Anterior cervical discectomy and fusion (ACDF) is. Solid radiographic fusion with a nonconstrained device 5 years after cervical arthroplasty

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1 J Neurosurg Spine 21: , 2014 AANS, 2014 Solid radiographic fusion with a nonconstrained device 5 years after cervical arthroplasty Case report Robert F. Heary, M.D., Ira M. Goldstein, M.D., Katarzyna M. Getto, B.S.N., and Nitin Agarwal, M.D. Department of Neurological Surgery, Rutgers New Jersey Medical School, Newark, New Jersey Cervical disc arthroplasty (CDA) has been gaining popularity as a surgical alternative to anterior cervical discectomy and fusion. Spontaneous fusion following a CDA is uncommon. A few anecdotal reports of heterotrophic ossification around the implant sites have been noted for the BRYAN, ProDisc-C, Mobi-C, PRESTIGE, and PCM devices. All CDA fusions reported to date have been in devices that are semiconstrained. The authors reported the case of a 56-year-old man who presented with left C-7 radiculopathy and neck pain for 10 weeks after an assault injury. There was evidence of disc herniation at the C6 7 level. He was otherwise healthy with functional scores on the visual analog scale (VAS, 4.2); neck disability index (NDI, 16); and the 36-item short form health survey (SF-36; physical component summary [PSC] score 43 and mental component summary [MCS] score 47). The patient underwent total disc replacement in which the DISCOVER Artificial Cervical Disc (DePuy Spine, Inc.) was used. The patient was seen at regular follow-up visits up to 60 months. At his 60-month follow-up visit, he had complete radiographic fusion at the C6 7 level with bridging trabecular bone and no motion at the index site on dynamic imaging. He was pain free, with a VAS score of 0, NDI score of 0, and SF-36 PCS and MCS scores of 61 and 55, respectively. Conclusions. This is the first case report that identifies the phenomenon of fusion around a nonconstrained cervical prosthesis. Despite this unwanted radiographic outcome, the patient s clinical outcome was excellent. ( Key Words total disc arthroplasty nonconstrained device cervical fusion cervical disc Anterior cervical discectomy and fusion (ACDF) is the gold standard in the treatment of degenerative disc disease and acute disc herniation, with proven successful outcomes. Excellent clinical and radiographic results have been seen in 85% 95% of all patients. 16,17 As some studies show that fusion alters cervical spine biomechanics, 4 there has been some debate whether ACDF causes adjacent-segment disease. As a result of this concern, cervical disc arthroplasty (CDA) has emerged as a treatment option that is specifically designed to preserve segmental motion. Several prospective, randomized, controlled clinical trials of CDA compared with ACDF have yielded promising results, and few complications or adverse events have been reported. 4,8 10,18,19,21,25,28 Spontaneous fusion following CDA is uncommon, but Abbreviations used in this paper: ACDF = anterior cervical discectomy and fusion; CDA = cervical disc arthroplasty; HO = heterotopic ossification; IDE = Investigational Device Exemption; MCS = mental component summary score; NDI = neck disability index; PCS = physical component summary score; SF-36 = 36-item short form health survey; VAS = visual analog scale. it has been reported. Reports of spontaneous fusion after CDA with the BRYAN Cervical Disc (Medtronic Sofamor Danek USA, Inc.) by Bartles and Donk as well as Parkinson and Sekhon were published in ,19 Multiple other articles mention occurrences of high-grade heterotopic ossification (HO) and/or spontaneous fusion after CDA with the ProDisc-C Total Disc Replacement system (Synthes Spine, Inc.), PCM (NuVasive, Inc.), Mobi-C Cervical Disc Prosthesis (LDR Spine USA, Inc.), SECURE-C Cervical Artificial Disc (Globus Medical, Inc.), and PRESTIGE Cervical Disc System (Globus Medical, Inc.). 3,6,7,12 14,16,22,24,27 All of the reported cases of fusion involving CDA occurred with devices that are semiconstrained. We report a case of spontaneous fusion around a nonconstrained device (DISCOVER Artificial Cervical Disc; DePuy Spine, Inc.). To our knowledge, this is the first description of such findings with a nonconstrained cervical prosthetic device. Case Report History and Presentation. A 56-year-old healthy J Neurosurg: Spine / Volume 21 / December

