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 learned Avoids risk to anterior vascular and visceral anatomy Relatively avascular plane can typically be developed Disadvantages Potentially greater discomfort than anterior approaches Potentially longer hospital stays Prone or sitting position typically required Increased incidence of postsurgical deformity Positioning Dorsal Cervical Anatomy Prone most common Chest/hip rolls Sitting Reduced bleeding Drainage of blood from operative site Improved ventilation Risk of air embolism Technically demanding for surgeon (especially instrumentation) 3 separate muscle groups generally mobilized as a unit Avascular midline plane Spinous processes of C2 and C7 most palpable C6 spinous process usually the lowest bifid process 1
Dissection Transmuscular approach Typically with tube retractor system Often less invasive and less painful Complications Most complications result from definitive procedure, not approach Positioning-related Ocular injury reported at 0.2% (keep pressure off globe) Brachial plexopathy if traction on shoulders Air embolism (more commonly reported in lumbar surgery) Drop in BP Drop in ETCO 2 Pressure points Sternum Iliac crests Knees Toes Dorsal Cervical Instrumentation 2
Indications Stand-alone laminectomy Multilevel corpectomy Kyphosis Stand alone if flexible Part of combined case if fixed Infection Tumor Trauma Dorsal Cervical Fixation Considerations Alignment of the spine Level involved-axial vs. subaxial Number of levels to instrument Pathology to be treated Bone quality Wire/cable Hooks Screw/plates Screw/rods Combinations Dorsal Cervical Fixation Wire/Cable Requires laminotomy Ligamentum flavum removed with curette Bend wire to approximate the shape of the lamina Pass from caudal to rostral Attach wire / cable to rod or bone 3
Interspinous Wiring Wire/Cable Interspinous Wiring Wire/Cable Used to restore posterior tension band after soft tissue injury or to augment other anterior or posterior fixation techniques Advantages Technically easy learning curve Large surface area for fusion Resists/produces translational forces 4
Wire/Cable Lateral Mass Fixation Disadvantages Need intact posterior elements Wire breakage or cutout Instrumentation into central canal Does not provide adequate corrective forces in: Distraction Compression Rotation Due to inherent problems with wiring, lateral mass fixation evolved Provides improved stability in axial load and rotation May be used throughout the subaxial spine from C3-7 Lateral Mass Screws Lateral Mass Screws Anatomical Factors Size Orientation Bone Quality Vertebral Artery Nerve Root Roy-Camille Technique Neutral projection Magerl Technique Rostral-lateral projection 5
Lateral Mass Screws Roy-Camille Technique Entry in midline of lateral mass Junction of upper and middle third Screws placed in sagittal plane Shorter screw length Higher risk of neurovascular injury Cooper PR, et al., Neurosurg, 23:300-306, 1988. Magerl Technique Entry medial to center of lateral mass Angle screws 25-30 laterally Parallel to facets (30-40 ) Lower risk of neurovascular injury Bicortical purchase stronger Lateral Mass Screws Magerl vs Roy-Camille Lateral Mass Fixation Hook plates Lateral mass plates Poly-axial screws and rods 6
Lateral Mass Plates Hook Plates Lateral Mass Plates A template may be used for planning of screw placement Holes are drilled, plate cut to size, screws placed into plate for fixation to the spine Lateral Mass Plates Disadvantages Advantages Difficult in deformity Rotational & axial stability correction Adaptable to multiple levels Difficult to line up holes in and across occipito-cervical plate to screw holes (fit spine junction to plate) Not reliant on lamina Difficulty crossing C-T junction Screw back out Obstruct fusion area Economic cost 7
Lateral Mass Polyaxial Screws Lateral Mass Polyaxial Screws Advantages Rotational & axial stability Adaptable to multiple levels & across occipitocervical and cervicothoracic junctionseasier compared to plates Not reliant on lamina Screws placed independently (fit instrumentation to spine) Contoured rods Useful in complex deformities Disadvantages Obstruct fusion area Economic cost Biomechanics Biomechanics Varying reports in the literature regarding biomechanics of Magerl vs. Roy-Camille trajectories Overall there was no difference in pullout using both techniques Level seemed to be important Roy-Camille greater pullout out resistance at C3/4 No significant difference was seen at C5/6 8
