Since the 1950s, anterior cervical discectomy and

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Comparison of 6-year Follow-up Result of Hybrid Surgery and Anterior Cervical Discectomy and Fusion for the Treatment of Contiguous Two- segment Cervical Degenerative Disc Diseases

Yang Xiong, MD, Lin Xu, MD, PhD, Xing Yu, MD, PhD, Yongdong Yang, MD, PhD, Dingyan Zhao, MD, PhD, Zhengguo Hu, MD, Chuanhong Li, MD, He Zhao, MD, Lijun Duan, MD, Bingbing Zhang, MD, Sixue Chen, MD, and Tao Liu, MD

Study Design. A retrospective study.

Objective. To compare the mid-term outcomes of hybrid surgery (HS) and anterior cervical discectomy and fusion (ACDF) for the treatment of contiguous two-segment cervical degenerative disc diseases.

Summary of Background Data. HS has become one of the most controversial subjects in spine communities, and the comparative studies of HS and ACDF in the mid- and long-term follow-up are rarely reported.

Methods. From 2009 to 2012, 42 patients who underwent HS (n ¼ 20) or ACDF (n ¼ 22) surgery for symptomatic contiguous two-level cervical degenerative disc diseases were included.

Clinical and radiological records, including Japanese Orthopedic Association (JOA), Neck Disability Index (NDI), Visual Analogue Scale (VAS), local cervical lordosis, and range of motion (ROM), were reviewed retrospectively. Complications were recorded and evaluated.

Results. Mean follow-up was 77.25 and 79.68 months in HS group and ACDF group, respectively (P > 0.05). Both in HS group and ACDF group, significant improvement for the mean JOA, NDI, and VAS scores was found at 2-week postoperation and at the last follow-up (P < 0.05). However, there were no

significant differences between the two groups (P > 0.05). At the last follow-up, the range of motion (ROM) of superior adjacent segments in ACDF group was significantly larger than HS group (P < 0.05), while the ROM of C2-C7 was significantly smaller (P < 0.05). In the HS group, two (10%) sagittal wedge deformi- ties, one (5%) heterotopic ossification, and one (5%) anterior migration of the Byran disc prosthesis were found. No symptomatic adjacent segment degeneration occurred in two groups.

Conclusion. HS appears to be an acceptable option in the management of contiguous two-segment cervical degenerative disc diseases. It yielded similar mid-term clinical improvement to ACDF, and demonstrated better preservation of cervical ROM. The incidence of postoperative sagittal wedge deformity was low; however, it can significantly reduce the cervical lordosis.

Key words: anterior cervical discectomy and fusion, arthroplasty, Bryan cervical disc prosthesis, cervical degenerative disc diseases, cervical spine, disc replacement, fusion, hybrid surgery, spine, two-segment, wedge deformity.

Level of Evidence: 4 Spine 2018;43:1418–1425

S

ince the 1950s, anterior cervical discectomy and fusion (ACDF) has gradually developed into the gold standard for the treatment of cervical degenerative disc diseases (CDDD). However, fusion and fixation has changed the normal biomechanical environment of cervical spine, the range of motion (ROM) of the operative segment was lost, and the load of adjacent segments were increased, which contributes to the adjacent segment degeneration (ASD).^1–3 Artificial cervical disc replacement (ACDR) was applied to reduce the risk of ASD. It could maintain the ROM of the operative segment while decompressing the nerve root, which could avoid the stress concentration in the adjacent segments of fusion. ACDR has obtained satisfied short- and middle-term clinical results in the last more than

From the Department of Orthopedics, Dongzhimen Hospital, Beijing Uni- versity of Chinese Medicine, Beijing, China.

Acknowledgment date: January 17, 2018. Acceptance date: February 27, 2018.

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work.

No relevant financial activities outside the submitted work.

Yang Xiong and Lin Xu contributed equally to this work as co-first author.

