SURGICAL TECHNIQUE
Lateral Mass Fixation in the Subaxial Cervical Spine Mark F. Kurd, MD, Paul W. Millhouse, MD, Gregory D. Schroeder, MD, Christopher K. Kepler, MD, MBA, and Alexander R. Vaccaro, MD, PhD
Abstract: The use of lateral mass screws and rods in the subaxial spine has become the standard method of fixation for posterior cervical spine fusions. Multiple techniques have been described for the placement of lateral mass screws, including the Magerl, the Anderson, and the An techniques. While these techniques are all slightly different, the overall goal is to obtain solid bony fixation while avoiding the neurovascular structures. The use of lateral mass screws has been shown to be a safe and effective technique for achieving a posterior cervical fusion. Key Words: lateral mass screws, posterior cervical stabilization, cervical myelopathy, cervical radiculopathy, cervical trauma, posterior cervical fixation, neck pain, cervical screws (J Spinal Disord Tech 2015;28:259–263)
INDICATIONS The indications for lateral mass fixation in the cervical spine are the same as for a posterior cervical fusion. These include: Provide increased stability after complex anterior cervical spine procedures, such as a multilevel corpectomy. Achieve fusion after an ACDF pseudarthrosis. Received for publication May 18, 2015; accepted May 26, 2015. From the The Rothman Institute at Thomas Jefferson University Hospital, Philadelphia, PA. P.W.M. has been a consultant for Pacira and has stock/stock options with Globus; G.D.S. has received travel/accommodations/meeting expense reimbursement from Medtronic; C.K.K. is a consultant for Healthgrades Inc.; and A.R.V. is a board member for AO Spine, Innovative Surgical Design, Association of Collaborative Spine Research, and Spinicity, as well as a consultant for DePuy, Medtronics, Stryker Spine, Globus, Stout Medical, Gerson Lehrman Group, Guidepoint Global, Medacorp, Innovative Surgical Design, Orthobullets, Expert testimony, Ellipse, and Vertex. A.R.V. is also employed by Rothman Institute and has received royalties from Medtronics, Stryker Spine, Biomet Spine, Globus, Aesculap, Thieme, Jaypee, Elsevier, and Taylor Francis. A.R.V. has stock/ stock options in Replication Medica, Globus, Paradigm Spine, Stout Medical, Spine Medica, Computational Biodynamics, Progressive Spinal Technologies, Spinology, Small Bone Innovations, Cross Current, In Vivo, Flagship Surgical, Advanced Spinal Intellectual Properties, Cytonics, Bonovo Orthopaedics, Electrocore, Gamma Spine, Location Based Intelligence, FlowPharma, R.S.I., Rothman Institute and Related Properties, Innovative Surgical Design, and Spinicity. Reprints: Gregory D. Schroeder, MD, The Rothman Institute at Thomas Jefferson University Hospital, 925 Chestnut St, Philadelphia, PA 19107 (e-mail: [email protected]). Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.
J Spinal Disord Tech
Volume 28, Number 7, August 2015
Stabilize the spine after multilevel laminectomy for cervical spondylotic myelopathy. Stabilize the spine after cervical spine trauma. Correct deformity of the cervical spine. Stabilize the spine after tumor resection. Stabilize the spine after infection.
OPERATING ROOM SETUP Instruments/Materials Required Jackson table (Orthopaedic Systems, Union City, CA) or standard OR table. Gardner-Wells tongs or a Mayfield head holder. Intraoperative fluoroscopy or radiography. Surgical loupes or microscope. High-speed burr. Lateral mass screw and rod system.
