Dorsal Fixation of the Thoracic and Lumbar Spine Techniques

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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 Techniques Thoracic and Lumbar Pedicle Fixation Hook Placement Sublaminar Cable/Wire Transfacet Screws Spinous process plate Translaminar Screws Cortical Screws 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 O 1

Thoracic Pedicle Fixation Relevant Anatomy Chord length generally increases as you progress caudally (body + pedicle length) T 1 T 3 26 34 mm T 4 T 6 34-44 mm T 7 T 12 36 50 mm Pedicle to neural

joint, lamina, and transverse process T4 T5 T6 T7 T8 T9 T10 T11 T12 Thoracic Pedicle Fixation Relevant Anatomy Soft Tissue and Vascular Structures Thoracic and Lumbar Pedicle Fixation Pre Operative

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

2 Thoracic Pedicle Fixation Relevant Anatomy Chord length generally increases as you progress caudally (body + pedicle length) T 1 T mm T 4 T mm T 7 T 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 T4 T5 T6 T7 T8 T9 T10 T11 T12 Thoracic Pedicle Fixation Relevant Anatomy Soft Tissue and Vascular Structures 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 T 4 T 8 ) Good visualization of both concave and convex pedicles in cases of coronal deformity Sagittal / coronal recons often helpful CT slightly underestimates pedicle width Volume averaging on each window Remember pedicles can adapt with oversized screws especially in adolescents (expansion or cutout by screw threads before fracture occurs) 2

Thoracic and Lumbar Pedicle Fixation Pre Operative Assessment Image guidance

flouroscopy (2D CAS) 3D flouroscopy (3D CAS) Two main trajectories of screw placement

trajectory allows uniaxial or multiaxial screws (coronal / sagittal deformity) 27% in

$as tumor, fracture, degenerative, iatrogenic) Salvage (?$ ) 62% MIT Lehman et al Spine 2003 Assisted free hand technique Flouroscopy ( AP T1 -

slightly variable and are based on posterior element anatomy that must be visualized

3 Thoracic and Lumbar Pedicle Fixation Pre Operative Assessment Image guidance Fluoroscopically assisted Stereotactic systems CT (3D CAS) Computer assisted flouroscopy (2D CAS) 3D flouroscopy (3D CAS) 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 Lehman et al Spine 2003 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 Assisted free hand technique Flouroscopy ( AP T1 - T4) Laminotomy (C7 and T1) 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 3

Exposure Limit dissection to fusion levels (reduce junctional kyphosis or transition syndromes) T-spine much easier to avoid facet disruption at

Osteotomize the inferior facet joint and remove articular cartillage on superior facet (3-4 mm) Do not disrupt joint at UIV Facetectomy Cortical

cancellous soft spot Entrance point Straight forward trajectory Starting point varies slightly at each level Place screw parallel to superior

If no lateral flouro (T1 T4) or pre-op films you can probe perpendicular to the dorsal cortical surface of the superior facet T1, T2, T11, T12

4 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 Facetectomy Thoroughly clean facet joints Osteotomize the inferior facet joint and remove articular cartillage on superior facet (3-4 mm) Do not disrupt joint at UIV Facetectomy Cortical burring 3 mm burr creates 3-4 mm posterior cortical breach Pedicle blush (cancellous bone) may be seen Generally use gearshift to search for cancellous soft spot Entrance point Straight forward trajectory Starting point varies slightly at each level Place screw parallel to superior endplate. If no lateral flouro (T1 T4) or pre-op films you can probe perpendicular to the dorsal cortical surface of the superior facet T1, T2, T11, T12 Anatomic trajectory Similar starting points at each level Sagittal angle O inclination using the superior or inferior endplates Can utilize pre-op films or intra-op flouro (below T 4 ) Mainly feel Transverse angulation increases as you go cephalad (0 15 O with a jump at T 1 ) Again mainly feel 4

Gearshift probing 2 mm blunt-tipped slightly curved probe Ventral pressure as search for pedicle Gearshift pointed laterally and insert to 15 20 mm Remove probe and turn tip medially and place tip

Then continue path down medial into the body (sudden advancement suggests penetration into ST) 35 40mm T 7 T 12 30 35mm T 4 T 6 20 25mm T 1 T 3 Gearshift probing Sagittal inclination (SFT) Parallel

