The goals of cervical deformity surgery should include deformity correction, restoration of horizontal gaze, decompression of neural elements, spinal stabilization with a biomechanically sound construct, and meticulous arthrodesis technique to prevent pseudoarthrosis and minimizing surgical complications. Many different surgical options exist, including anterior, posterior, or combined approaches. However, selecting the correct approach that ensures the optimal clinical outcome can be challenging and often controversial. In this last part of the cervical deformity review series, various posterior deformity correction techniques, including posterior cervical instrumentation and fusion with or without laminectomy, Smith-Petersen osteotomy (SPO), and pedicle subtraction osteotomy (PSO), are discussed in detail, along with an overview of clinical outcome and complications.
POSTERIOR SURGICAL TECHNIQUES
Posterior Instrumentation and Fusion with or without Decompression
Posterior cervical instrumentation and fusion is a procedure familiar to all spine surgeons. In the setting of cervical deformity correction, it can be used to correct a flexible curve without ventral compression or, much more often, as a part of circumferential fixation for cervical deformity correction.
The patient is brought into the operating room and undergoes general endotracheal anesthesia. One of the senior authors (VCT) secures the head in the Mayfield holder (Integra Life Sciences, Plainsboro, New Jersey), with the patient positioned on laminectomy rolls. The other senior author (KDR) prefers to use a Jackson table with bivector Gardner-Wells tongs (Zimmer Biomet, Warsaw, Indiana). With this technique, 2 separate ropes are used at different stages of the operation: the horizontal rope is used to stabilize the neck in the pre-corrected position, and the second extension rope is used after the osteotomy to facilitate osteotomy closure. Fifteen to 20 pounds are placed on the rope to maintain the neck position. The table is placed in a reverse Trendelenburg position to decrease intraoperative bleeding and intraocular pressure.
A meticulous midline dissection in the amuscular and avascular raphe is then performed. One of the senior authors (KDR) prefers to divide the bifid spinous processes with a bone cutter, keeping the paraspinal muscles attached. These are tagged, facilitating bone-to-bone closure at the conclusion of the operation. This technique also prevents having to suture into muscle, which obligates necrosing the captured muscle. Subperiosteal exposure of the lamina and lateral masses is performed. Care is taken to only expose enough of the lateral masses to place lateral mass screws and no further, as beyond the lateral masses, one encounters venous plexuses that bleed profusely. A more serious complication is that the dorsal nerves innervating the paraspinal muscles may be injured and can result in substantial muscle atrophy.
In general, patients with significant posterior compression are treated with either laminectomies (VCT) or laminoplasties (KDR). During posterior cervical fusion, the facet joints are exposed and the joint cartilage is denuded with curettes or small rasps. The joint space is then packed with autologous bone chips (KDR). Alternatively, machined interfacet allograft spacers can be used to augment posterior cervical fusion and the technique and advantages have been described elsewhere in literature.1 Spinal fixation at C2 can be achieved by screws placed in the pars, pedicle, or lamina. Standard lateral mass screws are used for fixation from C3 to C6; whereas pedicle screws are typically used for fixation at T1 and T2. Fixation into C7 is typically not performed to facilitate screw fixation into T1. Additional sublaminar hooks or translaminar screws can be used at the caudal part of the construct to reinforce the screw fixation if necessary.
Even with lordotic rods and compression, it is not uncommon to achieve inadequate lordosis, especially if the construct includes the upper thoracic spine.
To avoid inadequate correction, one of the senior authors (KDR) has described the use of spinous process cables or a third rod fixed into the spinous processes of C2 and thoracic vertebrae with subsequent compression to create additional lordosis. The spinous processes should be no more than 1 cm apart to create adequate lordosis. However, excessive extension of the neck during this maneuver may cause iatrogenic compression of the nerve roots, especially if there is radiographic foraminal stenosis preoperatively. Therefore, it may be necessary to perform prophylactic foraminotomies in these situations. If there are flexible segments with foraminal stenosis, the patient can be placed supine in the clinic and asked to maintain the neck extension for 10 to 15 min. If the patient develops any numbness, paresthesia, pain, or weakness in the arms, then a prophylactic foraminotomy should be performed.
