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Iatrogenic Cervical Deformity
Iatrogenic Cervical Deformity John M. Rhee, MD Iatrogenic deformities of the cervical spine are not uncommon and may be associated with either anterior or posterior operations. To minimize the “footprints” left behind from surgical interventions on the cervical spine, it is imperative not only to treat the present disorder but also avoid sowing the seeds of future problems, or at least create a milieu in which they can be easily addressed should they occur. Doing so requires attention to either correcting or preventing cervical deformities whenever possible during the index operation because the optimal method of treating iatrogenic cervical deformity remains its prevention. In treating established deformities, surgical decision making hinges on whether the deformity is rigid, flexible, or fused. Semin Spine Surg 23:173-180 © 2011 Elsevier Inc. All rights reserved. KEYWORDS cervical spine, deformity, kyphosis, postlaminectomy kyphosis, cervical fusion
I
atrogenic causes are not uncommon etiologies for cervical spine deformity. Although subtle degrees of malalignment after surgery may never be clinically evident, greater deformities may, depending on magnitude, create adverse consequences. These consequences can range from the obvious— such as postlaminectomy kyphosis with deformity and recurrent myelopathy—to the more subtle—such as the patient who develops multilevel cervical myelopathy in the setting of overall kyphosis rather than lordosis because of previous anterior cervical diskectomies having been performed without fusion (Fig. 1). In the latter instance, even if the index operation appeared to be a success on the basis of relief of neurologic symptoms at the time, the resultant deformity may now require a more complex surgical solution than if the patient had been fused in a lordotic position. For example, instead of a relatively straightforward laminoplasty to relieve the neural compression, a more complex fusion-based operation may be necessary to treat both cord compression and kyphosis. To minimize the “footprints” left behind from interventions on the cervical spine, it is imperative not only to treat the present disorder but also avoid sowing the seeds of future problems, or at least create a milieu in which they can be easily addressed should they occur. Doing so requires attention to either correcting or preventing cervical deformities
Department of Orthopaedic Surgery, Emory Spine Center, Emory University School of Medicine, Atlanta, GA. Address reprint requests to John M. Rhee, MD, Department of Orthopaedic Surgery, Emory Spine Center, Emory University School of Medicine, 59 Executive Park South, Suite 3000, Atlanta, GA 30329. E-mail: jmrhee@ emory.edu
1040-7383/$-see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1053/j.semss.2011.04.008
whenever possible during the index operation because the optimal method of treating iatrogenic cervical deformity remains its prevention.
Iatrogenic Deformity Associated with Anterior Cervical Surgery Anterior Cervical Diskectomy Without Fusion Performing anterior cervical diskectomy alone without fusion will virtually guarantee some degree of postoperative segmental kyphosis, even if the segment ultimately goes on to autofuse as it does in the majority of instances (Fig. 1). Admittedly, the incidence of developing clinically relevant kyphosis in the long term with the use of this approach is unknown, and the short-term results of diskectomy alone are generally reported to be good in the setting of adequate decompression.1 However, common sense and clinical experience suggest that avoiding procedures clearly associated with segmental kyphosis would be in the best long-term interest of a patient’s cervical spine—regardless of short-term improvements— because local kyphosis is more likely to predispose to global kyphosis over time. Thus, the largely historical practice of performing anterior cervical diskectomy without fusion is rarely indicated.
Anterior Cervical Diskectomy and Fusion Without Plating Unplated anterior cervical diskectomy and fusion (ACDF) is more likely to settle into kyphosis or at least lose lordosis than 173
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ever, very little is known about the fusion rates, alignment, and outcomes achieved with these implants.
Graft-Related Factors Potentially Causing Deformity The type of graft material used may also influence the likelihood of postoperative kyphosis. Generally, the likelihood of graft collapse with allograft increases as follows: irradiated, freeze-dried, and then fresh-frozen.7 Cancellous-based allografts, such as dense cancellous allografts, have also demonstrated greater propensity to resorption during healing than purely cortical grafts and thus may be more prone to kyphosis over time.8 The size of the graft may also influence the likelihood of segmental kyphosis. The graft should be large enough to gently distract the interspace, such that with loading in the upright position some settling can be accommodated without developing kyphosis. If a wide diskectomy is performed, wider or multiple grafts can be placed side by side in the disk space to improve surface contact, better distribute load across the endplates, and lessen the likelihood of settling and collapse (Fig. 4). In general for most ACDFs, a graft height 2-3 Figure 1 ACD without fusion: lateral radiograph of a 55-year-old man who had undergone an anterior cervical diskectomy at C56 without fusion many years previously. The segment has autofused but in segmental kyphosis (note also the widening of the gap between the spinous processes between C5 and C6). The overall alignment of the cervical spine is also somewhat kyphotic.
their plated counterparts (Fig. 2).2 Multilevel unplated fusions are particularly prone to result in overall kyphosis as the settling of multiple grafts magnifies the segmental kyphosis that develops at each level. Although the use of a plate does not absolutely guarantee the avoidance of kyphosis, most would agree that anterior cervical plates decrease the likelihood of developing not only radiographic (ie, clinically silent) but also clinically evident postoperative kyphoses, particularly in multilevel cases.3 These benefits of using plates must be tempered by meticulous placement to avoid plate-associated complications, such as screw and plate migration, as well as injury to adjacent disk spaces.4
ACDF with Stand-Alone Cages Recently, to avoid plate-related complications, cervical interbody cages that can be used as stand-alone devices have become more popular. However, several authors have noted the development of subsidence and kyphotic malalignment with stand-alone cervical cages,5,6 even when the bony endplates were not removed.5 The benefits of plating, at least to avoid kyphosis, seem inescapable, especially in cases in which the endplates are removed or in patients with poor bone quality. Newer cage designs allow for screw fixation through the cage and are touted as being zero-profile (Fig. 3). When these devices are used, adjacent segments can also be fused without the removal of previously placed plates. How-
Figure 2 ACDF without plate: lateral radiograph of a 67-year-old woman who had undergone an unplated C67 ACDF in the remote past with the use of an autologous iliac crest bone graft. Note that the segment has fused in a neutral to slightly kyphotic alignment.
