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Effect of posterior subsidence on cervical alignment after anterior cervical corpectomy and reconstruction using titanium mesh cages in degenerative cervical disease
Journal of Clinical Neuroscience 21 (2014) 1779–1785
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Journal of Clinical Neuroscience journal homepage: www.elsevier.com/locate/jocn
Clinical Study
Effect of posterior subsidence on cervical alignment after anterior cervical corpectomy and reconstruction using titanium mesh cages in degenerative cervical disease Jae-Won Jang, Jung-Kil Lee ⇑, Jung-Heon Lee, Hyuk Hur, Tae-Wan Kim, Soo-Han Kim Department of Neurosurgery, Chonnam National University Medical School & Research Institute of Medical Sciences, 671, Jebongno, Dong-gu, Gwangju 501-757, Republic of Korea
a r t i c l e
i n f o
Article history: Received 28 May 2013 Accepted 8 February 2014
Keywords: Cervical reconstruction Corpectomy Lordosis Posterior subsidence Titanium mesh cage
a b s t r a c t Subsidence after anterior cervical reconstruction using a titanium mesh cage (TMC) has been a matter of debate. The authors investigated and analyzed subsidence and its effect on clinical and radiologic parameters after cervical reconstruction using a TMC for degenerative cervical disease. Thirty consecutive patients with degenerative cervical spine disorders underwent anterior cervical corpectomy followed by reconstruction with TMC. Twenty-four patients underwent a single-level corpectomy, and six patients underwent a two-level corpectomy. Clinical outcomes were assessed using a Visual Analogue Scale (VAS), the Japanese Orthopedic Association (JOA) score and the Neck Disability Index (NDI). Fusion status, anterior and posterior subsidence of the TMC, segmental angle (SA) and cervical sagittal angle (CSA) were assessed by lateral and flexion-extension radiographs of the neck. The mean follow-up period was 27.6 months (range, 24 to 49 months). The VAS, NDI and JOA scores were all significantly improved at the last follow-up. No instances of radiolucency or motion-related pseudoarthrosis were detected on radiographic analysis, yielding a fusion rate of 100%. Subsidence occurred in 28 of 30 patients (93.3%). The average anterior subsidence of the cage was 1.4 ± 0.9 mm, and the average posterior subsidence was 2.9 ± 1.2 mm. The SA and CSA at the final follow-up were significantly increased toward a lordotic angle. Anterior cervical reconstruction using TMC and plating in patients with cervical degenerative disease provides good clinical and radiologic outcomes. Cage subsidence occurred frequently, especially at the posterior part of the cage. Despite the prominent posterior subsidence of the TMC, SA and CSA were improved on final follow-up radiographs, suggesting that posterior subsidence may contribute to cervical lordosis. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Anterior cervical corpectomy is an effective procedure for decompression of the spinal cord in patients with severe canal stenosis and anterior pathologies, especially when the disease involves one or two vertebral levels [1–3]. This procedure has been employed for various cervical disorders including cervical spondylosis, trauma, tumor, deformity correction, infection and rheumatoid arthritis [1,3]. Stabilization and reconstruction after corpectomy is challenging and may be accomplished with iliac crest or fibular strut autografts or with allografts. Concerns have been raised regarding the efficacy and potential complications of each of these fusion techniques. Although autologous iliac bone grafts are considered to be an ideal fusion material with a high fusion rate, ⇑ Corresponding author. Tel.: +82 62 220 6602; fax: +82 62 224 9865. E-mail address: [email protected] (J.-K. Lee). http://dx.doi.org/10.1016/j.jocn.2014.02.016 0967-5868/Ó 2014 Elsevier Ltd. All rights reserved.
this technique has been questioned due to its donor-site harvestrelated morbidities [4]. Fibula strut autografts are an alternative donor site but have been reported to be associated with stress fractures of the tibia, ankle instability and chronic pain. Allografts and bone substitutes have higher rates of nonunion than autografts and may be associated with a higher incidence of graft collapse [5–11]. Titanium mesh cages (TMC) are an alternative option that may help to avoid the complications related to graft collection and are gaining acceptance. TMC with local bone grafting from corpectomy have additional advantages including immediate anterior column stability, easy control of the cage length, good biocompatibility, reduced instrumentation-related morbidity and shorter operating times. The aim of this study was to evaluate the clinical results and effectiveness of TMC for post-corpectomy reconstruction of patients with cervical degenerative disease who underwent single or two-level anterior cervical corpectomy using TMC filled with autologous bone chips.
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2. Materials and methods 2.1. Study population From December 2006 to April 2010, a total of 30 patients underwent anterior cervical fusion using TMC (Pyramesh; Medtronic Sofamor Danek, Memphis, TN, USA) that were filled with autologous bone chips obtained from the corpectomy site, were reviewed. Anterior cervical plates (Zephir; Medtronic Sofamor Danek, Memphis, TN, USA) were also used to stabilize the affected segments in all patients. In general, corpectomies were performed when there was evidence of disease behind the vertebral body. The patient population included 19 men and 11 women. Their ages ranged from 24 to 78 years, with a mean age of 52.4 years. The mean follow-up period was 27.6 months (range, 24– 49 months). All 30 patients requiring cervical corpectomy had degenerative disease (16 cases of spondylosis, 12 cases of ossification of the posterior longitudinal ligament and two cases of ruptured discs). Of the 30 patients, 15 presented with myelopathy, and 15 patients presented with radiculopathy. Patients with neoplastic, traumatic and infectious diseases were excluded from the study. A summary of the preoperative characteristics of the 30 patients is provided in Table 1. 2.2. Surgical procedure Under general anesthesia, the patient was placed in the supine position with the neck slightly extended using a foam roll beneath the shoulders. No external traction was used. The cervical spine was exposed using a standard anterior right-sided approach medial to the sternocleidomastoid muscle, using a transverse incision for a single-level corpectomy and an oblique incision for two-level corpectomy. After dividing the platysma sharply at right angles to the skin incision, blunt finger dissection between the carotid sheath and esophagus was performed, thereby exposing the anterior cervical spine. Following this, the vertebral levels were identified radiographically, and the anterior longitudinal ligament was incised. An interbody pin distractor system was always used prior to performing discectomies above and below the affected site. After the adjacent discectomies, the anterior two-thirds of the vertebral body was excised using a rongeur, and the posterior third was removed using curettes and a high-speed drill. Autologous bone chips obtained from the excised vertebral body were used as the bone graft material. The posterior longitudinal ligament Table 1 Preoperative characteristics of patients with degenerative cervical spine disorders undergoing anterior cervical corpectomy and fusion Patients, n Sex Male Female
19 11
Age, years <50 50–60 >60
11 8 11
Diagnosis Degenerative disease Spondylosis OPLL Ruptured HNP
30 16 12 2
Symptoms Radiculopathy Myelopathy
15 15
HNP = herniated nucleus pulposus, OPLL = ossification of posterior longitudinal ligament.
