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33rd Annual Scientific Meeting proceedings

Stream: SA   |   Session: Spinal Trauma I
Date/Time: 08-07-2023 (09:40 - 10:10)   |   Location: Conference Hall Complex A
Biomechanics for Spinal Fracture Repair
Hettlich BF*
Independant consultant, Stuttgart, Germany.

Traumatic vertebral column injury in cats and dogs can occur as a consequence of high-energy trauma such as vehicular accidents, falls from heights, bite wounds and others. Trauma can include fractures and luxations, but also traumatic disk extrusion, spinal cord contusions, hemorrhage and other. Compared to cervical and lower lumbar, the thoracolumbar spine is the location with the most commonly reported traumatic injuries in cats and dogs. Since most of these injuries are due to high-energy trauma, concurrent shock, multiple vertebral column injuries, and other orthopedic or soft tissue injuries are common, requiring careful assessment of the animal during and after cardiovascular stabilization. The focus of this discussion will be biomechanical assessment of thoracolumbar spinal injuries.

A thorough neurological examination must carefully be done in order to determine lesion localization and neurologic severity. Diagnostic imaging is used to localize and define spinal injury, with emphasis on computed tomography for bony structures and magnetic resonance imaging for peri-spinous tissues and spinal cord. With information of the neurological examination, in particular severity such paresis or plegia, and presence of deep pain perception, as well as understanding of the location and type of injury, prognosis can be established and a treatment plan developed. One must bear in mind that loss of deep pain perception is an immensely important prognostic indicator.

The goal of surgical treatment is to reduce vertebral malalignment to relieve spinal cord and nerve root compression, and to preserve neurologic function. Surgical treatment is recommended when there is spinal instability, which can cause worsening of injury to neurovascular structures, and in cases of significant pain. Provided there is sufficient stability of the injury site and pain is manageable, animals can also be treated conservatively until sufficient bone healing or soft tissue scarring has occurred.

The vertebral column has to withstand flexion and extension, compression and torsion, and even traction. The nature and extent of abnormal movement that causes spinal instability is variable in different areas of the vertebral column. Thoracic vertebrae have small articular facets that provide little resistance to torsional forces, as opposed to the larger facets of lumbar vertebrae. However, the large spinous processes and extensive ligamentous attachments of the thoracic spine are very effective in limiting motion between vertebra. Individual variation among breeds may also play an important role in relative stability, which may influence treatment decision making.

The thoracic vertebral column (T1-T10) has considerable inherent rigidity, and injuries in this area are uncommon and typically require little additional stabilization. The thoracolumbar junction (T10-L2) is a very common site of trauma as the junctional area between the rigid thoracic spine and the lumbar spine. Caudal lumbar injuries (L3-L7) are also relatively common, and fractures of vertebrae L3-L5 carry a greater risk of severe deficits because of the higher likelihood of grey matter damage of the lumbosacral intumescence.

Similar to long-bone fractures, spinal fractures and luxations can be assessed using the scheme of mechanical, biologic and clinical factors (MBC), which might provide useful guidance during the decision making process in addition to the neurological status.

Clinical factors might included an owners’ ability/compliance to confine an animal with a conservatively treated spinal injury and the character of the animal (fractious or aggressive, hyperactive, difficult to confine versus compliant, calm and manageable).

Biologic factors assess blood supply and bone healing capacity of the local environment. While it is quite predictable what will lead to challenges with bone healing due to poor biology in long-bone fractures, it is rare to see such issues in vertebral injuries. Despite spinal injuries often being caused high-energy trauma, poor blood supply to affected vertebrae is usually not of clinical significance for healing. In case of open vertebral fractures due to i.e. bite wounds, a similar treatment approach needs to be implemented as for long-bone fractures. Mechanical factors assess the mechanical needs of a bone injury and what kind of treatment is required to neutralize forces and support healing. Fracture configuration is one of the most essential assessment points in regard to decision making for long-bone fractures. Due to the very different and complex bony anatomy of vertebrae, assessing stability of spinal injuries is different compared to long-bone fractures.

Various classification systems for vertebral column instability of the thoracolumbar have been developed for human trauma patients, with the goal of helping to decide whether an injury requires surgical intervention or not. Based on the human classification scheme by Denis (1983 and 1984), the 3-compartment system is often referenced in veterinary surgery. In this very simplified scheme, the thoracolumbar vertebral column is divided into 3 compartments/columns (dorsal, middle, ventral), with disruption of 2 or more of these compartments resulting in instability. The dorsal column consists of the laminae, spinous processes, and their associated ligaments. The middle column consists of the dorsal longitudinal ligament, dorsal annulus, and dorsal cortex of the vertebral bodies. The ventral column consists of the ventral longitudinal ligament, ventral annulus, and ventral cortex of the vertebral bodies. This scheme can be applied to spinal radiographs as well as advanced imaging and provides the clinician with a useful first-line imaging assessment of stability. It is important to note that Denis also included assessment of angulation and translation into his 3-column concept. The 3-compartment concept has recently been assessed in an ex-vivo canine study and results support that injury to 2 or all 3 compartments causes instability (Diamante 2020). The limitations of the 3-compartment approach are that it does not take into account the neurologic status of the patient, nor dynamic instability not apparent on imaging. The 3-compartment classification therefore should therefore be used as a helpful but additional tool in the decision making process.

In human spine, more complex classification systems have been developed for thoracolumbar spine injuries, with 2 prominent ones being the AOSpine Thoracolumbar Classification System and the TL Spinal Trauma Classification System (TLSTC).

The AOSpine system consists of a complex algorithm for morphologic classification of bone injuries and combines these scores with neurological status, injury to the posterior ligamentous complex (PLC) and co-morbidities. The TLSTC includes assessment of injury morphology, integrity of the PLC and neurological status and results in a numerical value, which predicts the need for surgery.

Morphology of vertebral injuries in cats and dogs has not been assessed on a large scale. Establishing such data would allow us to develop a canine and feline specific TL classification, which, in combination with other important assessments, could provide an even more reliable system for treatment decision making for clinical use.

These classification systems are based on the thoracolumbar spine. Extrapolation to the cervical and lumbosacral spine must be done with consideration for differences in anatomy and different consequences to the affected neural tissues (cervical spinal cord with risk of respiratory paralysis; spinal cord versus cauda equina).

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