Iatrogenic cervical deformity
175 kyphosis to develop as the construct settles over time, particularly in those patients with preexisting kyphosis (Fig. 5). Large clinical series are needed to determine the sagittal plane consequences of dynamic plates in the cervical spine.
Corpectomy
Figure 3 Zero profile cage: This patient presented with residual cord compression and nonunion after ACDF with a zero profile cage device, which allows for screw fixation into the endplates. The fixation is purported to provide additional stability versus stand-alone cages without screws, but few data are currently available on the efficacy of these devices in preserving alignment and achieving fusion.
mm greater than that of the preoperative disk will be sufficient to gently tension the interspace and provide a tight fit without overdistraction. It is also important to try to preserve the bony endplates as much as possible whenever doing ACDF to prevent subsidence and potential segmental kyphosis. Although the anterior and posterior “lips” of the cephalad endplate can be flattened to ensure good graft-host contact and decompress the floor of the spinal canal, respectively, the central portion of the endplate should be preserved to provide a structurally sound surface on which the graft can rest and resist significant subsidence.
Dynamic Cervical Plates Dynamic plates have been advocated as biomechanically favorable alternatives to rigid plating. Dynamic plates have been shown in biomechanical experiments to allow for better load sharing across the interbody graft vs rigid plates, which are more likely to stress shield the graft, particularly when the graft is undersized and graft-host contact is suboptimal. However, it is unclear as to whether dynamism leads to better clinical outcomes or fusion rates. In addition, one potential downside to dynamism may be a tendency for segmental
Anterior-only corpectomy constructs will generally demonstrate greater likelihood of losing lordosis than diskectomy constructs because a normally lordotic area of the spine is replaced by a relatively straight graft (bone or cage). The longer the corpectomy construct, the less lordosis that can be restored or preserved. Any negative consequences of endplate removal on sagittal plane alignment will also be magnified with corpectomy vs diskectomy. Although plating may be beneficial in 1- or perhaps 2-level corpectomy cases, plating multilevel corpectomies appears biomechanically unfavorable and is associated with high rates of graft displacement (up to 50% in 1 series of 3 level corpectomies).9 Furthermore, even if graft and plate failure do not occur, plates do not appear to protect against kyphosis with corpectomy constructs to the extent that they can with diskectomies. Finally, if one chooses to avoid complications of spanning plates across multilevel corpectomies by opting for unplated surgery instead, the spine will almost certainly settle into kyphosis or at best neutral alignment. The use of small “antikick” plates at the end of a construct to prevent kick out may have similar advantages in allowing settling of the construct and therefore better union rates than spanning plates, but they will, like their unplated counterparts, tend to heal in kyphosis or at best neutral. If multilevel corpectomies are neurologically necessary, supplemental posterior fixation and fusion should be considered. A circumferential approach should also be strongly considered in patients with poor bone quality (eg, osteoporosis, renal failure, infections, tumors), severe kyphosis preoperatively, or those with neuromuscular disorders leading to poor muscle control.
Malalignment Errors Introduced During Posterior Cervical Surgery Positioning Issues With posterior surgery, it is important to ensure that the spine is placed into a favorable alignment before fusion. However, a competing priority is that a neutral or slightly kyphotic alignment is helpful during decompression by decreasing the shingling or overlap of adjacent lamina onto each other and by enlarging the spinal canal. Therefore, in certain cases of decompression and fusion, it may be helpful to change the position of the neck from relative flexion during the decompression to the final desired position before securing the rods. Although proper positioning during posterior fusion is critical to maintaining sagittal plane alignment, the ability to actually correct kyphosis with instrumented posterior fusion by simply changing the neck position can be limited depending on its severity. If the kyphosis is flexible, a fair amount of correction may be obtained by positioning, but if extensive
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Figure 4 Double graft. (A) lateral radiograph status post 2 level ACDF C5-7. (B) Axial computed tomography scan through C67 demonstrates that 2 grafts were rotated 90° to the usual orientation and inserted to better fill the large disk space and provide better load sharing across the construct, which may then better preserve alignment with less segmental settling.
spondylosis coexists, the stiff anterior disk spaces may resist realignment. Even when passive correction of kyphosis is achievable by intraoperative positioning, concern exists regarding the loss of correction and kyphosis recurrence postoperatively as the spine settles into its former position in the absence of anterior column support and fixation. As it does so, associated proximal pullout of the posterior implants may occur. To avoid such complications, circumferential surgery
or corrective osteotomies should be considered depending on the nature and severity of the kyphosis.
Postfacetectomy Kyphosis Postoperative instability resulting from over aggressive facetecomy typically manifests as segmental spondylolisthesis with local kyphosis that may then progress to overall kypho-
Figure 5 Dynamic cervical plate. (A) preoperative lateral radiograph of a 36-year-old man with C56 cervical radiculopathy. Note the presence of segmental kyphosis through C56 preoperatively. (B) Postoperative day 1 radiograph after C56 ACDF with a dynamic cervical plate. (C) Significant settling has occurred at 6 months postoperatively because of excessive dynamism in the setting of a preoperative kyphosis.