was excised in all patients to complete decompression of the spinal cord and exiting nerve roots. The cartilage was cleaned from the endplates of the adjacent intact vertebral bodies, which were flattened with a high-speed drill or curettes, carefully preserving most of the cortical part of the endplates. After good pulsation was observed, thereby confirming anterior protrusion of the dural theca, the distance between the intact vertebral endplates was carefully measured. An appropriate TMC was selected and cut down to fit the corpectomy defect. After trimming the titanium mesh to fit the graft site, cancellous bone chips from the excised vertebral body were morselized and packed into the cage. The TMC, packed with the autograft, was then inserted into the corpectomy defect under traction. Cancellous bone from the corpectomy was applied around the lateral and anterior convexity of the cage. Finally, an anterior cervical plate was applied to achieve anterior cervical fixation. Proper hardware placement was confirmed by intraoperative fluoroscopy. Postoperatively, all patients wore a cervical collar brace for 4–6 weeks; early ambulation was encouraged. 2.3. Clinical assessment Clinical outcomes were assessed preoperatively and at the final follow-up using the Visual Analog Scale (VAS) for arm and neck pain (0 = no symptoms, 10 = maximum pain), the Neck Disability Index (NDI) and the Japanese Orthopedic Association (JOA) score. The NDI scoring system includes scores for pain intensity, personal care, lifting, reading, headaches, concentration, work, driving, sleeping, and recreation. The maximal NDI score is 50, and a lower score represents a better clinical condition. Myelopathic symptoms were rated according to the JOA scoring system for evaluation of functional neurologic status. The JOA scoring system used assessed motor function of the upper and lower extremities, sensory function of the trunk, upper and lower extremities, and bladder function. A total score of 17 is given to normal individuals. 2.4. Radiological assessment All patients underwent dynamic radiographs before surgery, immediately after surgery and at the final follow-up. CT scans were pe in selected patients depending on the clinical indication. The following parameters were assessed radiologically: segmental angle (SA), cervical sagittal angle (CSA) and anterior (AIBH) and posterior interbody height (PIBH). These parameters were determined based on neutral lateral radiographs taken with the patient in a standing position. The SA was defined as the angle formed between the lines drawn parallel to the cranial endplate of the most cranial vertebra and the caudal endplate of the most caudal vertebra at the fusion level (Fig. 1A). The CSA was defined as the angle formed by the lines drawn parallel to the caudal endplate of C2 and the caudal endplate of C7 (Fig. 1B). Anterior subsidence was defined as the difference in AIBH between the postoperative and final follow-up values, and posterior subsidence was defined as the difference in PIBH between the postoperative and final follow-up values. A solid fusion was diagnosed using the following radiologic parameters on lateral radiographs or CT scan: no movement or less than 2° of motion on dynamic radiographs; absence of lucency or halo around the screw or cage-bone interfaces; absence of screw back-out, plate breakage or migration; and osseous continuity through and/or around the cage and the adjacent upper and lower endplates. These measurements were performed by a single independent observer who was not involved with the surgery or care of patients. 2.5. Statistical analysis Radiographic parameters and clinical outcomes at the last follow-up were compared with preoperative data. Data were
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Fig. 1. (A) Sagittal radiograph showing the segmental angle (SA) between the lines drawn parallel to the cranial endplate of the most cranial vertebra and the caudal endplate of the most caudal vertebra in the fusion segment. (B) Sagittal radiograph showing the cervical sagittal angle (CSA) formed by the lines drawn parallel to the caudal endplate of C2 and the caudal endplate of C7. The anterior interbody height (AIBH) is the length between the anterior portions of the adjacent upper and lower endplates (arrowed line, left), and the posterior interbody height (PIBH) is the length between the posterior portions of the adjacent upper and lower endplates (arrowed line, right).
analyzed using the Statistical Package for the Social Sciences (SPSS, Chicago, IL, USA); the paired t-test and the Mann–Whitney U test were used for analyses. To identify the correlation between subsidence and age, Spearman correlation analysis was used. Data are presented as the mean ± standard deviation. For all analyses, a p value of < 0.05 was considered statistically significant. 3. Results Among the 30 patients, single-level corpectomy was performed in 24 patients; the fusion levels were C3 in one patient, C4 in three patients, C5 in 14 patients, C6 in five patients and C7 in one patient. Six patients underwent two-level corpectomy, at levels C4–5 in one patient and C5–6 in five patients. 3.1. Clinical outcomes A summary of the clinical outcomes is provided in Table 2. In most patients, neurologic recovery was most evident in the first 3 months postoperatively but slowed down somewhat between 6 and 12 months. The mean VAS scores for arm and neck pain, respectively, were 7.6 ± 1.6 and 6.9 ± 1.6 before surgery and 2.1 ± 1.0 and 2.6 ± 1.3 at the final follow-up. The difference was Table 2 Clinical parameters measured preoperatively and at last follow-up after anterior cervical corpectomy and fusion Parameter
Preoperative
Last follow-up
p value
VAS (neck) VAS (arm) NDI score JOA score
6.9 ± 1.6 7.6 ± 1.6 24.4 ± 4.8 11.1 ± 4.7
2.6 ± 1.3 2.1 ± 1.0 9.1 ± 2.8 12.9 ± 3.4
< 0.05 < 0.05 < 0.05 < 0.05
Data are presented as mean ± standard deviation. JOA = Japanese Orthopedic Association, NDI = Neck Disability Index, VAS = Visual Analogue Scale.
statistically significant compared with the preoperative scores (p < 0.05). The mean preoperative NDI score was 24.4 ± 4.8 and decreased to 16.9 ± 6.2 immediately after surgery. At the last follow-up, the score had improved to 9.1 ± 2.8, which was a statistically significant difference compared with preoperative scores (p < 0.05). With regard to myelopathic symptoms, the JOA score was 11.1 ± 4.7 points before surgery and increased to 12.9 ± 3.4 points at the final follow-up. This difference was also statistically significant (p < 0.05). Overall, the clinical symptoms of myelopathy and radiculopathy significantly improved after surgery. No patient had neurologic deterioration after surgical treatment. 3.2. Radiological outcomes Table 3 summarizes the comparisons of the degree of subsidence among patients who underwent single-level corpectomy, those who underwent two-level corpectomy and all patients. For patients who underwent a single-level corpectomy, the average AIBH was 53.6 ± 2.8 mm before surgery, 57.4 ± 2.4 mm immediately after surgery and 56.3 ± 2.1 mm at the last follow-up. The average PIBH was 52.8 ± 3.1 mm before surgery, 56.2 ± 3.7 mm immediately after surgery and 54.1 ± 3.8 mm at the last followup. For patients who underwent a two-level corpectomy, the mean AIBH was 69.1 ± 6.7 mm before surgery, 73.4 ± 8.1 mm immediately after surgery and 71.3 ± 5.3 mm at the last follow-up. The mean PIBH was 67.9 ± 7.1 mm before surgery, 73.1 ± 5.5 mm immediately after surgery and 69.7 ± 7.4 mm at the last followup. In both groups, the AIBH and PIBH were significantly increased immediately after surgery (p < 0.05). However, at the last followup, there was a significant decrease in the AIBH and PIBH (p < 0.05). Overall, the mean AIBH was 57.2 ± 8.9 mm before surgery, 60.8 ± 9.1 mm immediately after surgery and 58.8 ± 7.5 mm at the last follow-up. The mean PIBH in all patients was 56.7 ± 8.7 mm before surgery, 60.2 ± 8.2 mm immediately after surgery and 57.5 ± 8.1 mm at the last follow-up. The mean anterior
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Table 3 Comparison of anterior and posterior interbody height of single-level, two-level, and all patients before anterior cervical corpectomy and fusion, immediately after surgery, and at the final follow-up Preoperative
Postoperative
Final follow-up
p value
Single-level AIBH
53.6 ± 2.8
57.4 ± 2.4
56.3 ± 2.1
Single-level PIBH
52.8 ± 3.1
56.2 ± 3.7
54.1 ± 3.8
Two-level AIBH
69.1 ± 6.7
73.4 ± 8.1
71.3 ± 5.3
Two-level PIBH
67.9 ± 7.1
73.1 ± 5.5
69.7 ± 7.4
All AIBH
57.2 ± 8.9
60.8 ± 9.1
58.8 ± 7.5
All PIBH
56.7 ± 8.7
60.2 ± 8.2
57.5 ± 8.1
< 0.001* 0.036+ < 0.001* 0.009+ < 0.001* 0.012+ < 0.001* < 0.001+ < 0.001* 0.018+ < 0.001* < 0.001+ < 0.05
Average anterior subsidence Average posterior subsidence
1.4 ± 0.9 2.9 ± 1.2
patient age and amount of anterior subsidence (Table 5). There were no significant differences in the amount of anterior and posterior subsidence in patients with radiculopathy versus those with myelopathy (Table 6). 3.4. Procedure-related complications No patient in our series developed a hematoma or wound infection postoperatively. There were no instances of vertebral artery injury, recurrent laryngeal nerve palsy or esophageal or tracheal laceration. There was no case of hardware failure such as migration, breakage or collapse during the follow-up period. We did not encounter any adjacent segment stenosis or instability during the follow-up period. As a result, additional surgical procedures were not needed. 4. Discussion
