应用多聚醚酮椎间融合器修复Ⅱ型及Ⅱa型Hangman骨折：6个月随访评价

doi:10.3969/j.issn.2095-4344.2015.39.013

摘要/Abstract

摘要：

背景：Hangman骨折即创伤性枢椎滑脱，不稳定Hangman骨折的Ⅱ型、Ⅱa型及ⅡI型骨折需要手术治疗。咽后入路是上颈椎前路手术显露的常用手段。然而，重要结构周围的牵拉与分离使得手术程序复杂，增加了神经损伤的发生率。
目的：评价创新性应用多聚醚酮椎间融合器治疗Hangman骨折的临床疗效及安全性。
方法：收集Ⅱ型及Ⅱa型Hangman骨折患者8例，均进行C_2/3椎间融合。术后随访进行X射线检查，评价融合时间及内植物位置。比较术前与术后6个月骨折处成角及移位数据和复位情况，以颈椎创伤后评分评价功能恢复，以目测类比评分评价颈部疼痛。
结果与结论：所有8例患者均得以成功随访，平均随访13个月(6-26个月)。与术前相比，术后6个月患者颈椎创伤后评分增高，目测类比评分及成角畸形和移位均降低(P < 0.05)。全部患者末次随访未见颈部活动受限，术后3或6个月所有患者椎间均骨性融合，无相关并发症。结果证实，应用多聚醚酮椎间融合器治疗Ⅱ型及Ⅱa型Hangman骨折临床疗效及安全性均较好。

中国组织工程研究杂志出版内容重点：人工关节；骨植入物；脊柱；骨折；内固定；数字化骨科；组织工程

关键词: 骨科植入物, 脊柱植入物, 颈椎, 融合, Hangman骨折, 多聚醚酮, 咽后, 入路, 手术, 植入物, 史密斯-罗宾逊, 融合器

Abstract:

BACKGROUND: Unstable cases of Hangman’s fracture or traumatic spondylilisthesis which are type II, IIa and III should be treated surgically. Retropharyngeal approach was employed in exposure of anterior upper cervical region. However, dissection and traction around important structures make the procedure complicated and increase the chance of nerve injury.
OBJECTIVE: To evaluate the clinical curative effect and safety of an innovative operative technique in which a polyetheretherketone cage was used to perform cervical spinal fusion for the treatment of Hangman’s fracture.
METHODS: Eight patients with type II or IIa Hangman’s fracture were enrolled in this study and received cervical fusions at C2/3 levels. During follow-up postoperatively, they received X-ray examination. Fusion time and implant position were evaluated. The angle of deformity (α) and the displacement distance (β) were compared pre-operatively and 6-month post-operatively to measure reduction. The functional outcomes were also compared using the Post-Traumatic Neck Score (Mayo) pre-operatively and 6-month post-operatively, while neck pain was further investigated by Visual Analogue Scale score.
RESULTS AND CONCLUSION: All eight patients were followed-up successfully, with an average follow-up of 13 months (range 6-26 months). Compared with pre-operatively, Clinical Post-Traumatic Neck Score (Mayo) was increased, Visual Analogue Scale score, angle deformity (α) and displacement distance (β) were reduced at 6-month post-operatively (P < 0.05). Neck activity was not limited in final follow-up. Bone fusion was found in all patients at 3 or 6 months post-operatively, and no complication was detected. Results confirm that polyetheretherketone cage for type II and IIa Hangman’s fracture could achieve good outcomes and safety.

中国组织工程研究杂志出版内容重点：人工关节；骨植入物；脊柱；骨折；内固定；数字化骨科；组织工程

Key words: Tissue Engineering, Spine, Fractures, Bone, Intervertebral Disk

中图分类号:

R318

黄阳亮，钟祎，刘少喻. 应用多聚醚酮椎间融合器修复Ⅱ型及Ⅱa型Hangman骨折：6个月随访评价[J]. 中国组织工程研究, doi: 10.3969/j.issn.2095-4344.2015.39.013.

Huang Yang-liang, Zhong Yi, Liu Shao-yu. Polyetheretherketone cage for treating type II and type IIa Hangman’s fractures: 6-month follow-up[J]. Chinese Journal of Tissue Engineering Research, doi: 10.3969/j.issn.2095-4344.2015.39.013.

