Vertebral Fracture/Luxation! Mark Newman!! University of Sydney!! Melbourne Resident’s Forum 2014

Anatomy

Spinal Biomechanics! Vertebral motion unit!

! Osseous and soft tissue contributors to stability!! Fractures tend to occur at junction of immobile/mobile

areas!! Moment of resistance (Zotti et al Res Vet Sci 2011)!

! Resistance of bending forces of vertebral bodies!! Lowest around T9 and rising to L2!! Rising bone mineral density!! Adaptation to bending stress

Spinal Biomechanics! Forces acting on the spine!

! Dorsoventral bending (disc, vertebral body, dorsal elements)!

! Lateral bending (disc, facets, vertebral body, rib head)!! Torsion (disc, facets, rib head)!! Shear !! Axial compression (disc, vertebral endplates)!

! Relative contribution of each force in normal movement unknown!! Disc most important in bending and rotation (Schulz et al

AJVR 1996, Shires et al Prog Vet Neurol 1991)

Anatomical Influence! Thoracic spine!

! Inherently stable!! Small articular facets but large dorsal structures!

! Thoracolumbar junction (50% of VFL)!! Highly mobile!! Large facets!! Facets change orientation from ventrodorsal to saggital!

! Lumbar spine (25-30% of VFL)!! Relatively rigid!! Dorsoventral flexion

3 Column Model (Dennis Spine 1983)

3 Column Model (Dennis Spine 1983)! Dorsal column!

! Articular facets, laminae, dorsal spinous processes, interspinous ligaments, ligamentum flavum!

! Middle column!! Dorsal longitudinal ligament, dorsal annulus fibrosis,

dorsal vertebral cortex!! Ventral column!

! Ventral longitudinal ligament, remainder of intervertebral disc, ventral vertebral cortex

3-Column Model – Fracture Configurations! Compression !

! Failure of the ventral column under compression!

! Intact middle column acts as the hinge!

! Flexion injury

3-Column Model – Fracture Configurations! Burst!

! Failure of vertebral body (ventral and middle columns) under compression!

! Dorsal column is the hinge!! Flexion injury

3-Column Model – Fracture Configurations! Seat-Belt!

! Failure of dorsal and middle columns under tension!

! Ventral column may also be involved but maintains role as the hinge

3-Column Model – Fracture Configurations! Fracture-Dislocation!

! Failure of all columns!! A: flexion/rotation!! B: shear (hyperextension)!! C: flexion/distraction

3 Compartment Model (Sharp & Wheeler)! 3-column model!

! Based on mode of injury (stability inferred)!! Indications for surgery in humans different to quadripeds !

! Assesses ability of vertebral column to resist applied forces!

! Addresses integrity of:!! Intervertebral disc!! Vertebral body!! Articular facets!

! Serves as a guide to the fixation best suited to each fracture

3 Compartment Model (Sharp & Wheeler)! I – Disc failed, facets and body intact!

! Rotation, lateral bending, extension!! II – Facets failed, disc and body intact!

! Rotation!! III – Body failed, facets and disc intact!

! Bending, compression!! IV – Two or more components fail!

! Generally all forces

Imaging! Plain radiology (Kinns et al

Vet Rad Ultrasound 2006)!! 72% sensitivity for fractures!! 77.5% sensitivity for luxations!! 58% NPV for canal narrowing!! 52% NPV for fragments in

canal!! Poor for fractures involving

dorsal/middle compartments

Imaging! Significance of displacement!

! Not associated with outcome (McKee et al Vet Rec 1990) unless 100% (Bagley Vet Clin North Am 2000)!

! Displacement + axis deviation significantly associated with outcome in dogs (Bali et al VCOT 2009)

Advanced Imaging! CT gives greatest bone detail!

! Safe implant corridors!! MRI!

! Cord compression!! Disc extrusion!! Signal change – T2W hyperintensity!

! Correlation with outcome!! Levine et al JVIM 2009

Treatment! Prevent ongoing injury!

! Limit instability!! Relieve spinal cord compression!

! Realign spinal canal!! Apposition or near-apposition!

! Intervertebral disc!! Hemilaminectomy?!

! Fragments!! Human studies suggest unneccesary!! Must retropulsed and resorbed

Conservative Therapy! Non-surgical management!

! Indications poorly defined – ‘stable’ fractures!! Isolated facet fractures or disc extrusions!! Some body fractures!

! Difficult to immobilise thoracolumbar spine!! Patterson & Smith VCOT 1992!

! Selcer et al JAVMA 1991!! Shorter hospitalisation!! Longer recovery!! Surgically treated animals improved more but no

difference in eventual long term outcome

Surgical Management! Ventral stabilisation!

! Pins or screws/PMMA!! Plates!! ESF!

! Dorsal Stabilisation!! Spinous process plating!! Tension band/modified segmental spinal fixation!! Laminar plating

Implant Corridors! Watine et al JSAP 2006!

! Thoracic vertebrae!! Insertion angle opens from 22° to 44.5°!! Azygous vein 1mm away!

! Lumbar vertebrae!! Insertion angle 60°!! Vital structures more protected

Pin Penetration of the Canal! Hettlich et al Vet Surg 2010!! Left/right accuracy 93.1%!! Radiographs !

