Eur Spine J (2015) 24 (Suppl 2):S186–S196 DOI 10.1007/s00586-015-3838-9
REVIEW
Cervical spondylotic myelopathy: posterior decompression and pedicle screw fixation Kuniyoshi Abumi
Received: 26 February 2014 / Revised: 18 February 2015 / Accepted: 25 February 2015 / Published online: 27 March 2015 Ó Springer-Verlag Berlin Heidelberg 2015
Abstract Introduction Posterior decompression by laminoplasty and anterior decompression/fixation have been widely accepted, and they provide sufficient results for cervical spondylotic myelopathy. However, combined procedure of posterior decompression and reconstruction is favorable for some patients accompanying local kyphosis, segmental instability, previously operated conditions on the cervical spine, etc. Discussion Among posterior cervical instrumentations, pedicle screw fixation is a strong tool of stabilization of unstable segment and correction of deformities in sagittal and/or coronal planes for the patient with cervical spondylotic myelopathy. On the other hand, neurovascular complications including injury to the vertebral artery and nerve root cannot be completely eliminated. Even after surgeons became familiar with placement of cervical pedicle screws, screw malposition rate by freehand technique is high for patients with severe spondylotic condition. Surgeons must especially be careful for inserting pedicle screw in the cervical spine associating marked degenerative changes by spondylosis, and must obtain preoperatively sufficient anatomical information of the pedicle and surrounding structures. Conclusion Combined procedure of posterior reconstructive surgery using a pedicle screw fixation provides better clinical outcomes than laminoplasty alone for cervical spondylotic myelopathy accompanying local kyphosis or segmental instability. Further development of supporting tools for cervical pedicle screw insertion including aiming device, navigation system and neuromonitoring procedure are expected for safer screw insertion. K. Abumi (&) Sapporo Orthopaedic Hospital-Center for Spinal Disorders, 13-56, Hassam 13-4, Nishi-Ku, Sapporo 063-0833, Japan e-mail: [email protected]
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Keywords Cervical spondylotic myelopathy Pedicle screw fixation Cervical deformity
Introduction Cervical spondylotic myelopathy can be well managed by posterior decompression or anterior decompression and fusion with or without anterior plate. However, combined procedure of posterior decompression and reconstruction using pedicle or lateral mass screw fixation is favorable for some patients accompanying local kyphosis, segmental instability, previously operated conditions, etc. Despite increasing acceptance among spine surgeons of the use of pedicle screws in the lumbar and thoracic spine, screw insertion into the cervical pedicle has been considered too risky for the surrounding neurovascular structures, except at the C2 and C7. Leconte firstly reported C2 pedicle screw insertion for osteosynthesis of the C2 hangman fracture and followed be Borne at al. [1, 2]. Roy-Camille et al. [3] documented screw insertion into the C7 pedicles. The first report of pedicle screw insertion through the C3 to C6 was the description of techniques and report of 13 cases of pedicle fixation for traumatic lesions of the lower cervical spine by Abumi et al. [4] in 1994. Jeanneret et al. nearly simultaneously reported three cases of osteosynthesis of separation fracture of the articular mass in the middle cervical spine [5]. Abumi et al. expanded the indication of cervical screw fixation to non-traumatic lesions, reconstruction of the craniocervical junction and correction of cervical kyphosis [6–8]. Biomechanical studies revealed the superior stabilizing effect of pedicle screw fixation than other internal fixation procedures in the cervical spine [9, 10]. Johnson et al. and
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Table 1 Neurovascular complications directly related to pedicle screws in six published articles References
Abumi et al. [13]
Number of patients
Mean follow-up months (range)
Fusion success rate (%)
Neurovascular complications directly related to pedicle screw Vertebral artery injury
Nerve root injury
Spinal cord injury
99.40
1a
2
0
180
51.8 (13–84)
Kast et al. [14]
26
60 (31–86)
100
0
2
0
Yukawa et al. [15]
100
42.5 (16–79)
100
1a
1
0
Nakashima et al. [16]
84
49 (6–168)
97.60
2a
3
0
Wang et al. [17]
214
99.10
0
0
0
Hojo et al. [18]
283
–
2a
3
0
36.8 (5–65) – (24–96)
– No description a
Bleeding was stopped by bone wax packing in all patients, and no further complications of the brain were observed
Ito et al. demonstrated by biomechanical study that cervical pedicle screws provide a significantly lower rate of loosening at the bone screw interface, as well as higher strength after fatigue testing [11, 12]. On the other hand, even after surgeons became familiar with the placement of cervical pedicle screws, neurovascular complications including injury to the vertebral artery and nerve root cannot be completely eliminated (Table 1) [13–18]. Onishi et al. reported a case of late cerebral infarction by laterally perforated pedicle screw [19]. Screw malposition rate by freehand technique in patients with complicated anatomical conditions such as 26.7 % for rheumatoid arthritis or 16.6 % for spondylosis was especially high [18]. In recent years, modified screw insertion techniques [20–22], guiding devices or computer navigation systems have developed and increased the accuracy of screw insertion [23–27]. Indication and contraindication for cervical spondylotic myelopathy Pedicle screws are powerful tool for stabilization of the unstable motion segment caused by injury and by nontraumatic lesions including metastatic tumor, rheumatoid arthritis, destructive spondyloarthropathy, etc. This procedure is especially beneficial in conditions in which lamina or lateral masses is inadequate for stabilizing anchors because of marked osteoporosis or complicated anatomical condition by previous surgery. In addition, cervical pedicle screw fixation procedure allows rigid fixation to provide the high correction capability to restore physiological sagittal alignment of the cervical spine. Laminoplasty procedures have been used to manage cervical stenotic myelopathy caused by spondylosis with a narrow spinal
canal. This procedure provides sufficient decompressive effect for multisegmental stenotic myelopathy with normal cervical alignment in the sagittal plane. However, according to our previously published reports of multivariate logistic regression analysis, posterior decompression alone is less effective for the cervical spondylotic myelopathy with local kyphosis exceeding 13° than those for cervical spondylotic myelopathy without local kyphosis [28]. Cervical spondylotic myelopathy with kyphosis can be managed by anterior decompression and fixation. Another choice of pedicle screw systems has benefits in that they can restore cervical lordosis through a single posterior approach with simultaneous posterior decompression. Miyamoto et al. revealed that combined procedure of posterior reconstructive surgery using a pedicle screw or lateral mass screw fixation resulted in better clinical outcomes than laminoplasty alone for cervical spondylotic myelopathy accompanying local kyphosis [29]. Cervical spondylotic myelopathy accompanying segmental instability requiring posterior decompression also can be managed by simultaneous decompression and stabilization using pedicle screw fixation [30]. Salvage surgery for previous posterior or anterior surgery in cervical spondylotic myelopathy requiring posterior decompression and stabilization is adequate indication of simultaneous decompression and fixation using cervical pedicle screw procedure. The following conditions in cervical spondylotic myelopathy are contraindicated or inadequate for cervical pedicle screw fixation: (1) absent or extremely small pedicle; (2) pedicle of the vertebra associated with major anomalies of the vertebral artery; (3) an extremely large angle of pedicle axis to the sagittal plane; and (4) infection at the posterior portion of the cervical spine.
