| disease | Hyperextension Injury of the Cervical Spine |
Cervical spinal cord injuries caused by hyperextension trauma often present with mild or occult bone injuries, and X-rays typically show no abnormal signs, making them prone to be overlooked, which affects treatment. Such injuries are not uncommon, reportedly accounting for 29-50% of all types of cervical spine injuries. They are frequently associated with central cord syndrome and are more commonly seen in middle-aged and elderly individuals.
bubble_chart Pathogenesis
Hyperextension injuries of the cervical spine are commonly seen in situations such as sudden braking or collisions of high-speed vehicles. In such cases, due to the force of inertia, the face, jaw, and forehead are struck from the front (often by the windshield or the back of the front seat), causing the head and neck to hyperextend backward. Additionally, other forms of frontal force, such as falling from a height with the neck extended or violent upward and backward pulling of the neck, can produce similar outcomes.
Depending on the point of impact, this force can cause various injuries, including posterior cervical dislocation, Hangman's fracture, and odontoid fracture with atlantoaxial posterior dislocation, as previously mentioned. The most severe consequence, however, is damage to the spinal cord.
During normal cervical extension, the spinal cord and dural sac within the spinal canal are compressed and shortened in a folded manner (like an accordion). However, if the anterior longitudinal ligament is ruptured and the intervertebral space is separated, the spinal cord may instead be stretched. In this scenario, the dural sac plays a certain restraining role. If the injured person has a narrow cervical spinal canal, the spinal cord is prone to becoming trapped between the suddenly protruding, inward-invading ligamentum flavum and the anterior bony canal wall. This is especially true if there is a posterior herniated nucleus pulposus or osteophyte formation in the anterior spinal canal. The resulting counterforce pressure tends to concentrate around the central canal of the spinal cord, leading to congestion, edema, or hemorrhage in the surrounding area. If the damage around the central canal is mild, most pathological processes may be completely reversible. However, if the spinal cord injury is extensive and severe, full recovery is generally difficult, and residual sequelae are likely.
bubble_chart Pathological ChangesCervical hyperextension is often accompanied by spinal cord injury. Many authors believe that during hyperextension, the spinal cord may be compressed between the posteriorly folded ligamentum flavum and the posterior edge of the vertebral body, leading to injury centered around the central canal of the cervical spinal cord or the anterior part of the spinal cord. The corresponding clinical manifestations are central cord syndrome and anterior cord syndrome. To validate clinical observations and hypotheses regarding the mechanism of injury, Marar conducted cadaveric experiments, confirming that during forceful cervical extension, the cervical spine and spinal cord are compressed anteriorly and posteriorly. However, this type of spinal cord injury is not necessarily caused by cervical hyperextension injury; sometimes, vertical compressive forces causing vertebral burst fractures can also lead to this type of spinal cord injury. Data indicate that cervical hyperextension injuries most commonly result in central cord syndrome and anterior cord syndrome. In addition, severe incomplete spinal cord injuries and partial spinal cord injuries (atypical Brown-Sequard syndrome) can also occur. Therefore, central cord syndrome should not be equated with cervical hyperextension injury, as this type of spinal cord injury is often caused by cervical hyperextension injury, but the latter does not always result in central cord syndrome. The magnitude of the force, pre-existing degenerative changes in the cervical spine, and variations in the spinal canal can all influence the extent of cervical injury and the type of spinal cord injury. The cervical spine is most susceptible to central and anterior spinal cord injuries under hyperextension forces, but shear forces can also cause posterior displacement of the superior vertebral body at the injury level, leading to severe transverse-like injuries or partial injuries biased to one side. After the external force dissipates, the contraction of neck muscles and elastic recoil can result in immediate realignment, leaving little to no evidence of dislocation on X-rays.
1. Neck Symptoms In addition to pain in the posterior neck, due to the involvement of the anterior longitudinal ligament, there is also pain in the anterior neck. Neck movement is significantly restricted, especially extension (do not repeat the examination). There is often significant tenderness around the neck.
2. Spinal Cord Injury Symptoms Because the pathological changes are located around the central canal, the closer to the central canal, the more severe the lesion, so the deep part of the pyramidal tract is the first to be affected. Clinically, it manifests as more severe paralysis symptoms in the upper limbs than in the lower limbs, and more severe dysfunction in the hands than in the shoulders and elbows. Sensory dysfunction mainly manifests as the disappearance of temperature and pain sensations, while position sense and deep sensation remain, a phenomenon known as sensory dissociation. Severe cases may be accompanied by fecal incontinence and urinary retention.
bubble_chart Auxiliary Examination
1. X-ray Plain Film
Early lateral X-ray films after trauma are of the greatest significance for clinical diagnosis, and efforts should be made to obtain a clear plain film. Typical cases mainly show on X-ray films:
1. Widening of the vertebral external genitalia shadow. When the injury plane is high (rare), it mainly manifests as widening of the retropharyngeal soft tissue shadow (normally less than 4mm); when the injury plane is below the cervical 4～5 vertebral segments, the soft tissue shadow behind the laryngeal ventricle is significantly widened (normally not exceeding 13mm).
2. Widening of the intervertebral space. The height of the anterior edge of the damaged vertebral space often appears wider than other vertebral spaces, and a small bone fragment may be torn from the anterior lower edge of the upper vertebral body (accounting for about 15-20%).
2. MRI Examination
It is of great significance for the determination of herniation of intervertebral disc, soft tissue injury, and the extent of spinal cord involvement, and should be pursued if conditions permit.