Data are presented as mean ± standard deviation. Comparison of preoperative and postoperative values. + Comparison of postoperative and last follow-up values. AIBH = anterior interbody height, PIBH = posterior interbody height. *
subsidence was 1.4 ± 0.9 mm, and the posterior subsidence was 2.9 ± 1.2 mm. A significant difference was observed between anterior and posterior subsidence (p < 0.05). At the last follow-up, cage subsidence was observed in 28 patients (93.3%), but there was no statistically significant difference in subsidence between patients who underwent single-level and two-level corpectomies (p > 0.05). A summary of the SA and CSA outcomes is shown in Table 4. The negative values signify the cervical lordotic angle and the positive values signify the cervical kyphotic angle. The average sagittal CSA was 11.3 ± 6.1° (range, 15.1 to 19.5) before surgery, 11.6 ± 3.2° (range, 2.9 to 16.0) immediately after surgery (p > 0.05), and 16.3 ± 6.1° (range, 0.1 to 22.8) at the last follow-up. Although there was no significant difference in pre- and postoperative CSA, the CSA was significantly more lordotic at the last follow-up (p < 0.05). The average preoperative SA was 3.3 ± 3.8° (range, 8.9 to 9.8), which was corrected to 5.9 ± 2.1° (range, 2.1 to 13.6) immediately after surgery. At the last follow-up, the SA was 8.7 ± 2.3° (range, 2.6 to 18.6). The SA increased significantly after surgery, and the SA had increased further at the last follow-up (p < 0.05). Solid fusion was achieved in all patients at the last follow-up. Union was noted in all patients between the cage and the adjacent endplates. 3.3. Relationship between subsidence and age, myelopathy and radiculopathy Correlation analysis was performed to investigate the relationship between patient age and amount of subsidence. The amount of posterior subsidence was significantly positively correlated to patient age for single-level corpectomy (Spearman’s coefficient = 0.702; p < 0.05) and for all patients (Spearman’s coefficient = 0.601; p < 0.05). However, there was no significant correlation between
The use of a tricortical autologous bone graft from the iliac crest is the gold standard for reconstruction of corpectomy defects. However, donor site morbidity has been reported in up to 25% of patients undergoing this procedure, including prolonged donor site pain, nerve injury, infection and hematoma formation [11–13]. Among these, the most important problem was reported to be postoperative pain at the graft site. Silber et al. [14] reported chronic pain in 26.1% of patients and functional impairment in >10% of patients 48 months after iliac bone graft harvesting. Such concerns about donor site-related complications have led many surgeons to consider using allografts. When allografts are used, the morbidity associated with graft harvesting is avoided, but the disadvantages of allografts persist, including lower fusion rates, prolonged time to graft incorporation and potential risk of disease transmission [8,15–17]. Furthermore, bone graft collapse, graft migration/extrusion, telescoping, subsidence and resorption are common causes of autograft or allograft failure, resulting in pseudoarthrosis and kyphotic deformity [7,18–21]. Due to the potential disadvantages of structural bone grafts, synthetic cages such as TMC have been developed. TMC using autologous bone grafts from corpectomy bone chips can avoid donor site morbidity. TMC have large openings that provide excellent apposition of the end plate and bone graft to facilitate healing of the interface. They also permit lateral bony ingrowth along the length of the cage. Furthermore, TMC can provide immediate postoperative stability. In our series, an anterior cervical plate was used for stabilization in all patients. Anterior plate fixation provides a more rigid structure and results in a rapid solid fusion with a lower risk of graft-related complications. Although anterior plate fixation is not free from complications and morbidity, it has been shown to improve structural rigidity and prevent graft migration, late kyphotic collapse and pseudoarthrosis in multi-level fusions [22–25]. Cervical plates offer the advantage of improved initial stability in the postoperative period. Early spinal stability may lead to successful fusion. Graft stability may be due both to the anterior plate
Table 4 Radiological values of segmental angle and cervical sagittal angle measured before anterior cervical corpectomy and fusion, immediately after surgery, and at final follow-up Parameter Total 30 patients
Preoperative
Postoperative
Final follow-up
Segmental angle
3.3 ± 3.8
5.9 ± 2.1
8.7 ± 5.3
C2–7 angle (CSA)
11.3 ± 6.1
11.6 ± 3.2
15.3 ± 6.1
Data are presented as mean ± standard deviation. * Comparison of preoperative and postoperative. + Comparison of postoperative and last follow-up. CSA = cervical sagittal angle.
p value 0.023* 0.012+ 0.339* 0.037+
J.-W. Jang et al. / Journal of Clinical Neuroscience 21 (2014) 1779–1785 Table 5 Spearman’s correlation between age and cage subsidence after anterior cervical corpectomy and fusion Parameter
Single-level Two-level All patients
Anterior subsidence Posterior subsidence Anterior subsidence Posterior subsidence Anterior subsidence Posterior subsidence
Age r value
p value
0.230 0.702 0.276 0.414 0.342 0.601
0452 0.015* 0.374 0.172 0.271 0.023*
Data are shown in terms of r and p values by Spearman correlation analysis between age and subsidence. * p < 0.05. Table 6 Statistical analysis of cage subsidence between the radiculopathy and myelopathy groups after anterior cervical corpectomy and fusion Parameter
Radiculopathy group (n = 15)
Myelopathy group (n = 15)
p value
Age, years Anterior subsidence Posterior subsidence
49.2 ± 10.9 1.3 ± 1.1 2.8 ± 1.4
55.4 ± 12.7 1.5 ± 0.9 3.0 ± 1.5
0.164 0.432 0.572
Data are presented as mean ± standard deviation.
application and to the sharp teeth of the cage, which penetrate into the adjacent upper and lower endplates to provide relative internal stability. Postoperative spinal stability is closely related to clinical outcome. We had a good overall clinical outcome in our series. The VAS, NDI and JOA scores were all significantly improved at the last follow-up. Because the TMC is not radiolucent, it was difficult to determine if trabeculation had occurred. The fusion mass that surrounds the cages can be easier to assess with plain radiography than the fusion
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mass within the cages. We were also able to use indirect evidence to prove the presence of a successful fusion, such as a lack of movement on dynamic radiographs or the absence of peri-implant lucencies. Segmental stability was maintained on dynamic radiographs obtained from all patients during the follow-up period. Sagittal reconstruction of axial CT scans can be used to demonstrate bone growth within the TMC. The assessment of fusion by radiograph can be improved with the use of radiolucent carbon fiber and polyether-etherketone (PEEK) cages for interbody fusion. Although high fusion rates have been reported in the literature with this technique, a longer period was required to achieve solid fusion compared with a tricortical iliac autograft [26,27]. In vivo models showed that kyphosis plays an important role in increasing the degenerative changes in adjacent motion segments [28]. In our series, SA and CSA were well-restored postoperatively and were maintained in all patients until the last follow-up. Although corrections of the kyphotic angle were slowly lost in many patients by the time of final follow-up radiograph, severe collapse or significant recurrence of the deformity did not occur. The complications in the present study were relatively low. There were no new neurologic deficits, infections, recurrent laryngeal nerve injuries, cerebrospinal fluid leaks or esophageal or tracheal tears. However, subsidence of the cage into the end plates is one of the main concerns of this technique. Subsidence seemed to be unavoidable in the majority of patients who underwent TMC fusion and usually occurred before bone fusion was achieved. Excessive endplate removal, poor bone quality, increased patient age and multi-level corpectomy have been proposed as potential risk factors for subsidence [29]. Subsidence could diminish some of the advantages of TMC, such as restoration and maintenance of intervertebral disc height, enlargement of the stenotic neural foramen and immediate stabilization of operative segments. Severe subsidence can cause bucking of the yellow ligament and cervical misalignment. Chen et al. [30] reported the TMC
Fig. 2. Imaging studies of a 47-year-old man who underwent a C5 corpectomy. (A) Sagittal CT scan showing segmental ossification of the posterior longitudinal ligament in the cervical spine with kyphotic cervical alignment. (B) At the time of the last follow-up CT scan, the posterior subsidence of the cage was more prominent compared to the anterior subsidence. However, segmental angle and cervical sagittal angle were increased compared with preoperative measurements.
