Atlantoaxial Injury and Dysfunction

Background

Disability and instability of the unique atlantoaxial joint result in controversies regarding the management of acute trauma and also the screening evaluation of particular at-risk individuals. The purposes of this article are to define atlantoaxial instability; describe the relatively rare symptomatic lesions with significant morbidity and mortality; and, finally, discuss the rationale for and against screening and restricting activities of at-risk individuals.

Definition

Atlantoaxial instability (AAI), also known as atlantoaxial subluxation, is radiologically identified increased mobility or laxity between the body of the first cervical vertebra (atlas) and the odontoid process of the second cervical vertebra (axis). Subluxation can be anterior, posterior, or lateral, and symptoms occur as a result of cervical cord impingement.

Epidemiology

Although traumatic lesions involving the atlantoaxial region are relatively rare, certain disease states and conditions present a higher theoretical risk of instability due to increased atlantoaxial joint laxity.

Surveys indicate 10-25% of patients with trisomy 21 have AAI. Two thirds of these cases are due to laxity of transverse ligament, whereas one third are due to abnormal odontoid development. Although this association has been depicted on radiographs, the clinical incidence of serious cervical spine injury is not increased in this population compared with other populations.

About 25% of patients with rheumatoid arthritis have atlantoaxial instability, which is thought to be due to chronic inflammation. Congenital skeletal dysplasias may cause resultant odontoid hypoplasia. Marfan syndrome may involve to ligamentous laxity, and acute inflammatory processes can affect the retropharyngeal, neck or pharyngeal spaces.

Frequency

United States

Approximately 15-25% of all patients with trisomy 21 and about 25% of patients with rheumatoid arthritis have atlantoaxial injury or dysfunction.

Functional Anatomy

The articulation of the odontoid process of C2 (axis) with the anterior arch of C1 (atlas) allows for 50% of cervical lateral rotation. The transverse and alar ligaments maintain joint integrity and limit posterior motion of the odontoid process relative to the C1 anterior arch. Abnormal posterior translation (or subluxation) can cause cervical cord impingement with the potential for significant neurologic compromise and even death.

Sport Specific Biomechanics

During extremes of cervical flexion or extension, competent transverse and alar ligaments limit posterior translation of the odontoid process. Incompetent ligaments or a damaged odontoid process can allow for significant translation and potential damage in cases of cervical hyperflexion or hyperextension where axial compression is delivered to the head and cervical spine. Given the potentially serious sequelae of significant atlantoaxial dysfunction, patients with defined instability are restricted from participating in contact sports and in sports requiring significant cervical flexion or extension.

Treatment

Acute Phase

Rehabilitation Program

Physical Therapy

If asymptomatic AAI is detected on screening evaluation of an individual without recent trauma or inflammation, physical therapy may help in teaching patients proper head control and avoidance of extremes of motion or at-risk activities.

Medical Issues/Complications

Initial management of either traumatic or inflammation-induced AAI depends on the presence and progression of neurologic symptoms. An experienced neurosurgeon or spinal surgeon should be consulted in most, if not all, cases.

• Posterior fusion of the upper cervical spine with central cord decompression is indicated in any unstable atlantoaxial joint or in the presence of significant myelopathy. The patient should remain strictly immobilized while awaiting expedient surgical referral and procedures.

  Surgery is immediately indicated only in cases of irreducible canal compromise or progressive neurologic deterioration. Otherwise, it can be schedule on a less-emergent basis.

  Posterior fusion of the upper cervical spine may also be indicated in cases of os odontoideum (non-union of previous odontoid fracture) or other forms of odontoid aplasia or hypoplasia.

• Cases of inflammation-related subluxation may require reduction under general anesthesia with subsequent cast fixation or traction under the guidance of an experienced spinal surgeon.

• Traumatic or inflammation-induced acute AAI involving stable lesions without any neurologic symptoms may be reduced. The patients may be placed in halo brace with vest reduction and immobilization for 3 months. Repeat radiographs are necessary after reduction has been completed; several sources warn that deformity may still be possible, even after reduction.

• In children with confirmed radiographic evidence of transverse ligament disruption less than 3 weeks old, the likelihood of ligamentous healing increases with halo and vest management.

• In adults, healing of the transverse and alar ligaments is unreliable. Therefore, some authorities do not consider nonoperative management in adults, while others favor nonoperative management because of the risk of common surgical complications, the often-incomplete resolution of neurologic symptoms, and the lack of long-term data supporting surgical management.