Address correspondence and reprint requests to Xing Yu, MD, PhD, Depart- ment of Orthopedics, Dongzhimen Hospital, Beijing University of Chinese Medicine, No. 5 Haiyuncang Street, Dongcheng District, Beijing 100700, China; E-mail: yuxing34163@163.com

DOI: 10.1097/BRS.0000000000002639 1418 www.spinejournal.com

C ^ERVICAL S ^PINE

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10 years of clinical application.^4,5However, compared with ACDF, it is still hard to determine which is superior for the treatment of cervical spondylosis. Most of the clinical comparative studies between ACDF and ACDR were concen- trated in a single segment, and few of the double segmental control studies have been reported. In recent years, hybrid surgery (HS), which combined ACDR and ACDF, was adopted to cervical two-level or multilevel disc diseases.⁶ The aim was to maintain the stability of the surgical segments on the one hand, and on the other hand, to reduce the morbidity of ASD by preserving the surgical segmental activity. However, because of its relatively late emergence and the indications have not yet been unified, its value and feasibility of clinical application has become one of the most controversial subjects in spine communities.

The purpose of this study was to compare the mid-term outcomes and complications both clinically and radiograph- ically of HS and ACDF for the treatment of symptomatic contiguous two-segment CDDD.

MATERIALS AND METHODS

Inclusion and Exclusion Criteria

Inclusion criteria were (1) The patient was diagnosed as having symptomatic contiguous two-segment CDDD based on clinical and radiological evidence; (2) It was the first time that underwent HS or ACDF surgery after at least 6 weeks’

conservative treatment, which was ineffective; (3) So far, it was at least 5 years that from the initial surgery. Exclusion criteria were (1) The operative segment was discontinuous;

(2) Patients had undergone reoperation.

Patients

From 2009 and 2012, a total of 55 consecutive patients who underwent HS or double-level ACDF surgery for symptomatic contiguous two-level CDDD in our department were reviewed retrospectively. Forty-two patients (The rate of follow-up was 76.4%) were followed up for an average of 6 years (range, 5–9 years). Among them, 20 patients underwent HS and 22 patients underwent double-level ACDF surgery. The HS group performed a significantly longer operative time and more intraoperative blood loss than the ACDF group (P < 0.05), whereas there was no statistically significant difference in other parameters between the two groups (P > 0.05) (Table 1).

Device Description

Twenty Bryan cervical disc prostheses (Medtronic Sofamor Danek, Memphis, Tennessee, TN) and 20 MC plus anterior cervical intervertebral fusion cages (A self-locking stand-alone PEEK cage system; LDR, France) were used for all patients in the HS group; 44 MC plus anterior cervical intervertebral fusion cages were employed in the ACDF group.

Surgical Technique

A right-sided horizontal incision was made along the skin crease in the neck correlating to the target disc level and extended to the prevertebral fascia through the Smith-

Robinson approach. After the exposure, a complete discectomy and sufficient decompression of the spinal cord and nerve roots was carried out.

In HS group, the endplates were prepared with a high- speed burr to the fusion segment. An appropriately sized MC plus cage filled with allogeneic bone was placed in the inter- space position, followed by insertion of the fixation plate.

Then, to the adjacent disc arthroplasty segment, the retractor frame and dual track-milling guide were positioned on the anterior surfaces of the vertebral bodies. The endplates were prepared by cutting instruments to create two concave surfaces. Subsequently, an appropriate size of Bryan cervical disc was inserted into the prepared intervertebral space. Finally, a drainage tube was placed and incisions were closed layer by layer. After the operation, all patients were allowed to wear a neck collar for 4 weeks and to undergo proper functional exercise of neck and back muscles.

In ACDF group, two suitable MC plus cages filled with allogeneic bone were placed in the two contiguous inter- spaces, respectively. The other operations were the same as the HS group.

