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Chapter 25: Vertebral Fracture and Luxation Repair  213

                                                                  Table 25.1  Recommended insertion angles and landmarks for bicortical spinal
                                                                  implants.
                                                                    Location  Insertion angle from   Landmarks for insertion
                                                                           vertical
                                                                    T10    22° (20–25°)    Tubercle of ribs and base of accessory
                                                                    T11    28° (25–35°)    process
                                                                    T12    30.5° (25–35°)
                                                                    T13    44.5° (40–45°)
                                                                    L1–L6  60° (55–65°)    Junction between pedicle and
                                                                                           transverse process
                                                                  Source: Watine et al. [5].



                                                                  part of the lamina. Bone stock for implants is limited to the gener­
                                                                  ally small and narrow vertebral body. Rib head disarticulation can
                                                                  be   performed if needed for improved implant position.
                                                                  Alternatively, ribs may be utilized for certain types of fixation
                                                                  methods such as cerclage wiring to augment spinal stapling. The
                                                                  approach has to consider the thoracic cavity and the possible crea­
                                                                  tion of an iatrogenic pneumothorax. If the pleural space is opened,
                                                                  air can often be evacuated in conjunction with closure of the surgi­
                                                                  cal site via a large‐gauge over‐the‐needle catheter or temporary
                                                                  chest tube.  Lumbar  vertebrae have distinct  articular, transverse,
                                                                  and accessory processes, which provide helpful anatomical land­
                                                                  marks  for implantation.  General guidelines for insertion angles
                                                                  and landmarks for traditional bicortical implants are available
                                                                  (Table 25.1) but should be supplemented with CT images of the
                                                                  individual patient [5]. While the larger insertion angle for lumbar
                                                                  vertebrae (60° from vertical) provide maximum bone purchase
                                                                  based on imaging studies, this angle is challenging to achieve with
                                                                  a standard open approach due to soft tissue interference. Often the
               Figure  25.6  A locking compression plate (LCP) is applied to the ventral   angle is reduced to 30–45° to accommodate musculature without
               aspect of the cervical spine with monocortical screw fixation.  dramatic loss of bone purchase.
               placed into the bone near the endplate on both sides of a disc space.   Positioning and Approach
               While they are available in different lengths and sizes, their primary   For a standard dorsal approach, the patient is positioned in ventral
               application has been for cervical spondylomyelopathy rather than   recumbency and a bean bag and suction are used to maintain a
               cervical vertebral column trauma.                  straight body position. Additionally, tape can be used to further
                                                                  improve patient stability. It is important to maintain the spine as
                                                                  straight as possible to allow proper angling of pins into the vertebral
               Thoracolumbar Injury                               column. A liberal standard dorsal approach to the affected thoracic
               Vertebral column trauma most commonly affects the thoracolum­  or lumbar segments is performed. If the integrity of the vertebral
               bar spine, with a high incidence of injury at the thoracolumbar   canal has been compromised, extra caution must be employed to
               junction. Fractures or luxations of the cranial thoracic spine are rare   avoid inadvertent iatrogenic injury during elevation of the muscu­
               due to the inherent stability and protection afforded by the muscu­  lature. The approach must reach ventral enough to expose the rib
               lature of thoracic limbs and rib cage. The natural lever arm of the   heads of the thoracic vertebrae or the base of the transverse pro­
               lumbar spine against the less mobile thoracic spine creates a stress   cesses of the lumbar vertebrae to observe pertinent landmarks and
               riser at the thoracolumbar junction.               aid in implant placement.
                 Hyperflexion injuries are overrepresented, leading to caudal end­
               plate  fractures  and  luxations  at  the  affected  disc  space.  Rotational   Implant Selection
               forces can lead to articular process fractures, while hyperextension can   Implant size is based on vertebral pedicle width and vertebral body
               cause fractures of the vertebral lamina. Fractures of ribs and spinous   dimensions. Vertebrae of large dogs typically accept 3.5 mm screws
               and transverse processes, while not affecting the spinal cord directly,   or ⅛ inch pins, while smaller dogs usually require 2.7 mm screws or
               must be taken as evidence of significant trauma and initiate a thor­  3/32 inch pins. Depending on the implant type, the surgeon has a
               ough evaluation of the integrity of the affected vertebral column.  certain degree of freedom with implant sizes, for example when
                                                                  using a pin–PMMA construct in a large‐breed dog, ⅛ inch pins
               Anatomical Considerations                          can be placed for the main fixation with additional 3/32 inch pins.
               The anatomy of thoracic vertebrae poses several challenges to   In screw constructs, cortical screws are preferred over cancellous
               instrumentation. The articular processes become less distinct in   screws owing to their larger core and increased stiffness. In
               the cranial thoracic vertebrae and rib head articulations obscure   the  PMMA construct, positive‐profile end‐threaded pins are
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