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Figure 6 Postlaminoplasty kyphosis. (A) Kyphosis can develop after laminoplasty as well as laminectomy, but it tends not to be as severe. This patient presented having undergone previous French-door laminoplasty for myelopathy associated with ossification of the posterior longitudinal ligament (OPLL). As kyphosis developed, her myelopathy recurred. (B) Axial computed tomography myelogram demonstrates spinal cord compression from OPLL exacerbated by the kyphotic alignment. (C) Patient was treated with C5 and C6 corpectomy and removal of OPLL, resulting in elimination of her neurologic symptoms as shown in this 3-month postoperative radiograph. Because the endplates of C4 and C7 are relatively parallel, a straight strut graft could be inserted with low risk of distal graft extrusion (ie, no shear forces tending to cause distal kick out at C7). Preservation of the endplates along with the patient’s excellent bone quality allowed for anterior-only fixation without significant pistoning of the graft and some improvement in overall alignment.
sis as well. Although more commonly encountered when foraminotomies are performed in conjunction with laminectomies, such instability can occur even with foraminotomy alone, even minimally invasive approaches, if the appropriate anatomic boundaries are not appreciated.
Postlaminectomy Kyphosis Postlaminectomy kyphosis is a well-known complication of multilevel laminectomy, particularly in growing children10,11 but also in adults. Mikawa et al12 reported that 52% of patients demonstrated changes in cervical alignment after multilevel laminectomy, with 14% developing kyphosis. Guigui et al13 noted that 31% had a change in alignment vs preoperative, with 25% having increased kyphosis. Risk factors for kyphosis include younger age at time of surgery, 4 or more levels laminectomized, surgery involving the C2 lamina and its muscle attachments, performance of associated facetectomies, and increased preoperative range of motion.13,14 Preexisting lack of lordosis may be the most important risk factor because the posterior cervical musculature in such patients must already combat the mechanically unfavorable consequences of having the weight of the head fall anterior to the sagittal vertical axis of the cervical spine. Further compromising the extensor musculature and the posterior tension band (supra and inter spinous ligaments, ligamentum flavum, facet capsules) under these circumstances can then lead to a vicious cycle of kyphosis. Many patients who develop postlaminectomy kyphosis have initial improvement in their index neurologic symptoms with the decompressive operation. However, as the deforming forces progress and kyphosis worsens, they may complain of axial neck pain because of muscle fatigue, which can then advance to recurrent myelopathy as the spinal cord
drapes over the anterior structures. The uncovered dural sac may also become compressed posteriorly by the development of a postlaminectomy membrane. With continued progression, kyphosis can lead to loss of forward gaze, difficulty with swallowing and eating, and the need to prop up the neck with the upper extremities. The mainstay of treating postlaminectomy kyphosis is in its prevention. Currently, there are few if any indications for a multilevel laminectomy alone. In myelopathic patients who have favorable preexisting alignment, multilevel cord compression, and do not require fusion, laminoplasty is an alternative nonfusion operation that better preserves alignment and neurologic function than laminectomy. In those requiring posterior surgery but who present with unfavorable preexisting alignment, laminectomy with fusion or a combined anterior–posterior approach is recommended.
Postlaminoplasty Kyphosis Although laminoplasty was initially designed to prevent the development of postlaminectomy kyphosis, some loss of lordosis also occurs with laminoplasty as well (Fig. 6). In general, however, the loss of lordosis after laminoplasty tends to be less than that seen after laminectomy and much less commonly of clinical significance. Suk et al15 reported on average 5° loss of lordosis after laminoplasty, with 10.6% of patients developing an average of 12° of kyphosis. As one would predict, those who began with a lesser degree of lordosis (⬍10° preoperative) were more likely to develop kyphosis, as were those demonstrating more flexion than extension on preoperative dynamic radiographs. Loss of lordosis with laminoplasty may be lessened by sparing C2 and its muscle attachments. Takeshita et al16 found that the decrease in lordosis from C2-C7 was 8.3° if C2 was split during lamino-
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Figure 7 Flexible postlaminectomy kyphosis. (A) 43-year-old woman who presented status after C56 ACDF followed by a C3-6 laminectomy, resulting in mild cervical kyphosis and residual anterior spinal cord compression at C34 and C45. (B) She was treated with revision ACDF at C34 and C45, with improvement noted in overall alignment.
plasty, 5.2° with a dome-like laminotomy of C2, but only 1.5° if C2 was left completely intact. The importance of preserving C7 and its attachments is less clear. Kowatari et al17 found no difference in axial pain, Japanese Orthopaedic Association scores, or sagittal alignment whether the C7 attachments were preserved.
Surgical Strategies for Correction of Iatrogenic Deformity In symptomatic patients with significant iatrogenic kyphosis, a surgical approach is generally required, particularly if there is associated myelopathy. Extensor muscle strengthening with physical therapy may be useful in mild cases but will generally be insufficient in treating more severe cases. Goals of treatment include the following: (1) correction and fusion of deformity, ideally with a normalized sagittal vertical axis; (2) neurologic decompression; and (3) pain relief. The optimal surgical strategy will depend on whether the deformity is flexible, fixed, or fused.