3. Others
CT scanning also plays a certain role in the judgment of bone injury and nucleus pulposus prolapse, and can be selected as appropriate; attention should be paid to the presence of rare signs of vertebral plate fracture. Myelography should not be chosen during the acute phase.
Misdiagnosis due to unfamiliarity with this type of injury is not uncommon. Lack of understanding of the basic pathological changes and X-ray manifestations of cervical hyperextension injury, especially in patients with mild symptoms or the elderly, makes misdiagnosis more likely. Therefore, the following points should be noted during diagnosis:
1. A detailed history collection can often provide the mechanism of injury; for patients with craniocerebral injuries, the posture and force at the time of injury should also be understood.
2. Cervical spine X-rays should be taken for all cranial and facial injuries, and cervical spine imaging should be routine for any suspected patient to avoid cervical spine injury being masked by injuries to other areas.
3. The lateral X-ray must clearly show the structures of the upper and lower cervical spine. When upper cervical spine injury presents with lower neurological symptoms, attention must be paid to observing any changes in the lower craniocervical region, and flexion-extension lateral X-rays are of certain value.
4. The typical central cord syndrome often suggests cervical hyperextension injury, while other types of spinal cord injuries must be judged in conjunction with other tests.
5. When considering cervical spinal cord injuries caused by other mechanisms, such as vertebral body vertical compression fractures, these may also cause central cord syndrome.
bubble_chart Treatment Measures
The mechanism and pathological changes of cervical hyperextension injury suggest that there is no persistent bony stenosis of the spinal canal due to trauma, or significant fracture dislocation requiring reduction.
Non-surgical treatment
Once diagnosed, routine application of Glisson belt traction with a weight of 1.5 to 2.5 kg is commonly used. The traction position should be slightly flexed at 15°. Continuous traction is maintained for 2 to 3 weeks, followed by the use of a head-neck-thorax gypsum or plastic cervical collar for protection for 1 to 2 months. During the traction period, intravenous infusion of furosemide and dexamethasone is applied to facilitate dehydration and enhance the body's stress response. The purpose of traction is to immobilize the injured cervical segment, and the slightly flexed position allows the anterior cervical structures (ligaments, etc.) to heal, while the posterior structures, such as the folded ligamentum flavum, are stretched and restored to normal.
The author's unit selectively performed surgical treatment on 3 cases during traction therapy, with unsatisfactory results. Only a very few cases showing segmental instability after injury, worsening symptoms, and the presence of compressive factors should be considered for surgery. Anterior decompression with bone graft fusion is usually performed.
The central cord syndrome caused by hyperextension cervical injury usually has a relatively good prognosis, with milder symptoms recovering faster and more completely. Typically, the lower limbs begin to recover first, as early as 3 hours after the injury, followed by bladder function, with the upper limbs recovering the latest and hand function recovering the worst, often due to spinal cord injury affecting the anterior horn cells, leading to intrinsic muscle atrophy and residual functional impairment. Other types of spinal cord injury also depend on the severity of the injury.
Surgical treatment
Cervical spinal cord hyperextension injury is often associated with cervical degenerative hyperplasia, ossification of the posterior longitudinal ligament, etc., which are induced by cervical injury, and non-surgical treatment often has little effect. Therefore, selective surgical decompression creates favorable conditions for functional recovery.
Indications (1) No significant effect of non-surgical treatment after spinal cord injury and confirmation of the accurate injury segment; (2) Imaging studies such as X-ray, CT, or MRI show significant bone injury with spinal cord compression; (3) Clinical symptoms persist and tend to worsen during conservative treatment; (4) Associated with cervical spondylosis and ossification of the posterior longitudinal ligament, induced by trauma, surgical treatment is considered after the condition stabilizes.
Surgical treatment According to the location and extent of spinal cord compression, an appropriate approach and decompression method are selected. For anterior compression, such as single or a few segments, anterior decompression is performed. For posterior compression or extensive anterior compression due to ossification of the posterior longitudinal ligament, posterior decompression is chosen.
This type of injury should mainly be differentiated from the following conditions:
1. Anterior spinal artery syndrome
Because both can occur under completely similar traumatic conditions (e.g., sudden braking), and both present with paralysis, they are easily confused. For differentiation, refer to Table 1.
Table 1: Differential Diagnosis of Cervical Hyperextension Injury and Anterior Spinal Artery Syndrome
| Item | Cervical Hyperextension Injury | Anterior Spinal Artery Syndrome |
| Mechanism of Injury | Injury around the central canal of the spinal cord | Obstruction of the anterior spinal artery |
| Characteristics of Paralysis | Upper limb paralysis more severe than lower limb | Lower limb paralysis more severe than upper limb |
| Sensory Disturbance | Sensory dissociation | Mild, generally no sensory dissociation |
| Spinal Canal Imaging | Significantly widened | Generally normal |
| Osteophyte Formation | May be present, generally mild | Generally more pronounced |
2. Syringomyelia
The pathological changes and anatomical locations are similar, and the symptoms are alike, making them easily confused. However, this condition generally does not have a history of severe trauma, and X-ray plain films do not show widening of the spinal canal. MRI examination reveals the formation of a syrinx in the central spinal cord.
3. Acute Disc Herniation
Because this condition occurs suddenly, often after trauma, and is accompanied by spinal cord symptoms, differentiation is necessary. However, the trauma causing disc herniation is not necessarily severe, and even a simple cough can trigger it. The spinal cord involvement is mainly in the corticospinal tract, with rare sensory dissociation. MRI examination is definitive for diagnosis.
4. Others
Attention should also be paid to differentiating from cervical spinal canal stenosis, cervical spondylotic myelopathy, and other conditions affecting the spinal cord.
