Fixation Techniques for Spinal Fractures and Dislocations
World Small Animal Veterinary Association World Congress Proceedings, 2007
U. Matis, Prof. Dr. med. vet., Dr. med. vet. habil., DECVS
Clinic of Veterinary Surgery of the Ludwig-Maximilians-University
Munich, Germany

Spinal injuries are characteristically very painful and/or associated with neurological deficits, which usually correlate with the location of the lesion. Multiple vertebral lesions, which occur in about 10% of cases, may cause discrepancies between the radiographic and neurological findings. The following must be addressed before an operation:

1.  Life-threatening injuries should be treated or ruled out (e.g., skull/brain damage, pneumothorax and shock);

2.  Additional spinal cord injuries must be prevented (by placing patient on a board, cautious manipulation of patient); and

3.  Treatment method must be selected based on the radiographic and neurological findings.

Lateral and ventrodorsal radiographs should be taken to evaluate the extent of spinal column injury; however, these will not necessarily show the position of the vertebra at the time of injury. Thus, the neurological findings are more important than the results of radiography.

The neurological status is graded using the following scoring system:

Grade 1:

Pain only, without any neurological deficits

Grade 2:

Paresis or ataxia

Grade 3:

Paraplegia or quadriplegia

Grade 4:

Paraplegia or quadriplegia with urinary retention and overflow

Grade 5:

Paraplegia or quadriplegia with urinary retention and overflow and
absence of conscious pain sensation

Animals with grade 1 or 2 dysfunction are usually treated conservatively first with strict confinement and drugs that prevent post-traumatic ischemia and the release or activation of endogenous auto-destructive factors (free radicals, arachidonic acid metabolites, endogenous opioid peptides and opioid receptors, etc.). The preferred corticosteroid is methylprednisolone, which is administered as an intravenous bolus at a dose of 30 mg/kg body weight within a few hours of injury.

Conservative treatment may be successful in patients with mild neurological deficits. The patient is usually hospitalized to limit movement and to re-assess neurological function at regular intervals; deterioration of the neurological status may necessitate immediate surgical intervention.

Surgical treatment is indicated primarily for unstable injuries. Decompression is often achieved after fracture reduction, which is why (hemi)laminectomy is not routinely carried out. However, (hemi)laminectomy is indicated for removal of fragments displaced into the vertebral canal or treatment of disc herniation associated with compression of the spinal cord or nerve roots. (Hemi)laminectomy should be carried out only in association with fracture stabilization and not on its own.

For reduction, the intact vertebra adjacent to the fractured or luxated bones is grasped with bone holding forceps. Careful distraction usually suffices to reduce the fracture; however, leverage is sometimes required. Reduction is confirmed by assessing the vertebral processes. When the articular facets on either side are positioned correctly, reduction is considered successful.

Numerous stabilization techniques have been described in the literature. In our experience, vertebral body fixation methods that incorporate as few vertebrae as possible are superior to methods that involve dorsal fixation of the spinal processes over a longer stretch. To ensure optimal stability, collapse of the affected intervertebral space is acceptable or even desirable. Long-term re-evaluations have shown that the intervertebral space becomes smaller again after reduction and spinal fixation when spacers (cage or bone cement) are not used. The resultant instability favours loosening of implants, which have little purchase in the cancellous bone of the vertebrae.

A ventral approach is used in patients with cervical vertebral osteosynthesis and spondylodesis. Fractures of the vertebral body can be stabilized with a plate that is limited to the injured vertebra. Orthopedic wire suffices for fixation of physeal separation of the endplate. Spondylodesis involves distraction and filling of the unstable intervertebral space with bone cement or a cage filled with cancellous bone. The mobile vertebrae are then stabilized with a plate and a minimum of two screws per vertebra. Internal fixator systems with locking screws are advantageous for this because they provide better pull-out resistance and allow mono-cortical seating of the screws. For stabilization of atlantoaxial subluxation caused by fracture or hypoplasia of the dens, or ligament rupture, two transarticular screws are placed in a caudocranial divergent direction using a ventral approach. 3D-reconstruction of computed tomographic images is used to determine optimal screw placement. A T-plate can also be used, although the cranial screws in the ventral arch of C1 do not have much purchase. Another technique involves fixation of the spinal process of C2 to the dorsal arch of C1 using orthopaedic wire or suture material. To prevent compression-associated complications, C2 should not be pulled too close to C1. Lateral removal of the lamina may also be indicated in this procedure. Dorsal fixation cannot be ensured when the dorsal arch of C1 is not completely ossified.

Injuries of the thoracic vertebrae and thoracolumbar vertebral junction require decompression more often because the spinal canal is narrower in these regions. In patients with spondylolisthesis, vertebral body fixation is achieved with cross-pinning of the affected vertebra; threaded Steinmann pins are suitable for this. The pins should cross the intervertebral space as far apart from each other as possible and should engage the entire length of both vertebral bodies. Three vertebrae must be included in the fixation of a vertebral-body fracture. Techniques for this include transpedicular Steinmann pins that are stabilized with bone cement on their free end, unilateral or bilateral plates or a clamp rod internal fixator (CRIF). The disadvantage of plate osteosynthesis is that partial rib resection or luxation is necessary for plate placement on the thoracic vertebrae. Plates can be contoured better on the lumbar vertebrae, although care must be exercised to prevent compression of the nerve roots, especially in the regions caudal to and including L4. Instead of a dorsolateral approach, a ventral approach via laparotomy can also be used for plate placement. In general, bone plates with locking screws are preferred for vertebrae because they provide more angular stability in the soft cancellous bone. However, when planning the operation, it must be remembered that, unlike conventional plate screws, the direction of locking screws is not variable. With dorsolateral fixation, other alternatives to plate osteosynthesis include transpedicular pins and bone cement. A more elegant method is the use of a unilateral or bilateral CRIF, which provides better preservation of the spinal musculature.

Fracture-luxation at the lumbosacral junction seldom results in impairment of hind limb function, but frequently affects innervation of the bladder and rectum. For a better prognosis, the cauda equina should be examined via laminectomy. One transilial pin seldom achieves adequate stabilization. Likewise, screw fixation of the small articular facets is frequently inadequate. Fixation of lumbosacral luxation-fractures usually requires transpedicular pinning and bone cement, or a bilateral CRIF involving the iliosacral region.

The prognosis of spinal injuries depends mainly on the neurological status of the patient, the time between injury and repair and whether optimal stabilization can be achieved with minimally invasive technique. Animals with grade 1-3 injuries usually have a good prognosis for recovery, while the prognosis for grade 4 is less favourable. Grade 5 injuries generally carry a poor prognosis.


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Speaker Information
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Ulrike Matis, Prof. Dr. med. vet., Dr. med. vet. habil., DECVS
Clinic of Veterinary Surgery of the Ludwig-Maximilians-University

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