Congenital Cervical Anomalies and Special Needs Athletes

Jun Sup Kim, MD

Evan Baird, MD

Lindsay Andras, MD

Nomaan Ashraf, MD, MBA

Dr. Andras or an immediate family member is a member of a speakers’ bureau or has made paid presentations on behalf of Biomet and Medtronic; has stock or stock options held in Eli Lilly; and serves as a board member, owner, officer, or committee member of the Pediatric Orthopaedic Society of North America and the Scoliosis Research Society. Dr. Ashraf or an immediate family member is a member of a speakers’ bureau or has made paid presentations on behalf of Stryker; and serves as a paid consultant to Stryker. Neither of the following authors nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this article: Dr. Baird and Dr. Kim.

Introduction

Sports and exercise is especially essential for the well-being of children with special needs. It promotes psychological and physical well-being. Literature on rehabilitation and therapy of persons with physical disabilities has shown that athletic activity is related to improvements in locus of control, self-image, and life satisfaction.¹^,²^,³

Cervical spine injuries are common in sporting activities and can result in catastrophic impairment if appropriate steps to prevention and treatment are not instituted. Individuals with congenital or developmental anomalies of the cervical spine constitute a unique subset of patients for whom standard return-to-activity guidelines are not wholly applicable. Based on the myriad benefits of sports and exercise in this patient population, these patients should not be globally restricted from these activities. Rather, the clinician must consider the risks and dangers of the sport in question with respect to its therapeutic benefits. Additionally, it is the duty of the clinician to consider the specific congenital spinal anomalies that may pose an increased risk of neurologic injury.

Cervical spine instability should remain a consideration in the workup of the athlete with special needs, especially in the presence of certain anomalies or syndromes, such as Down syndrome, Klippel Feil syndrome, and Morquio syndrome. Instability can lead to compression of the spinal cord, and it often exists in conjunction with other pathology such as spinal stenosis, basilar invagination, and central nervous system (CNS) abnormalities such as Arnold-Chiari malformation.³

The majority of literature addressing this population is largely based on case series and level III evidence; however, because of the difficulty in gathering a more expansive body of literature, this information should not be discounted.

Clinical Evaluation

The decision to let an athlete return to play (RTP) should be based on medical history, physical examination, imaging, and the type of sport being played. There are no standardized criteria for RTP because the postinjury management of each individual is unique, especially in athletes with special needs. Children with cervical spine anomalies or instability may present with a variety of complaints, such as head or neck pain, loss of range of motion (ROM), signs of upper motor neuron involvement, or weakness.⁴ Many tracts of the spinal cord may be involved, and localizing sites of compression is often difficult. As such, the diagnosis and management of these anomalies are essential for the physician to recognize.

Posterior cord impingement affects the dorsal column, leading to changes or deficits in pain, proprioception, and vibratory sense. Anterior spinal column involvement affects the corticospinal tracts and may lead to muscle weakness and pathologic reflexes such as clonus, Babinski sign, spasticity and hyperreflexia of deep tendon reflexes. Involvement of the cerebellum may manifest as nystagmus, ataxia, and incoordination. Vertebral artery
compression compromises blood flow to the posterior cord, which may lead to syncopal episodes, dizziness, and decreased mental acuity. Cranial nerve compression as the nerves exit the medulla may occur from instability or anomalies such as basilar invagination. The more commonly involved cranial nerves include the trigeminal (V), glossopharyngeal (IX), vagus (X), accessory (XI), and hypoglossal (XII) nerves. A thorough neurologic examination should be recorded to evaluate for subtle changes.⁴

Radiographic assessment with plain imaging of the cervical spine should include lateral radiographs in neutral, flexion, and extension; open-mouth odontoid; and anteroposterior views. Compression and instability may occur at the occipitoatlantal and atlantoaxial regions; as such, the clinician should be mindful to examine this area closely to evaluate for basilar invagination, evidence of atlantoaxial instability, congenital anomalies of the cervical vertebrae such as synostosis, and anomalies of the odontoid such as os odontoideum.⁴ In the setting of abnormal neurologic examination findings, MRI offers a means of evaluating for signs of cord compression as well as associated CNS anomalies such as hydrocephalus, Chiari malformations, and syringomyelia. CT yields anatomic detail that may help in defining anomalies of the cervical vertebrae such as aplasia, hypoplasia, or os odontoideum as well as congenital synostosis such as that seen in Klippel Feil syndrome.