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Surgical procedure [31] Positioning and exposure A surgeon is recommended to stand at the head of the patient, to assure symmetrical insertion of the right and left screws. The C-arm monitor is placed at the side of the patient near the pelvis for providing the leading surgeon with a good view. The patient is placed prone on a fourpost frame using a horseshoe-type headrest or three-point pin fixation device. The shoulders are pulled caudally by a heavy bandage for intraoperative lateral fluoroscopic imaging of the lower cervical spine. Cranial end of the bandage must be applied on the acromion to obtain sufficient pulling force. However, too strong pulling force must be avoided considering possibility of brachial plexus palsy. A skin incision, longer than required for a standard spinous process wiring, is made. The cranially adjacent lamina of the most cranially fixed vertebra should entirely be exposed, taking care to protect the cranial facet joint capsules of the non-fixed segment. The paravertebral muscles are dissected laterally to expose the lateral margins of the articular masses completely for exact determination of the screw insertion point. Screw placement
Fig. 1 Pedicle screw starting points in the cervical spine. The cranial margin of the lamina of C2 can be the landmark for the point of screw penetration for C2 (asterisk). To confirm the screw insertion points in C2, a small spatula can be inserted into the spinal canal along the cranial margin of the C2 lamina to the medial surface of the pedicle of C2. The lateral margin of the articular mass of the cervical spine has a notch (white arrow). The screw starting points locate approximately below the lateral vertebral notch at C2, at C3–C6, at or slightly above the notch at C7. Screw starting points (black cross) are 2–4 mm medially from the notch
The points of screw insertion at the lateral mass from C3 through C7 are slightly laterally to the center of the articular mass and close to the inferior margin of the inferior articular process of the cranially adjacent vertebra. Surgeons must evaluate CT images carefully before screw insertion to check the shape, size and direction of the pedicle and condition of the lateral mass in each vertebra and in each individual. The cranial margin of the lamina of C2 is the landmark for the point of screw insertion for C2. To confirm the screw insertion points in C2, a Penfield retractor can be inserted into the spinal canal along the cranial margin of the C2 lamina to the medial surface of the pedicle of C2. The angle of the C2 pedicle axis to the sagittal plane is 15°–25° in the transverse plane. However, by 10°–20° of pedicle screw insertion angle to the sagittal plane, smaller angle than pedicle axis, is acceptable. The lateral margin of the articular mass of the cervical spine has a notch approximately at the same level of the pedicle. Precisely, the pedicles are located slightly below the lateral vertebral notch at C2, at C3–C6, at or slightly above the notch at C7 [32] (Fig. 1). The points of screw starting for the C3 through C7 pedicles are slightly laterally to the center of the articular mass and close to the inferior margin of the inferior articular process of the cranially adjacent vertebra. Confirmation of screw starting point for
C7 using lateral C-arm projection is sometimes disturbed by shoulder girdle in many patients. For those patients, small laminotomy at the cranial margin of the C7 lamina is helpful to see and touch the pedicle directly through the laminotomy portion. Craniocaudal orientation of the screw insertion point can be confirmed by a lateral image intensifier. The direction of the pedicle anatomical axis in the transverse plane varies from a minimum degree at the C2 pedicle to a maximum at the C5 pedicle. Therefore, screw insertion point considering the direction of the pedicle axis will be near the lateral margin of the lateral mass as recommended by several authors and direction is 40°–60° from the sagittal plane for the pedicle from C3 to C6, and smaller angle for C2 and C7 [33–35] (Fig. 2). However, the author usually creates a funnel-like-shaped hole at the screw insertion point down to the entrance of the pedicle using a high-speed burr with a diamond tip. Surgeons can get a wider range of freedom for screw insertion angle from the entrance of the pedicle cavity than from the poter portion of the lateral mass. Therefore, after creating a funnel-like hole, a screw can be inserted by a smaller oblique angle than the angle of the true anatomical axis of the pedicle (Fig. 3). The authors usually insert screws with angle of 25°–45° from the sagittal plane for the pedicle from C3 to C6. A small specially designed pedicle probe, a
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Fig. 2 Direction of cervical pedicle screw in three planes starting point of cervical pedicle screw insertion considering the direction of the pedicle axis will be near the lateral margin of the lateral mass. Screw direction to the sagittal plane is 40°–60° for C3–C6 [23]
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changes or by extremely small diameter are not suited for screw insertion because of a high possibility of screw malposition. In patients with marked degenerative changes in the lateral mass of the cervical spine, location of the starting point of the pedicle screw is hard to be found. In such case, orientation of screw insertion point can be obtained after resection of the proliferated lateral mass using high-speed burr. The screw diameter in the authors series was 3.5, 4.0, and 4.5 mm depending on the pedicle diameter of the each vertebra, and the length of screw was 20, 22, and 24 mm. Regarding the longitudinal connectors, plate was used for one or two segmental fixation, and 3/16 inches rod was employed for three or longer fixation. Karaikovic et al. suggested by their morphologic study that there is no safe zone anterior to the cervical vertebral bodies in the cervical spine except C2, and only C2 would allow bicortical purchase of pedicle screws without being close to important surrounding structures [36]. In the present author’s series, screw tips were not penetrated for C3–C7 vertebra; however, bicortical purchase was conducted for C2 in severely osteoporotic patient to increase the stability of the screw. Simultaneous posterior decompression and fixation
Fig. 3 Direction of cervical pedicle screw after funnel-like hole creation. Black broken line indicates anatomical axis of the pedicle. Point A on the right side of the lateral mass is the screw insertion point. Screw can be inserted between two black arrows. After resection of the outer portion of the lateral mass toward the entrance of the pedicle cavity as a funnel-like shape using high-speed burr (shaded portion on the left side of the pedicle), starting point of screw approach to the entrance of the pedicle cavity (Point B), and surgeon obtain more freedom of screw insertion angle (shaded portion on the vertebral body)
tap and screws are inserted into the pedicle under the guidance of lateral C-arm image to confirm the direction and insertion depth. The authors recommend checking a proper creation of screw insertion path with a cervical pedicle sounder with a small ball tip after probing and tapping (Fig. 4a–c). The angle of screw insertion in the sagittal plane should be parallel to the cranial endplate for the pedicles of C5 through C7, and a slightly cephalad direction in C2 through C4, according to anatomical angle of the pedicle in the sagittal plane (Fig. 5). A drill bit should not be used to make holes for screw placement. When the neurocentral junction in the cervical spine close to the base of the pedicle in the vertebral body is too hard to pass a pedicle probe, the junction can be perforated with a Kirschner wire or a high-speed diamond burr with its smallest size. At that time, a tip of wire or burr must not go deeper but only make the path for a pedicle probe to get into the vertebral body. The cervical pedicles without medullary canal by sclerotic