After completing the instrumentation, the surgical cavity is copiously irrigated and the bony surfaces are thoroughly decorticated with subsequent bone graft placement. Vancomycin powder (1 g) is placed in the wound to decrease the risk of surgical wound infection. A deep subfascial drain is placed and a superficial subdermal drain is added if the adipose layer is greater than 3 cm. The wound is then closed in multilayered fashion with interrupted sutures spaced about 1 cm apart. Meticulous hemostasis is achieved with bipolar electrocautery, thrombin-soaked gelfoam, and other hemostatic agents. One senior author (VCT) only closes with fascial sutures to avoid muscle necrosis; the other senior author (KDR) prefers to re-approximate the muscles by suturing around the small bony fragments created during the initial exposure from dividing the bifid spinous processes.
The SPO was originally described in 1945 to treat rigid deformity due to ankylosing spondylitis.2 An SPO performed at multiple levels are also known as a “Ponte osteotomy,” which was originally described in 1984 for treatment of Scheuermann's kyphosis.3 Ponte osteotomies rely on residual anterior column mobility to obtain kyphosis correction.
Performing cervical SPOs involves completely resecting both the superior and inferior articulating facets along with removal of the ligamentum flavum, lamina, and spinous processes at the indexed level. The pedicles and vertebral body are left intact. The vertebral arteries run in the foramen transversarium just anterior to the exiting nerve roots. After completing the SPO, kyphotic correction can be obtained by compressing posteriorly. The wound is then closed in the standard fashion as previously described. Iatrogenic nerve root compression can occur during correction from the superior articular facet impinging on the root or the pedicles compressing the root in a rostral-caudal direction. The lateral masses may not be robust enough to allow for application of significant compressive forces, and pedicle fixation should be considered in these situations.
Pedicle Subtraction Osteotomy
Cervical PSO is a powerful tool for correction of severe fixed cervical kyphotic deformities, especially in cases of ankylosing spondylitis or iatrogenic deformity from prior cervical spine surgeries. Patients may present with inability to maintain horizontal gaze, dysphagia, respiratory compromise, neurological deficits, or persistent and severe pain. Cervical osteotomies were traditionally performed in seated position, with the patient awake during surgery to provide immediate and frequent intraoperative neurological function testing. With modern neurological monitoring and anesthesia techniques, cervical PSO can be performed safely with general anesthesia in the prone position in experienced hands. Cervical PSO techniques have been described by one of the senior authors (KDR) previously.4
After general endotracheal anesthesia, the patient is placed in the prone position onto a Jackson table with a chest bolster, hip and thigh pads, along with some pillows to support the legs. The head is secured using a Mayfield head holder or Gardner-Wells tongs with ∼15 lbs of weight. Furthermore, the table is positioned in maximum amount of reverse Trendelenburg, which allows the surgeon to operate in a more level surgical field and minimizes blood loss from both decreased central venous pressure, as well as pooling of blood in the legs and abdomen. In patients with significant thoracolumbar kyphosis, additional pillows can be used to provide extra padding and to provide stable positioning for surgery.
If Gardener-Wells tongs are used, then 2 ropes are attached to the tongs: the horizontal rope is used to stabilize the neck in-line with deformity before any correction is made, and the second extension rope is used to facilitate osteotomy closure and keeps the head in an extended position after kyphosis correction (Figure 1). The anesthesia team can help to switch the weights from the flexion rope to the extension rope while the surgeon holds the Gardner-wells tongs through the sterile drape at the beginning of the osteotomy closure. The extension moment from the extension rope facilitates the deformity correction.
