Gait Patterns in Patients with Hereditary Spastic Paraparesis
Surgical techniques for cervical spine fixation · Dobermann, 10 y fs: 4 years after successful...
Transcript of Surgical techniques for cervical spine fixation · Dobermann, 10 y fs: 4 years after successful...
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Surgical techniques for cervicalspine fixation
Frank Steffen
PD Dr.med.vet. Dipl ECVN
Section neurology/neurosurgery
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When is surgical stabilization needed?
Border Collie: Tetraparesis after rolling over. Previous CT of cervical area withoutabnormalities.
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When is surgical stabilization needed?
• Fracture induced instability with stenosis
• Malformations (?)
• Degenerative conditions/IVDD (?)
• Failed decompressive procedure (ventral slot)
• Discospondylitis (?)
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Diskospondylitis C3-4GSD, 1y, cervical pain
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Same dog, after 10 days of antibiotics:non-ambulatory tetraparesis
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Failed ventral slot decompression
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Methods of cervical stabilization
• Indirect Decompression using stabilization/distraction/fusion procedures- Screw/Pins, PMMA - Locking plates- transarticular screws- Screw/washer – Technique- Intervertebral Distractor devices (bonegraft, cages made of titan- or
carbonfiber) with additional plating- intervertebral Distractors (PMMA-Plug, Stand-alone cage)
• disc prosthesis /Total disc replacement (TDR)
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Best procedure?
Short-term success rates were high (approximately 80 per cent), but there was a high rate of recurrence (around 20 per cent) after any surgical treatment, suggesting the possibility that the syndrome should be considered a multifocal disease of the caudal cervical region. Statistical analysis revealed no significant differences in success rates between the various reported decompressive surgical techniques
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„Level of evidence“
Quality hierarchy pyramid
Where weare
Where to go
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Bruecker et al. 1989
Intravertebral screws/pins-PMMA bridge
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Results
• Bruecker 1989: 93% successful, (37/40, 3-50 months follow-up)
8 dogs developed a second episode (domino-lesion)
Longterm success: 73%
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Corlazzoli
High risk for violation of vertebral canal, vertebral artery and intervertebral foramen
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Monocortical screw fixation was biomechanically equivalent to bicortical fixation
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McKee 1999
Screw/washer
initially successful in 78 dogs
Longterm outcome: 17/65 Domino-Lesions
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Interbody PMMA plug for distraction-stabilization of CCSM
Dixon et al., JAVMA, 1996
Fransson et al. Biomechanical evaluation of cervical intervertebral plug stabilization in an Ovine model. Vet Surg, 2007:Immediate postop high stability/Stability lost at 8 weeks/increased at 24 weeks. No bonyFusion, distraction not maintained.
Lewis et al. Vet Surg 2014
postop
1 y postop 1 y postop
22 dogs: 21 improved, 11 completely normal,
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Good results for cervical fractures
LOCKING PLATES: VCOT 2006
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Chihuahua, 8 yrsNon-ambulatory tetraparesis
Hydrated nucleuspulposus extrusion
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No improvement after ventral slot sxNon-ambulatory, persistent pain during 10 days
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Surgically induced instability with subtle subluxation?
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Revision sx: ambulatory status within 3 days
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Cervical malformations
Yorkshire Terrier, 1 y: generalized ataxia
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Caudal cervical spondylomyelopathy/DAWS
Early screw pullout: 2/6
Loss ofdistraction:all dogs
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Veterinary Surgery 2011
6/21 dogs implant loosening1/21 pseudarthrosis w secondary extradural compression
LOCKING PLATES PLUS INTERVERTEBRAL DISTRACTION
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Step 1
2
3
C6
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Postoperative X-ray
• Implant position
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1st goal: Decompression
pre post
C7
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Postoperative
No mineralisation
within cage
6 months
Signs of mineralisation
of bony graft
12 months
progressive
fusion
within cage
2nd goal: bony fusion
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Results (1 year follow-up)
• Clinical outcome: 9 dogs improved status, all dogs withoutsigns of pain
• 2 dogs: adjacent segment disease (Domino-lesion)
• Clinical improvement: 80%
• Technical outcome: 100% Implant stability
• Fusion rate: 100%
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How import is bony fusion?
„Without bony fusion, implant failure is a time dependent certainity“ (Human situation)
Assessment of bony fusion?Fusion cannot be fully assessed with imaging either RX nor CTOnly 14% of congruency between CT and histologic evaluation in an animal model(Cook et al., Spine, 2004)
Citeria for successful fusion:1. No evidence for implant loosening2. Absence of peri-implant lucency3. Bony bridging inside, dorsal and/or ventral to implantMcAfee et al, Spine, 2001
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Why (seemingly) better outcome with an intervertebral implant than with plating alone?
