Tetraparesis: Traumatic diseases

Spinal cord contusion and traumatic disc herniation

Clinical signs: Signs reflect the site of injury and can be multifocal. A careful neurological examination is therefore vital.

Pathogenesis: Traumatic injuries (e.g. road traffic accidents, falling from a height, horse kicks) often result in spinal cord injuries, usually with associated vertebral fractures and luxations. Sometimes animals suffer an obvious traumatic event (either witnessed, or with other external evidence), associated with acute onset of focal signs of spinal cord dysfunction with no evidence of a vertebral fracture or luxation. It is possible for sudden flexion or extension or axial loading of the vertebral column to occur without causing fractures or permanent luxations, but causing contusions to the spinal cord, focal haemorrhages or traumatic disc herniations. In the case of cats and non-chondrodystrophoid breeds of dog, the hemiated nucleus pulposus is often not mineralized and therefore causes a primarily concussive injury, with little or no compression.

Diagnosis: This is a presumptive diagnosis in the face of compatible history and clinical findings, with no evidence of vertebral facture or luxation on survey radiographs and CT images or myelography. The patient should be handled with extreme care until survey radiographs rule out the presence of an unstable vertebral fracture or luxation. The atlantoaxial junction should be evaluated very carefully, as this site is predisposed to injury. A collapsed disc space and focal extradural compression may indicate a traumatic disc herniation and focal swelling of the spinal cord may be present. MRI will identify focal oedema within the spinal cord and may reveal changes in the nucleus pulposus indicating herniation.

Treatment and prognosis: The protocols for medical management of acute spinal cord injuries with methylprednisolone sodium succinate are described in site. If there is significant compression of the spinal cord by hemiated disc material, decompressive surgery may be indicated. Management of the patient focuses on treatment of any other injuries, and rehabilitation (). Prognosis depends on the severity of injury: it is guarded in the tetraplegic patient with associated hypoventilation, but good if there is any motor function present.

Cervical vertebral fractures and luxations

Clinical signs: Neurological deficits reflect the site of the injury but, as a result of the relatively spacious vertebral canal in the cervical region, quite dramatic luxations can be associated with only minimal neurological deficits and pain (). It is not uncommon for neurological deterioration to occur days after the traumatic incident as a result of instability secondary to a fracture (). It is therefore important to obtain good quality cervical radiographs in any animal in which head and neck trauma are suspected ().

Pathogenesis: Vertebral fractures and luxations can result from pathological processes such as vertebral neoplasia and discospondylitis, but most commonly result from external trauma. Cervical vertebral injuries are less common than thoracolumbar injuries () but the atlantoaxial junction is relatively unstable (see atlantoaxial instability, above) and therefore particularly at risk. The axis is the most commonly fractured cervical vertebra because it acts as a fulcrum between the caudal cervical spine and the so-called cervicocranium (the skull, atlas, dens and body of the axis) ().

Diagnosis: Extreme care should be taken when evaluating these animals to avoid exacerbating injuries due to vertebral instability. Initial management of the critical patient is covered in site. A careful physical and neurological examination should be completed and stabilization of the patient undertaken if indicated. Lateral survey radiographs of the entire spine should be obtained. If there is no evidence of a vertebral fracture or luxation on the lateral views, the animal can be placed carefully on its back to obtain ventrodorsal projections of the spine (), or horizontal beam views can be obtained. The timing and type of further imaging indicated will depend on the neurological status of the animal and the radiographic findings but include CT scanning, myelography and MRI. Myelography or MRI is indicated if the clinical findings do not match the survey radiographic findings. CT of lesions identified on survey radiographs is appropriate if the radiographic and clinical findings are in agreement, to obtain good anatomical detail of the bone lesions and relative displacement of bone fragments. However, if the owner does not want spinal surgery to be performed (for financial or other reasons), further imaging will not usually help with case management. Also, the animal may have other medical problems that preclude anaesthesia at that time (e.g. cardiac arrhythmias secondary to trauma).

Treatment and prognosis: Treatment can be conservative or surgical. Conservative treatment includes placement of an external splint (in the case of unstable fractures or luxations), cage confinement, provision of analgesia and nursing care, and rehabilitation (). Conservative management is appropriate in cases with mild neurological deficits, minimally displaced fractures / luxations or no evidence of spinal cord compression. Splints should be placed on animals with evidence of vertebral instability () so as to prevent movement of the caudal cervical spine and the atlantoaxial junction. Correct splint placement is described in the section on atlantoaxial instability (). Surgical treatment is indicated in cases with severe neurological deficits or pain and evidence of compression or vertebral instability on imaging. Aims of surgery are to realign, stabilize and decompress the spinal cord and intervertebral foraminae (to prevent persistent nerve root pain). Stabilization is usually achieved by the placement of screws or pins in the vertebral bodies with application of polymethylmethacrylate cement around their protruding heads () but plates can also be used. A full discussion of surgical techniques is beyond the scope of this book and can be found in surgical texts ().

Prognostic factors have been evaluated in 56 dogs with cervical vertebral fractures (). Non-ambulatory tetraparesis and prolonged interval from trauma to referral (> 5 days) were associated with a worse outcome. Prompt identification and referral of these cases is therefore important. In dogs undergoing surgery, perioperative mortality was relatively high (4 of 11 dogs suffered cardiopulmonary arrest). This may reflect the need for ventilatory support in severely injured dogs, particularly if surgery is associated with further inadvertent iatrogenic damage. In the same study, 37 of 40 dogs managed conservatively recovered, indicating that the prognosis for recovery is good in dogs in which surgery is not indicated. Dogs with severe spinal cord injuries (tetraplegia) that require ventilatory support have a worse prognosis.