case report

CASE REPORT Kor J Spine 7(3):206-211, 2010

Recycling of Cervical Artificial Disc for the Symptomatic Adjacent Segment Disorder Combined with Instability on Total Disc Replacement Area: A Case Report Eun-Hyun Ihm1, Ho-Yeol Zhang2, Jeong-Yoon Park2, Kook-Hee Yang2 1

2

Department of Neurosurgery, Severance Hospital1, Yonsei University College of Medicine, Seoul, Korea Department of Neurosurgery, National Health Insurance Corporation Ilsan Hospital, Ilsan, Goyang, Korea

The authors describe the revision case of a 58‐year‐old man who presented with pain in the neck and both shoulders after C4‐5 cervical total disc replacement (C‐TDR) and C5‐6 anterior cervical discectomy and fusion (ACDF), and in whom there was evidence of instability with sagittal translation at the C4‐5 TDR level and of a herniated cervical disc (HCD) at the left side of C3‐4. The revision surgery was performed as follows: previous plate removal at the C5‐6 level, artificial disc removal and ACDF at the C4‐5 level with cage and previous plate insertion, and TDR at the C3‐4 level using the previously implanted C4/5 artificial disc. If instability develops at the level of an artificial disc, we perform additional posterior fusion or anterior removal of the artificial disc and fusion. However, if we encounter combined adjacent segment disc disease, we may reuse the unstable segment artificial disc at the adjacent segment and perform salvage anterior fusion on the unstable segment. This is the first report issued on the management of instability after previous C‐TDR involving a switch to ACDF and the use of new TDR at the adjacent level. Furthermore, we conceptually recommend a solution to an emerging problem of adjacent segment disease due to the heterotopic ossification (HO) after C‐TDR. Key Words: Cervical artificial disc • Adjacent segment degeneration • Heterotopic ossification

INTRODUCTION Patients with cervical radiculopathy due to degenerative disc disease are frequently treated by anterior cervical discectomy and fusion (ACDF), which is one of the most commonly performed operations nowadays. However, recently, cervical total disc replacement (C‐TDR) has been introduced as a potential alternative, because it maintains motion, decreases adjacent segment degeneration (ASD) and avoids other morbidities associated with fusion. Symptomatic multilevel cervical disc disease can also be treated using a novel hybrid surgical technique, involving com● Received: Jul 12, 2010 ● Accepted: Aug 31, 2010 ● Published: Sep 13, 2010 Corresponding Author: Ho‐Yeol Zhang, M.D. Department of Neurosurgery, National Health Insurance Corporation, Ilsan Hospital, 1232, Baeksok-dong Ilsan-gu, Goyang-si, Gyounggi-do 410-719, Korea Tel: +82-31-900-0256, Fax: +82-31-900-0589 E-mail: [email protected]

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bined cervical arthrodesis and C‐TDR2,22). Cervical artificial discs are designed for lifelong usage without exchange and thus, if we encounter the instability at an artificial disc replaced level, we perform additional posterior fusion or removal of the artificial disc and anterior fusion. However, if we also encounter ASD, we may reuse the artificial disc at the unstable segment to a new adjacent segment and perform salvage anterior fusion on the unstable segment. This case report describes the management of adjacent level cervical disc disease after prior hybrid surgery.

CASE REPORT A 58‐year‐old male presented with neck and right arm pain radiating to the thumb, after falling while mountaineering. Plain radiography showed C5‐6 dislocation. Magnetic resonance imaging (MRI) revealed a C5‐6 right side facet joint fracture with a right sided ruptured herniated cervical disc (HCD), HCD at C4‐5, right sided and asymptomatic HCD C3‐4, left sided (Fig. 1). Surgery was performed as for ACDF

Cervical artificial disc, Adjacent segment degeneration, Heterotopic ossification

Fig. 1. Initial radiologic findings in a 58‐year‐old male. Plain radiography showed C5‐6 dislocation. Magnetic resonance imaging (MRI) and computed tomography (CT) showed a C5‐6 right side facet joint fracture with a right sided ruptured herniated cervical disc (HCD), HCD C4‐5 right sided and asymptomatic HCD C3‐4 left sided.