Alternatively, if a Mayfield head clamp is utilized, then the clamp is released and the head gently extended after the PSO is performed to complete the osteotomy closure. The cervicothoracic junction is suitable for PSO for various reasons including: (1) the relatively safe location of the vertebral artery, which is anterior to the C7 transverse process; (2) relatively larger size of the spinal canal and mobility of the spinal cord at C7–T1; (3) and in the event of C8 nerve root injury, there is usually a reasonable preservation of hand function. Of note, the vertebral artery can take an aberrant course and ascend via the C7 foramen transversarium in up to 5% of the patients. Therefore, it is critical to carefully examine the preoperative images to check for any vascular anomaly. If the vertebral artery enters the foramen transversarium at C7, then the PSO can be performed at T1.
After prepping and draping, the cervical and upper thoracic spine is exposed in the standard fashion via a midline incision. Keeping the dissection directly midline is key in minimizing blood loss and tissue trauma during posterior cervical exposure. The proximal extent of exposure depends on the intended upper level of instrumentation. Every effort should be made to preserve the motion at the occipitocervical and atlantoaxial joints, if possible. If the entire cervical spine is already completely ankylosed, then extending instrumentation to the occiput can provide strong proximal fixation due to the thick bone found at the external occipital protuberance. Typically, the distal end of the construct is at either T3, T4, or T5, because it is preferable to have 3 to 4 levels of fixation points distal to the osteotomy site.
After adequate exposure, instrumentation is the next step prior to the osteotomy. C2 pedicle, pars, or translaminar screws can be placed if C2 fixation is needed. Lateral mass screws are inserted in the standard fashion at C3, C4, C5; pedicle screws are placed bilaterally from T2 to T4. There is often not enough space available for both C6 and T1 screws after PSO closure, therefore if C6 screw is placed then T1 screw will be omitted, and vice versa. The choice of which screw to include in the construct depends on whether the cranial or caudal end of the osteotomy requires more fixation points. After all screws are placed, the cervical spine is connected to the upper thoracic spine by using hinged rods to avoid the need for connectors. Rod placement is significantly easier if the screws are placed in a straight line, and it also avoids unnecessary rod bending and manipulation that can weaken the rod.
To begin the PSO, a complete C7 laminectomy is performed (Figure 2). The lamina and spinous process are removed en bloc and can be used as autograft. Subsequently, a high-speed burr is used to remove the caudal half of the C6 lamina and the cranial half of the T1 lamina, while the C6 and T1 spinous processes are left intact. Next, using a combination of the high-speed burr and a Leksell rongeur, the C7 lateral masses are carefully removed. The caudal aspect of the C6 inferior facet and the cranial aspect of the T1 superior facet are also removed. In addition, the pedicles of T1 must be exposed to ensure there is no residue superior articular process cranial to the T1 pedicle. Iatrogenic C8 nerve root compression can occur if there is any residue superior articular process during PSO closure. The nerve roots at C7 and C8 are completely exposed and visualized, with the C7 pedicle separating the two roots (Figure 3).
Next, small cottonoid patties are used to cover thecal sac and the C7, C8 roots. Penfield dissectors are then used to gently retract them away. The C7 pedicles are then carefully decancellized with the high-speed burr while leaving the C7 pedicle walls intact. Subsequent decancellization of vertebral body is initiated by passing the high-speed through the pedicles into the C7 vertebral body (Figure 4). After adequate vertebral body decancellization, the remaining pedicle walls are removed using pituitary rongeurs and fine reverse-angled curettes. Of note, the pedicle walls must be completely removed to avoid compression of C7 nerve roots during PSO closure. A Woodson elevator can be used to define the plane between the ventral dura and posterior vertebral wall. Subsequently, a cavity in the posterior superior portion of the vertebral body is created by using small round tamps and reverse-angled curettes (Figure 5). The cancellous bone in the vertebral body is then either pushed anteriorly or removed through the pedicle channels. Some authors have described using sequential taps for vertebral body decancellization during cervical PSO with good results.5
Finally, using Woodson and angled dural elevators, the posterior vertebral wall is impacted into the previously created cavity in the C7 vertebral body. This step should be achieved with relative ease if adequate decancellation has been completed. If the posterior cortex does not break easily, then additional cancellous bone must be removed from within the posterior vertebral body. Thrombin-soaked Gelfoam (Pfizer, New York, New York) or Surgiflo (Ethicon, Somerville, New Jersey) is then used to achieve hemostasis prior to PSO closure and deformity correction.