图/表（结果） 2

Quantitative analysis of participants
Eight patients were collected at the beginning, and they were all successfully follow-up for 6 months or longer. None of them was lost, so their data were put into final statistical analysis.
Clinical results
The mean operative time was 97.0±21.4 minutes (range 70-135) and the mean hemorrhage amount was 31±10.5 mL (range 20-50). We did not observe transient or permanent hoarseness, dysphagia and dysphonia. By Smith and Robinson approach, lower part of axis body could be exposed without difficulty in all of our patients. There were no further operations. Of the total 8 consecutive patients, follow-up evaluation data of 6 months or longer were available for all patients at a mean clinical follow-up of 13.0±6.21 months (range 6-26). The Clinical Post-Traumatic Neck Score (Mayo) was 51.88±7.38 (range 45-63) pre-operatively and 90.75±4.68 (range 83-95) at 6-month follow-up. There was a significant improvement (P=0.001). The pre-operative VAS scale score was 7.00±0.76 (range 6-8) and 6-month post-operative score was 1.13±0.64 (range 0-2). There was a significant difference between pre and post-operative results (P < 0.001) (Table 2). In our 6-month post-operative questionnaires of Neck Score, no patients complained of cervical movement limitation that disturbed daily activities; and cervical pain was relieved, no further oral analgesics were needed. On last follow-up, there was no cervical pain recorded either.
Radiographic results
Cervical radiograph examinations performed at the last follow-up visits showed no subsidence, collapse, breaking, or pseudarthrosis at the level of the implants. There was no bone material absorption or necrosis at the contiguous vertebral bodies, and no noticeable inflammatory reaction. There were no lucency gaps between fracture lines. Fusion was observed after 3 or 6 months in all of our patients.
The mean of angle deformity (α) pre-operatively was -7.50±8.05, and 6-month post-operatively was 5.00±6.52; the difference was significant (P=0.007). The mean of displacement distance (β) pre-operatively was 2.81±1.49, and 6-month post-operatively was 0.94±0.68, which was significant either (P=0.002) (Table 2).

Typical case
A traffic accident caused a 29-year-old man a hangman’s fracture, his _C2/3 disc and upper cervical ligaments were injured at the same time. He received solis fixation and reported a satisfied clinical outcome 6 months later (Figure 2).

参考文献

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引言

Hangman’s fracture, or traumatic spondylilisthesis of axis, accounts for 4%-7% of all cervical fractures/dislocations^[1-4]. To instruct the management of Hangman’s fracture, it was divided into three types by Effendi^[5-6], and modified into four types by Levine and Edwards^[7]. Although surgical indication for hangman’s fracture is still controversial, most authors agree that unstable cases which are types II, IIa and III should be treated surgically^{[2, 8-9]}.
Surgical technique for Hangman’s fracture can mainly be divided into two categories: anterior or posterior. In anterior operations, C_2/3 discectomy, autograft and plate fixation are the standard method^[10]; on the other hand, C₂ pedicle screw or C_2/3 pedicle/lateral mass screw fixation is currently popular in posterior operations^[11-13]. In clinical practices, the decision of surgical approach depends on surgeon’s training and experience, however, if displacement and/or angulation could not be reduced pre-operatively, posterior approach is not suggested^[2].
At present, anterior plating is commonly used in treatment of types II and IIa Hangman’s fracture for its rigid fixation and protection against graft complications; however, the high cervical retropharyngeal approach which is employed in surgical exposure involved lots of dissection and traction around important structures^[14-16]. As the consequence of complicate operative procedures, nerves could be mistaken into vessels and injured^[17].
Is there any alternative surgical method besides plate fixation and the retropharyngeal approach for Hangman’s fracture? To reduce iatrogenic operative injury and simplify surgical procedure, a polyetheretherketone cage (Solis, Stryker Corporation, Cestas, France) is employed in our innovative technique which was performed by Smith and Robinson approach. To our knowledge, this method has not been reported before. To demonstrate the reliability, this method is applied to a series of patients. After follow-up, functional and radiological results are evaluated.

材料方法

Design
This is a retrospective clinical study.

