Early Radiological Analysis of Cervical Arthroplasty with Bryan and Mobi-C Cervical Disc Prosthesis

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1 CLINICAL ARTICLE Kor J Spine 5(3): , 2008 Early Radiological Analysis of Cervical Arthroplasty with Bryan and Mobi-C Cervical Disc Prosthesis Ki Suk Choi, M.D., Il Tae Jang, M.D., Jae Hyeon Lim, M.D., Sang Won Lee, M.D., Hyang Kwon Park, M.D. Department of Neurosurgery, Nanoori Hospital, Seoul, Korea Objective: We investigated whether there are any different results in the overall sagittal alignment, neutral functional spine unit (FSU) angle and segmental FSU ROM (range of motion) angle from the patients undergone by cervical arthroplasty with two kinds of artificial cervical disc prostheses, Bryan and Mobi-C cervical disc. Methods: Twenty eight patients underwent anterior cervical discectomy and implantation of artificial cervical disc prosthesis; Eighteen of them underwent operation with Bryan and the rest of them with Mobi-C cervical disc prosthesis. These patients consist of fourteen females and fourteen males with mean age 46.9 years old and 9.4 months mean follow-up period. There were 4 cases of C 4-5, 18 cases of C 5-6 and 6 cases of C 6-7 level. We measured overall sagittal alignment, neutral FSU angle and segmental FSU ROM angle using lateral radiographs preoperatively and postoperatively. The clinical outcome was evaluated by neck disability index(ndi). Result: The average angle of overall sagittal alignments was changed from preoperatively to postoperatively in Bryan cervical disc group. It decreased 3.24 in cervical lordosis. However, in Mobi-C cervical disc group, the average angle of overall sagittal alignments was changed from preoperatively to postoperatively. It increased 6.56 in cervical lordosis. The averages of neutral FSU angles were preoperatively and postoperatively in Bryan cervical disc group, and were preoperatively and -9.7 postoperatively in Mobi-C cervical disc group. The averages of segmental FSU ROM angles were preoperatively and postoperatively in Bryan cervical disc group, and was 8.31 preoperatively and 13.6 postoperatively in Mobi-C cervical disc group. NDIs were 24.0 preoperatively and 5.9 postoperatively in Bryan cervical disc group, and 24.7 preoperatively and 8.7 postoperatively in Mobi-C cervical disc group. Conclusion: Postoperative cervical lordosis and segmental FSU ROM angle were increased in Mobi-C cervical disc group (p<0.05). To preserve segmental motion and avoid adjacent segment degeneration is to the focus in cervical arthroplasty. To preserve cervical lordosis after operation is physiologic than postoperative cervical kyphosis. It remains controversial whether cervical kyphosis influences clinical outcome after anterior cervical operation. The results of this study show that the technical and mechanical improvement of Bryan cervical disc prosthesis may be considered. Key Words: Bryan cervical disc ㆍ Cervical arthroplasty ㆍ Lordosis ㆍ Mobi-C cervical disc ㆍ Kyphosis INTRODUCTION Anterior cervical discectomy and fusion is one of the most durable procedures and has conformed its safety and efficacy. But inherent associated morbidity and procedural limitations are well known. Fusion following anterior cervical discectomy has been implicated in the acceleration of degenerative changes in adjacent spinal segments. Cervical arthroplasty, a procedure in which a degenerative segment is replaced with mechanical device that mimics cervical joint function, may represent progress in the treatment of degenerative disorders of the cervical spine. Arthroplasty offers the promise of maintaining functional spinal motion, thereby potentially avoiding adjacent-segment disease 2,7,8,11). Clinical experience involved spinal arthroplasty is limited Received: April 22, 2008 Accepted: July 14, 2008 Published: September 30, 2008 Corresponding Author: Hyang Kwon Park, M.D. Address of reprints: Department of Neurosurgery, Nanoori Hospital, 63-8, Nonhyun-dong Kangnam-gu, Seoul, , Korea Tel: , Fax: , spinecare@hanmail.net * 본논문의요지는 2007년도대한신경외과학회추계학술대회에서발표되었음. Kor J Spine 5(3) September