Next, the hinged rod is fixed into the thoracic pedicle screws. For the PSO closure, the surgeon carefully extends the neck by pulling on the Gardner-Wells tongs through the sterile drape (Figure 6). In the meantime, the traction weight is also switched to the extension rope. The osteotomy closure should not require much force if the bony resection is adequate (Figure 7). If the neck can’t be easily extended, then additional bone resection is required from the ventral portion of C7 vertebral body. During and after PSO closure, the C7 and C8 roots must be carefully examined to ensure there are no signs of nerve impingement. If the C7 and C8 roots are not completely free, then additional bony resection of the C6 inferior facet and the T1 superior facet may be required. As the neck is extended, the rostral part of the rod should engage the cervical lateral mass screws and C2 pars/pedicle screws. After adequate amount of correction is obtained, the rod is secured to the screws with locking caps. Neuromonitoring data are checked continuously throughout the case, but it is especially important during PSO closure to ensure that there is no iatrogenic injury to the spinal cord or nerve roots.
Lateral x-rays are then obtained to assess the amount of correction, as well as the overall cervical spine alignment. To maximize the chance of solid arthrodesis, local bone harvested throughout the procedure is collected and used as autograft. In addition, the C7 spinous process can be split in half in the sagittal plane, and then placed along the decorticated spinous processes of C6 and T1, secured in place with a double-braided titanium cable. Additional bone graft can be harvested from an upper thoracic spinous process to fill the gap between the C6 and T1 lateral masses if needed. Finally, the remainder of the local bone graft is used to fill the defect between the C6 and T1 laminae.
Lastly, the soft tissues are closed in a multi layered fashion to minimize dead space and to decrease the risk for infection. If there is excessive amount of redundant tissue after deformity correction, an ellipse of full-thickness skin can be cut out to eliminate the redundancy. Surgical drains are usually left in place and hemostasis is assured as each layer is closed. Postoperatively, patients can be immobilized in a hard cervical collar to facilitate fusion.
CLINICAL OUTCOME AND COMPLICATIONS
Complications from the anterior and posterior approaches to the spine include dysphagia, pseudoarthrosis, hardware failure, vocal cord paralysis, tracheal or esophageal injury, vertebral artery injury, spinal cord or nerve root injury, cerebral spinal fluid leak, and wound complications. In addition to these approach-related complications, posterior cervical osteotomies can cause additional complications, including both temporary and permanent neurological deficits.4 The overall rate of neurological injury has been reported to be up to 23% in cervical deformity correction.6 Specifically, C8 nerve root palsy appeared to be the most common complication during C7 PSO; however, these neurological complications are transient and improved with time in most cases.7
Etame et al8 reviewed the literature on long-term clinical outcome following surgical treatment of cervical kyphotic deformity. They found 14 retrospective studies with a total of 399 patients who had undergone cervical deformity surgery. The previously reported mortality rates ranged from 3.1% to 6.7%, major medical complications ranged from 3.1% to 44.4%, the rate of neurological complication rate was about 13.5%. Despite these complications, they found high patient satisfaction rate from these studies.
Traynelis reported a series of 27 patients undergoing total subaxial reconstruction with a minimum follow-up of 12 mo. The average follow-up period was 26 mo for all patients. One patient had died 6 wk following a non-complicated surgery and postoperative course. Five patients developed pneumonia, 1 had a minor pulmonary embolism, and 2 patients had wound infections. There was no patient with new postoperative neurological deficits. There was 1 single case of C8 radiculopathy that occurred 6 wk after surgery. At the final follow-up, no patient complained of dysphagia and all patients developed solid fusions at the treated levels.
