Dynamic Cervical Implants (DCI) versus Anterior Cervical Discectomy and Fusion (ACDF) in Single-Level Cervical Disc Disease (CDD): Clinical and Radiographic Outcome

Background Data: In spite of being successful, anterior cervical discectomy and fusion ACDF has some complications, among them, pseudoarthrosis, implant failure, and adjacent level disease. Dynamic Cervical Implants (DCI) are motion-preserving implants started to take part in treating cervical spondylotic disease with promising results. Purpose: To compare the clinical and radiographic outcomes of ACDF versus DCI in patients with degenerative cervical radiculoand/or myelopathy. Study Design: A prospective randomized controlled study. Patients and Methods: Forty patients with cervical spondylotic radiculoand/or myelopathy were recruited for this study. They were 21 males and 19 females with mean age of 458.9± years. They were randomly allocated for either the ACDF group including 20 patients undergoing ACDF using PEEK cages or the DCI group including 20 patients using DCI. Clinical outcome parameters were brachialgia VAS and NDI, and radiological outcome parameters were fusion rate, adjacent level changes, and segmental mobility. Results: The mean follow-up was 204± months. The mean VAS of brachialgia decreased from 8.7 preoperatively to 6.6 postoperatively in ACDF group, while it decreased from 8.8 to 6.4 in DCI with no significant differences in both groups. The mean NDI improved from 24.7±1.6 to 16.2±1.8 in ACDF group and from 23.9±2.1 to 15.8±2.0 in DCI group, with no significant difference in both groups. Fusin rate was 100% in ACDF group. Radiologically, adjacent level changes were reported in 5 (25%) patients in ACDF group, while these changes were only observed in 1 patient (5%) of the DCI group. Segmental mobility was preserved in all patients in the DCI group but was lost in 3 patients at final follow-up visit. Conclusion: Although clinical outcomes of both ACDF and DCI groups were not significantly different at final follow-up, radiographic parameters were relatively better in DCI group compared to ACDF group including segmental mobility preservation and adjacent level changes. (2019ESJ198)


INTRODUCTION
Anterior cervical discectomy and fusion (ACDF) is considered to be a highly successful surgical technique for cervical spondylosis associated with brachialgia and/or myelopathy. 1,2,4 Nonunion accounts for more than two-thirds of failures in ACDF surgeries and iliac bone graft morbidity is also reported in about one-third of multilevel fusion operations. 18,21 There are many types of cages used to avoid the complications associated with iliac bone grafting. 16,19,20 These problems include persistent donor-site pain, infection, hematoma formation, iliac crest fracture, and meralgia parasthetica. 6,21 However, in spite of being successful for many years, ACDF has its own complications in the form of nonunion, implant failure, and adjacent level disease which occurs due to the excessive motion observed at the levels immediately above and/or below the index level. 8,13,17,18 It has been proven to provide clinical stability after decompression. 5 However, although it achieves long-term success, ACDF is not without complications as there have been reports of pseudoarthrosis, implant failure, and adjacent level disease which occurs due to the significant amount of increased motion observed at the levels immediately above and below the fusion. However, greater compensation occurred at the inferior segments compared to the superior segments for the lower level fusions. 8,13,17,18,22 DCI is a titanium implant, originally invented in 2002 by Dr. Guy Matgé, Luxembourg. It was introduced in clinical use, in 2004. The design was modified to better accommodate the normal disc anatomy. The DCI implant with its motion preservation characters is unique implant. It stabilizes the cervical spine while still offering a limited, controlled flexion and extension movements allowing the spine to dynamically perform its function. It also acts as a shock absorber, preventing accelerated degeneration in adjacent segments. Thus, the DCI implant aims at combining the advantages of the gold standard "fusion" with a motion preservation philosophy. 15 The objective of this study is to compare the clinical and radiographic outcomes of ACDF versus DCI in patients with degenerative cervical radiculo-and/or myelopathy operated upon at Benha University Hospital.

PATIENTS AND METHODS
This is a prospective randomized controlled study comparing between ACDF and DCI in treating chronic cervical spondylotic radiculo-and/or myelopathy. We recruited 40 patients (21 males and 19 females) with mean age of 458.9± (range, 38-53) years. All patients presented with cervical spondylotic radiculo-and/or myelopathy and were admitted to the Neurosurgery Department, Benha University Hospital, between January 2015 and May 2019. All patients received conservative therapy for at least 3 months before being scheduled for surgery. Patients were randomly divided into two groups according to their hospital admission number sequences. ACDF group included 20 patients (11 males/9 females) with mean age of 44±9.7 (range, 38-50) years; DCI group included 20 patients (10 males/10 females) with mean age of 46±8.5 (range, 39-53 y) years. We included all patients with single-level MRI documented cervical disc disease who presented with cervical radiculo-and/or myelopathy and failed adequate conservative treatment. Patients with multiple cervical disc disease, osteoporosis, cervical canal stenosis, OPLL, or other systemic or local pathology were excluded from this study. Preoperative clinical evaluation comprised of the Visual Analogue Score (VAS) of arm pain and the Neck Disability Index (NDI). Radiographic workup included plain radiographs in the anteroposterior and lateral projections and Magnetic Resonance Imaging (MRI).