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Fig. 3. Schematic figure showing that posterior subsidence of the titanium mesh cage may create cervical lordosis during the follow-up period.
subsidence in 300 patients who underwent anterior cervical corpectomy. Cases of subsidence were classified as mild (1–3 mm) or severe (>3 mm). These investigators demonstrated TMC subsidence in 239 (79.7%) patients, of which 182 cases (60.7%) were mild and 57 (19.0%) were severe. Two-level corpectomy was more susceptible to severe subsidence compared with single-level corpectomy. In this study, cage subsidence was observed in 93.3% of patients; therefore, cage subsidence may be inevitable after anterior cervical reconstruction using TMC. However, it is not known if cage subsidence always has negative effects on fusion and cervical spine alignment after anterior reconstruction using TMC. This study showed that cage subsidence was not associated with significantly negative clinical results during the follow-up period. Moreover, subsidence may promote bone fusion by creating a broad contact surface between the cage and the vertebral body. Despite the fact that cage subsidence was observed in majority of our patients, fusion failure did not occur. We investigated anterior and posterior subsidence of the cage by measuring the AIBH and PIBH and found that cage subsidence was more severe on the posterior side compared to the anterior side of the cage. Several factors may explain why subsidence was more severe posteriorly than anteriorly. First, we positioned the TMC in the anterior two-thirds of the vertebral body after the corpectomy; therefore, the posterior part of cage contacted the weak, cancellous portion of the vertebral body, and the anterior part of cage contacted the hard cortical surface of the vertebral body. Second, the posterior body was more extensively drilled to remove posterior osteophytes or calcified ligaments. The bony endplate of the posterior part of the vertebral body therefore could be more damaged and more vulnerable to cage subsidence. Finally, the center of gravity is located in the posterior part of the cage due to cervical lordosis and the location of the cage, and greater compressive forces may act on the posterior part of the cage. Briefly, differences between the orientation of the TMC contact area and the endplates may be responsible for the unfavorable stress distribution that induces subsidence in this area. Interestingly, because subsidence was most prominent at the posterior rim of the TMC, it may help to maintain lordosis, as shown in Figure 2 and 3. In our study, both the SA and CSA were increased immediately after surgery and at the time of the last follow-up, despite the increasing posterior subsidence. These clinical and radiologic results suggest that minimal to moderate posterior subsidence of the TMC may have a positive effect on maintaining cervical alignment and functional outcomes. Generally, age reflects the bone mineral density, and it is well known that bone mineral density decreases as age increases. The present study showed that posterior subsidence was positively
correlated with age, but anterior subsidence was not correlated with age. This fact indicates that the posterior part of cage that contacted weak cancellous bone was more vulnerable to the sharp cage teeth, compared to the anterior part of cage, which is in contact with the hard cortical surface. Therefore, to obtain adequate posterior subsidence for cervical lordosis after fusion, excessive drilling of the posterior part of vertebral body should be avoided in elderly patients. 5. Conclusions The clinical and radiologic results of this study suggest that cervical reconstruction after single or two-level corpectomy can be safely and effectively performed using a TMC packed with autologous bone chips in conjunction with anterior cervical plating. This technique obviates the need for harvesting iliac bone grafts and results in solid anterior column reconstructions and good clinical outcomes. Cage subsidence was inevitable, but it tended to develop posteriorly due to the cage location, cervical lordosis and removal of posterior osteophytes. Despite the prominent posterior subsidence, SA and CSA were increased at the time of the last followup; thus, posterior subsidence may contribute to cervical lordosis. Conflicts of Interest/Disclosures The authors declare that they have no financial or other conflicts of interest in relation to this research and its publication. Acknowledgements This study was financially supported by Chonnam National University, 2011. References [1] Eleraky MA, Llanos C, Sonntag VK. Cervical corpectomy: report of 185 cases and review of the literature. J Neurosurg 1999;90:35–41. [2] Macdonald RL, Fehlings MG, Tator CH, et al. Multilevel anterior cervical corpectomy and fibular allograft fusion for cervical myelopathy. J Neurosurg 1997;86:990–7. [3] Mayr MT, Subach BR, Comey CH, et al. Cervical spinal stenosis: outcome after anterior corpectomy, allograft reconstruction, and instrumentation. J Neurosurg 2002;96:10–6. [4] Dorai Z, Morgan H, Coimbra C. Titanium cage reconstruction after cervical corpectomy. J Neurosurg 2003;99:3–7. [5] An HS, Simpson JM, Glover JM, et al. Comparison between allograft plus demineralized bone matrix versus autograft in anterior cervical fusion. A prospective multicenter study. Spine (Phila Pa 1976) 1995;20:2211–6. [6] Banwart JC, Asher MA, Hassanein RS. Iliac crest bone graft harvest donor site morbidity. A statistical evaluation. Spine (Phila Pa 1976) 1995;20:1055–60.
J.-W. Jang et al. / Journal of Clinical Neuroscience 21 (2014) 1779–1785 [7] Bishop RC, Moore KA, Hadley MN. Anterior cervical interbody fusion using autogeneic and allogeneic bone graft substrate: a prospective comparative analysis. J Neurosurg 1996;85:206–10. [8] Fernyhough JC, White JI, LaRocca H. Fusion rates in multilevel cervical spondylosis comparing allograft fibula with autograft fibula in 126 patients. Spine (Phila Pa 1976) 1991;16:S561–564. [9] Gaudinez RF, English GM, Gebhard JS, et al. Esophageal perforations after anterior cervical surgery. J Spinal Disord 2000;13:77–84. [10] Martin GJ Jr, Haid RW Jr, MacMillan M, et al. Anterior cervical discectomy with freeze-dried fibula allograft. Overview of 317 cases and literature review. Spine (Phila Pa 1976) 1999;24:852–8. [11] Sawin PD, Traynelis VC, Menezes AH. A comparative analysis of fusion rates and donor-site morbidity for autogeneic rib and iliac crest bone grafts in posterior cervical fusions. J Neurosurg 1998;88:255–65. [12] Sevki K, Mehmet T, Ufuk T, et al. Results of surgical treatment for degenerative cervical myelopathy: anterior cervical corpectomy and stabilization. Spine (Phila Pa 1976) 2004;29:2493–500. [13] Schnee CL, Freese A, Weil RJ, et al. Analysis of harvest morbidity and radiographic outcome using autograft for anterior cervical fusion. Spine (Phila Pa 1976) 1997;22:2222–7. [14] Silber JS, Anderson DG, Daffner SD, et al. Donor site morbidity after anterior iliac crest bone harvest for single-level anterior cervical discectomy and fusion. Spine (Phila Pa 1976) 2003;28:134–9. [15] Floyd T, Ohnmeiss D. A meta-analysis of autograft versus allograft in anterior cervical fusion. Eur Spine J 2000;9:398–403. [16] Malloy KM, Hilibrand AS. Autograft versus allograft in degenerative cervical disease. Clin Orthop Relat Res 2002:27–38. [17] Meding JB, Stambough JL. Critical analysis of strut grafts in anterior spinal fusions. J Spinal Disord 1993;6:166–74. [18] Sasso RC, Ruggiero Jr RA, Reilly TM, et al. Early reconstruction failures after multilevel cervical corpectomy. Spine (Phila Pa 1976) 2003;28:140–2.