C5‐6 with a cage and plate and C‐TDR with Mobi‐C® (LDR spine, USA) at C4‐5 to prevent adjacent segment (C3‐4) degeneration (Fig. 2). During this procedure, we found the C4‐5 disc had been ruptured, and thus, performed C-TDR at C4‐5. After recovering from surgery, he was free of right arm and neck pain and was discharged hospital without any problems. However, during the follow‐up at our outpatient department, he complained of pain in the neck and both shoulders, which was more severe on the left side, especially when driving. Flexion lateral radiography at 5 months postoperatively revealed instability with sagittal translation at the C4‐5 TDR level. He was readmitted and cervical myelography‐computed tomography (CT) was performed because MRI couldn’t to visualize the C‐TDR level, because the Mobi‐C® unit was a metal on polyethylene device, comprised of an ultra high molecular weight polyethylene (UHMWPE) mobile insert and two spinal plates consisting of a cobalt, chromium and molybdenum alloy (CoCrMo, ISO 5832‐12)4), which produces substantial MRI artifacts. Cervical myelography-CT revealed a HCD at C3‐4 left sided and an artificial disc well‐positioned with good settling, hypermobile flexion and extension at the C4‐5 TDR level and good fusion at the C5‐6 ACDF level (Fig. 3). A second operation was performed. At the C4‐5 level, the Mobi‐C® was removed and replaced with a new cage and the

Fig. 2. Radiographs after the first operation. ACDF at C5‐6 with a cage and plate and C‐TDR with a Mobi‐C® on C4‐5 to prevent adjacent segment C3‐4 degeneration.


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Fig. 3. Radiologic findings at 5‐months after the first surgery. Flexion lateral radiograph showing instability with sagittal translation at the C4‐5 TDR level. Cervical myelography‐CT showing a HCD at C3‐4 left sided and good settling and position at the C4‐5 TDR level, and good fusion at the C5‐6 ACDF level.

Fig. 4. Radiologic findings at 12‐months after the second surgery. The plate was removed from the C5‐6 level, and Mobi‐C® was removed from the C4‐5 level and replaced with a new cage and the plate. The C3‐4 level was treated by cervical TDR, which was achieved from the C4‐5 level. This flexion and extension lateral radiographs show good motion without sagittal translation at C3‐4, and good fixation without sinking the C4‐5 and C5‐6 levels.

previous plate at C5‐6. The C3‐4 level was treated by cervical TDR, which was achieved from the C4‐5 level. After this second operation, the neck and shoulder pain disappeared completely and this symptom‐free state was maintained at his final follow‐up at 12 months postoperatively. His flexion and extension lateral radiographs revealed good motion without sagittal translation at C3‐4 and good fixation without sinking at C4‐5 and C5‐6 (Fig. 4).

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DISCUSSION C‐TDR using an artificial disc prosthesis is an emerging procedure for the preservation of spinal motion and potentially decreases stress on adjacent segments and prevents or lessens ASD. Also, in cases of 2‐level cervical disc disease with insuff-


icient cervical motion at one level, hybrid surgery consisting of C‐TDR at the mobile level combined with ACDF at the spondylotic level, may be a reasonable alternative to 2‐level cervical disc operations2,22). After C4‐5 TDR in the described case, immediate postoperative symptoms were improved, but over the time, the neck and shoulder pain redeveloped. Furthermore, the patient showed instability of sagittal translation on flexion radiographs. This was considered by our fault of surgical choice. Initially, the C5‐6 fracture/dislocation occurred during mountaineering and thus, the C4‐5 disc rupture, which was found intraoperatively, was presumed to have been caused by trauma. In other words, the intervertebral disc was ruptured by trauma and the surrounding soft tissue might have been damaged microscopically, although, no evidence of instability on flexion, extension and lateral radiographs was observed after the mountaineering incident. Therefore, if C‐TDR had been done at the level with removal of the anterior longitudinal ligament (ALL), discectomy and removal of the posterior longitudinal ligament (PLL), it would have been difficult to maintain stability and postoperative continuous motion could have caused gradual instability. Therefore, we suggest that traumatic HCD be considered a contraindication for TDR, and that it should be added to the known exclusion criteria for C‐TDR1,13,20,26). Then if a patient develops adjacent segment HCD with an unstable previous C‐TDR as occurred in our case, the surgical options are; 1) C‐TDR at the adjacent level and salvage fusion at the unstable C‐TDR level, or 2) ACDF at both levels. If a patient develops heterotopic ossification (HO) without