Intervertebral spacers increase construct stiffness significantely
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Subsidence
• Loss of distraction due to impression of the cage intoendplates: 9/14 dogs within first 6 weeks postop
Human cage surgery: 30% subsidenceC6-7 highest riskNo influence on outcome or fusionBartels et al. Neurosurgery, 2006
Problems associated with cage/plate stabilisation
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Macroscopic appearance of subsided cage
Vertebral canal
Enplate after removal of subsided cageNote „foot print“ of the implant,
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Major complication: adjacent segment disease (ASD)/Domino lesion
Incidence: 20-30% in all stabilizing procedures, weeks –years after the procedure
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ASD
• Developement of new radiculopathy or myelopathy referable to a motionsegment adjacent to the site of a previous arthrodesis of the cervical spine
• ASD cannot be distinguished from natural progression of a degeneratedspinal unit
• New lesions occur also after medical or non-stabilizing procedures (Da Costa, JAVMA, 2007)
Adjacent segmentdegeneration6 months postoppresent in 11/11 dogs
(Steffen et al. 2011)
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Prevention of ASD
• Careful soft tissue preparation (i.e. elevation of longus colliinstead of transection) because of supportive role ofmusculolig. Structures
• Avoid injury to adjacent disc during distraction
• plate should be 5mm away from the endplate
• Screws angled away from endplate(Kepler et al. Orthop Clin N Am 2012)
• Avoid overdistraction of affected level (personal observation)
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ASD 4 weeks after distracton –fusion procedure
Traction responsive lesion
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Management of ASD
• No guidelines in veterinary medicine
• Humans: ASD plate arthrodesis and stand-alone cage fusionreported to be effective (Kepler et al. Orthop Clin N Am 2012)
• Canine: medical treatment provided only short-term controlof ASD (Steffen et al., 2011)
• Surgical managment (probably) mandatory for
cervical ASD in dogs
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Surgical management of ASD: BMD 7 y
Immediate postoptraction responsiveAnnulus protrusion C6-7
Severe neck pain 12 weekspostop
C7
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Adjacent level sx: Removal of original plates and, distraction using a 2nd carbonfiber fusioncage C5-6, ventral plating over 3 vertebrae
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Dobermann, 10 y fs: 4 years after successful C6-7 stabilization.Acute onset of cervical pain and paraparesis
Disc degeneration and protrusion with compression of C5-6. Bony bridging ventral to the plates (white arrow)
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Adjacent level sx: Because of a solid bonybridge C6-7 screws were removedonly unilaterally. A new locking plate was placedon-top the original and fixed withscrews with a larger diameter through original corridors.
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Further evolutions I
L-Cox Distractable cage
Similar biomechanical stability as a locking plate
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Further evolutions II
Corlazzoli D.
ACVIM Proceedings 2013
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The new kid: disc arthroplastyOriginal idea: preserving cervical spinal segment motion thereby reducingthe risk for ASD.
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JAVMA 2011
Adequate spinal cord decompression was achievedIntervertebral mobility was not achieved or lost in both casesdue to collaps of the IVD space/subsidence of the implant
Cervical disc arthroplasty using the Adamo spinal disc in 30 dogs affected by DAWS atSingle and multiple levels. Proceeding, ECVN/ESVN 26th Symp Paris 2013
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Human cervical surgery
Optimistic notion that TDR would lower the rate of complications has not materialised
Statistically, there is the same risk für ASD after disk-athroplasty (16%) and stabilization procedures (18%)
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Disc replacement using Pro-Disc C versus fusion: a prospective randomisedand controlled radiographic and clinical study
Nabhan et al., Eur Spine J 2007
significant pain reduction postoperatively, without significant difference between both groups (P > 0.05). Cervical spine disc prosthesis preserves cervical spine segmental motion within the first 6 months after surgery. The clinical results are the same when compared to the early results following ACDF
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Why is TDR not more effective than ACDF?Possible explanation
• Preserving motion is less important than uniform load-transmission
• Load-transmission over endplate is critical and requires completeosseus integration between implant and enplate over a large foot-print.
• Bone-implant interface = mixture of fibrous tissue and bone => Continued pain despite rigid fixation
• Irregular load transmission occurs in degenerated discs andintervertebral devices with „small foot prints“ (cage, articifical discs(insufficient load transfer due to deficient interface between implantand endplate)
• Common goal of ACDF and artifical discs: produce optimal loadtransfer over a large foot-print with 100% bony integration
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Summary
• Is a stabilizing procedure superior to a non-stabilizingdecompression?
• Many procedures for management of DAWS/CCSM have been described and will be described in nearfuture
• Level of evidence of each?
• No „state-of-the-art“ procedure can be recommendedat present (see Jeffery/McKee, 2001)
• Randomized, prospective studies comparing theprocedures using standardized outcome measures
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Your turn