! Sensitivity 50%!! Specificity 83%!

! CT !! Sensitivity 93.4%!! Specificity 86%

Pins + PMMA! Versatile!! Strong in flexion, extension, torsion!

! At least that of intact spine (Walker et al Vet Surg 2002)!! Depends on configuration(David Hall, pers comm)!

! Threaded pins preferred!! Less pull-out!! Less migration!! Firm anchorage of cement!

! 3+ implants per vertebra, screws inferior to pins!! Garcia et al Vet Surg 1994

Vertebral Body Plating! Swaim JAVMA 1971!

! Technical feasibility of small dorsolateral body plates on adjacent vertebrae!

! Recommended sacrificing nerve roots!! Clinical use substantiated!

! Downes et al JSAP 2009!! Conventional plates superseded by

locking plates?!! SOP (McKee & Downes JSAP 2006)!! PAX?

Internal Fixation Systems! Walter et al Vet Surg 1986!

! Dorsal + vertebral body plate strongest followed by vertebral body plate!

! Waldron et al Prog Vet Neurol 1991!! Pins + PMMA strongest

External Skeletal Fixation! Blunt tipped pins ideal + arches!! Open!

! Lanz et al Vet Neurology Neurosurgery 2009!

! 3 dogs – good reduction with no complications!

! Poor follow-up!! Closed!

! Wheeler et al Vet Surg 2007!! 5 dogs – good to excellent

function in all !! Fixators in place up to 282 days

External Skeletal Fixation! Open vs closed!

! Wheeler et al Vet Surg 2002!! Both open and closed application different from the ideal

angle/depth!! Better bone purchase in closed!! Difficult to apply to thoracic especially open!

! Strength -Walker et al Vet Surg 2002!! Eight pin/arch combo stiffer than bilateral type I ESF!! Comparable to Eight pin/PMMA combo

Modified Segmental Spinal Stabilisation! Longitudinal Steinmann pins held in

place with wire through spinous processes!

! McAnulty et al, Vet Surg 1986!! 4 dogs 10-56 kg, all unstable fractures!! 1 broken pin at 18 months!

! Not recommended?!! Wire pull-out!! No ventral support!! Suited to thoracic fractures

Tension Band Fixation! Voss & Montavon JAVMA 2004!

! Modification of MSSS!! 38 dogs/cats up to 45kg!! Unstable fractures!

! Vertebral body involvement!! 78% complete or functional!! 11% implant or fixation failure!

! Dogs >16kg

Laminar Plating! Benefit of dorsal

stabilisation!! Potentially more cortices!! Knell et al AJVR 2011!

! Lower ROM and NZ than vertebral body plating!

! VBP constructs: bone failure at facet joints!

! LP constructs: construct faillure!

! Less screw loosening in LP (1/9) than VBP (5/9)

Laminar Plating! Knell et al AJVR 2011!! Angles of instertion L1/

L2!! Lamina = approx 20°

ventral, 10° dorsal!! Facet = 24° ventral, 12°

dorsal!! Screw penetration 1/24!

! Screw did not follow drill hole

Spinous Plating! Krauss et al VCOT 2012!

! Similar function to tension band stabilisation!

! 15 unstable fractures!! 80% complete or functional

outcome !! No implant failure!! Spinous process

demineralisation!! Rischen et al Vet Surg 1987!

! No change in underlying vascularity!

! Demineralisation by 8 weeks!! Foreign body reaction

Prognosis! Surgical technique!

! Results seem fairly comparable across techniques!! 80-100%!! Complication rates vary!

! Significance of absent nociception!! Very poor recovery rates – avg 5%!! Spinal walking – rim of peripheral surviving tracts?

References➢ Bali MS, Lang J, Jaggy A, et al: Comparative study of vertebral fractures

and luxations in dogs and cats. Vet Comp Orthop Traumatol 22:47, 2009.!➢ Bruce CW, Brisson BA, Gyselinch K: Spinal fracture and luxation in dogs

and cats: a retrospective evaluation of 95 cases. Vet Comp Orthop Traumatol 21:280, 2008.!

➢ Denis F: The three column spine and its significance in the classification of acute thoracolumbar spinal injuries. Spine 8:817, 1983.!

➢ Downes CJ, Gemmill TJ, Gibbons SE, et al: Hemilaminectomy and vertebral stabilization for the treatment of thoracolumbar disc protrusion in 28 dogs. J Small Anim Pract 50:525, 2009.!

➢ Garcia JNP, Milthorpe BK, Russel D, et al: Biomechanical study of canine spinal fracture fixation using pins or bone screws with polymethylmethacrylate. Vet Surg 23:322, 1994.!

➢ Hettlich BF, Fosgate GT, Levine JM, et al: Accuracy of conventional radiography and computed tomography in predicting implant position in relation to the vertebral canal in dogs. Vet Surg 39(6):680, 2010.!

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➢ Schulz KS, Waldron DR, Grant JW, et al: Biomechanics of the thoracolumbar vertebral column of dogs during lateral bending. Am J Vet Res 57:1228, 1996!

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➢ Voss K, Montavon PM: Tension band stabilization of fractures and luxations of the thoracolumbar vertebrae in dogs and cats: 38 cases (1993–2002). J Am Vet Med Assoc 225:78, 2004. !

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