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[19] Vaccaro AR, Falatyn SP, Scuderi GJ, et al. Early failure of long segment anterior cervical plate fixation. J Spinal Disord 1998;11:410–5. [20] Wang JC, Hart RA, Emery SE, et al. Graft migration or displacement after multilevel cervical corpectomy and strut grafting. Spine (Phila Pa 1976) 2003;28:1016–21 [discussion 1021–2]. [21] Zdeblick TA, Ducker TB. The use of freeze-dried allograft bone for anterior cervical fusions. Spine (Phila Pa 1976) 1991;16:726–9. [22] Böhler J, Gaudernak T. Anterior plate stabilization for fracture-dislocations of the lower cervical spine. J Trauma 1980;20:203–5. [23] Caspar W, Barbier DD, Klara PM. Anterior cervical fusion and Caspar plate stabilization for cervical trauma. Neurosurgery 1989;25:491–502. [24] Caspar W, Geisler FH, Pitzen T, et al. Anterior cervical plate stabilization in one- and two-level degenerative disease: overtreatment or benefit? J Spinal Disord 1998;11:1–11. [25] Connolly PJ, Esses SI, Kostuik JP, et al. Anterior cervical fusion: outcome analysis of patients fused with and without anterior cervical plates. J Spinal Disord 1996;9:202–6. [26] Kanayama M, Hashimoto T, Shigenobu K, et al. Pitfalls of anterior cervical fusion using titanium mesh and local autograft. J Spinal Disord Tech 2003;16:513–8. [27] Nakase H, Park YS, Kimura H, et al. Complications and long-term follow-up results in titanium mesh cage reconstruction after cervical corpectomy. J Spinal Disord Tech 2006;19:353–7. [28] Oda I, Cunningham BW, Buckley RA, et al. Does spinal kyphotic deformity influence the biomechanical characteristics of the adjacent motion segments? An in vivo animal model. Spine (Phila Pa 1976) 1999;24:2139–46. [29] Das K, Couldwell WT, Sava G, et al. Use of cylindrical titanium mesh and locking plates in anterior cervical fusion. Technical note. J Neurosurg 2001;94:174–8. [30] Chen Y, Chen D, Guo Y, et al. Subsidence of titanium mesh cage: a study based on 300 cases. J Spinal Disord Tech 2008;21:489–92.
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Journal of Clinical Neuroscience journal homepage: www.elsevier.com/locate/jocn
Clinical Study
Effect of posterior subsidence on cervical alignment after anterior cervical corpectomy and reconstruction using titanium mesh cages in degenerative cervical disease Jae-Won Jang, Jung-Kil Lee ⇑, Jung-Heon Lee, Hyuk Hur, Tae-Wan Kim, Soo-Han Kim Department of Neurosurgery, Chonnam National University Medical School & Research Institute of Medical Sciences, 671, Jebongno, Dong-gu, Gwangju 501-757, Republic of Korea
a r t i c l e
i n f o
Article history: Received 28 May 2013 Accepted 8 February 2014
Keywords: Cervical reconstruction Corpectomy Lordosis Posterior subsidence Titanium mesh cage
a b s t r a c t Subsidence after anterior cervical reconstruction using a titanium mesh cage (TMC) has been a matter of debate. The authors investigated and analyzed subsidence and its effect on clinical and radiologic parameters after cervical reconstruction using a TMC for degenerative cervical disease. Thirty consecutive patients with degenerative cervical spine disorders underwent anterior cervical corpectomy followed by reconstruction with TMC. Twenty-four patients underwent a single-level corpectomy, and six patients underwent a two-level corpectomy. Clinical outcomes were assessed using a Visual Analogue Scale (VAS), the Japanese Orthopedic Association (JOA) score and the Neck Disability Index (NDI). Fusion status, anterior and posterior subsidence of the TMC, segmental angle (SA) and cervical sagittal angle (CSA) were assessed by lateral and flexion-extension radiographs of the neck. The mean follow-up period was 27.6 months (range, 24 to 49 months). The VAS, NDI and JOA scores were all significantly improved at the last follow-up. No instances of radiolucency or motion-related pseudoarthrosis were detected on radiographic analysis, yielding a fusion rate of 100%. Subsidence occurred in 28 of 30 patients (93.3%). The average anterior subsidence of the cage was 1.4 ± 0.9 mm, and the average posterior subsidence was 2.9 ± 1.2 mm. The SA and CSA at the final follow-up were significantly increased toward a lordotic angle. Anterior cervical reconstruction using TMC and plating in patients with cervical degenerative disease provides good clinical and radiologic outcomes. Cage subsidence occurred frequently, especially at the posterior part of the cage. Despite the prominent posterior subsidence of the TMC, SA and CSA were improved on final follow-up radiographs, suggesting that posterior subsidence may contribute to cervical lordosis. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Anterior cervical corpectomy is an effective procedure for decompression of the spinal cord in patients with severe canal stenosis and anterior pathologies, especially when the disease involves one or two vertebral levels [1–3]. This procedure has been employed for various cervical disorders including cervical spondylosis, trauma, tumor, deformity correction, infection and rheumatoid arthritis [1,3]. Stabilization and reconstruction after corpectomy is challenging and may be accomplished with iliac crest or fibular strut autografts or with allografts. Concerns have been raised regarding the efficacy and potential complications of each of these fusion techniques. Although autologous iliac bone grafts are considered to be an ideal fusion material with a high fusion rate, ⇑ Corresponding author. Tel.: +82 62 220 6602; fax: +82 62 224 9865. E-mail address: [email protected] (J.-K. Lee). http://dx.doi.org/10.1016/j.jocn.2014.02.016 0967-5868/Ó 2014 Elsevier Ltd. All rights reserved.
this technique has been questioned due to its donor-site harvestrelated morbidities [4]. Fibula strut autografts are an alternative donor site but have been reported to be associated with stress fractures of the tibia, ankle instability and chronic pain. Allografts and bone substitutes have higher rates of nonunion than autografts and may be associated with a higher incidence of graft collapse [5–11]. Titanium mesh cages (TMC) are an alternative option that may help to avoid the complications related to graft collection and are gaining acceptance. TMC with local bone grafting from corpectomy have additional advantages including immediate anterior column stability, easy control of the cage length, good biocompatibility, reduced instrumentation-related morbidity and shorter operating times. The aim of this study was to evaluate the clinical results and effectiveness of TMC for post-corpectomy reconstruction of patients with cervical degenerative disease who underwent single or two-level anterior cervical corpectomy using TMC filled with autologous bone chips.