Surgical Procedure
The patients underwent the procedure under general anesthesia (I.V. and inhalational anesthesia) in supine position with the neck slightly extended. All patients underwent operation utilizing the anterior Smith-Robinson approach from the right side. Surgical procedures were uniformly conducted in both groups including skin incision, subcutaneous dissection, platysma muscle splitting, and strap muscle dissection. The target level was determined using fluoroscopy and disc material was removed and cortical endplates were partially curetted, opening the posterior longitudinal ligament. Following this, in the ACDF group, a suitable sized PEEK cage (Orthofix Inc., Lewisville, TX) was inserted. The hollow of the cage was loaded with Demineralized Bone Matrix (DBM); in the DCI group, a DCI (Z-Brace Dynamic Fusion Cage TM , Baui Biotech Co., Ltd., Taiwan) titanium containing material was inserted. The implant position was checked with fluoroscopy and meticulous hemostasis and wound closure in layers without drain were performed. Postoperatively, all patients wore a rigid collar for 6weeks and then started a physiotherapy course, regaining their normal activity gradually. At follow-up, patients were followed at the outpatients' clinic and evaluated clinically and radiographically at 6-week and then at 3-month intervals. At each visit, they submitted to neurological evaluations (motor, sensory, or reflex) and reported the VAS of the arm pain and NDI. They were also submitted to plain radiographs (flexion/extension, AP, and lateral views) reporting signs of fusion, preserved segmental motion, and adjacent level changes, including disc space narrowing and worsening of spondylotic changes. Fusion was assessed by bony bridging between the implant and the facing endplates based on plain radiographs. Both endplates were required to be incorporated in order for the subject to be judged as fused. Segmental mobility was assessed using Cobb's angle measurement.

RESULTS
The mean follow-up period was 21 ±3 months (range 18-24). The operated levels distributed homogenously in both groups are depicted on Chart 1. At the last follow-up, the mean VAS of brachialgia decreased from 8.7±1.1 to 6.6±0.8 in ACDF group, while it decreased from 8.8±1.2 to 6.4±1.0 in DCI group. The NDI improved from 24.7±1.6 to 16.2±1.8 in ACDF group, while in the DCI group it improved from 23.9±2.1 to 15.8±2.0, depicting significant improvement in both parameters in both patients' groups (Table 1). Fusion occurred in all cases of ACDF. Five out of 20 patients (25%) had radiological changes of aggravated spondylosis in the index level in ACDF group, while in DCI group we had only 1 (5%) which may be of clinical importance ( Table  2). The mobility of the operated segments was preserved in 17 out of total 20 patients in the DCI group. Loss of mobility across the operated segment was reported in 3 patients; this was due to excessive calcification over the implant in 2 patients and due to improper positioning of the implant in another patient. There was no reported DCI migration or sinking in any of our patients. In 1 patient, there was a malpositioned implant slightly deviated to one side with no other sequela. There were no reported significant morbidity or mortality throughout this study.

Journal
ACDF has been considered for a long time to be the gold standard for treating the cervical disc disease. However, concerns regarding symptomatic adjacent segment disease, that needs reoperation, have evolved and necessitate surgeons to try to find another solution that preserves the normal spine motion at the cervical level and avoids this problem. 15 Total disc replacement (TDR) or arthroplasty trials started to take place in spine practice, aiming to restore and maintain the segmental motion, function, and normal physiological anatomy, while successfully treating the patient's symptoms. Heterotopic ossifications and implant-related complications of the TDR itself made the procedure under continuous evaluations. Many types and forms of TDR implants were introduced in the market; none of them fulfill all the criteria of the ideal TDR prosthesis. 10 Therefore, the need for an intermediate solution between static fusion and TDR rapidly increases. If the interbody implant can maintain a controlled movement in the affected motion segment, results are supposed to be better and adjacent level disease secondary to fusions is supposed to be delayed. The DCI implant is theoretically supposed to achieve that target. The spring-like flexibility of the Dynamic Cage allows axial displacement and flexion and extension with normal cervical movements. If a great effort is encountered, the self-engagement of the cage can protect the cage slippage to maintain adequate stability. The hollowing of the cage provides a tunnel for bone fusion, while the porous coating on the upper/under surfaces of the cage may promote the expected fusion. Although multilevel DCI has been reported, most surgeons prefer DCI in single-level CDD excluding active infection or displacement more than 5 mm from their inclusion criteria. 15 Regarding DCI arthroplasty, it is a procedure that was invented by Dr Matgé in 2002 and then developed and presented to clinical practice by Paradigm Spine (New York, NY, USA). 10 The two main criteria of dynamic cage are being U-shaped with hook teeth at the anterior edge and the axial flexibility. DCI arthroplasty has several advantages: (1) a wide spectrum of indications and being a relatively simple surgical technique 7 ; (2) a shock absorbing device that limits axial rotation and lateral bending, thus exacerbating facet joint stress 12 ; (3) allowing axial compression in flexion and limited extension, with motion at the index level relatively close to the intact value 14 ; (4) no friction at the metallic surface when the DCI functions, thus no local or systemic reaction to debris. 7 In our study, 40 patients were randomly classified equally into two groups with comparable age and sex distributions and with comparable complaints due to their cervical disc disease. In ACDF group, PEEK cage fusion was utilized; in the DCI group, intervertebral DCI implant. Both groups were followed up clinically and radiologically for comparable periods. Clinical status of both groups showed significant improvement. Although clinical outcomes between the two groups were not significantly different at final follow-up, radiographic parameters were relatively well maintained in our DCI group compared to our ACDF group.

CONCLUSION
Although clinical outcomes of both ACDF and DCI groups were not significantly different at final follow-up, radiographic parameters were relatively better in DCI group compared to our ACDF group including segmental mobility preservation and adjacent level changes. We recommend future study with a larger sample and longer follow-up period for more assessment of the validity of the DCI and evaluation of its effect on adjacent level pathology.