Measurement of Radiologic and Clinical Outcomes All the clinical data for the present study were collected before surgery, 2 weeks postoperation, and at the 59 years‘

postoperative review. The Japanese Orthopedic Association (JOA) score was used to evaluate myelopathic status, the Neck disability index (NDI) score was used to evaluate clinical symptom remission and daily activities, and the Visual analog scale (VAS) score was used to evaluate the intensity of neck and arm pain.

TABLE 1.

Summary of the Demographics and Perioperative Parameters: the HS Group versus ACDF Group

Variable HS ACDF

No. of patients, n 20 22

Age, yrs 54.40 8.56 55.77 8.69

Sex (M/F) 8/12 7/15

Disease course 50.10 34.75 59.45 23.26 Symptom

Myelopathy 5 7

Radiculopathy 8 10

Myeloradiculopathy 7 5

Levels

C3/4 and C4/5 3 2

C4/5 and C5/6 4 6

C5/6 and C6/7 13 14

Operative time, min 138.50 19.13 124.55 24.20 Blood loss, mL 31.25 10.99 22.50 9.605 Follow-up, months 77.25 17.61 79.68 15.44 Compared with the ACDF group, the operative time and the blood loss in the HS group were significantly higher.

P < 0.05 compared with the ACDF group.

ACDF indicates anterior cervical discectomy and fusion; HS, hybrid surgery.

Spine www.spinejournal.com 1419

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Furthermore, a series of plain radiographs were taken by all patients for radiological assessment, including antero- posterior and lateral radiographs and dynamic lateral radiographs at maximum extension and maximum flexion. The local lordosis of the treated segments was measured using the Harrison posterior tangent method at a neutral position of cervical spine lateral radiographs. The ROM of superior and inferior adjacent segment to the operation, and the ROM of C2-C7 was measured using the Cobb angle between full flexion and extension in lateral radiographs.

In addition, the superior or inferior vertebral sagittal wedge deformity (SWD) of the operated segment was evaluated using a semiquantitative visual grading system, which was introduced by Genant et al.⁷ (grade, 0–3). Heterotopic ossification (HO) was evaluated according to McAfee classification⁸ (grade, 0–4). And information on prosthesis- related complications were collected.

Statistical Analysis

All data were analyzed using SPSS (version 22.0; IBM, Armonk, New York, NY). The results were expressed as mean

standard deviation (SD). The Wilcoxon signed rank test and paired-samples t tests were used to evaluate quantitative data between preoperative and postoperative parameters. Indepen- dent-samples t test or Mann-Whitney U tests were used for comparing qualitative data between the two groups. A P value < 0.05 was considered statistically significant.

RESULTS

Clinical Outcomes

Compared with preoperative values, the mean JOA, NDI, and VAS scores in both the HS and ACDF groups

significantly improved 2 weeks after surgery (P < 0.05) and remained highly improved at the last follow-up (P < 0.05). But there were no significant differences between the two groups (P > 0.05). A summary of clinical outcomes is presented in Table 2, and the changes in JOA, NDI, and VAS scores are shown in Figure 1A to D.

Radiological Outcomes

The mean local lordosis of the treated segments in both HS and ACDF groups were significantly increased at the last follow-up, respectively (P < 0.05). But no significant difference between the two groups was found both before surgery and at the last follow-up (P > 0.05). In the ACDF group, the mean ROM of superior adjacent segment was 10.07 4.82 before surgery, which significantly increased to 13.26 5.95 at the last follow-up (P < 0.05). Between the two groups, the mean ROM of superior adjacent segment was similar preoperatively, but was significantly different at the last follow-up (P < 0.05). The mean ROM of inferior adjacent segment showed no significant difference before surgery and at the last follow-up between the two groups (P > 0.05). At the last follow-up, the mean ROM of C2–C7 of the HS group was 36.16 14.09. For the ACDF group, it significantly decreased to 26.82 13.43 (P < 0.05). And the significant differences in the ROM of C2–C7 were found at the last follow-up between the two groups (P < 0.05). A summary of main radiological outcomes is presented in Table 3.