Positioning Often times patients who are undergoing a posterior cervical fusion have significant compression on the spinal cord, if this is the case, an awake fiber-optic intubation should be considered and the chin-lift, jaw-thrust maneuver should be avoided. In addition, baseline neuromonitoring (multimodal monitoring including transcranial motor-evoked potential monitoring) should be performed before positioning the patient, and an arterial line should be placed so that the mean arterial pressure can be closely monitored and kept >80 mm Hg. After the patient has been successfully intubated, and baseline neuromonitoring has been established, the authors prefer to use Gardner-Wells tongs to support the head. The patient is then placed prone on a Jackson table and bivector traction is applied to the tongs (Fig. 1). With bivector traction, one of the ropes can be used to pull inline traction, which may be helpful when performing the decompression, and 1 rope can be used to provide an extension moment which helps recreate lordosis at the time of fusion. Twelve to 15 pounds of weight is adequate for traction. The patient should be placed as close to the head of the bed as possible to obtain the greatest extension moment. The patient may be placed in approximately 30 degrees of reverse Trendelenburg. This positioning will result in an increased venous return and a decrease in bleeding during the exposure. After all bony prominences have been well padded, the patient’s arms are tucked, and the shoulders can be gently taped down to allow for improved intraoperative radiographic visualization of the lower cervical spine. Aggressive traction on the shoulders should be avoided, as this can lead to a brachial plexopathy (Fig. 2). www.jspinaldisorders.com |
Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.
259
J Spinal Disord Tech
Kurd et al
Volume 28, Number 7, August 2015
SURGICAL TECHNIQUE Step 1: Incision and Exposure Before the incision, the skin is injected with 0.5% lidocaine with epinephrine to help with hemostasis. The prominent C2 and C7 spinous processes can often be palpated and used to locate the incision; however, fluoroscopy can be beneficial in smaller cases. The epidermis is divided sharply, and then electrocautery is used to dissect down to the spinous processes. During the approach, it is critical to stay in the midline, as this is a natural avascular plane between the right and left paraspinal musculature. If the dissection remains in this plane, the dissection is often relatively bloodless, but significant bleeding will occur if the dissection is out of this plane. Once the spinous process has been visualized, bilateral paramedian fascial incisions are made, and subperiosteal dissection of the musculature off the posterior elements is performed using a combination of electrocautery and a Cobb elevator. Careful attention must be paid not to breach the interlaminar space with the electrocautery. This is particularly important with the Gardner-Wells traction as the interlaminar space may be increased. An intraoperative lateral fluoroscopic or radiographic image should be used to verify the level. Importantly, the facet capsules should not be violated until the levels have been verified, as disruption of the facet capsules can lead to autofusion. Once the levels have been verified, a wide exposure is required, such that the lateral border of the lateral mass can be easily visualized and palpated. FIGURE 1. Photograph of a patient with bivector traction. The weights are in the flexion moment in (A) and the extension moment in (B).
Step 2: Special Considerations at C2 and C7 If possible, care should be taken not to disrupt the nuchal ligaments or the semispinalis cervicis off of the C2 spinous process, as releasing this muscle may lead to an increase in postoperative neck pain and kyphosis. Leaving this intact will rarely prevent an adequate decompression, as an adequate decompression can often be achieved by undercutting “doming” the lamina of C2. However, if undercutting the lamina is not sufficient, preservation of the semispinalis cervicis should not jeopardize the adequacy of the neurological decompression. If the muscle must be released from C2, it should be tagged with a suture to facilitate reattachment upon closure. Similarly, because of the increased height of the C7 spinous process, it provides a substantial increase in the moment arm of the extensor musculature. Because of this, the C7 spinous process and muscle attachments should be preserved if possible.
Step 3: Preparing the Tack for Lateral Mass Screws FIGURE 2. Photograph demonstrating the reverse Trendelenburg positioning of the patient.
260 | www.jspinaldisorders.com
It is the authors preferred treatment to prepare the holes for the lateral mass screws before the decompression. Three common techniques have been described, the Magerl, the Anderson, and the An technique (Fig. 3). Copyright
r
2015 Wolters Kluwer Health, Inc. All rights reserved.
Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.
J Spinal Disord Tech
Volume 28, Number 7, August 2015
Lateral Mass Fixation in the Cervical Spine
FIGURE 3. Schematic representation of the Magerl, the Anderson, and the An technique for the placement of lateral mass screws.
These techniques are all very similar, aiming cephalad to avoid the exiting nerve root, and lateral to avoid the vertebral artery. J Magerl Technique ’ Starting point: 1 mm medial and 1 mm superior to the midpoint of the lateral mass. ’ Angle: 25 degrees lateral and approximately 30 degrees cephalad (parallel to the facet joint). J Anderson Technique ’ Starting point: 1 mm medial to the midpoint of the lateral mass. ’ Angle: 10 degrees lateral and 30–40 degrees cephalad.