Time and settings
From January 2010 to September 2012, polyetheretherketone cage fixation for Hangman’s fracture was performed in selected patients admitted to our hospital.

Subjects
This research was designed as a clinical retrospective study in a single center. The diagnosis was made when bi-lateral lamina fractures of axis were recognized. The surgical inclusion criteria were: (1) patients manifested neurologic deficits and/or the fracture was determined to be unstable (i.e., angulation more than 11° and/or translation more than 3.5 mm); (2) type II or IIa Hangman’s fracture (Levine and Edwards’ classification). The exclusion criteria were that (1) type I or III Hangman’s fracture (Levine and Edwards’ classification); (2) in addition to Hangman’s fracture there are other spine fractures; (3) the fracture cannot be reduced by skill traction; (4) not suitable to be treated surgically. In total, eight consecutive patients were identified. Among these patients, there were five men and three women. Average age at surgery was 25.9 years (range 19 to 34 year). The majority of fracture cause was vehicle accidents (5 cases, 62.5%). Other causes were fall from a height (2 cases, 25%) and head trauma (1 case, 12.5%). Two stable cases were excluded; one with type III fracture was treated by posterior approach and one patient with unfavorable health condition was treated non-operatively. Furthermore, preoperative cervical three-dimensional-CT scan was used to exclude other cervical fractures in all of our patients and preoperative MRI was conducted to detect spinal cord compression and upper cervical disc/ligament injuries. Demographic information and classification according to Levine and Edwards were recorded (Table 1).

According to the classification of Levine and Edwards, there were four cases of type II and four cases of type IIa fractures. In addition to the Hangman’s fracture, one of these patients had a posterior tear fracture of the C₂ vertebral body, two patients had transverse foramen fractures, and one had a vertebral body bone cyst, who was not adequate for plate fixation. On MRI images, there were signal changes in all patients at the C_2/3 intervertebral discs, and four of those changes were combined with anterior/posterior ligament injuries. One of our patients had symptomatic anterior spinal cord compression by disc extrude. All patients complained of limited cervical motion and neck pain, their neurologic functions were evaluated by Frankel Performance Scale; however, except one patient complained paresthesia around both upper and lower limbs, there was no muscle weakness or pathological signs in other patients. One of our patients was associated with tongue injury which located at the basis and the bleeding was stopped by suture. One of our patients was associated with cerebral concussion and scalp injury.

The design and performance of this study conformed to ethical standards of Helsinki Declaration and our national legislation. It was approved by Medical Ethical Committee of our institution. Before enrolment, patients were enquired whether or not willing to take part in a scientific research and informed consent forms were signed by themselves.

Methods
Implants
The operations were performed using polyetheretherketone (PEEK) cages (Stryker Corporation, Cestas, France). The width of the cage, either 12 or 14 mm, was decided by intra-operative measurements; the high of the cage was 1 to 2 mm taller than preoperative disc high of C_3/4 to secure stability.

Pre-operative preparation
Before surgery, all of our patients received skull traction; the initial weight was 2 kg, if no further displacement could be observed on regular examination of X-ray pictures, traction weight would be increased until 1/10 of body weight. Simultaneously, traction angle was adjusted until the fracture was reduced.

Surgical procedures
The same team of doctors performed all the operations. Under general endotracheal anesthesia, patients were positioned supine with the neck extended and slightly left rotated. A left skin incision was made according to Smith and Robinson approach. The incision was about 4 cm long with its middle point located on the level of superior boarder of thyroid cartilage. Blunt dissections were employed through fascial spaces to reach the avascular plane on C₃ vertebral body. Extreme care was taken to differentiate nerve from vessels which went across this area. After exposure of C₃, the dissection moved upward and went along with the avascular plane. A needle was inserted into the C2/3 disc space to confirm anatomical position under fluoroscope. After exposure of axis body (usually limited to the lower 1/3), the anchoring pin of distracter was drilled into the cortex. Robinson-spondylodesis procedure was performed to remove discoligamental injuries while preserving osteal endplates (Figure 1). After distraction of the disc space, an adequate size Solis which filled with autograft trabecular bone was put into the operative segment. The bone was harvested from the iliac crest with a T-shaped driver to minimize pain at the donor site. After removal of distracter, the stability of Solis was checked by anterior drawing, and then fluoroscope was used to detect the implant’s position. All of our patients were treated postoperatively with a plastic collar which had to be worn constantly for 3 months.