Laminoplasty, laminectomy and foraminotomy with pedicle screw fixation can be conducted for cervical spondylotic myelopathy with unstable segment. Author recommends screw insertion prior to posterior decompression avoiding handling of instrumentation over the exposed dura mater. Simple plate fixation is preferred for one- or two-segment fixation (Fig. 6a, b). Alignment of screw head in the coronal plane may be off in multilevel fixation. Therefore, a rod with a screw rather than plate is recommended for multilevel fixation over three segments. Correction of cervical deformities Correction of cervical kyphosis: Pedicle screw procedure is a strong tool for correction of the deformities in the cervical spine. Plates and rods are contoured in the sagittal plane with the expected correction of kyphotic deformity. Correction of the kyphosis is performed by tightening the nuts or by rotating the rods using rod holders. As a consequence, the posterior part of the cervical spine can be shortened. Therefore, surgeons must be careful to avoid excessive shortening of the spine because of the potential for the development of a nerve root lesion by foraminal stenosis. If preoperative radiological assessments revealed marked stenosis of the neural foramina, even though it was asymptomatic, prophylactic foraminotomy is recommended especially at C4/5 level. Flexible kyphosis can be managed by single posterior approach (Fig. 7a, b);
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Fig. 4 Regulation of screw insertion using C-arm. a Two broken lines indicate cranial and caudal margin of the pedicle. b Pedicle probe must be advanced between two broken lines. c Tapping of
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screw insertion hole. Authors recommend confirming proper creation of screw insertion path after probing and tapping using pedicle sounder
Pitfalls to avoid Surgeons must keep in mind that there must be a limitation of placing pedicle screws in the cervical spine due to anatomical variations of the pedicle or the vertebral artery. Possible complications which directly relate to pedicle screw insertion in the cervical spine are nerve root injuries by cranially or caudally misplaced screws, vertebral artery injuries or obstruction by laterally misplaced screw and injuries to the dural sac or the spinal cord by medially misplaced screw. Vertebrae with abnormal morphology on the pedicle or vertebral artery especially associate high risk of neurovascular complication. Neo et al. [34] reported 29 % of screw perforation rate from the cervical pedicle in patients with cervical degenerative vertebra. In their series, no symptomatic neurovascular complication was occurred by perforated screws. Morphology of the pedicle
Fig. 5 Screw direction in the sagittal plane. The intended angle of screw insertion in the sagittal plane is parallel to the cranial endplate for the C5–C7 pedicles, and slightly cephalad for the C2–C4 pedicles because of the pedicle angle in the sagittal plane
however, rigid, fixed or marked kyphosis requires combined anterior and posterior approach (Fig. 8a, b). Correction of cervical scoliosis: Case of cervical scoliosis requiring surgical correction is uncommon. However, if necessary, the deformity is correctable using this procedure applying distraction force on the concave side. Application of compression force on the convex side is not recommended considering iatrogenic nerve root complication by foraminal stenosis (Fig. 9a, b).
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According to the previous morphometric studies of the cervical pedicle, outer pedicle diameter is more than 5 mm in most cervical vertebrae, and for those pedicles, screws can be inserted. If outer pedicle diameter is less than 4 mm, screw insertion is quite difficult or impossible and then alternative fixation anchors, such as lateral mass screws or posterior wirings, are recommended. Thin cut axial CT scans (adjusted to the bone windows) with 1.0–2.0 mm slice are recommended for accurate evaluation of pedicle diameters to measure the pedicle width, which helps surgeons to choose the appropriate pedicle screw diameter, length, and direction in the transverse plane. Figure 11 shows diameter differences between the left and the right pedicle in the same vertebra (Fig. 10). This diameter difference in the same vertebra shows that the vertebral artery
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Fig. 6 Simultaneous posterior decompression and monosegmental fixation. A patient with cervical spondylotic myelopathy associated with segmental instability at C3/4. a X-ray films in flexion and extension position showing segmental instability at C3/4. MRI images
demonstrate narrowed spinal canal and spinal cord compression. b Postoperative X-ray film shows C3/4 single level pedicle screw/plate fixation. Axial CT scans demonstrate location of inserted screws
on the side of smaller pedicle diameter is dominant so that surgeons must pay special attentions to pedicle screw insertion on this side. Since the thinnest cortex of the pedicle is always at the lateral cortex, the medial cortex of the pedicle can be used as a guide to insert a screw into the vertebral body through the pedicle isthmus.
involving the vertebral artery. The incidence of ischemic brain complication caused by unilateral obstruction of the vertebral artery has been reported low. However, if the dominant side of the vertebral artery was injured, serious neurological complications could occur. Magnetic resonance angiograph (MRA) and CT angiograph (CTA) provide information regarding the right–left domination and anatomical variations to the vertebral artery. MRA or CTA must be conducted for the patients if there is an evidence of the abnormalities or even a suspect of these abnormalities on plain CT or MR images. The vertebral artery sometimes
Conditions of the vertebral artery Preoperative evaluation of the morphology of the vertebral artery is indispensable to prevent serious complications
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Fig. 7 Correction of flexible kyphosis. a A patient with cervical spondylotic myelopathy with 38° of flexible kyphosis developed after open door laminoplasty. Anterior aspect of the spinal cord was compressed at the apex of kyphosis. b Scar tissue covering the dura matter was detached prior to correction of kyphosis avoiding spinal
cord compression by buckling of scar tissue. Kyphosis was corrected to 5° by single posterior approach. Postoperative MRI demonstrated sufficient spinal cord decompression by correction of kyphosis. 10/17 points of JOA score improved to 14/17 points
crooks into the vertebral body with loops, and screw insertion into the ipsilateral side of the pedicle is too risky to the artery (Fig. 11). In these situations, pedicle screw insertion into the ipsilateral side of the pedicle must be omitted, or alternative fixation anchors including lateral mass screws or wiring procedures have to be employed. Recent morphometric analysis by Tomasino et al. [37] concerning the relationship between the vertebral artery and the cervical pedicles showed that pedicle diameter, safe zone, and occupational relation of the vertebral artery in the transverse foramen showed considerable individual variations so that the risks to the neurovascular structures
associated with pedicle screw placement must be assessed individually.