The midpoint of the lateral mass is identified, and using a 2 mm high-speed burr, a pilot hole is drilled 1 mm medial to the midpoint of the lateral mass (Fig. 4). Once the pilot hole has been drilled, we use a 2.5 mm drill with a 12 mm stop to drill the track for the screw. The drill is angled 15 degrees cephalad and 30 degrees lateral. A ball-tipped probe is used to ensure that the lateral mass has not been breached, and the hole is tapped. Bone wax is then placed in the hole to maintain hemostasis, and the next lateral mass track is prepared.
J An Technique ’ Starting point: 1 mm medial to the midpoint of the lateral mass. ’ Angle: 30–33 degrees lateral and 15–17 degrees cephalad. The authors prefer to use the An technique. We ensure that the borders of the lateral mass can be easily seen and palpated. The superior and inferior borders are defined by the dorsal edge of the facet joints. The lateral border is the lateral edge of the bone, and the medial border is the transition between the lateral mass and the lamina. This can often be identified by a slight depression in the bone. Copyright
r
2015 Wolters Kluwer Health, Inc. All rights reserved.
FIGURE 4. Photograph demonstrating a pilot hole for a lateral mass screw. This hole is 1 mm medial to the center of the lateral mass. www.jspinaldisorders.com |
Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.
261
J Spinal Disord Tech
Kurd et al
It is important to make sure that the starting point for all of the lateral mass screws are aligned, as redrilling a lateral mass screw track may comprise the screw purchase. Once all of the screw holes have been completed, the decompression, if necessary, can be performed.
Step 4: Cervical Laminectomy Multiple techniques can be used to perform a cervical laminectomy, including performing the entire laminectomy with a combination of Leksell and Kerrison rongeurs; however, our preferred technique is to perform the bulk of the decompression using a highspeed burr. The burr is used to create a trough along the border of the lamina and the facet. It is possible to safely use the burr to cut entirely through the lamina, and this technique is especially important in severely stenotic canals, as it avoids inserting instruments into an already tight canal, as this may result in a spinal cord injury. Alternatively, a thin layer of cortical bone can be left and a 1 mm Kerrison rongeur can be used to remove this final layer. Once the troughs are completed bilaterally, a combination of a towel clamp to grip the posterior elements, and a curved curette or a Penfield 4 to release the adhesions is used to remove the lamina en bloc. A pedicle-to-pedicle decompression should be performed to ensure the neural elements are completely decompressed. Once the decompression is completed, it is necessary to prepare the fusion bed. This is done by making sure the entire facet capsules as well as any visible cartilaginous endplate have been removed at each level. In addition, the dorsal aspect of the facet can be decorticated.
Step 5: Placement of the Lateral Mass Screws Following the decompression and preparation of the fusion bed, a ball-tipped probe can be used to identify the tracks for the lateral mass screws.
Volume 28, Number 7, August 2015
When placing the lateral mass screws care must be taken to ensure that they are inserted in the same trajectory as the holes so as to not fracture the lateral mass (Fig. 5). Once all of the screws are placed, the position of the head may need to be adjusted to ensure that the cervical spine is fused in the appropriate alignment. This can be done by changing the traction weights from the flexion vector to the extension vector on the Gardner-Wells tongs. Once the alignment has been evaluated, the rods are placed and secured. A lateral radiograph can be used to verify the alignment. Lastly, bone graft (commonly local autograft from the decompression) is placed in the facets as well as over the dorsal aspect of the lateral masses.
POSTOPERATIVE PROTOCOL The postoperative protocol is somewhat determined by the indication for the surgery; however, for the majority of cases, patients are instructed to wear a hard cervical collar for 6–12 weeks postoperatively. In almost all cases a deep drain is placed, and it is generally removed on postoperative day 2. A multilayer wound closure is critical with reapproximation of the muscle and reattachment of the fascia to any remaining bony elements. Smoking and nonsteroidal anti-inflammatory medications should be avoided for at least 6 weeks.