motion at the C‐TDR level and adjacent segment HCD, the options would be; 1) C‐TDR at the adjacent level without touching the HO level, 2) ACDF at both levels, or 3) ACDF at the HO‐fused level and recycling of the artificial disc at the adjacent level. Several authors have reported bony fusion around a cervical disc prosthesis and loss of motion3-5,11,14,15,17,20,23,24). Furthermore, in the cases, segmental motion disappeared when HO developed. If ACDF is performed at the HO‐fused level and the artificial disc is used at other level it may be an alternative treatment option1,16). And also, this would be economically beneficial to the patient. When an artificial disc level is fused by HO, the artificial disc is in a non‐functional state, that is, the disc is not subject to wear and tear and only performs a weight‐bearing function. This is similar to the hibernation state of animals in terms of a lack of active motion and a minimal metabolism. In addition, the recycling of a HO‐fused artificial disc has effects that a similar in some respects to awakening from hibernation. In case of HO occurrence only at ALL, not PLL, the way of awakening from hibernation might be the removal of HO from ALL areas. In other circumstances, such as, for HO at both the ALL and PLL (Fig. 5), combined HCD arises from an adjacent level or another level and the dormant artificial disc can be recycled to the affected level and ACDF be performed at the HO‐fused level. It remains unclear whether ASD results from increased strain caused by an iatrogenically rigid motion segment6,10) or from the progression of the natural history of degenerative change7,21). Hilibrand, et al. reported the results of a large re-

Fig. 5. Radiologic findings at 3.5‐years after C‐TDR, showing HO around the C‐TDR and no segmental motion at this level.


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trospective series and found that symptomatic ASD occurred at a relatively constant incidence of 2.9% annually. In addition and they predicted that 25.6% of patients that undergo anterior cervical fusion, will develop new symptomatic disease at an adjacent segment within 10 years of surgery7). Given that at least one in four patients who undergo successful cervical fusion will require further surgery for accelerated ASD at some time8,19,20), this salvage fusion surgery provides a highly cost effective solution if ASD has occurred in a patient with HO development at a prior C‐TDR level. As mention above, the Mobi‐C® device is made of metal on polyethylene and is composed of two CoCrMo alloy spinal plates and an ultra high molecular weight polyethylene (UHMWPE) mobile insert. This mobile insert is self‐centering on the inferior endplate and each movement of the superior plate induces the mobile insert to be repositioned on the inferior spinal plate. Both the superior and inferior spinal plates contain two rows of inclined‐shaped teeth that are located laterally on each plate to ensure the primary ﬁxation. A titanium and hydroxyapatite plasma spray coating is applied to the bony interface surfaces of the superior and inferior plates to encourage subsequent bony integration4). Of course, recycling the artificial disc may cause a problem of these osseointegration. However, Pitzen presented, in his report, that osseointegration was not yet totally achieved until 12 weeks after implantation18). Moreover, most of the published studies on the topic report good or excellent osseointegration of the disc prosthesis, however, these studies were limited to only animal models5,9,12). In our case, after the second operation, the neck and shoulder pain disappeared completely and this was maintained at final follow‐up. His flexion and extension lateral radiographs revealed good motion without sagittal translation, prosthesis loosening and osteolysis at C3‐4 and good fixation without sinking at C4‐5 and C5‐6. Thus, we believe even if artificial disc coating materials were damaged microscopically, or inert, this has no or minimal effect on settling or the osseointegration of the implanted artificial disc.

CONCLUSION Instability of C‐TDR with neck pain or a growing bony spur with recurrent radiculopathy at the operated level causes surgeons considerable consternation. Most solutions to this problem require additional posterior fusion or artificial disc removal and anterior fusion surgery. However, when symptomatic ASD is combined, salvage fusion surgery at the unstable artificial disc level can be combined with the reuse of the artificial disc at the adjacent segment. We experienced of challenging issue of TDR and switched

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from the previous TDR to the ACDF and performed the new TDR at the adjacent level. Of course, more cases and long‐ term follow up will be needed to fully assess and to make conclusion about the ability of recycling of the artificial disc to provide the good answers to numerous questions asked by treatment of ASD after TDR. It is hoped, if symptomatic ASD and HO of a previous C‐TDR are combined, recycling the artificial disc will be used at the HO‐fused level.

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