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2. Materials and methods 2.1. Study population From December 2006 to April 2010, a total of 30 patients underwent anterior cervical fusion using TMC (Pyramesh; Medtronic Sofamor Danek, Memphis, TN, USA) that were filled with autologous bone chips obtained from the corpectomy site, were reviewed. Anterior cervical plates (Zephir; Medtronic Sofamor Danek, Memphis, TN, USA) were also used to stabilize the affected segments in all patients. In general, corpectomies were performed when there was evidence of disease behind the vertebral body. The patient population included 19 men and 11 women. Their ages ranged from 24 to 78 years, with a mean age of 52.4 years. The mean follow-up period was 27.6 months (range, 24– 49 months). All 30 patients requiring cervical corpectomy had degenerative disease (16 cases of spondylosis, 12 cases of ossification of the posterior longitudinal ligament and two cases of ruptured discs). Of the 30 patients, 15 presented with myelopathy, and 15 patients presented with radiculopathy. Patients with neoplastic, traumatic and infectious diseases were excluded from the study. A summary of the preoperative characteristics of the 30 patients is provided in Table 1. 2.2. Surgical procedure Under general anesthesia, the patient was placed in the supine position with the neck slightly extended using a foam roll beneath the shoulders. No external traction was used. The cervical spine was exposed using a standard anterior right-sided approach medial to the sternocleidomastoid muscle, using a transverse incision for a single-level corpectomy and an oblique incision for two-level corpectomy. After dividing the platysma sharply at right angles to the skin incision, blunt finger dissection between the carotid sheath and esophagus was performed, thereby exposing the anterior cervical spine. Following this, the vertebral levels were identified radiographically, and the anterior longitudinal ligament was incised. An interbody pin distractor system was always used prior to performing discectomies above and below the affected site. After the adjacent discectomies, the anterior two-thirds of the vertebral body was excised using a rongeur, and the posterior third was removed using curettes and a high-speed drill. Autologous bone chips obtained from the excised vertebral body were used as the bone graft material. The posterior longitudinal ligament Table 1 Preoperative characteristics of patients with degenerative cervical spine disorders undergoing anterior cervical corpectomy and fusion Patients, n Sex Male Female
19 11
Age, years <50 50–60 >60
11 8 11
Diagnosis Degenerative disease Spondylosis OPLL Ruptured HNP
30 16 12 2
Symptoms Radiculopathy Myelopathy
15 15
HNP = herniated nucleus pulposus, OPLL = ossification of posterior longitudinal ligament.
was excised in all patients to complete decompression of the spinal cord and exiting nerve roots. The cartilage was cleaned from the endplates of the adjacent intact vertebral bodies, which were flattened with a high-speed drill or curettes, carefully preserving most of the cortical part of the endplates. After good pulsation was observed, thereby confirming anterior protrusion of the dural theca, the distance between the intact vertebral endplates was carefully measured. An appropriate TMC was selected and cut down to fit the corpectomy defect. After trimming the titanium mesh to fit the graft site, cancellous bone chips from the excised vertebral body were morselized and packed into the cage. The TMC, packed with the autograft, was then inserted into the corpectomy defect under traction. Cancellous bone from the corpectomy was applied around the lateral and anterior convexity of the cage. Finally, an anterior cervical plate was applied to achieve anterior cervical fixation. Proper hardware placement was confirmed by intraoperative fluoroscopy. Postoperatively, all patients wore a cervical collar brace for 4–6 weeks; early ambulation was encouraged. 2.3. Clinical assessment Clinical outcomes were assessed preoperatively and at the final follow-up using the Visual Analog Scale (VAS) for arm and neck pain (0 = no symptoms, 10 = maximum pain), the Neck Disability Index (NDI) and the Japanese Orthopedic Association (JOA) score. The NDI scoring system includes scores for pain intensity, personal care, lifting, reading, headaches, concentration, work, driving, sleeping, and recreation. The maximal NDI score is 50, and a lower score represents a better clinical condition. Myelopathic symptoms were rated according to the JOA scoring system for evaluation of functional neurologic status. The JOA scoring system used assessed motor function of the upper and lower extremities, sensory function of the trunk, upper and lower extremities, and bladder function. A total score of 17 is given to normal individuals. 2.4. Radiological assessment All patients underwent dynamic radiographs before surgery, immediately after surgery and at the final follow-up. CT scans were pe in selected patients depending on the clinical indication. The following parameters were assessed radiologically: segmental angle (SA), cervical sagittal angle (CSA) and anterior (AIBH) and posterior interbody height (PIBH). These parameters were determined based on neutral lateral radiographs taken with the patient in a standing position. The SA was defined as the angle formed between the lines drawn parallel to the cranial endplate of the most cranial vertebra and the caudal endplate of the most caudal vertebra at the fusion level (Fig. 1A). The CSA was defined as the angle formed by the lines drawn parallel to the caudal endplate of C2 and the caudal endplate of C7 (Fig. 1B). Anterior subsidence was defined as the difference in AIBH between the postoperative and final follow-up values, and posterior subsidence was defined as the difference in PIBH between the postoperative and final follow-up values. A solid fusion was diagnosed using the following radiologic parameters on lateral radiographs or CT scan: no movement or less than 2° of motion on dynamic radiographs; absence of lucency or halo around the screw or cage-bone interfaces; absence of screw back-out, plate breakage or migration; and osseous continuity through and/or around the cage and the adjacent upper and lower endplates. These measurements were performed by a single independent observer who was not involved with the surgery or care of patients. 2.5. Statistical analysis Radiographic parameters and clinical outcomes at the last follow-up were compared with preoperative data. Data were
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Fig. 1. (A) Sagittal radiograph showing the segmental angle (SA) between the lines drawn parallel to the cranial endplate of the most cranial vertebra and the caudal endplate of the most caudal vertebra in the fusion segment. (B) Sagittal radiograph showing the cervical sagittal angle (CSA) formed by the lines drawn parallel to the caudal endplate of C2 and the caudal endplate of C7. The anterior interbody height (AIBH) is the length between the anterior portions of the adjacent upper and lower endplates (arrowed line, left), and the posterior interbody height (PIBH) is the length between the posterior portions of the adjacent upper and lower endplates (arrowed line, right).
analyzed using the Statistical Package for the Social Sciences (SPSS, Chicago, IL, USA); the paired t-test and the Mann–Whitney U test were used for analyses. To identify the correlation between subsidence and age, Spearman correlation analysis was used. Data are presented as the mean ± standard deviation. For all analyses, a p value of < 0.05 was considered statistically significant. 3. Results Among the 30 patients, single-level corpectomy was performed in 24 patients; the fusion levels were C3 in one patient, C4 in three patients, C5 in 14 patients, C6 in five patients and C7 in one patient. Six patients underwent two-level corpectomy, at levels C4–5 in one patient and C5–6 in five patients. 3.1. Clinical outcomes A summary of the clinical outcomes is provided in Table 2. In most patients, neurologic recovery was most evident in the first 3 months postoperatively but slowed down somewhat between 6 and 12 months. The mean VAS scores for arm and neck pain, respectively, were 7.6 ± 1.6 and 6.9 ± 1.6 before surgery and 2.1 ± 1.0 and 2.6 ± 1.3 at the final follow-up. The difference was Table 2 Clinical parameters measured preoperatively and at last follow-up after anterior cervical corpectomy and fusion Parameter
Preoperative
Last follow-up
p value
VAS (neck) VAS (arm) NDI score JOA score
6.9 ± 1.6 7.6 ± 1.6 24.4 ± 4.8 11.1 ± 4.7
2.6 ± 1.3 2.1 ± 1.0 9.1 ± 2.8 12.9 ± 3.4
< 0.05 < 0.05 < 0.05 < 0.05
Data are presented as mean ± standard deviation. JOA = Japanese Orthopedic Association, NDI = Neck Disability Index, VAS = Visual Analogue Scale.