Flexible and Passively Correctable Kyphosis In milder cases of postlaminectomy kyphosis, when the deformity is flexible and passively correctable, it may be reduced into the desired alignment and fused either anteriorly or posteriorly (Fig. 7). Anterior-only surgery has several advantages, including lower rates of morbidity, direct decompression of a spinal cord draped over a kyphos, the avoidance of additional surgery through a revision approach posteri-
orly, preservation of the posterior musculature that has already been compromised, and restoration of height to the anterior column through the use of structural grafts. However, the disadvantages of anterior-only surgery include relatively less secure fixation in the vertebral bodies vs the dorsal elements (especially in osteopenic patients) and the inability of anterior plates to restore the posterior tension band. Although anterior plates may “hold” the correction achieved through the placement of interbody grafts, they are at a relative mechanical disadvantage secondary to their action being anterior to the axis of rotation of the kyphotic deformity. Furthermore, if corpectomy is necessary to achieve neurologic decompression in the setting of a prior laminectomy, supplemental posterior instrumentation is recommended because the spine is rendered highly unstable because the 2 halves of the spine will then only be connected only by soft tissue.18 Posterior-only surgery can also be considered in this scenario of a flexible and passively correctable kyphosis. A prerequisite of posterior-only surgery is that sufficient spinal cord decompression can be achieved through realignment and restoration of lordosis in those with neurologic compression. In such patients as well as those with no neurologic compression, posterior surgery has the advantage of generally superior fixation vs anterior plates, particularly at the ends of the construct, where pedicle screws can be routinely placed into C2, C7, and the upper thoracic spine. In addition, posterior implants are at a mechanical advantage in correcting kyphosis in that they act posterior to the axis of rotation
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Figure 8 Postlaminectomy kyphosis. (A) Elderly woman status after multilevel laminectomy from C3-7 for myelopathy. She presented with severe myelopathy, neck pain, and inability to hold up her neck for horizontal gaze. Because of the severity of kyphosis as well as poor bone quality, she was treated with anterior and posterior reconstruction from C2-T2. (B) A 1-year postoperative x-ray demonstrates solid fusion and significant correction of deformity.
of the kyphotic deformity. However, posterior surgery also has disadvantages, including the need for a revision approach through scar with no dural protection because of previous laminectomy, further denervation and damage to the posterior musculature, greater perioperative pain than is typically encountered with an anterior approach, greater rates of wound infection, and relatively poor, limited surface areas for bone grafting and fusion. Furthermore, the lack of anterior column load sharing can lead to implant failure and screw pullout if the fixation is not optimal and the neck settles back towards its original kyphotic state— especially at the proximal end of the construct.
Fixed (Nonflexible) But Nonankylosed Postlaminectomy Kyphosis If the deformity is fixed but not fused, anterior-only or combined anterior release and correction followed by posterior fusion may be appropriate depending on patient bone quality and severity of kyphosis (Fig. 8). Again, a combined approach is best if multilevel anterior corpectomies are needed, whereas an anterior-only approach may suffice if multilevel diskectomies with segmental screw-plate fixation can be performed in a patient with adequate bone quality. Inability to restore the sagittal vertical axis makes loss of correction more likely because of persistence of deforming forces, and thus supplemental posterior fixation should be considered in such cases.
Fixed and Ankylosed Postlaminectomy Kyphosis If the deformity is not only fixed but also fused, then osteotomies may be required when the ankylosed segments are in such severe kyphosis that correction through the adjacent segments will not provide sufficient overall restoration of the sagittal vertical axis. Conversely, osteotomies may not be nec-
essary if the overall sagittal vertical axis can be restored by correction through the nonankylosed segments. The approach will be dictated by the location of the ankylosis. If the ankylosis is posterior, then a posterior approach should be performed first to osteotomize the area of ankylosis. Correction is obtained through the osteotomy, but supplemental anterior release and interbody grafting, followed by a second posterior approach to lock in the instrumentation (“back-front-back”) may be needed for maximal correction. If the area of ankylosis requiring correction is anterior, anterior osteotomy is performed first. Contingent upon sufficient correction and bone quality, anterior-only surgery may be performed in this setting. Otherwise, a posterior approach is performed to supplement the anterior correction. In patients demonstrating circumferential ankylosis, posterior osteotomies and establishment of fixation points, followed by anterior osteotomies and interbody grafting, followed by final posterior rod fixation and fusion will likely provide the best correction. Alternatively, a one stage pedicle subtraction osteotomy can be performed.
Conclusions The mainstay of treating iatrogenic deformity lies in its prevention. As such, there are very limited indications for performing multilevel laminectomy alone or anterior cervical diskectomy without fusion. Plating of ACDFs, particularly multilevel cases, may be helpful in preventing sagittal plane iatrogenic deformity. However, dynamic cervical plates may lead to loss of lordosis if excessive settling occurs during healing. Stand-alone anterior cervical cages may also be associated with significant settling and thus unfavorable sagittal plane consequences. When performing laminectomy with posterior fusion, the neck should be placed into a favorable alignment before locking down the instrumentation.
180 Laminoplasty better preserves alignment than laminectomy alone but loss of lordosis or even frank kyphosis can occur even with laminoplasty, especially if the preoperative alignment is not lordotic. Thus, the ideal indication for laminoplasty is in the patient preoperative lordosis. Depending on the severity of kyphosis and other factors, such as flexibility and bone quality, established iatrogenic deformities can be treated anteriorly, posteriorly, combined, or require osteotomies.
Disclosure The author is a consultant for Biomet Spine and reports royalties from Biomet Spine.