Outcome measurements
We conducted regular X-ray picture examinations at 1-week, 3-month, 6-month and the most recent follow-up postoperatively. The radiologic materials were evaluated for location of PEEK cages and condition of the operative levels. Fusion was considered complete when the following criteria were met^[18]: (1) trabecular bone across the interfaces and connects superior and inferior vertebral bodies. (2)Radiolucencies inside the cage disappeared. (3) Adequate disc height was restored, without collapse-induced kyphosis.
In order to investigate the stability of Solis, we measure angulation (α) and displacement (β) pre- and post-operatively. α was the angle between inferior border of axis and superior border of C₃, if the angle points anterior, it is considered to be negative, and if it points posterior, it is considered to be positive. β was the distance between the posterior border of axis and C3. These strategies were taken at the same time points which were at hospital admittance and 6-month follow-up visit. Fusion and strategy collection were confirmed by two different radiologic reviewers, who were blinded to the clinical outcome of our patients. If there was disagreement, a third person was consulted and decision was made by their discussion.
The postoperative functional outcomes were evaluated using the Clinical Post-Traumatic Neck Score (Mayo)^[19]. This score system contains critical information such as neck pain, cervical movement, neurological statue and daily leaving activities. Scores were recorded on same time points which were also at hospital admittance and at 6-month follow-up visit for better comparison. Simultanesouly, visual analogue scale (VAS) score was recorded when we are performing questionnaire of Neck Score to further investigate neck pain.
Statistical analysis
Data were analyzed by SPSS software (SPSS, Chicago, IL, USA) and presented as the mean ± SD. The Q-Q plot (a normality test) for an approximation to normal distribution was utilized. The paired t-test was generally applied for normally distributed data sets of angulation (α), displacement (β) and Neck Score. To compare different levels, Wilcoxon signed ranks test was used for VAS. A value of P < 0.05 (two-tailed) was considered significant and confidence interval was 95%.

讨论

The invention of PEEK cage technique for Hangman’s fracture comes from clinical practice. CT scan of our first patient disclosed a bone cyst on the vertebral body of axis. Obviously, plate fixation was not adequate. Therefore, we chose Solis fixation. During operation, convenient exposure and simplified operative procedures were received. Fusion successfully completed 3 month later without complication. To testify the reliability, it was applied to the following seven patients.

Compared with traditional method, using PEEK cage in treatment of Hangman’s fracture is simple, safe and feasible. The traditional high cervical retropharyngeal approach is accepted to expose upper cervical region^[10]. Although the exposure is sufficient and internal fixations including C_2/3 could be carried out, extensive dissection of neurovascular structures carries inherent risk. Nerves could be mistaken into vessels and ligated^[12]. Moreover, the operation procedures are complicated and time consuming. To solve these problems, we develop Solis fixation for Hangman’s fracture. In this method, Smith and Robison approach which is more familiar for surgeons could be adopted. However, by obstruction of the jaw, the exposure is limited to lower part of the axis body, where the space is not sufficient except for pin insertion. The pin functions as a retractor which separates muscles away and permits a triangle working area around disc space. This traction force is localized and minimizes irritation to sounding structures. Although it has to be applied continually, the preparation of disc space and insertion of cage will not cost more than half an hour. In our series, none of our patients developed hypoglossal or superior laryngeal nerve injury or other complications.

These excellent surgical outcomes are ensured by following strategies:
(1) Preoperative skill traction: The traction is critically important, not only because the fracture could be reduced, but also the function of upper cervical ligament could be testified pre-operatively. Since the stability of intravertebral device depends on compressive loads, the flexibility of upper cervical ligament is the key element of a successful surgery.