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Nerve root complication by iatrogenic foraminal stenosis Some neural foramina in patients with degenerative disorders or rheumatoid arthritis are narrow on preoperative images. From our experience and the report by Heller et al. [38] who used lateral mass screws, in those with preoperative narrow neural foramina, there is a risk of iatrogenic nerve root impingement due to worsening of foraminal stenosis caused by either anterior translation or correction
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Fig. 8 Correction of rigid kyphosis. a A patient with mild cervical spondylotic myelopathy accompanied 43° of rigid kyphosis. (1) Preoperative MRI demonstrated spinal cord compression at the apex of kyphosis. A sagittal image of the CT scan appreciates the rigidity of deformity. b The patient underwent three-staged correction surgery by single anesthesia: (1) C4 corpectomy with bilateral uncinectomy of
C4 and C5, (2) Posterior correction after C3–5 laminectomy, (3) anterior strut grafting with expandable cage. 43° of preoperative kyphosis improved to 8°, and myelopathy disappeared completely. Left side of C2 screw was stopped at the pars interarticularis considering the high riding vertebral artery
of kyphosis by reduction procedures. According to the previous report by Hojo et al. and Nakashima et al. [16, 39], rate of C5 nerve root lesion by foraminal stenosis of C4/5 is especially high. Surgeons should keep in mind not to apply excessive compression force posteriorly at the segments with preoperative foraminal stenosis while correcting kyphotic deformity. Otherwise, prophylactic foraminotomies before correction of cervical kyphosis are recommended in patients with marked stenosis of the neural foramina. Reconstructive CT images in the oblique plane can provide useful information about the conditions of the neural foramina. Besides the iatrogenic foraminal stenosis, excessive caudal traction of the shoulder girdle for C-arm projection may be the cause of brachial nerve palsy presenting similar
nerve symptoms as foraminal stenosis. Diminish or decrease of EMG activity or MEP (motor evoked potential) during surgery may demonstrate decrease of nerve root function, and recovery of EMG or MEP after additional foraminotomy or release of pulling force may define the cause. Combination of cervical pedicle screws with lateral mass screws Combined use of C2 and/or C7 pedicle screws with C3–C6 lateral mass screws are more widespread and less technically demanding than single use of pedicle screws for cervical reconstructive surgery [40, 41]. The combined use must provide similar biomechanical stability to the reconstructed cervical spine as pedicle screw fixation. However,
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Fig. 9 Correction of cervical scoliosis. a Preoperative images demonstrate 31° of scoliosis after laminoplasty. The patient suffered from severe radiculopathy of left C5 and C6 caused by C4/5 and C5/6 foraminal stenosis. Preoperative CT scans demonstrate proliferated degenerative changes of the left lateral mass. b Outer layer of the proliferated lateral mass of C4–C6 was resected using high-speed burr to obtain orientation of screw insertion point. After pedicle screw
insertion, foraminotomy at C4/5 and C5/6 and correction of scoliosis by application of distraction force on the concave site were conducted. Preoperative radiculopathy healed almost completely. Postoperative images show sufficient correction of scoliosis. Postoperative CT images show proper screw placement in each vertebra and enlarged C4/5 and C5/7 neural foramina (white arrow)
the combined use usually require longer fixation sacrificing stable motion segments to provide sufficient stability than pedicle screw fixation.
tool for correction of cervical deformities in sagittal and/or coronal planes for the patient with cervical spondylotic myelopathy. In addition, the patients with cervical spondylotic myelopathy associating segmental instability can be managed by simultaneous decompression and stabilization using pedicle screw fixation. On the other hand, even with the application of established surgical techniques, neurovascular complications including injury to the vertebral artery and nerve root cannot be completely eliminated. Even after surgeons became familiar with the
Summary Biomechanical studies revealed the superior stabilizing effect of pedicle screw fixation than other internal fixation procedures in the cervical spine. This procedure is a strong
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Fig. 10 Retrogression of the pedicle at the dominant side of the vertebral artery. a The left and right pedicles in the same vertebra differ extremely in diameter. The foramen transversarium enlarges in
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the smaller side of the pedicle (white arrow). b The vertebral artery is dominant in the ipsilateral side of enlarged foramen transversarium (black arrow)
References
Fig. 11 Tortuous course of the vertebral artery. CT images show abnormal shape of the foramen transversarium of left C5 and right C6 (arrow head). Angiograph demonstrates tortuous course of the vertebral artery at left C5 and right C6 (arrow)
placement of cervical pedicle screws, screw malposition rate by freehand technique is high for patients with severe spondylotic condition. Surgeons must especially be careful for inserting pedicle screw in the cervical spine associating marked degenerative changes by spondylosis, and must obtain preoperatively sufficient anatomical information of the pedicle and surrounding structures. Combined procedure of posterior reconstructive surgery using a pedicle screw fixation provides better clinical outcomes than laminoplasty alone for cervical spondylotic myelopathy accompanying local kyphosis or segmental instability. Further development of supporting tools for cervical pedicle screw insertion including aiming device, navigation system and neuromonitoring procedure is expected for safer screw insertion. Conflict of interest Author declares that there is no actual or potential conflict of interest with organizations in relation to this article.
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biomechanical study on strength of fixation. J Spinal Disord Tech. Feb 27 [Epub ahead of print] Abumi K, Shono Y, Ito M, Taneichi T, Kotani Y, Kaneda K (2000) Complication of pedicle screw fixation in reconstructive surgery of the cervical spine. Spine (Phila Pa 1976) 25(8):962–969 Kast E, Mohr K, Richter HP, Bo¨rm W (2006) Complication of transpedicular screw fixation in the cervical spine. Eur Spine J 15(3):327–334 Yukawa Y, Kato F, Yoshihara H, Yanase M, Ito K (2006) Cervical pedicle screw fixation in 100 cases of unstable cervical injuries: pedicle axis views obtained using fluoroscopy. J Neurosurg Spine 5(6):488–493 Nakashima H, Yukawa Y, Imagama S, Kanemura T, Kamiya M, Yanase M, Ito K, Machino M, Yoshida G, Ishikawa Y, Matsuyama Y, Ishiguro N, Kato F (2012) Complications of cervical pedicle screw fixation for nontraumatic lesions: a multicenter study of 84 patients. J Neurosurgery Spine 16(3):238–247 Wang YS, Xie JM, Yang ZD, Zhao Z, Zhang Y, Li T, Liu LP (2013) Computed tomography assessment of lateral pedicle wall perforation by free–hand subaxial cervical pedicle screw placement. Arch Orthop Trauma Surg 133:901–909 Hojo Y, Ito M, Suda K, Oda I, Yoshimoto H, Abumi K (2014) A multicenter study on accuracy and complications of freehand placement of cervical pedicle screws under lateral fluoroscopy in different pathological conditions: CT-based evaluation of more than 1,000 screws. Eur Spine J 23:2166–2174 Onishi E, Sekimoto Y, Fukumitsu R, Yamagata S, Matsushita M (2010) Cerebral infarction due to an embolism after cervical pedicle screw fixation. Spine (Phila Pa 1976) 35(2):E63–E66 Lee SH, Kim KT, Abumi K, Suk KS, Lee JH, Park HJ (2012) Cervical pedicle screw placement using the ‘‘key slot technique’’: the feasibility and learning curve. J Spinal Disord Tech 25(8):415–421 Jo DJ, Eun-Min Seo EM, Kim KT, Kim SM, Lee SH (2012) Cervical pedicle screw insertion using the technique with direct exposure of the pedicle by laminoforaminotomy. J Korean Neurosurg Soc 52(5):459–465 Ryken TC, Owen BD, Christensen GE, Reinhardt JM (2009) Image-based drill templates for cervical pedicle screw placement. J Neurosurg Spine 10(1):21–26 Richter M, Cakir B, Schmidt R (2005) Cervical pedicle screws: conventional versus computer-assisted placement of cannulated screw. Spine (Phila Pa 1976) 30(20):2280–2287 Rajasekaran S, Kanna PR, Shetty TA (2010) Intra-operative computer navigation guided cervical pedicle screw insertion in thirty-three complex cervical spine deformities. J Craniovertr Junction Spine 1(1):38–43 Ito Y, Sugimoto Y, Tomioka M, Hasegawa Y, Nakago K, Yagata Y (2008) Clinical accuracy of 3D fluoroscopy-assisted cervical pedicle screw insertion. J Neurosurg Spine 9(5):450–453 Ishikawa Y, Kanemura T, Yoshida G, Ito Z, Muramoto A, Ohno S (2010) Clinical accuracy of three-dimensional fluoroscopybased computer-assisted cervical pedicle screw placement: a retrospective comparative study of conventional versus computer-assisted cervical pedicle screw placement. J Neurosurg Spine 13(5):606–611