Complications

At the last follow-up, two cases (10%; one in Grade 1 and one in Grade 2, respectively; Figure 2A–F) of vertebral SWD were found in the HS group; both occurred at the TABLE 2.

Summary of the JOA, NDI, and VAS Scores of the Two Groups (Mean SD)

HS ACDF P

JOA

Pre-op 13.65 1.35 14.36 0.79 0.08

2-week 16.65 0.49 16.82 0.50 0.14

The last 16.55 0.61 16.73 0.46 0.34

NDI

Pre-op 37.66 17.24 29.50 11.07 0.08

2-week 7.05 4.51 6.07 2.65 0.84

The last 6.65 4.52 6.13 2.40 0.70

VAS of neck pain

Pre-op 4.35 1.66 3.36 0.95 0.05

2-week 0.40 0.63 0.31 0.52 0.49

The last 0.75 0.64 0.41 0.50 0.08

VAS of arm pain

Pre-op 4.75 1.77 4.36 1.00 0.43

2-week 0.40 0.60 0.23 0.43 0.35

The last 0.65 0.67 0.45 0.51 0.38

Compared with preoperative values, there were statistically significant differences in JOA, NDI, and VAS scores at the last follow-up in the two groups.

P < 0.05 compared with Pre-op.

ACDF indicates anterior cervical discectomy and fusion; HS, hybrid surgery; JOA, Japanese Orthopedic Association; NDI, Neck Dysfunction Index; SD, standard deviation; VAS, Visual Analogue Scale.

1420 www.spinejournal.com

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inferior vertebra of the arthroplasty segment. Compared with 1 week after surgery, both of their local lordosis of treated segments decreased significantly at the last follow- up (P < 0.05). One case (5%) of Grade 4 HO disc was detected in the HS group (Figure 3A–C). And one (5%) had anterior migration of the Byran disc prosthesis without symptoms (Figure 4A–D), which occurred at 2 years postoperation. And no changes were found at the last follow-up.

Asymptomatic ASD was detected, one (5%) in the HS group and two (9%) in the ACDF group. Totally, 64 segments with MC plus prosthesis in the two groups achieved bone fusion.

DISCUSSION

After more than half a century of development, ACDF has been widely performed to the treatment of double-level or multilevel CDDD, which has achieved satisfied clinical outcomes. However, many surgeons have been perplexed

by symptomatic ASD with a prolonged follow-up. For most of the contiguous double-level CDDD in general, the degree of degeneration of the two segments is different. Therefore, ACDF could be applied to the one with more severe degenerative segment, and ACDR could be applied to the adjacent degenerative segment in accordance with the following five conditions: 1. The ROM of the segment is at least 68; 2. The height loss of the intervertebral space is less than 80% of the normal adjacent segment; 3. There is no obvious instability or excessive ROM of the segment; 4. There is no obvious canal stenosis, which may be caused by ossification of posterior longitudinal ligament of multiple segments or hypertrophy of ligamenta flava, etc.; 5. There was no obvious osteoporosis. In recent years, it has been reported that the treatment of HS to the double-level CDDD has achieved satisfied short and middle-term clinical outcome.

Compared with ACDF, HS is an effective alternative inven- tion for the treatment of multilevel cervical spondylosis to

A B

C D

Figure 1. The changes in clinical outcomes. (A) JOA; (B) NDI; (C) VAS of NP; (D) VAS of AP. ACDF indicates anterior cervical discectomy and fusion; AP, arm pain; HS, hybrid surgery; NP, neck pain.

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Figure 2. Two cases of SWD (above: a 54-year-old female patient; below: a 47-year-old male patient). The arrow points to the position of SWD. (A) Lateral radiograph, 1 week postoperation. (B) Lateral radiograph, at the last follow-up, SWD (grade 1) was found at C6. (C) Dynamic lateral radiographs at maximum extension and maximum flexion, at the last follow-up, the ROM of C2–C7 (508) was maintained.