Complications C5 palsy J C5 nerve root palsies are one of the most common complications after posterior cervical fusions. Many risk factors have been associated with this complication, including preexisting foraminal stenosis, wide C5 laminectomies, and significant spinal cord drift. It is currently unclear whether a C5 foraminotomy can help prevent this complication. J Most patients make a full recovery; however, it may take up to 2 years. Nerve root injury J This can occur if the lateral mass screw is started to caudal or not angled sufficiently cephalad. Any patients with new radicular symptoms postoperatively (even in the C5 distribution) should undergo advanced imaging to ensure that a screw is not malpositioned. Vascular injury
FIGURE 5. Photograph demonstrating the appropriate position of 4 lateral mass screws.
262 | www.jspinaldisorders.com
J A vertebral artery injury is extremely rare; however, it is critical that the surgeon review the vascular anatomy before every cervical case to Copyright
r
2015 Wolters Kluwer Health, Inc. All rights reserved.
Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.
J Spinal Disord Tech
Volume 28, Number 7, August 2015
ensure that there is not an aberrant vertebral artery. If a vascular injury occurs during preparation of the screw track, hemostasis can often be achieved by packing the hole with bone wax. Anesthesia and vascular surgery should be notified immediately if this complication occurs.
PEARLS AND PITFALLS Lateral mass screws should be angled lateral and superiorly to obtain solid bony fixation and avoid the exiting nerve root and the vertebral artery.
Copyright
r
2015 Wolters Kluwer Health, Inc. All rights reserved.
Lateral Mass Fixation in the Cervical Spine
If you are having a difficult time determining your cephalad angle, you can decorticate the facets. Your angle should be approximately the angle of the facet. If the C7 lateral mass is small, consider a C7 pedicle screw. Avoid disrupting the attachments to the C2 and C7 spinous processes. Many of the patients undergoing a posterior cervical fusion have significant spinal cord compression. It is critical that anesthesia and the nursing staff are aware of this, and every precaution is taken to prevent a spinal cord injury during intubation and positioning.
www.jspinaldisorders.com |
Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.
263
Lateral Mass Fixation in the Subaxial Cervical Spine Mark F. Kurd, MD, Paul W. Millhouse, MD, Gregory D. Schroeder, MD, Christopher K. Kepler, MD, MBA, and Alexander R. Vaccaro, MD, PhD
Abstract: The use of lateral mass screws and rods in the subaxial spine has become the standard method of fixation for posterior cervical spine fusions. Multiple techniques have been described for the placement of lateral mass screws, including the Magerl, the Anderson, and the An techniques. While these techniques are all slightly different, the overall goal is to obtain solid bony fixation while avoiding the neurovascular structures. The use of lateral mass screws has been shown to be a safe and effective technique for achieving a posterior cervical fusion. Key Words: lateral mass screws, posterior cervical stabilization, cervical myelopathy, cervical radiculopathy, cervical trauma, posterior cervical fixation, neck pain, cervical screws (J Spinal Disord Tech 2015;28:259–263)
INDICATIONS The indications for lateral mass fixation in the cervical spine are the same as for a posterior cervical fusion. These include: Provide increased stability after complex anterior cervical spine procedures, such as a multilevel corpectomy. Achieve fusion after an ACDF pseudarthrosis. Received for publication May 18, 2015; accepted May 26, 2015. From the The Rothman Institute at Thomas Jefferson University Hospital, Philadelphia, PA. P.W.M. has been a consultant for Pacira and has stock/stock options with Globus; G.D.S. has received travel/accommodations/meeting expense reimbursement from Medtronic; C.K.K. is a consultant for Healthgrades Inc.; and A.R.V. is a board member for AO Spine, Innovative Surgical Design, Association of Collaborative Spine Research, and Spinicity, as well as a consultant for DePuy, Medtronics, Stryker Spine, Globus, Stout Medical, Gerson Lehrman Group, Guidepoint Global, Medacorp, Innovative Surgical Design, Orthobullets, Expert testimony, Ellipse, and Vertex. A.R.V. is also employed by Rothman Institute and has received royalties from Medtronics, Stryker Spine, Biomet Spine, Globus, Aesculap, Thieme, Jaypee, Elsevier, and Taylor Francis. A.R.V. has stock/ stock options in Replication Medica, Globus, Paradigm Spine, Stout Medical, Spine Medica, Computational Biodynamics, Progressive Spinal Technologies, Spinology, Small Bone Innovations, Cross Current, In Vivo, Flagship Surgical, Advanced Spinal Intellectual Properties, Cytonics, Bonovo Orthopaedics, Electrocore, Gamma Spine, Location Based Intelligence, FlowPharma, R.S.I., Rothman Institute and Related Properties, Innovative Surgical Design, and Spinicity. Reprints: Gregory D. Schroeder, MD, The Rothman Institute at Thomas Jefferson University Hospital, 925 Chestnut St, Philadelphia, PA 19107 (e-mail: [email protected]). Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.