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Eur Spine J (2015) 24 (Suppl 2):S186–S196 27. Miyamoto H, Uno K (2009) Cervical pedicle screw insertion using a computed tomography cutout technique. JNeurosurg Spine 11:681–687 28. Suda K, Abumi K, Ito M, Shono Y, Kaneda K, FujiyaM (2003) Local kyphosis reduces surgical outcomes of expansive open door laminoplasty for cervical spondylotic myelopathy. Spine (Phila Pa 1976) 28(12):1258–1262 29. Miyamoto H, Maeno K, Uno K, Kakutani K, Nishida K, Sumi M (2014) Outcomes of surgical intervention for cervical spondylotic myelopathy accompanying local kyphosis (comparison between laminoplasty alone and posterior reconstruction using the screwrod system). Eur Spine J 23(2):341–346 30. Abumi K, Kaneda K, Shono Y, Fujiya M (1999) One–stage posterior decompression and reconstruction of the cervical spine by using pedicle screw fixation systems. J Neurosurg 90(1 Suppl):19–26 31. Abumi K, Ito M, Sudo H (2011) Subaxial Cervical Pedicle Screw Fixation. In: Bridwell KH, DeWald RL (eds) The textbook of operative spine surgery 3rd Edn, Wolters Kluwer/Lippincott, Williams & Wilkins, Philadelphia, pp 321–334 32. Karaikovic EE, Daubs MD, Madsen RW, Gaines J RW (1997) Morphologic characteristics of human cervical pedicles. Spine (Phila Pa 1976) 22(5):493–550 33. Richter M, Cakir B, Schmidt R (2005) Cervical pedicle screws: conventional versus computer-assisted placement of cannulated screws. Spine 30(20):2290–2297 34. Neo N, Sakamoto T, Fujibayashi S, Nakamura T (2005) The clinical risk of vertebral artery injury from cervical pedicle screws inserted in degenerative vertebrae. Spine (Phila Pa 1976) 30(24):2800–2805 35. Reinhold M, Magerl F, Rieger M, Blauth M (2007) Cervical pedicle screw placement: feasibility and accuracy of two insertion techniques based on morphometric data. Eur Spine J 16(1):47–56 36. Karaikovic EE, Yngsakmongkol W, Griffiths HJ, Gaines RW (2002) Possible complications of anterior perforation of the vertebral body using cervical pedicle screws. J Spinal Disord Tech 15(1):75–78 37. Tomasino A, Parikh K, Koller H, Zink W, Tsiouris AJ, Steinberger J, Ha¨rtl R (2010) The vertebral artery and the cervical pedicle: morphometric analysis of a critical neighborhood. J Neurosurg Spine (Phila Pa 1976) 13(1):52–60 38. Heller JG, Silcox III DH, Sutterlin III CE (1995) Complications of posterior cervical plating. Spine (Phila Pa 1976) 20(22):2442–2448 39. Hojo Y, Ito M, Abumi K, Kotani Y, Sudo H, Takahata M, Minami A (2010) A late neurological complication following posterior correction surgery of severe cervical kyphosis. Eur Spine J 20(6):890–898 40. Albert TJ, Klein GR, Joffe D, Vaccaro AR (1998) Use of cervicothoracic junction pedicle screws for reconstruction of complex cervical spine pathology. Spine 23(14):1596–1599 41. Deen HG, Birch BD, Wharen RE, Reimer R (2003) Lateral mass screw-rod fixation of the cervical spine: a retrospective clinical series with 1-year follow-up. Spine J 3(6):489–495
REVIEW
Cervical spondylotic myelopathy: posterior decompression and pedicle screw fixation Kuniyoshi Abumi
Received: 26 February 2014 / Revised: 18 February 2015 / Accepted: 25 February 2015 / Published online: 27 March 2015 Ó Springer-Verlag Berlin Heidelberg 2015
Abstract Introduction Posterior decompression by laminoplasty and anterior decompression/fixation have been widely accepted, and they provide sufficient results for cervical spondylotic myelopathy. However, combined procedure of posterior decompression and reconstruction is favorable for some patients accompanying local kyphosis, segmental instability, previously operated conditions on the cervical spine, etc. Discussion Among posterior cervical instrumentations, pedicle screw fixation is a strong tool of stabilization of unstable segment and correction of deformities in sagittal and/or coronal planes for the patient with cervical spondylotic myelopathy. On the other hand, neurovascular complications including injury to the vertebral artery and nerve root cannot be completely eliminated. Even after surgeons became familiar with placement of cervical pedicle screws, screw malposition rate by freehand technique is high for patients with severe spondylotic condition. Surgeons must especially be careful for inserting pedicle screw in the cervical spine associating marked degenerative changes by spondylosis, and must obtain preoperatively sufficient anatomical information of the pedicle and surrounding structures. Conclusion Combined procedure of posterior reconstructive surgery using a pedicle screw fixation provides better clinical outcomes than laminoplasty alone for cervical spondylotic myelopathy accompanying local kyphosis or segmental instability. Further development of supporting tools for cervical pedicle screw insertion including aiming device, navigation system and neuromonitoring procedure are expected for safer screw insertion. K. Abumi (&) Sapporo Orthopaedic Hospital-Center for Spinal Disorders, 13-56, Hassam 13-4, Nishi-Ku, Sapporo 063-0833, Japan e-mail: [email protected]
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Keywords Cervical spondylotic myelopathy Pedicle screw fixation Cervical deformity
Introduction Cervical spondylotic myelopathy can be well managed by posterior decompression or anterior decompression and fusion with or without anterior plate. However, combined procedure of posterior decompression and reconstruction using pedicle or lateral mass screw fixation is favorable for some patients accompanying local kyphosis, segmental instability, previously operated conditions, etc. Despite increasing acceptance among spine surgeons of the use of pedicle screws in the lumbar and thoracic spine, screw insertion into the cervical pedicle has been considered too risky for the surrounding neurovascular structures, except at the C2 and C7. Leconte firstly reported C2 pedicle screw insertion for osteosynthesis of the C2 hangman fracture and followed be Borne at al. [1, 2]. Roy-Camille et al. [3] documented screw insertion into the C7 pedicles. The first report of pedicle screw insertion through the C3 to C6 was the description of techniques and report of 13 cases of pedicle fixation for traumatic lesions of the lower cervical spine by Abumi et al. [4] in 1994. Jeanneret et al. nearly simultaneously reported three cases of osteosynthesis of separation fracture of the articular mass in the middle cervical spine [5]. Abumi et al. expanded the indication of cervical screw fixation to non-traumatic lesions, reconstruction of the craniocervical junction and correction of cervical kyphosis [6–8]. Biomechanical studies revealed the superior stabilizing effect of pedicle screw fixation than other internal fixation procedures in the cervical spine [9, 10]. Johnson et al. and
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Table 1 Neurovascular complications directly related to pedicle screws in six published articles References
Abumi et al. [13]
Number of patients
Mean follow-up months (range)
Fusion success rate (%)
Neurovascular complications directly related to pedicle screw Vertebral artery injury
Nerve root injury
Spinal cord injury
99.40
1a
2
0
180
51.8 (13–84)
Kast et al. [14]
26
60 (31–86)
100
0
2
0
Yukawa et al. [15]
100
42.5 (16–79)
100
1a
1
0
Nakashima et al. [16]
84
49 (6–168)
97.60
2a
3
0
Wang et al. [17]
214
99.10
0
0
0
Hojo et al. [18]
283
–
2a
3
0
36.8 (5–65) – (24–96)
– No description a
Bleeding was stopped by bone wax packing in all patients, and no further complications of the brain were observed