(D) Lateral radiograph, 1 week postoperation. (E) Lateral radiograph, at the last follow-up, SWD (grade 2) was found at C5. (F) Dynamic lateral radiographs at maximum extension and maximum flexion, at the last follow-up, the ROM of C2-C7 (228) was maintained.

TABLE 3.

Summary of the Main Radiological Outcomes of the Two Groups (Mean SD)

HS ACDF P

The local lordosis of the treated segments

Pre-op 1.63 6.25 2.75 7.48 0.60

The last 5.57 7.70 6.61 4.40 0.59

The ROM of superior adjacent segment

Pre-op 11.34 6.49 10.07 4.82 0.45

The last 9.26 6.07 13.26 5.95^y 0.04

The ROM of inferior adjacent segment

Pre-op 5.52 4.03 6.04 3.90 0.72

The last 5.10 3.46 6.65 3.87 0.18

The ROM of C2-C7

Pre-op 38.99 13.96 35.34 15.39 0.43

The last 36.16 14.09 26.82 13.43^y 0.03

Compared with preoperative values, there were statistically significant differences in the local lordosis of the treated segments in the HS group. And there were statistically significant differences both in the local lordosis and the ROMs in the ACDF group.

P < 0.05.

yP < 0.01 compared with Pre-op.

ACDF indicates anterior cervical discectomy and fusion; HS, hybrid surgery; ROM, range of motion; SD, standard deviation.

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preserve cervical ROM and reduce the risk of ASD.^{9 – 14}Lu et al.¹² performed a systematic review; the result showed that C2–C7 ROM was significantly greater after HS than ACDF, while superior and inferior segment ROM measure- ments were significantly lower. In short-term follow-up, the postoperative C2–C7 ROM in HS group was closer to the physiological status. Similar results have been found in some other related studies.^11,13 However, it has also been reported that multilevel ACDFs do not significantly increase the risk of ASD at the C7–T1 level, and ASD occurred mainly in the middle region of cervical spine (C4–6), especially when the surgery failed to restore or maintain the cervical lordosis.^15,16

Clinically, in our study, the VAS of neck and arm pain, JOA, and NDI assessment in both groups achieved better scores at the last follow-up (P < 0.05). But there was no significant difference between the two groups. The result showed that, based on careful selection of patients, HS could produce a satisfactory clinical outcome in middle-term follow-up, which was equal to ACDF. Ji et al.¹⁰indicated that, compared with ACDF, HS led to better NDI and C2- C7 ROM recovery, and less adjacent ROM increase over a 2-year follow-up. But it became similar with 5 years of follow-up. Hey et al.¹⁷performed HS, ACDF, and ACDR surgery on 21 patients with two segments and three segments cervical spondylosis. The result indicated that HS

Figure 4. An anterior migration of the Byran disc prosthesis was found in a 45-year-old female patient. The arrow points to the position of anterior device migration. (A) One-week post operation. (B) The anterior device migration (approximate 2.8 mm) was found at 2-year follow- up primarily. (C) The migration (approximate 2.9 mm) had not obviously increased. (D) At the last follow-up, the anterior device migration (approximate 2.9 mm) had not increased and the upper endplate was in a fixed position.

Figure 3. A HO (grade 4) case of a 51-year-old male patient. The arrow points to the position of HO. (A) Preoperative lateral X-rays of the cervical spine. (B) One-week postoperation. (C) At the last follow-up, HO (grade 4) was found on C4–5, before which a bridging trabecular bone continuous between adjacent endplates, and ASD was found on C5–6.

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appeared comparable to ACDF and ACDR in terms of safety and feasibility, and superior in terms of earlier return to work.