(2) The height of cage: The source of stability of intravertebral dives depends on compressive loads which are produced by distraction of the disc space. The insertion of higher graft is associated with significant greater compressive forces (6 mm vs. 8 mm)^[20]. In our series, relatively larger implant which 1 or 2 mm taller than the size of C_3/4 disc space was used to ensure stability; however, a concern arises that the reliability of Solis in traumatic conditions should be questioned. To answer this question, we checked stability after removal of distracter by anterior drawing actions. The external force did not create migration or rotation, and the fixation was rigid. Post-operatively, the stability of C_2/3 segment which was provided by Solis fixation kept the fracture from deformity. It was demonstrated by analyzing of displacement and angulation data collected at 6-month follow-up when all operative segments were solid fused. Significant difference was disclosed. Therefore, the stability which provided by Solis fixation for Hangman’s fracture is sufficient and reliable.

(3) The characteristic of Solis: There are several cervical intervertebral fusion devices available; however, Solis (Stryker Spine) was chosen for the following reasons. First, the material PEEK has an elastic modulus closer to that of bone^[21-22], damages caused by stress shielding could be better avoided and the resulting mechanical stimulus would provide a beneficial environment for bone growth; Second, the upper and lower titanium spikes that anchor the vertebral body provide immediate fixation between the cage and the adjacent vertebral bodies, and it is not necessary to destroy endplate while planting the device. Therefore, an abundant horizontal contact area for bone growth was provided; moreover, PEEK is radiolucent, which allowing a better radiographic assessment of bone fusion than titanium. The clinical outcome used at lower cervical region was satisfied^{[9, 23-24]}.

(4) Surgical resection of C_2/3 disc: Since disc original pain had been well recognized, disc injury of Hangman’s fracture is important^[25-26]. Some non-surgically treated Hangman’s fracture patients developed strong and persistent neck pain. For example, Watanabe reviewed nine patients who underwent conservative treatment and found out four of them had neck pain^[27]. We believed that the symptom came from the injured C_2/3 disc and ligaments^[28]. Since self-repair mechanism is not sufficient in these structures, degeneration and atrophy will produce cervical instability or neck pain^{[17, 29]}. Therefore, discoligamental injury which is a critical pathological change in Hangman’s fracture should be recognized as early as possible^[30]. Surgery should be offered to patients who are associated with severe disc injury. We identified disc injury pre-operatively on MRI examination. After surgical intervention, there was no cervical pain reported on 6-month and last follow-up questionnaire of VAS and Neck Scores.

However, a little complication could be observed in our cases. A slight implant migration was discovered in one of our patients. In this case, satisfied reduction was accomplished by pre-operative skull traction and implant position was checked by intra-operative fluoroscope. Moreover, anterior drawing of the implants did not create migration. However, displacement and angulation were recognized 1 week post-operation. Compared with other cases, the cause lied in pre-operative 5 mm displacement which was the largest in our series. We hypothesize that excessive injury of surrounding soft tissue and ligament will produce delay loosening of the implant. Therefore, 5 mm displacement or more should be considered as contraindication for this technique. Although the patient was asymptomatic, longer follow-up is needed^[27].
The major limitation of this study is the small number of patients, which precludes absolute conclusions with regard to the utility of Solis in treatment of Hangman’s fracture. Moreover, the functional and radiologic outcomes were almost equal with the results of previous clinical studies concerning plate fixation, except operative complications, such as hypoglossal nerve injury^[15]. Although clinical study demonstrated the feasibility of Solis fixation, the stability still has to be further investigated by biomechanical researches. Hence, it is recommended in the following conditions: (1) type II and IIa Hangman’s Fractures with obvious C_2/3 disc injury and/or angulation more than 11° and/or translation more than 3.5 mm; (2) the displacement should be no more than 5 mm; (3) the fracture could be reduced by skull traction.

As the posterior elements are destroyed and they need to be reconstructed posteriorly, we do not recommend anterior operation on type III Hangman’s fracture cases^[31]. If surgery was intended for type I Hangman’s fracture to prevent neck pain, Solis fixation is also recommended.

Using Solis in the treatment of Hangman’s fracture could simplify operative procedures and reduce the risk of nerve injury. By distraction-compression loads, both of angle and displace deformity corrections could be corrected and maintained. All of our patients showed no signs of fracture nonunion. We recommend this method for clinical practice. However, patient selection is very important and must correspond to proper indications. Additionally, in order to confirm our preliminary impressions, studies with larger series of patients and longer term follow-ups are warranted.