Ito et al. demonstrated by biomechanical study that cervical pedicle screws provide a significantly lower rate of loosening at the bone screw interface, as well as higher strength after fatigue testing [11, 12]. On the other hand, even after surgeons became familiar with the placement of cervical pedicle screws, neurovascular complications including injury to the vertebral artery and nerve root cannot be completely eliminated (Table 1) [13–18]. Onishi et al. reported a case of late cerebral infarction by laterally perforated pedicle screw [19]. Screw malposition rate by freehand technique in patients with complicated anatomical conditions such as 26.7 % for rheumatoid arthritis or 16.6 % for spondylosis was especially high [18]. In recent years, modified screw insertion techniques [20–22], guiding devices or computer navigation systems have developed and increased the accuracy of screw insertion [23–27]. Indication and contraindication for cervical spondylotic myelopathy Pedicle screws are powerful tool for stabilization of the unstable motion segment caused by injury and by nontraumatic lesions including metastatic tumor, rheumatoid arthritis, destructive spondyloarthropathy, etc. This procedure is especially beneficial in conditions in which lamina or lateral masses is inadequate for stabilizing anchors because of marked osteoporosis or complicated anatomical condition by previous surgery. In addition, cervical pedicle screw fixation procedure allows rigid fixation to provide the high correction capability to restore physiological sagittal alignment of the cervical spine. Laminoplasty procedures have been used to manage cervical stenotic myelopathy caused by spondylosis with a narrow spinal
canal. This procedure provides sufficient decompressive effect for multisegmental stenotic myelopathy with normal cervical alignment in the sagittal plane. However, according to our previously published reports of multivariate logistic regression analysis, posterior decompression alone is less effective for the cervical spondylotic myelopathy with local kyphosis exceeding 13° than those for cervical spondylotic myelopathy without local kyphosis [28]. Cervical spondylotic myelopathy with kyphosis can be managed by anterior decompression and fixation. Another choice of pedicle screw systems has benefits in that they can restore cervical lordosis through a single posterior approach with simultaneous posterior decompression. Miyamoto et al. revealed that combined procedure of posterior reconstructive surgery using a pedicle screw or lateral mass screw fixation resulted in better clinical outcomes than laminoplasty alone for cervical spondylotic myelopathy accompanying local kyphosis [29]. Cervical spondylotic myelopathy accompanying segmental instability requiring posterior decompression also can be managed by simultaneous decompression and stabilization using pedicle screw fixation [30]. Salvage surgery for previous posterior or anterior surgery in cervical spondylotic myelopathy requiring posterior decompression and stabilization is adequate indication of simultaneous decompression and fixation using cervical pedicle screw procedure. The following conditions in cervical spondylotic myelopathy are contraindicated or inadequate for cervical pedicle screw fixation: (1) absent or extremely small pedicle; (2) pedicle of the vertebra associated with major anomalies of the vertebral artery; (3) an extremely large angle of pedicle axis to the sagittal plane; and (4) infection at the posterior portion of the cervical spine.
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Surgical procedure [31] Positioning and exposure A surgeon is recommended to stand at the head of the patient, to assure symmetrical insertion of the right and left screws. The C-arm monitor is placed at the side of the patient near the pelvis for providing the leading surgeon with a good view. The patient is placed prone on a fourpost frame using a horseshoe-type headrest or three-point pin fixation device. The shoulders are pulled caudally by a heavy bandage for intraoperative lateral fluoroscopic imaging of the lower cervical spine. Cranial end of the bandage must be applied on the acromion to obtain sufficient pulling force. However, too strong pulling force must be avoided considering possibility of brachial plexus palsy. A skin incision, longer than required for a standard spinous process wiring, is made. The cranially adjacent lamina of the most cranially fixed vertebra should entirely be exposed, taking care to protect the cranial facet joint capsules of the non-fixed segment. The paravertebral muscles are dissected laterally to expose the lateral margins of the articular masses completely for exact determination of the screw insertion point. Screw placement
Fig. 1 Pedicle screw starting points in the cervical spine. The cranial margin of the lamina of C2 can be the landmark for the point of screw penetration for C2 (asterisk). To confirm the screw insertion points in C2, a small spatula can be inserted into the spinal canal along the cranial margin of the C2 lamina to the medial surface of the pedicle of C2. The lateral margin of the articular mass of the cervical spine has a notch (white arrow). The screw starting points locate approximately below the lateral vertebral notch at C2, at C3–C6, at or slightly above the notch at C7. Screw starting points (black cross) are 2–4 mm medially from the notch
The points of screw insertion at the lateral mass from C3 through C7 are slightly laterally to the center of the articular mass and close to the inferior margin of the inferior articular process of the cranially adjacent vertebra. Surgeons must evaluate CT images carefully before screw insertion to check the shape, size and direction of the pedicle and condition of the lateral mass in each vertebra and in each individual. The cranial margin of the lamina of C2 is the landmark for the point of screw insertion for C2. To confirm the screw insertion points in C2, a Penfield retractor can be inserted into the spinal canal along the cranial margin of the C2 lamina to the medial surface of the pedicle of C2. The angle of the C2 pedicle axis to the sagittal plane is 15°–25° in the transverse plane. However, by 10°–20° of pedicle screw insertion angle to the sagittal plane, smaller angle than pedicle axis, is acceptable. The lateral margin of the articular mass of the cervical spine has a notch approximately at the same level of the pedicle. Precisely, the pedicles are located slightly below the lateral vertebral notch at C2, at C3–C6, at or slightly above the notch at C7 [32] (Fig. 1). The points of screw starting for the C3 through C7 pedicles are slightly laterally to the center of the articular mass and close to the inferior margin of the inferior articular process of the cranially adjacent vertebra. Confirmation of screw starting point for
C7 using lateral C-arm projection is sometimes disturbed by shoulder girdle in many patients. For those patients, small laminotomy at the cranial margin of the C7 lamina is helpful to see and touch the pedicle directly through the laminotomy portion. Craniocaudal orientation of the screw insertion point can be confirmed by a lateral image intensifier. The direction of the pedicle anatomical axis in the transverse plane varies from a minimum degree at the C2 pedicle to a maximum at the C5 pedicle. Therefore, screw insertion point considering the direction of the pedicle axis will be near the lateral margin of the lateral mass as recommended by several authors and direction is 40°–60° from the sagittal plane for the pedicle from C3 to C6, and smaller angle for C2 and C7 [33–35] (Fig. 2). However, the author usually creates a funnel-like-shaped hole at the screw insertion point down to the entrance of the pedicle using a high-speed burr with a diamond tip. Surgeons can get a wider range of freedom for screw insertion angle from the entrance of the pedicle cavity than from the poter portion of the lateral mass. Therefore, after creating a funnel-like hole, a screw can be inserted by a smaller oblique angle than the angle of the true anatomical axis of the pedicle (Fig. 3). The authors usually insert screws with angle of 25°–45° from the sagittal plane for the pedicle from C3 to C6. A small specially designed pedicle probe, a