2 KS Choi, et al. to compare with what is derived from cervical fusion. The Bryan Cervical Disc prosthesis (Medtronic Sofamor Danek, Memphis, TN) has showed to yield the suitable clinical 1,5) results following one- and two-level disc replacement. We think that the radiological results following implantation of two cervical arthroplasty devices, Bryan and MobiC cervical disc may be interesting. MATERIALS AND METHODS All the patients presenting with cervical disc herniation producing radiculopathy and/or myelopathy, for whom anterior cervical discectomy was recommended, were considered as the candidates for arthroplasty as an alternative to fusion. The single-level disease patients were selected. Spinal instability, active infection, multi-level spondylosis, and lack of motion at the segment are exclusion criteria. Twenty eight patients, fourteen females and fourteen males, who were selected from the single-level disease underwent anterior cervical discectomy and artificial disc replacement surgery. Eighteen of twenty eight patients were implanted with Bryan cervical disc and ten patients were implanted with Mobi-C cervical disc prosthesis (LDR medical, Troyes, France). At least six months was considered as the followup period after operation. The mean postoperative followup period was 9.4 months (range; 6 to 14 months), 9.72 months in Bryan cervical disc and 8.86 months in MobiC cervical disc. The mean age of patients was 46.9 years old (range; years old). The overall sagittal alignment (C2 to C7), neutral FSU angle, and segmental FSU ROM angle were measured on lateral and flexion/extension radiographs. For the absolute values of cervical angulation, the lordotic angles are showed as negative values and kyphotic angles as positive. The clinical outcome was evaluated by neck disability index (NDI) preoperatively and postoperatively. Fig. 1. Preoperative and postoperative x-ray of Bryan cervical disc. A and B: radiograph of neutral posture, C and D: radiograph of flexion posture, E and F: radiograph of extension posture. 112 Kor J Spine 5(3) September 2008

3 Early Radiological Analysis of Cervical Arthroplasty with Bryan and Mobi-C Cervical Disc Prosthesis Fig. 2. Preoperative and postoperative x-ray of Mobi-C cervical disc. A and B: radiograph of neutral posture, C and D: radiograph of flexion posture, E and F: radiograph of extension posture. RESULTS A total of twenty eight cervical artificial discs, eighteen Bryan cervical discs and ten Mobi-C cervical discs, were placed in twenty eight patients. The artificial discs were placed at C4-5 in four cases, C5-6 in eighteen cases and C6-7 in six cases. The average of overall sagittal alignments was preoperatively and postoperatively in Bryan cervical disc group, and preoperatively and postoperatively in Mobi-C cervical disc group (p<0.05). The average of segmental FSU ROM angle was preoperatively and postoperatively in Bryan cervical disc group, and was 8.31 preoperatively and 13.6 postoperatively in Mobi-C cervical disc group (p<0.05). The average of neutral FSU angles was preoperatively and postoperatively in Bryan cervical disc group, and was Fig. 3. Overall sagittal alignment of Bryan and Mobi-C cer- vical disc. Cervical lordosis was increased in Mobi-C cervical disc group than Bryan preoperatively and -9.7 postoperatively in Mobi-C cervical disc group. NDI was 24.0 preoperatively and 5.9 postoperatively in Bryan cervical disc group, and 24.7 Kor J Spine 5(3) September

4 KS Choi, et al. Table 1. Radiological results of two artificial cervical discs Bryan cervical disc group Mobi-C cervical disc group Preoperative postoperative Preoperative postoperative Overall sagittal alignment (p<0.05) Neutral FSU angle FSU ROM (p<0.05) Fig. 4. Postoperative FSU ROM angle of Bryan and Mobi-C cervical disc. Postoperative FSU ROM angle was increased in Mobi-C cervical disc group. preoperatively and 8.7 postoperatively in Mobi-C cervical disc group. The statistical analysis was used as the Wilcoxon Signed-Rank test. A P value of 0.05 was significantly considered. DISCUSSION Anterior cervical discectomy and fusion routinely achieves satisfying results. Furthermore, fusion has been shown in large studies to be safe, to produce only rare complications, and to be associated with a mortality rate of 0% 6). But cervical fusion alters the biomechanics of the fused segment and neighboring levels as well. Compensatory hypermobility is the most likely cause of the accelerated degeneration of adjacent segments, as reported by several authors 4,7,9,11). Symptomatic adjacent-segment disease defined by Hilibrand and colleagues 7) as new-onset radiculopathy or myelopathy following cervical fusion occurred annually in nearly 3% of the patients they reviewed. Wigfield and coworkers 11) compared motion pre- and postoperatively in patients who underwent fusion and Bryan disc-augmented arthroplasty and found a significant increase in adjacent-segment motion in discs that were normal be- fore fusion surgery. Conversely, adjacent-segment motion decreased in the patients treated with arthroplasty. Duggal, et al. 3), found improved motion after Bryan disc surgery. Robertson, et al. 10), reviewed the results of a pros pective randomized study and found a lower incidence of symptomatic adjacent-segment disease in patients treated with the Bryan disc compared with fusion. Segmental FSU ROM angles were preoperative and postoperative in Bryan disc group, and were preoperative 8.31 and postoperative 13.6 in Mobi-C disc group. Segmental FSU ROM angle were increased in 5.29 in Mobi-C disc group, but were decreased in 0.57 in Bryan disc group. On the basis of results, Mobi-C artificial disc device may preserve segmental FSU ROM angle and thus may play an effective function in prevention of adjacentsegment degeneration than Bryan artificial disc device. An adverse effects of cervical arthroplasty include segmental kyphosis, heterotrophic ossification, expulsion of prosthesis, and delayed fusion 12). Segmental kyphosis could potentially affect every arthroplasty case. In operation of Bryan artificial disc, postoperative kyphosis was caused by several factors, including overmilling at the dorsal endplate, the angle of Bryan disc insertion, structural absence of lordosis in the Bryan disc, surgical procedure to remove the entire posterior longitudinal ligament, and preexisting kyphosis 13). Overmilling at the dorsal endplate resulted in postoperative reduction of posterior vertebral height. Yi, et al., 12) postulated another method to calculate the angle of Bryan disc insertion that the prosthesis is inserted parallel to the angle of the native disc space. Mobi-C artificial disc does not have any endplate milling and preparation procedure except curettage for exposure of bony endplate. Therefore, Mobi-C artificial disc is possible to insert parallel to the angle of the native disc space. The average of preoperative overall sagittal alignments were in Bryan disc group and in Mobi-C disc group. But last postoperative follow up radiographs 114 Kor J Spine 5(3) September 2008