Kim et al9 reported a series of 38 patients who underwent anterior cervical osteotomy with or without posterior SPOs with an average follow-up of 3.4 yr (range, 1.0–6.3 yr). The mean angular correction was 23° and 33° for the anterior osteotomy with and without posterior PSO, respectively. There was less average translational correction in patients with anterior osteotomy only compared with patients with anterior osteotomy + PSO (1.3 vs 3.7 cm, P = .03). The neck disability index improved in all groups with similar scores (20 vs 19.7, P = .78). There were no new postoperative neurological deficits.
Most recently, Smith et al10 conducted a prospective multicenter study consisted of 78 patients who underwent cervical deformity surgery. They found that the overall complication rate was 43.6%, including 28.2% of patients with at least 1 minor complication, and 24.4% of patients with at least 1 major complication. Dysphagia (11.5%), postoperative C5 palsy (6.4%), surgical site infection (6.4%), and respiratory failure (5.1%) were among the most common complications. There was 1 (1.3%) mortality. The combined approach (anterior-posterior or posterior-anterior-posterior) had the highest early complication rate (79.3%), followed by posterior only (68.4%), followed by anterior-only (27.3%).
Cervical spine deformity can significantly impair a patient's quality of life. Various surgical strategies and techniques exist to treat this challenging condition. Regardless of the specific surgical approach used, a solid understanding of spine biomechanics, a thorough preoperative neurological examination, a detailed review of preoperative images, careful surgical planning, and meticulous surgical techniques are essential to ensure the best clinical outcome in cervical deformity correction.
Vincent C Traynelis is a consultant for and a patent holder with Medtronic. He receives institutional fellowship support from Globus. K Daniel Riew receives royalties from Biomet and Medtronic, receives grants from AOSpine, Cerapedics, and Medtronic, and receives honorarium from NASS and AOSpine. The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.
1. Tan LA, Straus DC, Traynelis VC. Cervical interfacet spacers and maintenance of cervical lordosis. J Neurosurg Spine. 2015;22(5):466-469.
2. Smith-Petersen MN, Larson CB, Aufranc OE. Osteotomy of the spine for correction of flexion deformity in rheumatoid arthritis. J Bone Jt Surg. 1945;27:1-11.
3. Ponte A, Vero B, Siccardi GL. Surgical treatment of Scheuermann's hyperkyphosis. In: Bologna RB, editor. Bologna, Italy: Aulo Gaggi; 1984:75-80.
4. Wollowick AL, Kelly MP, Riew KD. Pedicle subtraction osteotomy in the cervical spine.Spine. 2012;37(5):E342-E348.
5. Deviren V, Scheer JK, Ames CP. Technique of cervicothoracic junction pedicle subtraction osteotomy for cervical sagittal imbalance: report of 11 cases. J Neurosurg Spine. 2011;15(2):174-181.
6. Etame AB, Than KD, Wang AC, La Marca F, Park P. Surgical management of symptomatic cervical or cervicothoracic kyphosis due to ankylosing spondylitis. Spine. 2008;33(16):E559-E564.
7. Tokala DP, Lam KS, Freeman BJ, Webb JK. C7 decancellisation closing wedge osteotomy for the correction of fixed cervico-thoracic kyphosis. Eur Spine J. 2007;16(9):1471-1478.
8. Etame AB, Wang AC, Than KD, La Marca F, Park P. Outcomes after surgery for cervical spine deformity: review of the literature. Neurosurg Focus. 2010;28(3):E14.
9. Kim HJ, Piyaskulkaew C, Riew KD. Anterior cervical osteotomy for fixed cervical deformities. Spine. 2014;39(21):1751-1757.
10. Smith JS, Ramchandran S, Lafage V, et al. Prospective multicenter assessment of early complication rates associated with adult cervical deformity surgery in 78 patients. Neurosurgery. 2016;79(3):378-388.
In this manuscript, the authors present an excellent experience-driven discussion of posterior correction techniques for cervical spine kyphotic deformities. The strengths and weaknesses of each technique are described, along with clinical pearls for avoiding common pitfalls. This manuscript is of interest to all spinal surgeons and should be required reading for those new to the field.