References 1. Savolainen S, Rinne J, Hernesniemi J: A prospective randomized study of anterior single-level cervical disc operations with long-term followup: Surgical fusion is unnecessary. Neurosurgery 43:51-55, 1998 2. Wang JC, McDonough PW, Endow K, et al: The effect of cervical plating on single-level anterior cervical discectomy and fusion. J Spinal Disord 12:467-471, 1999 3. Wang JC, McDonough PW, Endow KK, et al: Increased fusion rates with cervical plating for two-level anterior cervical discectomy and fusion. Spine 25:41-45, 2000 4. Park JB, Cho YS, Riew KD: Development of adjacent-level ossification in patients with an anterior cervical plate. J Bone Joint Surg Am 87:558563, 2005 5. Gercek E, Arlet V, Delisle J, et al: Subsidence of stand-alone cervical cages in anterior interbody fusion: warning. Eur Spine J 12:513-516, 2003
J.M. Rhee 6. Barsa P, Suchomel P: Factors affecting sagittal malalignment due to cage subsidence in standalone cage assisted anterior cervical fusion. Eur Spine J 16:1395-1400, 2007 7. Vaccaro AR, Cirello J: The use of allograft bone and cages in fractures of the cervical, thoracic, and lumbar spine. Clin Orthop Relat Res 394:1926, 2002 8. Rhee JM, Patel N, Yoon ST, et al: High graft resorption rates with dense cancellous allograft in anterior cervical discectomy and fusion. Spine (Phila PA) 32:2980-2984, 2007 9. Vaccaro AR, Falatyn SP, Scuderi GJ, et al: Early failure of long segment anterior cervical plate fixation. J Spinal Disord 11:410-415, 1998 10. Yasuoka S, Peterson HA, MacCarty CS: Incidence of spinal column deformity after multilevel laminectomy in children and adults. J Neurosurg 57:441-445, 1982 11. Bell DF, Walker JL, O’Connor G, et al: Spinal deformity after multiplelevel cervical laminectomy in children. Spine (Phila PA) 19:406-411, 1994 12. Mikawa Y, Shikata J, Yamamuro T: Spinal deformity and instability after multilevel cervical laminectomy. Spine 12:6-11, 1987 13. Guigui P, Benoist M, Deburge A: Spinal deformity and instability after multilevel cervical laminectomy for spondylotic myelopathy. Spine 23: 440-447, 1998 14. Katsumi Y, Honma T, Nakamura T: Analysis of cervical instability resulting from laminectomies for removal of spinal cord tumor. Spine 14:1171-1176, 1989 15. Suk KS, Kim KT, Lee JH, et al: Sagittal alignment of the cervical spine after the laminoplasty. Spine 32:E656-E660, 2007 16. Takeshita K, Seichi A, Akune T, et al: Can laminoplasty maintain the cervical alignment even when the C2 lamina is contained? Spine 30: 1294-1298, 2005 17. Kowatari K, Ueyama K, Sannohe A, et al: Preserving the C7 spinous process with its muscles attached: effect on axial symptoms after cervical laminoplasty. J Orthop Sci 14:279-284, 2009 18. Riew KD, Hilibrand AS, Palumbo MA, et al: Anterior cervical corpectomy in patients previously managed with a laminectomy: short-term complications. J Bone Joint Surg Am 81:950-957, 1999
I
atrogenic causes are not uncommon etiologies for cervical spine deformity. Although subtle degrees of malalignment after surgery may never be clinically evident, greater deformities may, depending on magnitude, create adverse consequences. These consequences can range from the obvious— such as postlaminectomy kyphosis with deformity and recurrent myelopathy—to the more subtle—such as the patient who develops multilevel cervical myelopathy in the setting of overall kyphosis rather than lordosis because of previous anterior cervical diskectomies having been performed without fusion (Fig. 1). In the latter instance, even if the index operation appeared to be a success on the basis of relief of neurologic symptoms at the time, the resultant deformity may now require a more complex surgical solution than if the patient had been fused in a lordotic position. For example, instead of a relatively straightforward laminoplasty to relieve the neural compression, a more complex fusion-based operation may be necessary to treat both cord compression and kyphosis. To minimize the “footprints” left behind from interventions on the cervical spine, it is imperative not only to treat the present disorder but also avoid sowing the seeds of future problems, or at least create a milieu in which they can be easily addressed should they occur. Doing so requires attention to either correcting or preventing cervical deformities
Department of Orthopaedic Surgery, Emory Spine Center, Emory University School of Medicine, Atlanta, GA. Address reprint requests to John M. Rhee, MD, Department of Orthopaedic Surgery, Emory Spine Center, Emory University School of Medicine, 59 Executive Park South, Suite 3000, Atlanta, GA 30329. E-mail: jmrhee@ emory.edu
1040-7383/$-see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1053/j.semss.2011.04.008
whenever possible during the index operation because the optimal method of treating iatrogenic cervical deformity remains its prevention.
Iatrogenic Deformity Associated with Anterior Cervical Surgery Anterior Cervical Diskectomy Without Fusion Performing anterior cervical diskectomy alone without fusion will virtually guarantee some degree of postoperative segmental kyphosis, even if the segment ultimately goes on to autofuse as it does in the majority of instances (Fig. 1). Admittedly, the incidence of developing clinically relevant kyphosis in the long term with the use of this approach is unknown, and the short-term results of diskectomy alone are generally reported to be good in the setting of adequate decompression.1 However, common sense and clinical experience suggest that avoiding procedures clearly associated with segmental kyphosis would be in the best long-term interest of a patient’s cervical spine—regardless of short-term improvements— because local kyphosis is more likely to predispose to global kyphosis over time. Thus, the largely historical practice of performing anterior cervical diskectomy without fusion is rarely indicated.
Anterior Cervical Diskectomy and Fusion Without Plating Unplated anterior cervical diskectomy and fusion (ACDF) is more likely to settle into kyphosis or at least lose lordosis than 173
J.M. Rhee
174
ever, very little is known about the fusion rates, alignment, and outcomes achieved with these implants.
Graft-Related Factors Potentially Causing Deformity The type of graft material used may also influence the likelihood of postoperative kyphosis. Generally, the likelihood of graft collapse with allograft increases as follows: irradiated, freeze-dried, and then fresh-frozen.7 Cancellous-based allografts, such as dense cancellous allografts, have also demonstrated greater propensity to resorption during healing than purely cortical grafts and thus may be more prone to kyphosis over time.8 The size of the graft may also influence the likelihood of segmental kyphosis. The graft should be large enough to gently distract the interspace, such that with loading in the upright position some settling can be accommodated without developing kyphosis. If a wide diskectomy is performed, wider or multiple grafts can be placed side by side in the disk space to improve surface contact, better distribute load across the endplates, and lessen the likelihood of settling and collapse (Fig. 4). In general for most ACDFs, a graft height 2-3 Figure 1 ACD without fusion: lateral radiograph of a 55-year-old man who had undergone an anterior cervical diskectomy at C56 without fusion many years previously. The segment has autofused but in segmental kyphosis (note also the widening of the gap between the spinous processes between C5 and C6). The overall alignment of the cervical spine is also somewhat kyphotic.