J Spinal Disord Tech
Volume 28, Number 7, August 2015
Stabilize the spine after multilevel laminectomy for cervical spondylotic myelopathy. Stabilize the spine after cervical spine trauma. Correct deformity of the cervical spine. Stabilize the spine after tumor resection. Stabilize the spine after infection.
OPERATING ROOM SETUP Instruments/Materials Required Jackson table (Orthopaedic Systems, Union City, CA) or standard OR table. Gardner-Wells tongs or a Mayfield head holder. Intraoperative fluoroscopy or radiography. Surgical loupes or microscope. High-speed burr. Lateral mass screw and rod system.
Positioning Often times patients who are undergoing a posterior cervical fusion have significant compression on the spinal cord, if this is the case, an awake fiber-optic intubation should be considered and the chin-lift, jaw-thrust maneuver should be avoided. In addition, baseline neuromonitoring (multimodal monitoring including transcranial motor-evoked potential monitoring) should be performed before positioning the patient, and an arterial line should be placed so that the mean arterial pressure can be closely monitored and kept >80 mm Hg. After the patient has been successfully intubated, and baseline neuromonitoring has been established, the authors prefer to use Gardner-Wells tongs to support the head. The patient is then placed prone on a Jackson table and bivector traction is applied to the tongs (Fig. 1). With bivector traction, one of the ropes can be used to pull inline traction, which may be helpful when performing the decompression, and 1 rope can be used to provide an extension moment which helps recreate lordosis at the time of fusion. Twelve to 15 pounds of weight is adequate for traction. The patient should be placed as close to the head of the bed as possible to obtain the greatest extension moment. The patient may be placed in approximately 30 degrees of reverse Trendelenburg. This positioning will result in an increased venous return and a decrease in bleeding during the exposure. After all bony prominences have been well padded, the patient’s arms are tucked, and the shoulders can be gently taped down to allow for improved intraoperative radiographic visualization of the lower cervical spine. Aggressive traction on the shoulders should be avoided, as this can lead to a brachial plexopathy (Fig. 2). www.jspinaldisorders.com |
Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.
259
J Spinal Disord Tech
Kurd et al
Volume 28, Number 7, August 2015
SURGICAL TECHNIQUE Step 1: Incision and Exposure Before the incision, the skin is injected with 0.5% lidocaine with epinephrine to help with hemostasis. The prominent C2 and C7 spinous processes can often be palpated and used to locate the incision; however, fluoroscopy can be beneficial in smaller cases. The epidermis is divided sharply, and then electrocautery is used to dissect down to the spinous processes. During the approach, it is critical to stay in the midline, as this is a natural avascular plane between the right and left paraspinal musculature. If the dissection remains in this plane, the dissection is often relatively bloodless, but significant bleeding will occur if the dissection is out of this plane. Once the spinous process has been visualized, bilateral paramedian fascial incisions are made, and subperiosteal dissection of the musculature off the posterior elements is performed using a combination of electrocautery and a Cobb elevator. Careful attention must be paid not to breach the interlaminar space with the electrocautery. This is particularly important with the Gardner-Wells traction as the interlaminar space may be increased. An intraoperative lateral fluoroscopic or radiographic image should be used to verify the level. Importantly, the facet capsules should not be violated until the levels have been verified, as disruption of the facet capsules can lead to autofusion. Once the levels have been verified, a wide exposure is required, such that the lateral border of the lateral mass can be easily visualized and palpated. FIGURE 1. Photograph of a patient with bivector traction. The weights are in the flexion moment in (A) and the extension moment in (B).