2 R. F. Heary et al. Fig. 2. Axial (left) and sagittal (right) T2-weighted MR images demonstrating a diffusely bulging disc obliterating the CSF space with greater severity on left side. man presented with neck pain and left arm weakness that began following an assault. His symptoms had not improved after 3 months of conservative treatment (including physical therapy). On physical examination, he had weakness of his left triceps, finger extensors, and wrist flexion, along with decreased sensation in the C-7 dermatomes bilaterally. A CT scan demonstrated an autofusion at the C5 6 level (Fig. 1). An MRI of the cervical spine revealed a disc herniation at C6 7, which was greater on the left side (Fig. 2). Plain radiographs, with flexion and extension views, demonstrated no dynamic instability. His clinical status was consistent with a traumatic C-7 radiculopathy. He was otherwise healthy with functional scores on the visual analog scale (VAS, 4.2); neck disability index (NDI, 16); and the 36-item short form health survey (SF-36; physical component summary [PSC] score 43 and mental component summary [MCS] score 47). Operation. A routine, right-sided, anterior cervical approach was used to perform a microsurgical removal of the C6 7 disc. Electrocautery was used judiciously during the approach for hemostasis. The posterior annulus fibrosus and the posterior longitudinal ligament were resected along with some posterior osteophytes. The dura mater was visualized and noted to be intact. Following the manufacturer s recommendations for insertion, a DISCOVER disc (size 16.7 mm 17.2 mm 6 mm) was inserted. This device was inserted as part of an FDA investigational device exemption (IDE) study. Intraoperative fluoroscopy confirmed proper alignment of the device in the cervical spine. After copious irrigation with normal saline, a standard layered closure was performed. Postoperative Course. The patient experienced complete resolution of both his neck and arm pain shortly after the surgery. His motor examination status improved over the next several months; at his 2-year follow-up, he was pain free and had only minor weakness (Grade 5-/5) remaining in his left hand. His clinical outcome was superb; however, the postoperative radiographic parameters were not as successful. Cervical spine radiographs, with flexion and extension views, were acquired at 2 and 6 weeks; 3 (Fig. 3) and 6 (Fig. 4) months, and 1 and 2 (Fig. 5) years postoperatively. By 1 year after the operation, there was concern on plain radiographs about fusion across the operative level. The 2-year postoperative CT scans, obtained as part of the FDA IDE protocol, demonstrated a complete fusion around the prosthesis (Fig. 6). At his 5-year follow-up evaluation, cervical spine radiographs, with flexion and extension views, clearly demonstrated fusion across the operative level (Fig. 7). There was also evidence of HO at the adjacent C5 6 level. Clear bridg- Fig. 1. CT scan demonstrating preoperative fusion at C5 6. Fig. 3. Plain radiographs, with flexion (left) and extension (right) views, taken 3 months after the index surgical procedure. A comparison (flexion and extension) demonstrates 4.5 mm of motion. 952 J Neurosurg: Spine / Volume 21 / December 2014

3 Fusion after arthroplasty with a nonconstrained device Fig. 4. Plain radiographs, with flexion (left) and extension (right) views, taken 6 months after the index surgical procedure. A comparison (flexion and extension) demonstrates 0.5 mm of motion, which is consistent with what many neurosurgeons would deem to be within the limits denoting fusion. ing trabecular bone, around the DISCOVER implant, was evident across the C6 7 segment. Postoperative functional outcomes scores at the 60-month follow-up evaluation were as follows: VAS score of 0; NDI score of 0; and SF- 36 PCS and MCS scores of 61 and 55. respectively. Discussion Fusions across segments treated by CDA are known to occur. To date, all of the devices that have fused are semiconstrained. 21,27 By definition, a device is considered to be constrained if it includes a mechanical stop within the physiological range of motion; semiconstrained if there is a mechanical stop outside of the normal range of motion; and unconstrained if the implant has no mechanical stop at all. 10,28 Our case study describes a complete fusion around a prosthesis that is classified as nonconstrained. This device design preserves greater amounts of segmental Fig. 6. Reconstructed CT scans taken at the FDA IDE protocol time point of 2 years postoperatively. Left: Solid arthrodesis present with bridging trabecular bone clearly visualized ventral to the C6 7 DISCOV- ER device; Class IV HO is also apparent at the C5 6 level. Right: Solid bony arthrodesis is apparent around the lateral edges of the DIS- COVER device on the coronal view, which demonstrates a symmetrical midline placement of the device. motion than a semiconstrained design. As such, this represents the first reported case where, despite no mechanical stop incorporated as a part of the device, a complete radiographic arthrodesis was demonstrated on both plain films and CT scans at long-term follow-up. Despite the promising, short-term clinical results after CDA, there has been a recent increase in the reporting of HO around the prosthesis (Table 1). Heterotopic ossification is commonly defined as a formation of bone outside the skeletal system. This phenomenon is widely known in the field of total hip or knee arthroplasty and has been classified by McAfee et al. for lumbar total disc replacement. 