their plated counterparts (Fig. 2).2 Multilevel unplated fusions are particularly prone to result in overall kyphosis as the settling of multiple grafts magnifies the segmental kyphosis that develops at each level. Although the use of a plate does not absolutely guarantee the avoidance of kyphosis, most would agree that anterior cervical plates decrease the likelihood of developing not only radiographic (ie, clinically silent) but also clinically evident postoperative kyphoses, particularly in multilevel cases.3 These benefits of using plates must be tempered by meticulous placement to avoid plate-associated complications, such as screw and plate migration, as well as injury to adjacent disk spaces.4
ACDF with Stand-Alone Cages Recently, to avoid plate-related complications, cervical interbody cages that can be used as stand-alone devices have become more popular. However, several authors have noted the development of subsidence and kyphotic malalignment with stand-alone cervical cages,5,6 even when the bony endplates were not removed.5 The benefits of plating, at least to avoid kyphosis, seem inescapable, especially in cases in which the endplates are removed or in patients with poor bone quality. Newer cage designs allow for screw fixation through the cage and are touted as being zero-profile (Fig. 3). When these devices are used, adjacent segments can also be fused without the removal of previously placed plates. How-
Figure 2 ACDF without plate: lateral radiograph of a 67-year-old woman who had undergone an unplated C67 ACDF in the remote past with the use of an autologous iliac crest bone graft. Note that the segment has fused in a neutral to slightly kyphotic alignment.
Iatrogenic cervical deformity
175 kyphosis to develop as the construct settles over time, particularly in those patients with preexisting kyphosis (Fig. 5). Large clinical series are needed to determine the sagittal plane consequences of dynamic plates in the cervical spine.
Corpectomy
Figure 3 Zero profile cage: This patient presented with residual cord compression and nonunion after ACDF with a zero profile cage device, which allows for screw fixation into the endplates. The fixation is purported to provide additional stability versus stand-alone cages without screws, but few data are currently available on the efficacy of these devices in preserving alignment and achieving fusion.
mm greater than that of the preoperative disk will be sufficient to gently tension the interspace and provide a tight fit without overdistraction. It is also important to try to preserve the bony endplates as much as possible whenever doing ACDF to prevent subsidence and potential segmental kyphosis. Although the anterior and posterior “lips” of the cephalad endplate can be flattened to ensure good graft-host contact and decompress the floor of the spinal canal, respectively, the central portion of the endplate should be preserved to provide a structurally sound surface on which the graft can rest and resist significant subsidence.
Dynamic Cervical Plates Dynamic plates have been advocated as biomechanically favorable alternatives to rigid plating. Dynamic plates have been shown in biomechanical experiments to allow for better load sharing across the interbody graft vs rigid plates, which are more likely to stress shield the graft, particularly when the graft is undersized and graft-host contact is suboptimal. However, it is unclear as to whether dynamism leads to better clinical outcomes or fusion rates. In addition, one potential downside to dynamism may be a tendency for segmental
Anterior-only corpectomy constructs will generally demonstrate greater likelihood of losing lordosis than diskectomy constructs because a normally lordotic area of the spine is replaced by a relatively straight graft (bone or cage). The longer the corpectomy construct, the less lordosis that can be restored or preserved. Any negative consequences of endplate removal on sagittal plane alignment will also be magnified with corpectomy vs diskectomy. Although plating may be beneficial in 1- or perhaps 2-level corpectomy cases, plating multilevel corpectomies appears biomechanically unfavorable and is associated with high rates of graft displacement (up to 50% in 1 series of 3 level corpectomies).9 Furthermore, even if graft and plate failure do not occur, plates do not appear to protect against kyphosis with corpectomy constructs to the extent that they can with diskectomies. Finally, if one chooses to avoid complications of spanning plates across multilevel corpectomies by opting for unplated surgery instead, the spine will almost certainly settle into kyphosis or at best neutral alignment. The use of small “antikick” plates at the end of a construct to prevent kick out may have similar advantages in allowing settling of the construct and therefore better union rates than spanning plates, but they will, like their unplated counterparts, tend to heal in kyphosis or at best neutral. If multilevel corpectomies are neurologically necessary, supplemental posterior fixation and fusion should be considered. A circumferential approach should also be strongly considered in patients with poor bone quality (eg, osteoporosis, renal failure, infections, tumors), severe kyphosis preoperatively, or those with neuromuscular disorders leading to poor muscle control.
Malalignment Errors Introduced During Posterior Cervical Surgery Positioning Issues With posterior surgery, it is important to ensure that the spine is placed into a favorable alignment before fusion. However, a competing priority is that a neutral or slightly kyphotic alignment is helpful during decompression by decreasing the shingling or overlap of adjacent lamina onto each other and by enlarging the spinal canal. Therefore, in certain cases of decompression and fusion, it may be helpful to change the position of the neck from relative flexion during the decompression to the final desired position before securing the rods. Although proper positioning during posterior fusion is critical to maintaining sagittal plane alignment, the ability to actually correct kyphosis with instrumented posterior fusion by simply changing the neck position can be limited depending on its severity. If the kyphosis is flexible, a fair amount of correction may be obtained by positioning, but if extensive
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Figure 4 Double graft. (A) lateral radiograph status post 2 level ACDF C5-7. (B) Axial computed tomography scan through C67 demonstrates that 2 grafts were rotated 90° to the usual orientation and inserted to better fill the large disk space and provide better load sharing across the construct, which may then better preserve alignment with less segmental settling.
spondylosis coexists, the stiff anterior disk spaces may resist realignment. Even when passive correction of kyphosis is achievable by intraoperative positioning, concern exists regarding the loss of correction and kyphosis recurrence postoperatively as the spine settles into its former position in the absence of anterior column support and fixation. As it does so, associated proximal pullout of the posterior implants may occur. To avoid such complications, circumferential surgery
or corrective osteotomies should be considered depending on the nature and severity of the kyphosis.