Step 2: Special Considerations at C2 and C7 If possible, care should be taken not to disrupt the nuchal ligaments or the semispinalis cervicis off of the C2 spinous process, as releasing this muscle may lead to an increase in postoperative neck pain and kyphosis. Leaving this intact will rarely prevent an adequate decompression, as an adequate decompression can often be achieved by undercutting “doming” the lamina of C2. However, if undercutting the lamina is not sufficient, preservation of the semispinalis cervicis should not jeopardize the adequacy of the neurological decompression. If the muscle must be released from C2, it should be tagged with a suture to facilitate reattachment upon closure. Similarly, because of the increased height of the C7 spinous process, it provides a substantial increase in the moment arm of the extensor musculature. Because of this, the C7 spinous process and muscle attachments should be preserved if possible.
Step 3: Preparing the Tack for Lateral Mass Screws FIGURE 2. Photograph demonstrating the reverse Trendelenburg positioning of the patient.
260 | www.jspinaldisorders.com
It is the authors preferred treatment to prepare the holes for the lateral mass screws before the decompression. Three common techniques have been described, the Magerl, the Anderson, and the An technique (Fig. 3). Copyright
r
2015 Wolters Kluwer Health, Inc. All rights reserved.
Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.
J Spinal Disord Tech
Volume 28, Number 7, August 2015
Lateral Mass Fixation in the Cervical Spine
FIGURE 3. Schematic representation of the Magerl, the Anderson, and the An technique for the placement of lateral mass screws.
These techniques are all very similar, aiming cephalad to avoid the exiting nerve root, and lateral to avoid the vertebral artery. J Magerl Technique ’ Starting point: 1 mm medial and 1 mm superior to the midpoint of the lateral mass. ’ Angle: 25 degrees lateral and approximately 30 degrees cephalad (parallel to the facet joint). J Anderson Technique ’ Starting point: 1 mm medial to the midpoint of the lateral mass. ’ Angle: 10 degrees lateral and 30–40 degrees cephalad.
The midpoint of the lateral mass is identified, and using a 2 mm high-speed burr, a pilot hole is drilled 1 mm medial to the midpoint of the lateral mass (Fig. 4). Once the pilot hole has been drilled, we use a 2.5 mm drill with a 12 mm stop to drill the track for the screw. The drill is angled 15 degrees cephalad and 30 degrees lateral. A ball-tipped probe is used to ensure that the lateral mass has not been breached, and the hole is tapped. Bone wax is then placed in the hole to maintain hemostasis, and the next lateral mass track is prepared.
J An Technique ’ Starting point: 1 mm medial to the midpoint of the lateral mass. ’ Angle: 30–33 degrees lateral and 15–17 degrees cephalad. The authors prefer to use the An technique. We ensure that the borders of the lateral mass can be easily seen and palpated. The superior and inferior borders are defined by the dorsal edge of the facet joints. The lateral border is the lateral edge of the bone, and the medial border is the transition between the lateral mass and the lamina. This can often be identified by a slight depression in the bone. Copyright
r
2015 Wolters Kluwer Health, Inc. All rights reserved.
FIGURE 4. Photograph demonstrating a pilot hole for a lateral mass screw. This hole is 1 mm medial to the center of the lateral mass. www.jspinaldisorders.com |
Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.
261
J Spinal Disord Tech
Kurd et al
It is important to make sure that the starting point for all of the lateral mass screws are aligned, as redrilling a lateral mass screw track may comprise the screw purchase. Once all of the screw holes have been completed, the decompression, if necessary, can be performed.
