level are 2 standard deviations below normal, and this cutoff value has often been used to define congenital cervical spinal stenosis. ⁹^,¹⁰

The Torg ratio (▶ Fig. 17.2), calculated as the spinal canal-to-vertebral body ratio on lateral view radiographs, is a frequently used parameter for assessing congenital cervical spinal stenosis. In determining this value, the sagittal diameter of the vertebral body is measured at the mid-point and the sagittal diameter of the spinal canal is measured between the posterior surface of the vertebral body and the posterior margin of the spinal canal. In comparing the use of this ratio with the use of midsagittal canal diameter as diagnostic tools for cervical spinal stenosis, Pavlov et al ¹¹ proposed a cutoff value of 0.82 for identifying congenital cervical stenosis. The use of this measurement rather than midsagittal canal diameter offers the benefit of eliminating magnification errors in radiography caused by differences in target distance, object-to-film distance, and body type.

Fig. 17.2 Lateral radiograph of the cervical spine demonstrating calculation of the Torg ratio. A Midsagittal diameter of the spinal canal measured from the posterior surface of the vertebral body to the nearest point of the corresponding lamina. B Midsagittal diameter of the vertebral body as measured at the center of the body.

The use of the Torg ratio for assessing cervical spinal stenosis, particularly in athletes, has received criticism for its poor positive predictive value for finding true stenosis. Blackley et al ¹² found a poor correlation between the Torg ratio and canal diameter shown by computed tomography (CT), and Prasad et al ¹³ found that Torg ratio correlated poorly with room available for the cord as shown by magnetic resonance imaging (MRI). Herzog et al ¹⁴ argue that these criteria have low specificity in determining true stenosis when used among football players because of the players’ larger vertebral body diameters; larger vertebral bodies among football players result in smaller Torg ratios, even though their canal diameters may be normal.

Horne et al ¹⁵ proposed the lateral mass measurement-to-canal diameter (LM/CD) ratio as a new radiographic indicator of developmental cervical spinal stenosis. In determining this ratio, the LM is measured as the distance between the lateral mass and posterior vertebral body and the CD is measured as the distance between the spinolaminar line and posterior vertebral body. Using an LM/CD ratio ≥ 0.735 at C5 to identify developmental cervical stenosis in the adult population, the authors reported a favorable statistical profile (specificity 80%, sensitivity 76%). ¹⁵

MRI and CT imaging provide better resolution of soft-tissue structures in the spine, allowing for the detection of both developmental and acquired stenosis. These imaging modalities have been used to identify congenital stenosis based on several criteria, including Torg ratio < 0.82 ¹⁶ and loss of cerebrospinal fluid (CSF) signal surrounding the spinal cord. ¹⁷ MRI of the entire cervical spine in both axial and sagittal views using both T1- and T2-weighted images provides comprehensive evaluation of cervical stenosis. ¹⁸

17.3 Risk of Neurological Injury in Cervical Trauma with Congenital Stenosis

17.3.1 Permanent Neurological Injury

Patients with congenital cervical spinal stenosis generally remain asymptomatic until the onset of spondylotic changes leads to further narrowing of the cervical spinal canal. However, patients with congenital stenosis are at greater risk of certain neurological injuries after trauma to the cervical spine.

Numerous studies have reported a link between congenital cervical spinal stenosis and traumatic spinal cord injury (SCI). In 98 patients who had experienced closed cervical spine fractures and/or dislocations, Eismont et al ¹⁹ found a correlation between midsagittal canal size as seen on radiographs and the occurrence and degree of neurological impairment after injury. All of the 14 patients in that study with complete quadriplegia had canal diameters less than the average of patients with no neurological deficit. In another study, Kang et al ²⁰ examined the Torg ratio and midsagittal canal diameters on radiographs of 288 patients who had sustained acute fractures or dislocations of the cervical spine. The authors found that a sagittal canal diameter < 13 mm was strongly associated with SCI and that the SCI group had smaller Torg ratios and canal diameters.

Patients with congenital stenosis are also at elevated risk of SCI in cases of structurally insignificant cervical trauma. In patients who had experienced minor cervical trauma, Aebli et al ²¹ reviewed the radiological characteristics of 45 patients without neurological symptoms and 68 patients suffering from acute cervical SCI and found significantly smaller Torg ratios among the SCI group relative to those without SCI. They did not, however, detect an inverse relationship between Torg ratio and severity of SCI (as assessed by American Spinal Injury Association impairment score), and the Torg ratios did not differ between patients who did or did not fully recover after SCI. The authors propose that patients with a Torg ratio below 0.7 be considered at elevated risk for acute cervical SCI after minor cervical trauma.

In a 2012 study, Takao et al ²² noted that a congenitally narrow spinal canal may be an important risk factor for traumatic cervical SCI. Of the 30 patients with a history of traumatic cervical SCI without major fracture or dislocation at the C3–C4 segment, 27 (90%) had cervical spinal stenosis as determined by sagittal CSF column diameter < 8 mm at this segment, whereas only 61 (6.75%) of 607 healthy volunteers had cervical spinal stenosis at C3–C4. Furthermore, the authors found that the incidence for traumatic cervical SCI without major fracture or dislocation at the C3-C4 segment for patients with cervical spine canal stenosis was 124.5 times higher than those without canal stenosis.

In 53 patients with distractive-extension injuries, Song et al ²³ divided patients into one of four categories based on the severity of their SCI: A (complete), B (incomplete), C (radiculopathy), or D (normal). Using this categorization, the authors found an inverse relationship between Torg ratio and severity of symptoms. In another 103 patients with similar injuries, stenosis, as determined by Torg ratio, was found in 20% of patients, and prognosis was worse among patients in this group. ²⁴

17.3.2 Transient Cervical Neurapraxia

Much of the literature regarding cervical trauma in patients with congenital spinal stenosis focuses on athletes in contact sports and the relative risk for cervical cord neurapraxia (CCN). CCN is an acute transient neurological injury to the cervical cord that involves sensory changes, such as burning pain, numbness, or tingling, with or without motor changes ranging from weakness to complete paralysis. It most often occurs in athletes with congenitally narrow cervical spinal canals as a result of hyperflexion or hyperextension injury. ²⁵ Symptoms generally subside within 15 minutes but can persist for up to 48 hours. Such injuries compress the spinal cord by a “pincer” mechanism in which the spinal cord is pinched between the inferior margin of the one vertebra and lamina of the vertebra below it (▶ Fig. 17.3). ²⁶ The prevalence of these injuries has been estimated at 7 in 10,000 football players. ⁸

Fig. 17.3 Schematic depicting the “pincer” mechanism that can result in transient cervical neurapraxia. During a hyperextension injury, the spinal canal narrows and the cord becomes pinched between the posteroinferior edge of a vertebral body and the subjacent lamina.

Among 24 patients with history of CCN, Torg et al ²⁷ found radiographic evidence of congenital cervical stenosis in 17 patients. Relative to a control group, the neurapraxia group had significant stenosis as determined by both sagittal canal diameter and Torg ratio. In a later work, Torg et al ²⁸

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