Postfacetectomy Kyphosis Postoperative instability resulting from over aggressive facetecomy typically manifests as segmental spondylolisthesis with local kyphosis that may then progress to overall kypho-
Figure 5 Dynamic cervical plate. (A) preoperative lateral radiograph of a 36-year-old man with C56 cervical radiculopathy. Note the presence of segmental kyphosis through C56 preoperatively. (B) Postoperative day 1 radiograph after C56 ACDF with a dynamic cervical plate. (C) Significant settling has occurred at 6 months postoperatively because of excessive dynamism in the setting of a preoperative kyphosis.
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Figure 6 Postlaminoplasty kyphosis. (A) Kyphosis can develop after laminoplasty as well as laminectomy, but it tends not to be as severe. This patient presented having undergone previous French-door laminoplasty for myelopathy associated with ossification of the posterior longitudinal ligament (OPLL). As kyphosis developed, her myelopathy recurred. (B) Axial computed tomography myelogram demonstrates spinal cord compression from OPLL exacerbated by the kyphotic alignment. (C) Patient was treated with C5 and C6 corpectomy and removal of OPLL, resulting in elimination of her neurologic symptoms as shown in this 3-month postoperative radiograph. Because the endplates of C4 and C7 are relatively parallel, a straight strut graft could be inserted with low risk of distal graft extrusion (ie, no shear forces tending to cause distal kick out at C7). Preservation of the endplates along with the patient’s excellent bone quality allowed for anterior-only fixation without significant pistoning of the graft and some improvement in overall alignment.
sis as well. Although more commonly encountered when foraminotomies are performed in conjunction with laminectomies, such instability can occur even with foraminotomy alone, even minimally invasive approaches, if the appropriate anatomic boundaries are not appreciated.
Postlaminectomy Kyphosis Postlaminectomy kyphosis is a well-known complication of multilevel laminectomy, particularly in growing children10,11 but also in adults. Mikawa et al12 reported that 52% of patients demonstrated changes in cervical alignment after multilevel laminectomy, with 14% developing kyphosis. Guigui et al13 noted that 31% had a change in alignment vs preoperative, with 25% having increased kyphosis. Risk factors for kyphosis include younger age at time of surgery, 4 or more levels laminectomized, surgery involving the C2 lamina and its muscle attachments, performance of associated facetectomies, and increased preoperative range of motion.13,14 Preexisting lack of lordosis may be the most important risk factor because the posterior cervical musculature in such patients must already combat the mechanically unfavorable consequences of having the weight of the head fall anterior to the sagittal vertical axis of the cervical spine. Further compromising the extensor musculature and the posterior tension band (supra and inter spinous ligaments, ligamentum flavum, facet capsules) under these circumstances can then lead to a vicious cycle of kyphosis. Many patients who develop postlaminectomy kyphosis have initial improvement in their index neurologic symptoms with the decompressive operation. However, as the deforming forces progress and kyphosis worsens, they may complain of axial neck pain because of muscle fatigue, which can then advance to recurrent myelopathy as the spinal cord
drapes over the anterior structures. The uncovered dural sac may also become compressed posteriorly by the development of a postlaminectomy membrane. With continued progression, kyphosis can lead to loss of forward gaze, difficulty with swallowing and eating, and the need to prop up the neck with the upper extremities. The mainstay of treating postlaminectomy kyphosis is in its prevention. Currently, there are few if any indications for a multilevel laminectomy alone. In myelopathic patients who have favorable preexisting alignment, multilevel cord compression, and do not require fusion, laminoplasty is an alternative nonfusion operation that better preserves alignment and neurologic function than laminectomy. In those requiring posterior surgery but who present with unfavorable preexisting alignment, laminectomy with fusion or a combined anterior–posterior approach is recommended.
Postlaminoplasty Kyphosis Although laminoplasty was initially designed to prevent the development of postlaminectomy kyphosis, some loss of lordosis also occurs with laminoplasty as well (Fig. 6). In general, however, the loss of lordosis after laminoplasty tends to be less than that seen after laminectomy and much less commonly of clinical significance. Suk et al15 reported on average 5° loss of lordosis after laminoplasty, with 10.6% of patients developing an average of 12° of kyphosis. As one would predict, those who began with a lesser degree of lordosis (⬍10° preoperative) were more likely to develop kyphosis, as were those demonstrating more flexion than extension on preoperative dynamic radiographs. Loss of lordosis with laminoplasty may be lessened by sparing C2 and its muscle attachments. Takeshita et al16 found that the decrease in lordosis from C2-C7 was 8.3° if C2 was split during lamino-
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Figure 7 Flexible postlaminectomy kyphosis. (A) 43-year-old woman who presented status after C56 ACDF followed by a C3-6 laminectomy, resulting in mild cervical kyphosis and residual anterior spinal cord compression at C34 and C45. (B) She was treated with revision ACDF at C34 and C45, with improvement noted in overall alignment.
plasty, 5.2° with a dome-like laminotomy of C2, but only 1.5° if C2 was left completely intact. The importance of preserving C7 and its attachments is less clear. Kowatari et al17 found no difference in axial pain, Japanese Orthopaedic Association scores, or sagittal alignment whether the C7 attachments were preserved.
Surgical Strategies for Correction of Iatrogenic Deformity In symptomatic patients with significant iatrogenic kyphosis, a surgical approach is generally required, particularly if there is associated myelopathy. Extensor muscle strengthening with physical therapy may be useful in mild cases but will generally be insufficient in treating more severe cases. Goals of treatment include the following: (1) correction and fusion of deformity, ideally with a normalized sagittal vertical axis; (2) neurologic decompression; and (3) pain relief. The optimal surgical strategy will depend on whether the deformity is flexible, fixed, or fused.