In the present study, the C2–C7 ROM in HS group was greater than ACDF group (P < 0.05), while the ROM of superior adjacent segments was lower (P < 0.05). No symptomatic complications occurred in both groups. Our find- ings suggest that HS could reduce the motional compensation of the superior adjacent segment and maintain the global ROM of cervical spine effectively. Radiolog- ically, the middle-term follow-up outcome of HS is superior to that in the ACDF.

SWD was found in some early studies, which substance was sagittal wedge fracture of the thoracolumbar vertebra.¹⁸And, it is devastating burst fractures and dislocations that mostly occurred in the cervical spine,¹⁹ SWD being reported rarely. At the last follow-up in this study, two (10%, one male and one female) SWDs were found in the HS group. Both of their local lordosis of the treated segment decreased significantly (P < 0.05), and even the local kypho- sis appeared (the male patient: 158 at one week after surgery, -28 at the last follow-up; the female patient: 68 one week after surgery, -108 at the last follow-up). Because of the osteophyte in the lateral facet intervertebral joint, the male patient has almost completely lost the ROM in the Byran implanted segment. A satisfied ROM was still maintained by the female patient. No related clinical symptoms were found in both of them. The physiological lordosis of the cervical spine has an important impact on the final clinical outcome, especially for patients with double-level or multilevel CDDD in the long-term follow-up.^20,21The local loss of cervical lordosis may contribute to the change of dynamic kinematics of the cervical spine and increase the biomechanical compressive stress on the anterior part of the vertebra in neighboring segments, which promote the degeneration of adjacent segment.²² Conversely, the incidence of ASD would be lowered by reducing the loss of lordotic alignment, and improving the final clinical outcome as well.^23,24

Most vertebra fracture result from routine everyday activities, which seemingly benign activities—for example, bending or lifting light objects—produce remarkably large loads. Under the premise of intact posterior ligament system, the violence is expended upon the anterior of the vertebral body and a wedge compression fracture results. Similarly, the weight of the head is borne by the cervical spine. And SWD may occur at a violent flexion or extension of the head, where more loads are transferred to the anterior part of the cervical vertebra body. In addition, in order to find a satisfactory position for the Bryan disc during the operation (The height of the prosthesis was fixed at 8 mm), the upper and lower endplates are polished repeatedly, and the position of the retractor frame and dual track-milling guide can also contribute to the bone loss of the upper and lower vertebra, especially for the patients with osteoporosis or the premenopausal female patients.²⁵ This may also be an important factor in the postoperative SWD of the cervical vertebra. The two SWD patients in this

study belong to the middle-aged crowd (male: 47 years, female: 54 years, average 50.5 years). The male patient has a smoking history of more than 10 years, and the female patient had entered menopause. What is more, both of them were long-term volt case workers. Therefore, we come to the conclude that the severe bone loss may be the main cause of the two SWDs in our study. And the increased load during their daily life had accelerated the process of the bone loss in the anterior part of the vertebra.

When it reached a certain degree, it will eventually cause the SWD of the vertebra. The results indicate that postoperative SWD may reduce the local cervical lordosis of the treated segment, but it has no significant impact on the mid-term clinical outcomes. The serious loss of bone mass may be the most important risk factor for SWD. And the key to reduce the incidence of SWD lies in careful preoperative patient selection and strict postoperative management of the bone loss, especially for the patient with potential risk factors for osteoporosis.

CONCLUSION

HS appears to be an acceptable option in the management of contiguous two-segment CDDD. It yielded similar mid- term clinical improvement to ACDF and demonstrated significantly better preservation of cervical ROM at an average of 6 years’ follow-up. The incidence of postoperative SWD was low; however, it can significantly reduce the cervical lordosis.

Key Points

Hybrid surgery yielded similar mid-term clinical improvement to ACDF.

H y b r i d s u r g e r y d e m o n s t r a t e d e f f e c t i v e preservation of cervical ROM at an average of 6 years’ follow-up.

The incidence of postoperative sagittal wedge deformity is low; however, it can significantly reduce the cervical lordosis.

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