Considerations for Specific Disorders

Basilar Invagination

Basilar invagination refers to a deformity wherein the odontoid process is located further cephalad than the normal state, violating the foramen magnum, which may be significant enough to encroach on the brainstem. This condition increases the risk of neurologic injury or circulatory compression, especially with contact sports. The etiologies may be basiocciput hypoplasia, occipital condyle hypoplasia, atlas hypoplasia, the presence of an incomplete ring of C1 with subsequent lateral masses diastasis, achondroplasia, or atlanto-occipital assimilation. Additionally, between 25% and 35% of patients with basilar invagination have associated spinal abnormalities such as Chiari malformation, syringomyelia, syringobulbia, and hydrocephalus.⁵

Patients with basilar invagination may exhibit torticollis, restricted neck movements, a low hairline, and a webbed or short neck. Caetano De Barros et al described 66 cases of basilar invagination and found that the most common clinical symptoms that induced the patient to seek medical attention were weakness in the lower limbs (68%), gait unsteadiness (56%), and headache (53%). Paraesthesias, often localized to the upper limbs, appeared in 43% of cases. Dizziness and dysphagia were described in 37% of patients. The age of presentation in patients without Chiari malformations was commonly in the second decade of life (58%), with 86% presenting within the first 3 decades of life. Notably, a comparative study of symptoms in patients with isolated basilar impression and isolated Arnold-Chiari syndrome has shown that basilar invagination most frequently manifested as weakness and paraesthesias in the limbs, but patients with Arnold-Chiari syndrome presented most often with unsteadiness of gait.⁶

Similarly, Goel et al reported on 190 patients surgically treated with basilar invagination who were divided into two groups—patients with and without Chiari malformations. Symptom presentation was relatively acute in patients without Chiari malformations (group one), but those with Chiari malformations (group two) experienced long-standing and progressive symptomology. Whereas pyramidal symptoms dominated in group one patients, those in group two experienced spinothalamic sensory dysfunction and ataxia as well as motor and deep sensory dysfunction. Trauma was a major factor that influenced acute development of symptoms in those patients without Chiari malformations. The age of presentation in patients with basilar invagination associated with Chiari malformation was reported to be most common in the third decade (44%), with 88% of patients presenting between the second and fourth decades of life. Goel et al postulated that symptoms in the group of patients without Chiari malformations were a result of brainstem compression by the odontoid process, but those with Chiari malformations could be explained by the crowding of neural structures at the foramen magnum.⁷

Numerous radiographic measurements have been described that assess the degree of basilar invagination; these include the lines of Chamberlain, McGregor, and McRae, which gauge the relationship of the odontoid to the foramen magnum (Figure 13-1). Chamberlain’s line originates from the dorsal margin of the hard palate to the posterior edge of the foramen magnum. It is considered abnormal if the tip of the dens is greater than 5 mm proximal to Chamberlain’s line.
McGregor’s line is drawn from the posterior edge of the hard palate to the most caudal point of the occiput. The odontoid tip should not protrude more than 4.5 mm above the McGregor Line. McRae’s line defines the opening of the foramen magnum, from the basion to the opisthion. If the tip of the dens is below this line, then basilar invagination is not substantial, and the patient is expected to be asymptomatic.⁴^,⁵

FIGURE 13-1 Lines assessing the degree of basilar invagination: Chamberlain, McGregor, and McRae lines, which gauge the relationship of the odontoid to the foramen magnum. ADI = atlantodens interval, SAC = space available for cord. (Adapted from Copley LA, Dormans JP: Cervical spine disorders in infants and children. J Am Acad Orthop Surg 1998;6:204–214.)

Vaccaro and colleagues summarized RTP criteria for athletes with cervical spine injuries.⁸ The authors also described congenital anomalies of the spine and placed them in three categories: no contraindications, relative contraindications, and absolute contraindications to RTP. Considering that many of these patients with basilar invagination already present with symptoms of motor weakness and gait instability, there is an extraordinary potential for catastrophic neurologic injury from direct compression of the brainstem by the odontoid. Goel et al showed that many patients presented acutely with symptoms of basilar impression (i.e., motor weakness) after minor trauma.⁷ Therefore, radiographic evidence of basilar invagination is an absolute contraindication to participation in contact sports.

Os Odontoideum

Anomalies of the odontoid are a spectrum ranging from aplasia to hypoplasia to os odontoideum. The distinction is better defined in radiologic terms because these anomalies may lead to atlantoaxial instability with similar clinical presentation. In 1886, Giacomini first coined the term os odontoideum as a condition in which the dens was separated from the axis body.⁹ Although there is debate as to whether the etiology is of a congenital or traumatic nature, sound management requires a thorough appreciation of the natural history of this entity. Given that the transverse atlantal ligament (TAL) may be rendered ineffective at restraining atlantoaxial motion, the secondary ligamentous restraints of the dens become lax over time, leading to instability. The free ossicle of the os odontoideum moves with the anterior arch of the atlas. Over time, this instability becomes multidirectional and may lead to neurologic symptoms.¹⁰

When initially described, os odontoideum was thought to be the result of a congenital failure of fusion between the dens and the remainder of the axis. However, studies have demonstrated that the failure of fusion of the secondary ossification center of the dens, which normally develops by age 3 years and fuses by age 12 years to the remainder of the axis, is a separate entity known as persistent ossiculum terminale (Figure 13-2).¹¹^,¹²^,¹³ Persistent ossiculum terminale differs from os odontoideum in that the fragment is smaller in size and located above the TAL. As a result, ossiculum terminale is less likely to result in clinically significant instability, although cases of neurologic deficit resulting from progressive atlantoaxial dislocation have been reported.¹¹

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