Step 4: Cervical Laminectomy Multiple techniques can be used to perform a cervical laminectomy, including performing the entire laminectomy with a combination of Leksell and Kerrison rongeurs; however, our preferred technique is to perform the bulk of the decompression using a highspeed burr. The burr is used to create a trough along the border of the lamina and the facet. It is possible to safely use the burr to cut entirely through the lamina, and this technique is especially important in severely stenotic canals, as it avoids inserting instruments into an already tight canal, as this may result in a spinal cord injury. Alternatively, a thin layer of cortical bone can be left and a 1 mm Kerrison rongeur can be used to remove this final layer. Once the troughs are completed bilaterally, a combination of a towel clamp to grip the posterior elements, and a curved curette or a Penfield 4 to release the adhesions is used to remove the lamina en bloc. A pedicle-to-pedicle decompression should be performed to ensure the neural elements are completely decompressed. Once the decompression is completed, it is necessary to prepare the fusion bed. This is done by making sure the entire facet capsules as well as any visible cartilaginous endplate have been removed at each level. In addition, the dorsal aspect of the facet can be decorticated.
Step 5: Placement of the Lateral Mass Screws Following the decompression and preparation of the fusion bed, a ball-tipped probe can be used to identify the tracks for the lateral mass screws.
Volume 28, Number 7, August 2015
When placing the lateral mass screws care must be taken to ensure that they are inserted in the same trajectory as the holes so as to not fracture the lateral mass (Fig. 5). Once all of the screws are placed, the position of the head may need to be adjusted to ensure that the cervical spine is fused in the appropriate alignment. This can be done by changing the traction weights from the flexion vector to the extension vector on the Gardner-Wells tongs. Once the alignment has been evaluated, the rods are placed and secured. A lateral radiograph can be used to verify the alignment. Lastly, bone graft (commonly local autograft from the decompression) is placed in the facets as well as over the dorsal aspect of the lateral masses.
POSTOPERATIVE PROTOCOL The postoperative protocol is somewhat determined by the indication for the surgery; however, for the majority of cases, patients are instructed to wear a hard cervical collar for 6–12 weeks postoperatively. In almost all cases a deep drain is placed, and it is generally removed on postoperative day 2. A multilayer wound closure is critical with reapproximation of the muscle and reattachment of the fascia to any remaining bony elements. Smoking and nonsteroidal anti-inflammatory medications should be avoided for at least 6 weeks.
Complications C5 palsy J C5 nerve root palsies are one of the most common complications after posterior cervical fusions. Many risk factors have been associated with this complication, including preexisting foraminal stenosis, wide C5 laminectomies, and significant spinal cord drift. It is currently unclear whether a C5 foraminotomy can help prevent this complication. J Most patients make a full recovery; however, it may take up to 2 years. Nerve root injury J This can occur if the lateral mass screw is started to caudal or not angled sufficiently cephalad. Any patients with new radicular symptoms postoperatively (even in the C5 distribution) should undergo advanced imaging to ensure that a screw is not malpositioned. Vascular injury
FIGURE 5. Photograph demonstrating the appropriate position of 4 lateral mass screws.
262 | www.jspinaldisorders.com
J A vertebral artery injury is extremely rare; however, it is critical that the surgeon review the vascular anatomy before every cervical case to Copyright
r
2015 Wolters Kluwer Health, Inc. All rights reserved.
Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.
J Spinal Disord Tech
Volume 28, Number 7, August 2015
ensure that there is not an aberrant vertebral artery. If a vascular injury occurs during preparation of the screw track, hemostasis can often be achieved by packing the hole with bone wax. Anesthesia and vascular surgery should be notified immediately if this complication occurs.
PEARLS AND PITFALLS Lateral mass screws should be angled lateral and superiorly to obtain solid bony fixation and avoid the exiting nerve root and the vertebral artery.
Copyright
r
2015 Wolters Kluwer Health, Inc. All rights reserved.
Lateral Mass Fixation in the Cervical Spine
If you are having a difficult time determining your cephalad angle, you can decorticate the facets. Your angle should be approximately the angle of the facet. If the C7 lateral mass is small, consider a C7 pedicle screw. Avoid disrupting the attachments to the C2 and C7 spinous processes. Many of the patients undergoing a posterior cervical fusion have significant spinal cord compression. It is critical that anesthesia and the nursing staff are aware of this, and every precaution is taken to prevent a spinal cord injury during intubation and positioning.
www.jspinaldisorders.com |
Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved.
263