statistically significant compared with the preoperative scores (p < 0.05). The mean preoperative NDI score was 24.4 ± 4.8 and decreased to 16.9 ± 6.2 immediately after surgery. At the last follow-up, the score had improved to 9.1 ± 2.8, which was a statistically significant difference compared with preoperative scores (p < 0.05). With regard to myelopathic symptoms, the JOA score was 11.1 ± 4.7 points before surgery and increased to 12.9 ± 3.4 points at the final follow-up. This difference was also statistically significant (p < 0.05). Overall, the clinical symptoms of myelopathy and radiculopathy significantly improved after surgery. No patient had neurologic deterioration after surgical treatment. 3.2. Radiological outcomes Table 3 summarizes the comparisons of the degree of subsidence among patients who underwent single-level corpectomy, those who underwent two-level corpectomy and all patients. For patients who underwent a single-level corpectomy, the average AIBH was 53.6 ± 2.8 mm before surgery, 57.4 ± 2.4 mm immediately after surgery and 56.3 ± 2.1 mm at the last follow-up. The average PIBH was 52.8 ± 3.1 mm before surgery, 56.2 ± 3.7 mm immediately after surgery and 54.1 ± 3.8 mm at the last followup. For patients who underwent a two-level corpectomy, the mean AIBH was 69.1 ± 6.7 mm before surgery, 73.4 ± 8.1 mm immediately after surgery and 71.3 ± 5.3 mm at the last follow-up. The mean PIBH was 67.9 ± 7.1 mm before surgery, 73.1 ± 5.5 mm immediately after surgery and 69.7 ± 7.4 mm at the last followup. In both groups, the AIBH and PIBH were significantly increased immediately after surgery (p < 0.05). However, at the last followup, there was a significant decrease in the AIBH and PIBH (p < 0.05). Overall, the mean AIBH was 57.2 ± 8.9 mm before surgery, 60.8 ± 9.1 mm immediately after surgery and 58.8 ± 7.5 mm at the last follow-up. The mean PIBH in all patients was 56.7 ± 8.7 mm before surgery, 60.2 ± 8.2 mm immediately after surgery and 57.5 ± 8.1 mm at the last follow-up. The mean anterior
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Table 3 Comparison of anterior and posterior interbody height of single-level, two-level, and all patients before anterior cervical corpectomy and fusion, immediately after surgery, and at the final follow-up Preoperative
Postoperative
Final follow-up
p value
Single-level AIBH
53.6 ± 2.8
57.4 ± 2.4
56.3 ± 2.1
Single-level PIBH
52.8 ± 3.1
56.2 ± 3.7
54.1 ± 3.8
Two-level AIBH
69.1 ± 6.7
73.4 ± 8.1
71.3 ± 5.3
Two-level PIBH
67.9 ± 7.1
73.1 ± 5.5
69.7 ± 7.4
All AIBH
57.2 ± 8.9
60.8 ± 9.1
58.8 ± 7.5
All PIBH
56.7 ± 8.7
60.2 ± 8.2
57.5 ± 8.1
< 0.001* 0.036+ < 0.001* 0.009+ < 0.001* 0.012+ < 0.001* < 0.001+ < 0.001* 0.018+ < 0.001* < 0.001+ < 0.05
Average anterior subsidence Average posterior subsidence
1.4 ± 0.9 2.9 ± 1.2
patient age and amount of anterior subsidence (Table 5). There were no significant differences in the amount of anterior and posterior subsidence in patients with radiculopathy versus those with myelopathy (Table 6). 3.4. Procedure-related complications No patient in our series developed a hematoma or wound infection postoperatively. There were no instances of vertebral artery injury, recurrent laryngeal nerve palsy or esophageal or tracheal laceration. There was no case of hardware failure such as migration, breakage or collapse during the follow-up period. We did not encounter any adjacent segment stenosis or instability during the follow-up period. As a result, additional surgical procedures were not needed. 4. Discussion
Data are presented as mean ± standard deviation. Comparison of preoperative and postoperative values. + Comparison of postoperative and last follow-up values. AIBH = anterior interbody height, PIBH = posterior interbody height. *
subsidence was 1.4 ± 0.9 mm, and the posterior subsidence was 2.9 ± 1.2 mm. A significant difference was observed between anterior and posterior subsidence (p < 0.05). At the last follow-up, cage subsidence was observed in 28 patients (93.3%), but there was no statistically significant difference in subsidence between patients who underwent single-level and two-level corpectomies (p > 0.05). A summary of the SA and CSA outcomes is shown in Table 4. The negative values signify the cervical lordotic angle and the positive values signify the cervical kyphotic angle. The average sagittal CSA was 11.3 ± 6.1° (range, 15.1 to 19.5) before surgery, 11.6 ± 3.2° (range, 2.9 to 16.0) immediately after surgery (p > 0.05), and 16.3 ± 6.1° (range, 0.1 to 22.8) at the last follow-up. Although there was no significant difference in pre- and postoperative CSA, the CSA was significantly more lordotic at the last follow-up (p < 0.05). The average preoperative SA was 3.3 ± 3.8° (range, 8.9 to 9.8), which was corrected to 5.9 ± 2.1° (range, 2.1 to 13.6) immediately after surgery. At the last follow-up, the SA was 8.7 ± 2.3° (range, 2.6 to 18.6). The SA increased significantly after surgery, and the SA had increased further at the last follow-up (p < 0.05). Solid fusion was achieved in all patients at the last follow-up. Union was noted in all patients between the cage and the adjacent endplates. 3.3. Relationship between subsidence and age, myelopathy and radiculopathy Correlation analysis was performed to investigate the relationship between patient age and amount of subsidence. The amount of posterior subsidence was significantly positively correlated to patient age for single-level corpectomy (Spearman’s coefficient = 0.702; p < 0.05) and for all patients (Spearman’s coefficient = 0.601; p < 0.05). However, there was no significant correlation between
The use of a tricortical autologous bone graft from the iliac crest is the gold standard for reconstruction of corpectomy defects. However, donor site morbidity has been reported in up to 25% of patients undergoing this procedure, including prolonged donor site pain, nerve injury, infection and hematoma formation [11–13]. Among these, the most important problem was reported to be postoperative pain at the graft site. Silber et al. [14] reported chronic pain in 26.1% of patients and functional impairment in >10% of patients 48 months after iliac bone graft harvesting. Such concerns about donor site-related complications have led many surgeons to consider using allografts. When allografts are used, the morbidity associated with graft harvesting is avoided, but the disadvantages of allografts persist, including lower fusion rates, prolonged time to graft incorporation and potential risk of disease transmission [8,15–17]. Furthermore, bone graft collapse, graft migration/extrusion, telescoping, subsidence and resorption are common causes of autograft or allograft failure, resulting in pseudoarthrosis and kyphotic deformity [7,18–21]. Due to the potential disadvantages of structural bone grafts, synthetic cages such as TMC have been developed. TMC using autologous bone grafts from corpectomy bone chips can avoid donor site morbidity. TMC have large openings that provide excellent apposition of the end plate and bone graft to facilitate healing of the interface. They also permit lateral bony ingrowth along the length of the cage. Furthermore, TMC can provide immediate postoperative stability. In our series, an anterior cervical plate was used for stabilization in all patients. Anterior plate fixation provides a more rigid structure and results in a rapid solid fusion with a lower risk of graft-related complications. Although anterior plate fixation is not free from complications and morbidity, it has been shown to improve structural rigidity and prevent graft migration, late kyphotic collapse and pseudoarthrosis in multi-level fusions [22–25]. Cervical plates offer the advantage of improved initial stability in the postoperative period. Early spinal stability may lead to successful fusion. Graft stability may be due both to the anterior plate
Table 4 Radiological values of segmental angle and cervical sagittal angle measured before anterior cervical corpectomy and fusion, immediately after surgery, and at final follow-up Parameter Total 30 patients
Preoperative
Postoperative
Final follow-up
Segmental angle
3.3 ± 3.8
5.9 ± 2.1
8.7 ± 5.3
C2–7 angle (CSA)
11.3 ± 6.1
11.6 ± 3.2
15.3 ± 6.1
Data are presented as mean ± standard deviation. * Comparison of preoperative and postoperative. + Comparison of postoperative and last follow-up. CSA = cervical sagittal angle.
p value 0.023* 0.012+ 0.339* 0.037+
J.-W. Jang et al. / Journal of Clinical Neuroscience 21 (2014) 1779–1785 Table 5 Spearman’s correlation between age and cage subsidence after anterior cervical corpectomy and fusion Parameter
Single-level Two-level All patients
Anterior subsidence Posterior subsidence Anterior subsidence Posterior subsidence Anterior subsidence Posterior subsidence
Age r value
p value
0.230 0.702 0.276 0.414 0.342 0.601
0452 0.015* 0.374 0.172 0.271 0.023*
Data are shown in terms of r and p values by Spearman correlation analysis between age and subsidence. * p < 0.05. Table 6 Statistical analysis of cage subsidence between the radiculopathy and myelopathy groups after anterior cervical corpectomy and fusion Parameter
Radiculopathy group (n = 15)
Myelopathy group (n = 15)
p value
Age, years Anterior subsidence Posterior subsidence
49.2 ± 10.9 1.3 ± 1.1 2.8 ± 1.4
55.4 ± 12.7 1.5 ± 0.9 3.0 ± 1.5
0.164 0.432 0.572
Data are presented as mean ± standard deviation.