5 Gearshift probing 2 mm blunt-tipped slightly curved probe Ventral pressure as search for pedicle Gearshift pointed laterally and insert to mm Remove probe and turn tip medially and place tip down to base of prior hole Then continue path down medial into the body (sudden advancement suggests penetration into ST) 35 40mm T 7 T mm T 4 T mm T 1 T 3 Gearshift probing 2 mm blunt-tipped slightly curved probe Ventral pressure as search for pedicle Gearshift pointed laterally and insert to mm Remove probe and turn tip medially and place tip down to base of prior hole Then continue path down medial into the body (sudden advancement suggests penetration into ST) 35 40mm T 7 T mm T 4 T mm T 1 T 3 Gearshift probing Sagittal inclination (SFT) Parallel to superior endplate or perpendicular to dorsal surface of superior facet (pre-op films). Mainly feel with probe Transverse inclination (SFT / AT) Increases from 0 O 15 O from T 12 T 2 with lami at T 1 as big jump in inclination (pre-op films). Mainly feel with probe Work from cranial to caudal or caudal to cranial to visualize trends of entry point at each successive level Sagittal inclination (AT) O inclination from a line parallel to the superior or inferior endplates Can utilize pre-op films or intra-op flouro (below T 4 ) Mainly feel Palpation Once probe removed observe for CSF Palpate all four walls and floor using flexible ball tipped probe Majority of wall perforations are lateral Can determine chord length with probe If wall breach occurs can redirect screw with tap (utilize AT) Undertap pedicle tract 4.2 tap for 5.2 scew 4.0 tap for 5.0 screw Repalpate 5

Confirmation of screw placement Imaging True AP and lateral flouroscopy (T 1 T 4 AP) Screw crossing midline of body (? medial wall breach) Screw not crossing medial cortical wall of the pedicle (?

6 Confirmation of screw placement Imaging True AP and lateral flouroscopy (T 1 T 4 AP) Screw crossing midline of body (? medial wall breach) Screw not crossing medial cortical wall of the pedicle (? lateral wall breach) Screws that intersect an endplate (SFT) and should not extend beyond 75-80% of vertebral body sagittal distance (T 1 T 4 ) EMG Useful T 6 T 12 Stimulate screws intra-op and monitor rectus abdominis muscle Rod contouring and correction 3D contouring useful to have 2 or more rod holders Missing the Pedicle Most often too lateral Look at other successful holes/screws Importance for moving in a uniform fashion Assess landmarks Move starting point more medial Aim medial Missing the Pedicle If successfully locate Make sure utilize correct pedicle hole Use a k-wire, cannulated tap and/or screw If can t easily locate pedicle Most often skip unless at ends of construct Missing the Pedicle Don t be afraid (really proud) to perform laminotomy, fluoroscopy Use salvage technique Anatomic trajectory In out in Etc. 6

7 In Out In Lumbar Pedicle Anatomy Less variability compared to thoracic spine L1-L5 Steady increase in transverse width Slight decrease but fairly stable sag width Significant increase in transverse angle Only small changes in sagittal angle, neutral at L1 7

8 Lumbar Pedicle Screw Free Hand Technique Entry point classically described as intersection of TP and inferolateral facet margin Roy-camille: medial entry straight ahead technique Wienstien: lateral entry with converging screws Kraig : up and in to obtain sub-chondral purchase Trajectory Decorticate entry point with burr Use pedicle probe or curette to advance down pedicle into body. Placement Use ball-tipped probe to feel for cortical breech Place screw +/- tapping Adjuncts: image guidance, fluoroscopy, direct visualization of pedicle Placement 8

9 Screw size? Pedicle diameter measured at isthmus Pick largest diameter screw that will fit inner cortical diameter (C) Length 5 mm short of ant cortex on lateral x-ray Placement Cortical Screws Typically 4.5 X mm screws Cortical Lumbar Screws Mobbs TJ.Orthopedic Surgery

Magerl described translaminar facet screw

cadavers tested in short term and long term

term NO DIFFERENCE between fixation except

term NO DIFFERNCE, no decrease in fixation

10 History FACET SCREWS Boucher first described true transfacet fixation in 1959 Magerl described translaminar facet screw fixation in 1984 Clinical Data Lumbar cadavers tested in short term and long term cyclic loading conditions Results Short term NO DIFFERENCE between fixation except in flexion-stiffer with facet screws Long term NO DIFFERNCE, no decrease in fixation FACET SCREWS PROVIDE EQUAL FIXATION TO PSF-BETTER IN FLEXION 10

11 Percutaneous Transfacet Fusion 11

$DDD Facet Screw fixation Contraindications: Isthmic spondylolisthesis Prior laminectomy Lamina fracture Severe osteoperosis$ Instability Deformity Anterior column deficiency Facet Screws Goal is to insert perpendicular to orientation of facet

Instability Deformity Anterior column deficiency Facet Screws Goal is to insert perpendicular to orientation of facet

12 Translaminar facet screws 1 or two level fixation when no reduction needed Most commonly used for dorsal fixation w/ ALIF in DDD Facet Screw fixation Contraindications: Isthmic spondylolisthesis Prior laminectomy Lamina fracture Severe osteoperosis Instability Deformity Anterior column deficiency Facet Screws Goal is to insert perpendicular to orientation of facet Stiffness approximately equivalent to pedicle screw fixation in 360 degree fusion (Sasso) Advantages: Small exposure Cost Low profile 12

13 Entry point Trajectory 13

Dorsal Cervical Surgeries and Techniques

Dorsal Cervical Approaches Dorsal Cervical Surgeries and Techniques Gregory R. Trost, MD Professor and Vice Chair of Neurological Surgery University of Wisconsin-Madison Advantages Straightforward Easily