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Fig. 2 Direction of cervical pedicle screw in three planes starting point of cervical pedicle screw insertion considering the direction of the pedicle axis will be near the lateral margin of the lateral mass. Screw direction to the sagittal plane is 40°–60° for C3–C6 [23]
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changes or by extremely small diameter are not suited for screw insertion because of a high possibility of screw malposition. In patients with marked degenerative changes in the lateral mass of the cervical spine, location of the starting point of the pedicle screw is hard to be found. In such case, orientation of screw insertion point can be obtained after resection of the proliferated lateral mass using high-speed burr. The screw diameter in the authors series was 3.5, 4.0, and 4.5 mm depending on the pedicle diameter of the each vertebra, and the length of screw was 20, 22, and 24 mm. Regarding the longitudinal connectors, plate was used for one or two segmental fixation, and 3/16 inches rod was employed for three or longer fixation. Karaikovic et al. suggested by their morphologic study that there is no safe zone anterior to the cervical vertebral bodies in the cervical spine except C2, and only C2 would allow bicortical purchase of pedicle screws without being close to important surrounding structures [36]. In the present author’s series, screw tips were not penetrated for C3–C7 vertebra; however, bicortical purchase was conducted for C2 in severely osteoporotic patient to increase the stability of the screw. Simultaneous posterior decompression and fixation
Fig. 3 Direction of cervical pedicle screw after funnel-like hole creation. Black broken line indicates anatomical axis of the pedicle. Point A on the right side of the lateral mass is the screw insertion point. Screw can be inserted between two black arrows. After resection of the outer portion of the lateral mass toward the entrance of the pedicle cavity as a funnel-like shape using high-speed burr (shaded portion on the left side of the pedicle), starting point of screw approach to the entrance of the pedicle cavity (Point B), and surgeon obtain more freedom of screw insertion angle (shaded portion on the vertebral body)
tap and screws are inserted into the pedicle under the guidance of lateral C-arm image to confirm the direction and insertion depth. The authors recommend checking a proper creation of screw insertion path with a cervical pedicle sounder with a small ball tip after probing and tapping (Fig. 4a–c). The angle of screw insertion in the sagittal plane should be parallel to the cranial endplate for the pedicles of C5 through C7, and a slightly cephalad direction in C2 through C4, according to anatomical angle of the pedicle in the sagittal plane (Fig. 5). A drill bit should not be used to make holes for screw placement. When the neurocentral junction in the cervical spine close to the base of the pedicle in the vertebral body is too hard to pass a pedicle probe, the junction can be perforated with a Kirschner wire or a high-speed diamond burr with its smallest size. At that time, a tip of wire or burr must not go deeper but only make the path for a pedicle probe to get into the vertebral body. The cervical pedicles without medullary canal by sclerotic
Laminoplasty, laminectomy and foraminotomy with pedicle screw fixation can be conducted for cervical spondylotic myelopathy with unstable segment. Author recommends screw insertion prior to posterior decompression avoiding handling of instrumentation over the exposed dura mater. Simple plate fixation is preferred for one- or two-segment fixation (Fig. 6a, b). Alignment of screw head in the coronal plane may be off in multilevel fixation. Therefore, a rod with a screw rather than plate is recommended for multilevel fixation over three segments. Correction of cervical deformities Correction of cervical kyphosis: Pedicle screw procedure is a strong tool for correction of the deformities in the cervical spine. Plates and rods are contoured in the sagittal plane with the expected correction of kyphotic deformity. Correction of the kyphosis is performed by tightening the nuts or by rotating the rods using rod holders. As a consequence, the posterior part of the cervical spine can be shortened. Therefore, surgeons must be careful to avoid excessive shortening of the spine because of the potential for the development of a nerve root lesion by foraminal stenosis. If preoperative radiological assessments revealed marked stenosis of the neural foramina, even though it was asymptomatic, prophylactic foraminotomy is recommended especially at C4/5 level. Flexible kyphosis can be managed by single posterior approach (Fig. 7a, b);
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Fig. 4 Regulation of screw insertion using C-arm. a Two broken lines indicate cranial and caudal margin of the pedicle. b Pedicle probe must be advanced between two broken lines. c Tapping of
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screw insertion hole. Authors recommend confirming proper creation of screw insertion path after probing and tapping using pedicle sounder
Pitfalls to avoid Surgeons must keep in mind that there must be a limitation of placing pedicle screws in the cervical spine due to anatomical variations of the pedicle or the vertebral artery. Possible complications which directly relate to pedicle screw insertion in the cervical spine are nerve root injuries by cranially or caudally misplaced screws, vertebral artery injuries or obstruction by laterally misplaced screw and injuries to the dural sac or the spinal cord by medially misplaced screw. Vertebrae with abnormal morphology on the pedicle or vertebral artery especially associate high risk of neurovascular complication. Neo et al. [34] reported 29 % of screw perforation rate from the cervical pedicle in patients with cervical degenerative vertebra. In their series, no symptomatic neurovascular complication was occurred by perforated screws. Morphology of the pedicle
Fig. 5 Screw direction in the sagittal plane. The intended angle of screw insertion in the sagittal plane is parallel to the cranial endplate for the C5–C7 pedicles, and slightly cephalad for the C2–C4 pedicles because of the pedicle angle in the sagittal plane
however, rigid, fixed or marked kyphosis requires combined anterior and posterior approach (Fig. 8a, b). Correction of cervical scoliosis: Case of cervical scoliosis requiring surgical correction is uncommon. However, if necessary, the deformity is correctable using this procedure applying distraction force on the concave side. Application of compression force on the convex side is not recommended considering iatrogenic nerve root complication by foraminal stenosis (Fig. 9a, b).
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According to the previous morphometric studies of the cervical pedicle, outer pedicle diameter is more than 5 mm in most cervical vertebrae, and for those pedicles, screws can be inserted. If outer pedicle diameter is less than 4 mm, screw insertion is quite difficult or impossible and then alternative fixation anchors, such as lateral mass screws or posterior wirings, are recommended. Thin cut axial CT scans (adjusted to the bone windows) with 1.0–2.0 mm slice are recommended for accurate evaluation of pedicle diameters to measure the pedicle width, which helps surgeons to choose the appropriate pedicle screw diameter, length, and direction in the transverse plane. Figure 11 shows diameter differences between the left and the right pedicle in the same vertebra (Fig. 10). This diameter difference in the same vertebra shows that the vertebral artery
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Fig. 6 Simultaneous posterior decompression and monosegmental fixation. A patient with cervical spondylotic myelopathy associated with segmental instability at C3/4. a X-ray films in flexion and extension position showing segmental instability at C3/4. MRI images
demonstrate narrowed spinal canal and spinal cord compression. b Postoperative X-ray film shows C3/4 single level pedicle screw/plate fixation. Axial CT scans demonstrate location of inserted screws
on the side of smaller pedicle diameter is dominant so that surgeons must pay special attentions to pedicle screw insertion on this side. Since the thinnest cortex of the pedicle is always at the lateral cortex, the medial cortex of the pedicle can be used as a guide to insert a screw into the vertebral body through the pedicle isthmus.