Flexible and Passively Correctable Kyphosis In milder cases of postlaminectomy kyphosis, when the deformity is flexible and passively correctable, it may be reduced into the desired alignment and fused either anteriorly or posteriorly (Fig. 7). Anterior-only surgery has several advantages, including lower rates of morbidity, direct decompression of a spinal cord draped over a kyphos, the avoidance of additional surgery through a revision approach posteri-
orly, preservation of the posterior musculature that has already been compromised, and restoration of height to the anterior column through the use of structural grafts. However, the disadvantages of anterior-only surgery include relatively less secure fixation in the vertebral bodies vs the dorsal elements (especially in osteopenic patients) and the inability of anterior plates to restore the posterior tension band. Although anterior plates may “hold” the correction achieved through the placement of interbody grafts, they are at a relative mechanical disadvantage secondary to their action being anterior to the axis of rotation of the kyphotic deformity. Furthermore, if corpectomy is necessary to achieve neurologic decompression in the setting of a prior laminectomy, supplemental posterior instrumentation is recommended because the spine is rendered highly unstable because the 2 halves of the spine will then only be connected only by soft tissue.18 Posterior-only surgery can also be considered in this scenario of a flexible and passively correctable kyphosis. A prerequisite of posterior-only surgery is that sufficient spinal cord decompression can be achieved through realignment and restoration of lordosis in those with neurologic compression. In such patients as well as those with no neurologic compression, posterior surgery has the advantage of generally superior fixation vs anterior plates, particularly at the ends of the construct, where pedicle screws can be routinely placed into C2, C7, and the upper thoracic spine. In addition, posterior implants are at a mechanical advantage in correcting kyphosis in that they act posterior to the axis of rotation
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Figure 8 Postlaminectomy kyphosis. (A) Elderly woman status after multilevel laminectomy from C3-7 for myelopathy. She presented with severe myelopathy, neck pain, and inability to hold up her neck for horizontal gaze. Because of the severity of kyphosis as well as poor bone quality, she was treated with anterior and posterior reconstruction from C2-T2. (B) A 1-year postoperative x-ray demonstrates solid fusion and significant correction of deformity.
of the kyphotic deformity. However, posterior surgery also has disadvantages, including the need for a revision approach through scar with no dural protection because of previous laminectomy, further denervation and damage to the posterior musculature, greater perioperative pain than is typically encountered with an anterior approach, greater rates of wound infection, and relatively poor, limited surface areas for bone grafting and fusion. Furthermore, the lack of anterior column load sharing can lead to implant failure and screw pullout if the fixation is not optimal and the neck settles back towards its original kyphotic state— especially at the proximal end of the construct.
Fixed (Nonflexible) But Nonankylosed Postlaminectomy Kyphosis If the deformity is fixed but not fused, anterior-only or combined anterior release and correction followed by posterior fusion may be appropriate depending on patient bone quality and severity of kyphosis (Fig. 8). Again, a combined approach is best if multilevel anterior corpectomies are needed, whereas an anterior-only approach may suffice if multilevel diskectomies with segmental screw-plate fixation can be performed in a patient with adequate bone quality. Inability to restore the sagittal vertical axis makes loss of correction more likely because of persistence of deforming forces, and thus supplemental posterior fixation should be considered in such cases.
Fixed and Ankylosed Postlaminectomy Kyphosis If the deformity is not only fixed but also fused, then osteotomies may be required when the ankylosed segments are in such severe kyphosis that correction through the adjacent segments will not provide sufficient overall restoration of the sagittal vertical axis. Conversely, osteotomies may not be nec-
essary if the overall sagittal vertical axis can be restored by correction through the nonankylosed segments. The approach will be dictated by the location of the ankylosis. If the ankylosis is posterior, then a posterior approach should be performed first to osteotomize the area of ankylosis. Correction is obtained through the osteotomy, but supplemental anterior release and interbody grafting, followed by a second posterior approach to lock in the instrumentation (“back-front-back”) may be needed for maximal correction. If the area of ankylosis requiring correction is anterior, anterior osteotomy is performed first. Contingent upon sufficient correction and bone quality, anterior-only surgery may be performed in this setting. Otherwise, a posterior approach is performed to supplement the anterior correction. In patients demonstrating circumferential ankylosis, posterior osteotomies and establishment of fixation points, followed by anterior osteotomies and interbody grafting, followed by final posterior rod fixation and fusion will likely provide the best correction. Alternatively, a one stage pedicle subtraction osteotomy can be performed.
Conclusions The mainstay of treating iatrogenic deformity lies in its prevention. As such, there are very limited indications for performing multilevel laminectomy alone or anterior cervical diskectomy without fusion. Plating of ACDFs, particularly multilevel cases, may be helpful in preventing sagittal plane iatrogenic deformity. However, dynamic cervical plates may lead to loss of lordosis if excessive settling occurs during healing. Stand-alone anterior cervical cages may also be associated with significant settling and thus unfavorable sagittal plane consequences. When performing laminectomy with posterior fusion, the neck should be placed into a favorable alignment before locking down the instrumentation.
180 Laminoplasty better preserves alignment than laminectomy alone but loss of lordosis or even frank kyphosis can occur even with laminoplasty, especially if the preoperative alignment is not lordotic. Thus, the ideal indication for laminoplasty is in the patient preoperative lordosis. Depending on the severity of kyphosis and other factors, such as flexibility and bone quality, established iatrogenic deformities can be treated anteriorly, posteriorly, combined, or require osteotomies.
Disclosure The author is a consultant for Biomet Spine and reports royalties from Biomet Spine.
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