12/28/2015 1 Pedicle, Facet, Cortical, and Translaminar Screw Techniques Gregory R. Trost, MD Professor and Vice Chair of Neurological Surgery University of Wisconsin-Madison Dorsal Fixation of the Thoracic and Lumbar Spine • Thoracic and Lumbar Pedicle Fixation • Hook Placement • Sublaminar Cable/Wire • Transfacet Screws • Spinous process plate • Translaminar Screws • Cortical Screws Techniques Thoracic Pedicle Fixation Relevant Anatomy • Three anatomic characteristics of the pedicle affect screw size and position – Pedicle diameter • Transverse width • Sagittal width – Angle of the pedicle trajectory • Transverse angle • Sagittal angle – Length of pedicle - vertebral body complex (chord length) • Varies for anatomic versus “straight forward” technique Thoracic Pedicle Fixation Relevant Anatomy • Pedicle is auricular in shape – Transverse diameter critical – determines screw diameter • “plasticity of pedicle” – Smallest diameter T 4 –T 8 – Transverse diameter T 3 –T 1 – Medial pedicle cortex 2-3x thicker than lateral – Transverse diameter is often altered in deformity • Transverse angle changes –T 12 pedicles neutral or even divergent and pedicles converge as progress cephalad with T1 pedicle trajectory approx 25 - 35 O
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Dorsal Fixation of the Thoracic and Lumbar Spine Workshop... · •Flouroscopy ( AP T1 - T4) •Laminotomy (C7 and T1) Thoracic Screw Placement Free Hand Technique • Starting points
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12/28/2015
1
Pedicle, Facet, Cortical, and Translaminar Screw Techniques
Gregory R. Trost, MD
Professor and Vice Chair of Neurological Surgery
University of Wisconsin-Madison
Dorsal Fixation of the Thoracic and Lumbar Spine
• Thoracic and Lumbar Pedicle Fixation• Hook Placement• Sublaminar Cable/Wire• Transfacet Screws• Spinous process plate• Translaminar Screws • Cortical Screws
Techniques
Thoracic Pedicle Fixation Relevant Anatomy
• Three anatomic characteristics of the pedicle affect screw size and position– Pedicle diameter
• Transverse width• Sagittal width
– Angle of the pedicle trajectory• Transverse angle• Sagittal angle
– Length of pedicle - vertebral body complex (chord length)
• Varies for anatomic versus “straight forward”technique
Thoracic Pedicle Fixation Relevant Anatomy
• Pedicle is auricular in shape– Transverse diameter critical –
determines screw diameter• “plasticity of pedicle”
– Smallest diameter T4 – T8
– Transverse diameter T3 – T1
– Medial pedicle cortex 2-3x thicker than lateral
– Transverse diameter is often altered in deformity
• Transverse angle changes– T12 pedicles neutral or even
divergent and pedicles converge as progress cephalad with T1 pedicle trajectory approx 25 - 35O
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Thoracic Pedicle Fixation Relevant Anatomy
• Chord length generally increases as you progress caudally (body + pedicle length)– T1 – T3 26 – 34 mm– T4 – T6 34 - 44 mm– T7 – T12 36 – 50 mm
• Pedicle to “neural” distance– Distance between pedicle and
corresponding nerve root is equal along superior and inferior aspect
– Dura touches medial pedicle• Worse at concavity in deformity
• Relationship of pedicle to facet joint, lamina, and transverse process
Thoracic Pedicle Fixation Relevant Anatomy
Soft Tissue and Vascular Structures
T4
T5
T6
T7
T8
T9
T10
T11
T12
Thoracic and Lumbar Pedicle Fixation
Pre Operative Assessment• Plain X-ray
– Sagittal plane deformity• True AP view of pedicles difficult• Obtained only in the vertebral segments that are
perpendicular to the x-ray beam (beam may need to be angled above and below the apex to visualize true pedicle dimensions
• Supine / Push-prone x-rays may be helpful• Must have 36” standing films with knees/hips extended• Lying flex – ext films (lat decub)
– Coronal plane defomity• Side bending views may be helpful• Pedicle assessment often difficult• 36” films and lying flex – ext films
Thoracic and Lumbar Pedicle Fixation
Pre Operative Assessment• CT scan
– Best modality to evaluate pedicle anatomy (a “must” at T4 – T8)
– Good visualization of both concave and convex pedicles in cases of coronal deformity
Thoracic Screw Placement• Two main trajectories of
screw placement (often determined by pathology)– Straight forward trajectory
(SFT)• Straight forward trajectory allows
uniaxial or multiaxial screws (coronal / sagittal deformity)
• 27% in pullout strength compared to AT
– Anatomic trajectory (AT)• Multiaxial screws much easier
(stabilization for anterior / posterior pathology such as tumor, fracture, degenerative, iatrogenic)
• Salvage (?) – 62% MIT Lehman et al Spine 2003
Lehman et al Spine 2003
Assisted free hand technique•Flouroscopy ( AP T1 -T4)•Laminotomy (C7 and T1)
Thoracic Screw Placement Free Hand Technique
• Starting points for AT and SFT for thoracic vertebrae are slightly variable and are based on posterior element anatomy that must be visualized intraop. (exposure, exposure, exposure)– Transverse process– Base of the superior
articular process– Lateral portion of the
lamina / pars
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Thoracic Screw Placement Free Hand Technique
• Exposure– Limit dissection to fusion levels
(reduce junctional kyphosis or transition syndromes)
– T-spine much easier to avoid facet disruption at termini than in LS spine
– Expose to tip of T-piece bilaterally and lateral joint / lamina / pars