Surgical Intervention

Posterior fusion of asymptomatic individuals with AAI, such as patients with Down syndrome, remains controversial. While some authorities advocate fusion to reduce the risk of a catastrophic trauma to the spine, others do not recommend fusion if the patient remains asymptomatic. It is important to note that the incidence of serious cervical spine injury is not increased in patients with Down syndrome and AAI, as compared with other athletic populations. Posterior fusion of the upper cervical spine is mainly indicated in symptomatic individuals.

Consultations

A spinal surgeon or neurosurgeon should be consulted in all cases of acute AAI. In cases of asymptomatic AAI found on screening examination, referral is indicated to confirm the diagnosis and possible activity restrictions.

Recovery Phase

Rehabilitation Program

Physical Therapy

After prolonged immobilization, physical therapy can increase cervical range of motion and assist in regaining strength deficits due to immobilization. An experienced therapist can also emphasize the need to avoid at-risk activities and extremes of cervical flexion and/or extension.

Surgical Intervention

Posterior cervical fusion is indicated in patients who present with a deformity that has been present for longer than 3 months or with recurrence after 6 weeks of immobilization. Such fusion can also be considered in the patient with chronic AAI who develops acute symptoms or neurologic compromise.

Medication

Acute Phase

Rehabilitation Program

Physical Therapy

If asymptomatic AAI is detected on screening evaluation of an individual without recent trauma or inflammation, physical therapy may help in teaching patients proper head control and avoidance of extremes of motion or at-risk activities.

Medical Issues/Complications

Initial management of either traumatic or inflammation-induced AAI depends on the presence and progression of neurologic symptoms. An experienced neurosurgeon or spinal surgeon should be consulted in most, if not all, cases.

• Posterior fusion of the upper cervical spine with central cord decompression is indicated in any unstable atlantoaxial joint or in the presence of significant myelopathy. The patient should remain strictly immobilized while awaiting expedient surgical referral and procedures.

  Surgery is immediately indicated only in cases of irreducible canal compromise or progressive neurologic deterioration. Otherwise, it can be schedule on a less-emergent basis.

  Posterior fusion of the upper cervical spine may also be indicated in cases of os odontoideum (non-union of previous odontoid fracture) or other forms of odontoid aplasia or hypoplasia.

• Cases of inflammation-related subluxation may require reduction under general anesthesia with subsequent cast fixation or traction under the guidance of an experienced spinal surgeon.

• Traumatic or inflammation-induced acute AAI involving stable lesions without any neurologic symptoms may be reduced. The patients may be placed in halo brace with vest reduction and immobilization for 3 months. Repeat radiographs are necessary after reduction has been completed; several sources warn that deformity may still be possible, even after reduction.

• In children with confirmed radiographic evidence of transverse ligament disruption less than 3 weeks old, the likelihood of ligamentous healing increases with halo and vest management.

• In adults, healing of the transverse and alar ligaments is unreliable. Therefore, some authorities do not consider nonoperative management in adults, while others favor nonoperative management because of the risk of common surgical complications, the often-incomplete resolution of neurologic symptoms, and the lack of long-term data supporting surgical management.

Surgical Intervention

Posterior fusion of asymptomatic individuals with AAI, such as patients with Down syndrome, remains controversial. While some authorities advocate fusion to reduce the risk of a catastrophic trauma to the spine, others do not recommend fusion if the patient remains asymptomatic. It is important to note that the incidence of serious cervical spine injury is not increased in patients with Down syndrome and AAI, as compared with other athletic populations. Posterior fusion of the upper cervical spine is mainly indicated in symptomatic individuals.

Consultations

A spinal surgeon or neurosurgeon should be consulted in all cases of acute AAI. In cases of asymptomatic AAI found on screening examination, referral is indicated to confirm the diagnosis and possible activity restrictions.

Recovery Phase

Rehabilitation Program

Physical Therapy

After prolonged immobilization, physical therapy can increase cervical range of motion and assist in regaining strength deficits due to immobilization. An experienced therapist can also emphasize the need to avoid at-risk activities and extremes of cervical flexion and/or extension.

Surgical Intervention

Posterior cervical fusion is indicated in patients who present with a deformity that has been present for longer than 3 months or with recurrence after 6 weeks of immobilization. Such fusion can also be considered in the patient with chronic AAI who develops acute symptoms or neurologic compromise.