Safety Analysis of 1026 consecutive lateral mass screws CT evaluation NO neural or vascular injury MOST had 14mm screws placed Safety Structures at risk include the facet joint, vertebral artery and nerve root Safety profile decreases for Roy-Camille as one descends the spine Facet joint greatest risk Safety profile constant for Magerl Greatest risk for nerve root at C3/4, least at C5/6 Risk of vertebral artery injury is low Lowest with 15 degree lateral angle Ebraheim et al. What size screws to use? Ebraheim et al. Spine 1998 Conclusions 14-15mm in the RC technique 15-16mm in the Magerl technique a short screw may be placed at C7 Bicortical Fixation? 30% greater pull-out resistance Heller et al., JBJS 1996 I generally place long unicortical screws unless needed for pathology Tumor Osteoporosis 9
Options Skip Pedicle screw Lateral mass screw What about C7? C7 pedicle screw superior biomechanically at CTJ C7 Pedicle Screws Often times difficult to place Breach seen 8 to 13% of the time Jones et al., Spine 1997 If unable to place, combination of C6 and C7 lateral mass seems similar to C7 pedicle screw when linked to T1 Cervical spinous process wiring does not improve stiffness when combined with C6 or C7 lateral mass screws Rhee et al., Spine 2005 C7 Pedicle Screw Placement Other Options Cervical transfacet screws Cervical pedicle screws Inferior facet removal Perform C 7 laminotomy Define superior and medial edge of pedicle 1 2 mm inferior to C6-7 joint Sagittal angle 10 O inferior 25 0-30 0 medial 20 30 mm screws Pre-op CT 10
Transarticular Facet Screws Transarticular Facet Screws Magerl s translaminar approach is already being used successfully in the lumbar spine. 94-100% fusion rates in single level lumbar fusions. Biomechanically similar stabilization to pedicle screws in the lumbar spine (Deguchi et al.) Transfacet Screws 13 human cadaver spines 2 level instrumentation with lateral mass plates or transarticular facet screws Tested in flexion/extension/torsion No difference seen between each fixation type in two level instrumentation Starting point, midfacet Screws are angled 40 deg caudally and 20 deg laterally 10-12mm screw Good for bail out of failure to place a lateral mass screw 11
Mid Cervical Pedicle Screws C 5 C 6 Technically possible Pre operative imaging is necessary with up to 6 % of pedicles being to small Cervical pedicular anatomy can be highly variable Screw misplacement rate may be unacceptable at 16.8 % (7.1 % critical and 9.7 % not critical) Karaikovic et al; Spine, 2001 Nov 15; 26 (22): 2456-62 Some series with higher success rate Abumi et al; Spine, 2000 Apr 15; 25 (8): 962-9 Given the risk and safer alternatives, justification needed for use Lateral mass screws Skipping a level or side Navigational aids if necessary Mid Cervical Pedicle Screws C 5 C 6 Advantages Strength of pedicle No hardware in spinal canal Posterior elements not required for fixation Purchases anterior and posterior columns Force exerted closer to IAR Short segment fixation potential Application of corrective forces possible Distraction Compression Rotation Lateral translation Mid Cervical Pedicle Screws C 5 C 6 Disadvantages Steep learning curve Potential neurovascular complications Osteoporosis Pedicle pathology Mid Cervical Pedicle Screws C 5 C 6 Cervical pedicular anatomy can be highly variable patient-patient level-level side-side Pre-op CT imaging Intra-operative Fluoroscopy Laminectomy Computer assisted Techniques Improved Accuracy Has Limitations 12
Cervicothoracic Junction Do you cross the CTJ, end there, how to decide? In reality, we really don t know Options Skip C7 and instrument to T1 and/or T2 Skip C6 and instrument C7 and T1 and/or T2 Place screws at all levels, C6, C7, T1 and/or T2 Conclusions Multiple options exist for fixation of the dorsal cervical spine Individualize choice per pathology and biomechanics Consider COST$$$$$$$$$$ Rely on your own experience and the techniques that work best in your hands 13