5 Early Radiological Analysis of Cervical Arthroplasty with Bryan and Mobi-C Cervical Disc Prosthesis showed that overall sagittal alignment was in Bryan disc group and in Mobi-C disc group. Postoperative cervical lordotic angle increased in 6.56º in Mobi-C disc group, but decreased in 3.24 in Bryan disc group. Neutral FSU angle increased in 8.77 in Mobi-C disc group and increased in 2.12 in Bryan disc group. The result of study showed that the patients operated with Mobi-C artificial disc had more lordotic sagittal alignment and increased in neutral FSU angle and segmental FSU ROM angle. The arthroplasty is operation preserving physiologic segmental motion. Increased postoperative cervical lordosis is more physiologic than kyphosis. Maintaining functional spinal motion decreases an adjacent segment problem. The radiological results were good at Mobi-C disc group. But, clinical outcome was not different in both groups. We think that the longer follow-up and improvement of device mechanism and operative technique may be needed in artificial disc prosthesis. CONCLUSION We analyzed preoperative and postoperative overall sagittal alignment, neutral FSU angle and segmental FSU ROM of two different artificial disc devices using lateral radiographs. The postoperative radiologic results from the Mobi-C cervical disc group were more lordotic in overall sagittal alignment, were increased in segmental FSU ROM angle than Bryan cervical disc group, and statistically significant. However, the operative cases and the follow-up period were not sufficient. The further study was needed. REFERENCES 1. Anderson PA, Sasso RC, Rouleau JP, Carlson CS, Goffin J: The Bryan Cervical Disc: Wear properties and early clinical results. Spine J 4:S303-S309, Baba H, Furusawa N, Imura S, Kawahara N, Tsuchiya H, Tomita K: Late radiographic findings after anterior cervical fusion for spondylotic myeloradiculopathy. Spine 18: , Duggal N, Pickett GE, Rouleau JP: Kinematic analysis of the Bryan cervical disc prosthesis. Paper presented at the Annual Meeting of the Cervical Spine Research Society. Boston, December 9, Goffin J, Geusens E, Vantomme N, Quintens E, Waerzeggers Y, Depreitere B, et al: Long-term follow-up after interbody fusion of the cervical spine. J Spinal Disord Tech 17:79-85, Goffin J, Van Calenbergh F, van Loon J, Casey A, Kehr P, Liebig K, et al: Intermediate follow-up after treatment of degenerative disc disease with the Bryan Cervical Disc Prothesis: Single-level and bi-level. Spine 28: , Hacker RJ, Cauthen JC, Gilbert TJ, Griffith SL: A prospective randomized multicenter clinical evaluation of an anterior cervical fusion cage. Spine 25: , Hillibrand AS, Yoo JU, Carlson GD, Palumbo MA, Jones PK, Bohlman HH: Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis. J Bone Joint Surg Am 81: , Matsunaga S, Kabayama S, Yamamoto T, Yone K, Sakou T, Nakanishi K: Strain on intervertebral discs after anterior cervical decompression and fusion. Spine 24: , Robbins MM, Hillibrand AS: Post-arthrodesis adjacent segment degeneration, in Vaccaro A, Anderson DG, Crawford A, benzel E, Regan J(eds): Complications of Pediatric and Adult Spine Surgery. New York: Marcel Dekker, 2004, pp Robertson JT, Papadopoulos SM, Traynelis VC: Assessment of adjacent segment disease in patients treated with cervical fusion or cervical arthroplasty: A prospective 2- year study. Paper presented at the Annual Meeting of the Cervical Spine Research Society. Boston, December 9, Wigfield C, Gill S, Nelson R, Langdon I, Metcalf N, Robertson J: Influence of an artificial cervical joint compared with fusion on adjacent-level motion in the treatment of cervical degenerative disc disease. J Neurosurg (Suppl 1) 96:17-21, Yi S, Shin HC, Kim KN, Park HK, Jang IT, Yoon DH: Modified techniques to prevent sagittal imbalance after cervical arthroplasty. Spine 32: , Yoon DH, Yi S, Shin HC, Kim KN, Kim SH: Clinical and radiological results following cervical arthroplasty. Acta Neurochir(wien) 148: , 2006 Kor J Spine 5(3) September