involving the vertebral artery. The incidence of ischemic brain complication caused by unilateral obstruction of the vertebral artery has been reported low. However, if the dominant side of the vertebral artery was injured, serious neurological complications could occur. Magnetic resonance angiograph (MRA) and CT angiograph (CTA) provide information regarding the right–left domination and anatomical variations to the vertebral artery. MRA or CTA must be conducted for the patients if there is an evidence of the abnormalities or even a suspect of these abnormalities on plain CT or MR images. The vertebral artery sometimes
Conditions of the vertebral artery Preoperative evaluation of the morphology of the vertebral artery is indispensable to prevent serious complications
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Fig. 7 Correction of flexible kyphosis. a A patient with cervical spondylotic myelopathy with 38° of flexible kyphosis developed after open door laminoplasty. Anterior aspect of the spinal cord was compressed at the apex of kyphosis. b Scar tissue covering the dura matter was detached prior to correction of kyphosis avoiding spinal
cord compression by buckling of scar tissue. Kyphosis was corrected to 5° by single posterior approach. Postoperative MRI demonstrated sufficient spinal cord decompression by correction of kyphosis. 10/17 points of JOA score improved to 14/17 points
crooks into the vertebral body with loops, and screw insertion into the ipsilateral side of the pedicle is too risky to the artery (Fig. 11). In these situations, pedicle screw insertion into the ipsilateral side of the pedicle must be omitted, or alternative fixation anchors including lateral mass screws or wiring procedures have to be employed. Recent morphometric analysis by Tomasino et al. [37] concerning the relationship between the vertebral artery and the cervical pedicles showed that pedicle diameter, safe zone, and occupational relation of the vertebral artery in the transverse foramen showed considerable individual variations so that the risks to the neurovascular structures
associated with pedicle screw placement must be assessed individually.
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Nerve root complication by iatrogenic foraminal stenosis Some neural foramina in patients with degenerative disorders or rheumatoid arthritis are narrow on preoperative images. From our experience and the report by Heller et al. [38] who used lateral mass screws, in those with preoperative narrow neural foramina, there is a risk of iatrogenic nerve root impingement due to worsening of foraminal stenosis caused by either anterior translation or correction
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Fig. 8 Correction of rigid kyphosis. a A patient with mild cervical spondylotic myelopathy accompanied 43° of rigid kyphosis. (1) Preoperative MRI demonstrated spinal cord compression at the apex of kyphosis. A sagittal image of the CT scan appreciates the rigidity of deformity. b The patient underwent three-staged correction surgery by single anesthesia: (1) C4 corpectomy with bilateral uncinectomy of
C4 and C5, (2) Posterior correction after C3–5 laminectomy, (3) anterior strut grafting with expandable cage. 43° of preoperative kyphosis improved to 8°, and myelopathy disappeared completely. Left side of C2 screw was stopped at the pars interarticularis considering the high riding vertebral artery
of kyphosis by reduction procedures. According to the previous report by Hojo et al. and Nakashima et al. [16, 39], rate of C5 nerve root lesion by foraminal stenosis of C4/5 is especially high. Surgeons should keep in mind not to apply excessive compression force posteriorly at the segments with preoperative foraminal stenosis while correcting kyphotic deformity. Otherwise, prophylactic foraminotomies before correction of cervical kyphosis are recommended in patients with marked stenosis of the neural foramina. Reconstructive CT images in the oblique plane can provide useful information about the conditions of the neural foramina. Besides the iatrogenic foraminal stenosis, excessive caudal traction of the shoulder girdle for C-arm projection may be the cause of brachial nerve palsy presenting similar
nerve symptoms as foraminal stenosis. Diminish or decrease of EMG activity or MEP (motor evoked potential) during surgery may demonstrate decrease of nerve root function, and recovery of EMG or MEP after additional foraminotomy or release of pulling force may define the cause. Combination of cervical pedicle screws with lateral mass screws Combined use of C2 and/or C7 pedicle screws with C3–C6 lateral mass screws are more widespread and less technically demanding than single use of pedicle screws for cervical reconstructive surgery [40, 41]. The combined use must provide similar biomechanical stability to the reconstructed cervical spine as pedicle screw fixation. However,
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Fig. 9 Correction of cervical scoliosis. a Preoperative images demonstrate 31° of scoliosis after laminoplasty. The patient suffered from severe radiculopathy of left C5 and C6 caused by C4/5 and C5/6 foraminal stenosis. Preoperative CT scans demonstrate proliferated degenerative changes of the left lateral mass. b Outer layer of the proliferated lateral mass of C4–C6 was resected using high-speed burr to obtain orientation of screw insertion point. After pedicle screw
insertion, foraminotomy at C4/5 and C5/6 and correction of scoliosis by application of distraction force on the concave site were conducted. Preoperative radiculopathy healed almost completely. Postoperative images show sufficient correction of scoliosis. Postoperative CT images show proper screw placement in each vertebra and enlarged C4/5 and C5/7 neural foramina (white arrow)
the combined use usually require longer fixation sacrificing stable motion segments to provide sufficient stability than pedicle screw fixation.
tool for correction of cervical deformities in sagittal and/or coronal planes for the patient with cervical spondylotic myelopathy. In addition, the patients with cervical spondylotic myelopathy associating segmental instability can be managed by simultaneous decompression and stabilization using pedicle screw fixation. On the other hand, even with the application of established surgical techniques, neurovascular complications including injury to the vertebral artery and nerve root cannot be completely eliminated. Even after surgeons became familiar with the
Summary Biomechanical studies revealed the superior stabilizing effect of pedicle screw fixation than other internal fixation procedures in the cervical spine. This procedure is a strong
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Fig. 10 Retrogression of the pedicle at the dominant side of the vertebral artery. a The left and right pedicles in the same vertebra differ extremely in diameter. The foramen transversarium enlarges in
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the smaller side of the pedicle (white arrow). b The vertebral artery is dominant in the ipsilateral side of enlarged foramen transversarium (black arrow)
References
Fig. 11 Tortuous course of the vertebral artery. CT images show abnormal shape of the foramen transversarium of left C5 and right C6 (arrow head). Angiograph demonstrates tortuous course of the vertebral artery at left C5 and right C6 (arrow)
placement of cervical pedicle screws, screw malposition rate by freehand technique is high for patients with severe spondylotic condition. Surgeons must especially be careful for inserting pedicle screw in the cervical spine associating marked degenerative changes by spondylosis, and must obtain preoperatively sufficient anatomical information of the pedicle and surrounding structures. Combined procedure of posterior reconstructive surgery using a pedicle screw fixation provides better clinical outcomes than laminoplasty alone for cervical spondylotic myelopathy accompanying local kyphosis or segmental instability. Further development of supporting tools for cervical pedicle screw insertion including aiming device, navigation system and neuromonitoring procedure is expected for safer screw insertion. Conflict of interest Author declares that there is no actual or potential conflict of interest with organizations in relation to this article.
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