application and to the sharp teeth of the cage, which penetrate into the adjacent upper and lower endplates to provide relative internal stability. Postoperative spinal stability is closely related to clinical outcome. We had a good overall clinical outcome in our series. The VAS, NDI and JOA scores were all significantly improved at the last follow-up. Because the TMC is not radiolucent, it was difficult to determine if trabeculation had occurred. The fusion mass that surrounds the cages can be easier to assess with plain radiography than the fusion
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mass within the cages. We were also able to use indirect evidence to prove the presence of a successful fusion, such as a lack of movement on dynamic radiographs or the absence of peri-implant lucencies. Segmental stability was maintained on dynamic radiographs obtained from all patients during the follow-up period. Sagittal reconstruction of axial CT scans can be used to demonstrate bone growth within the TMC. The assessment of fusion by radiograph can be improved with the use of radiolucent carbon fiber and polyether-etherketone (PEEK) cages for interbody fusion. Although high fusion rates have been reported in the literature with this technique, a longer period was required to achieve solid fusion compared with a tricortical iliac autograft [26,27]. In vivo models showed that kyphosis plays an important role in increasing the degenerative changes in adjacent motion segments [28]. In our series, SA and CSA were well-restored postoperatively and were maintained in all patients until the last follow-up. Although corrections of the kyphotic angle were slowly lost in many patients by the time of final follow-up radiograph, severe collapse or significant recurrence of the deformity did not occur. The complications in the present study were relatively low. There were no new neurologic deficits, infections, recurrent laryngeal nerve injuries, cerebrospinal fluid leaks or esophageal or tracheal tears. However, subsidence of the cage into the end plates is one of the main concerns of this technique. Subsidence seemed to be unavoidable in the majority of patients who underwent TMC fusion and usually occurred before bone fusion was achieved. Excessive endplate removal, poor bone quality, increased patient age and multi-level corpectomy have been proposed as potential risk factors for subsidence [29]. Subsidence could diminish some of the advantages of TMC, such as restoration and maintenance of intervertebral disc height, enlargement of the stenotic neural foramen and immediate stabilization of operative segments. Severe subsidence can cause bucking of the yellow ligament and cervical misalignment. Chen et al. [30] reported the TMC
Fig. 2. Imaging studies of a 47-year-old man who underwent a C5 corpectomy. (A) Sagittal CT scan showing segmental ossification of the posterior longitudinal ligament in the cervical spine with kyphotic cervical alignment. (B) At the time of the last follow-up CT scan, the posterior subsidence of the cage was more prominent compared to the anterior subsidence. However, segmental angle and cervical sagittal angle were increased compared with preoperative measurements.
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Fig. 3. Schematic figure showing that posterior subsidence of the titanium mesh cage may create cervical lordosis during the follow-up period.
subsidence in 300 patients who underwent anterior cervical corpectomy. Cases of subsidence were classified as mild (1–3 mm) or severe (>3 mm). These investigators demonstrated TMC subsidence in 239 (79.7%) patients, of which 182 cases (60.7%) were mild and 57 (19.0%) were severe. Two-level corpectomy was more susceptible to severe subsidence compared with single-level corpectomy. In this study, cage subsidence was observed in 93.3% of patients; therefore, cage subsidence may be inevitable after anterior cervical reconstruction using TMC. However, it is not known if cage subsidence always has negative effects on fusion and cervical spine alignment after anterior reconstruction using TMC. This study showed that cage subsidence was not associated with significantly negative clinical results during the follow-up period. Moreover, subsidence may promote bone fusion by creating a broad contact surface between the cage and the vertebral body. Despite the fact that cage subsidence was observed in majority of our patients, fusion failure did not occur. We investigated anterior and posterior subsidence of the cage by measuring the AIBH and PIBH and found that cage subsidence was more severe on the posterior side compared to the anterior side of the cage. Several factors may explain why subsidence was more severe posteriorly than anteriorly. First, we positioned the TMC in the anterior two-thirds of the vertebral body after the corpectomy; therefore, the posterior part of cage contacted the weak, cancellous portion of the vertebral body, and the anterior part of cage contacted the hard cortical surface of the vertebral body. Second, the posterior body was more extensively drilled to remove posterior osteophytes or calcified ligaments. The bony endplate of the posterior part of the vertebral body therefore could be more damaged and more vulnerable to cage subsidence. Finally, the center of gravity is located in the posterior part of the cage due to cervical lordosis and the location of the cage, and greater compressive forces may act on the posterior part of the cage. Briefly, differences between the orientation of the TMC contact area and the endplates may be responsible for the unfavorable stress distribution that induces subsidence in this area. Interestingly, because subsidence was most prominent at the posterior rim of the TMC, it may help to maintain lordosis, as shown in Figure 2 and 3. In our study, both the SA and CSA were increased immediately after surgery and at the time of the last follow-up, despite the increasing posterior subsidence. These clinical and radiologic results suggest that minimal to moderate posterior subsidence of the TMC may have a positive effect on maintaining cervical alignment and functional outcomes. Generally, age reflects the bone mineral density, and it is well known that bone mineral density decreases as age increases. The present study showed that posterior subsidence was positively
correlated with age, but anterior subsidence was not correlated with age. This fact indicates that the posterior part of cage that contacted weak cancellous bone was more vulnerable to the sharp cage teeth, compared to the anterior part of cage, which is in contact with the hard cortical surface. Therefore, to obtain adequate posterior subsidence for cervical lordosis after fusion, excessive drilling of the posterior part of vertebral body should be avoided in elderly patients. 5. Conclusions The clinical and radiologic results of this study suggest that cervical reconstruction after single or two-level corpectomy can be safely and effectively performed using a TMC packed with autologous bone chips in conjunction with anterior cervical plating. This technique obviates the need for harvesting iliac bone grafts and results in solid anterior column reconstructions and good clinical outcomes. Cage subsidence was inevitable, but it tended to develop posteriorly due to the cage location, cervical lordosis and removal of posterior osteophytes. Despite the prominent posterior subsidence, SA and CSA were increased at the time of the last followup; thus, posterior subsidence may contribute to cervical lordosis. Conflicts of Interest/Disclosures The authors declare that they have no financial or other conflicts of interest in relation to this research and its publication. Acknowledgements This study was financially supported by Chonnam National University, 2011. References [1] Eleraky MA, Llanos C, Sonntag VK. Cervical corpectomy: report of 185 cases and review of the literature. J Neurosurg 1999;90:35–41. [2] Macdonald RL, Fehlings MG, Tator CH, et al. Multilevel anterior cervical corpectomy and fibular allograft fusion for cervical myelopathy. J Neurosurg 1997;86:990–7. [3] Mayr MT, Subach BR, Comey CH, et al. Cervical spinal stenosis: outcome after anterior corpectomy, allograft reconstruction, and instrumentation. J Neurosurg 2002;96:10–6. [4] Dorai Z, Morgan H, Coimbra C. Titanium cage reconstruction after cervical corpectomy. J Neurosurg 2003;99:3–7. [5] An HS, Simpson JM, Glover JM, et al. Comparison between allograft plus demineralized bone matrix versus autograft in anterior cervical fusion. A prospective multicenter study. Spine (Phila Pa 1976) 1995;20:2211–6. [6] Banwart JC, Asher MA, Hassanein RS. Iliac crest bone graft harvest donor site morbidity. A statistical evaluation. Spine (Phila Pa 1976) 1995;20:1055–60.
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