15 The 5-grade system is as follows: Class 0, no HO; Class I, HO present, without affecting the intervertebral space; Class II, HO with new bone formation in the disc space, without blocking or articulating between the adjacent-level endplates; Class III, bridging ossifica- Fig. 5. Plain radiographs with flexion (left) and extension (right) views, taken 2 years after the index surgical procedure. A comparison (flexion and extension) demonstrates 0 mm of motion and bridging trabecular bone consistent with fusion. J Neurosurg: Spine / Volume 21 / December 2014 Fig. 7. Plain radiographs with flexion (left) and extension (right) views, taken 5 years after the index surgical procedure. Well-corticated fusion is present across the ventral disc space, and no motion can be detected when comparing the positioning of the spinous processes on the views at the extremes of neck motion (flexion and extension). 953

4 R. F. Heary et al. TABLE 1: Cervical disc arthroplasty devices with FDA approval Device Company Date Approved Design* HO Reported* ProDisc-C Total Disc Replacement Synthes Spine, Inc. 12/17/2007 semiconstrained 28 yes 5 PRESTIGE Cervical Disc System Medtronic Sofamor Danke USA, Inc. 07/16/2007 semiconstrained 1 yes 11 BRYAN Cervical Disc Medtronic Sofamor Danke USA, Inc. 05/12/2009 semiconstrained 28 yes 5 SECURE-C Cervical Artificial Disc Globus Medical, Inc. 09/28/2012 semiconstrained 10 yes 23 PCM Cervical Disc System NuVasive, Inc. 10/26/2012 semiconstrained 1 yes 20 Mobi-C Cervical Disc Prosthesis LDR Spine USA, Inc. 08/07/2013 semiconstrained 26 yes 5 * Citation refers to the study in which design was described and/or HO was reported. tions with movement of the prosthesis still possible but a limited range of motion; and Class IV, complete bony ankylosis or fusion without movement of the CDA in active flexion and extension. The incidence of HO after cervical CDA varies greatly in the literature, from as high as 66% to as low as 0%. 24 There has been a strong association of the development of HO with subsequent loss of motion of the implanted artificial discs. If the motion of the CDA is limited, then the artificial disc may behave like a cage and lead to arthrodesis. Complete fusion around a CDA, also referred to as Class IV HO, has been reported in the literature in only a few cases. Two case studies described fusion around the BRYAN disc in 2005, 2,19 and several prospective studies list spontaneous fusions as an adverse event in the BRYAN, Mobi-C, PRESTIGE, ProDisc-C, PCM, and SECURE-C discs. 3,6,7,12 14,16,22,24,27 In our case, as in many other reported cases, the clinical outcome did not correlate with the radiographic results the patient had full relief of symptoms clinically with exceptional functional outcome results according to scores on validated outcomes analysis scales. While prior reports of fusions occurred in semiconstrained discs in which a mechanical stop was present, the present case represents the first clinical example of a fusion developing when no mechanical stop is present in a cervical artificial disc implant. Disclosure Dr. Goldstein is a consultant for Zimmer, Biomet, and Alphatec. He receives teaching honoraria from DePuy Spine, Inc. Dr. Heary receives research support from DePuy Spine, Inc., that is unrelated to the topic presented in this case report. Both Drs. Heary and Goldstein are co-investigators in the FDA IDE trial Multi-Center, Prospective, Randomized Controlled Trial Comparing Cervical Arthroplasty to Anterior Cervical Discectomy and Fusion (ACDF) for the Treatment of Cervical Degenerative Disc Disease (DDD), also referred to as DISCOVER. The authors report that all treatment described in the present case report was performed with the strict adherence to the highest ethical standards, and the authors do not believe that industry funding has had any effects on the results or interpretation of the results presented in this paper. Author contributions to the study and manuscript preparation include the following. Conception and design: Heary, Agarwal. Acquisition of data: Heary, Agarwal. Analysis and interpretation of data: Heary, Agarwal. Drafting the article: Heary, Agarwal. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Statistical analysis: Heary. Administrative/ technical/material support: Heary, Getto. Study supervision: Heary. References 1. Artificial intervertebral disc arthroplasty for treatment of degenerative disc disease of the cervical spine. 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