Periprostetic Osteolysis After 2 Level Cervical Disc Arthroplasty Featuring Artificial Nucleus

Periprostetic Osteolysis After 2 Level Cervical Disc Arthroplasty Featuring Artificial Nucleus

Corresponding author: Dr. Christoph P. Hofstetter, University of Washington, Department of Neurological Surgery, Campus Box 356470, Room RR734, 1959 NE Pacific Street Seattle, WA, 98195-6470 USA, Tel: (206) 543-3571; Fax: (206) 543-8315,

Email: Received: 03-05-2017


Artificial disc cervical arthroplasties are commonly performed with favorable outcomes. Here we present a rare case of Peri- prostetic Osteolysis in the cervical spine of a 60 year-old man who underwent placement of a C4/5 and C5/6 M6-C cervical disc arthroplasty (Spinal Kinetics, CA, USA) in 2007 in Germany. This novel implant mimics the human disc by incorporating an artifi- cial annulus between two titanium plates. The patient did well initially but then presented 8 years after the procedure with neck and bilateral upper extremity radiculopathy. Pre-operative imaging revealed extensive periprosthetic osteolysis in the vertebral bodies of C4, C5, and C6. The patient subsequently underwent removal of the artificial discs, corpectomy, and a combined ante- rior and posterior reconstruction. Pathological evaluation of vertebral body bone adjacent to the implants confirmed metallic particles and extensive foreign body giant cell reaction. The patient’s symptoms resolved and he achieved arthrodesis 1-year af- ter surgery. The current report presents a rare case of periprosthetic osteolysis in a patient status post cervical disc arthroplasty. Thus, neck pain or cervical radiculopathy in patients who have received a disc arthroplasty should lead to radiographic workup in order to rule out catastrophic failure.

Keywords: M6-C artificial disc arthroplasty; periprosthetic osteolysis; cervical arthroplasty


Multiple mechanisms exist for early prosthetic failure includ- ing infection, pain, and adjacent fractures. Mechanisms for late prosthetic failure, however, are likely a result of osteolysis re- sulting in aseptic loosening of hardware from adjacent bone. While normal bone is maintained via a balance of osteoblastic and osteoclastic mechanisms, particles released by prosthetic and articulating surfaces of the bone-prosthetic interface over time tips the physiological bone milieu in favor of osteolysis [1]. This results in failure of prosthetics and biomechanical instability resulting in clinical symptoms that can include pain, motor weakness, and parasthesias. Mechanisms of os- teolysis are likely multifactorial but are theorized to include

infiltration of macrophages into periprosthetic bone, absorp- tion of iatrogenic particles, release of pro-inflammatory cyto- kines, and dysregulation of osteoblastic-osteoclastic balance towards an osteoclastic-predominant microenvironment [2]. Multiple sources describe late prosthetic failure in total hip arthroplasties though there is a dearth of evidence in cervical spine arthroplasties. Kang et al. reported two patients with late failure of cervical disc arthroplasty likely due to osteolysis based on radiographic evidence [3]. Here we present a patient and show relevant pathology for a man who presented to the University of Washington with neck pain and right upper ex- tremity pain and was found to have failure of a disc arthroplas- ty due to periprosthetic osteolysis.


The patient is a 61-year-old man who had previously under- gone a C4-5 and C5-6 M6-C cervical disc arthroplasty (Spinal Kinetics, CA, USA) in 2007 in Germany. He re-presented in 2015 with severe neck pain and pain radiating into his right shoul- der and arm. In an outside hospital, a surgical procedure to re- move osteophytes at C4, C5, and C6 was proposed. Intraoper- atively, there was evidence of broken artificial disc fragments, which were removed. Following this surgery, he had complete relief of right shoulder and arm pain. He re-presented in July 2015 with neck pain, bilateral shoulder pain, and distal up- per extremity numbness. The patient reported a visual analog scale (VAS) of 2/10 for his neck pain and 1/10 for his bilateral shoulder pain. His neck disability score was 34/50 (severe). Pre-operative imaging revealed extensive osteolysis on either side of the artificial disc implants with evidence of lytic-type lesions at C4, C5, and C6 (Figure 1A and B).

Given this bony instability the patient underwent removal of his C4-5 and C5-6 artificial discs. Intraoperatively, it was noted that the artificial discs had disintegrated and multiple shat- tered fragments were found and removed (Figure 1C). A C5 corpectomy was performed and the bony defect was repaired using a titanium cage filled with cellular allograft bone matrix (ViVigen®, DePuy Synthes, MA, USA). A C4-6 anterior plate ar- throdesis (Skyline®, DePuy Snythes, MA, USA) was placed and the anterior construct was backed up with posterior C4-6 lat- eral mass screws (Synapse TM DePuy Snythes, MA, USA). There were no intra-operative or post-operative complications.

Post-operative upright radiographs are shown in Figure 1D. Pathological evaluation of bone showed focally devitalized bone with granulation tissue, metallic particles, and foreign body giant cell reaction (Figure 2). Post-operatively, his pain was improved. He was discharged home on post-operative day four.

Figure 1. Preoperative sagittal (A) and coronal (B) CT scan reveals extensive osteolytic changes adjacent to the disc arthroplasties. (C) Intraoperative image during the C5 corpectomy. Note the gradient of metallic particles originating in particular from the C4/5 device. (D) Postoperative lateral x-ray depicts appropriate position of hardware.

Figure 2. Hematoxylin and Eosin stain of periprostetic vertebral body bone. Please note the presence of metallic particles (arrows) and mul- tinucleated giant cells (arrow heads).

The patient returned to our clinic 1 year following the proce- dure. His VAS for neck pain has decreased to 1. His neck dis- ability index had decreased to 12. His 1-year follow-up CT scan revealed radiographic fusion at the site of reconstruction (Figure 3).

Figure 3. Solid arthrodesis is confirmed by a 1-year follow up sagittal CT scan.



Mechanisms of late prosthetic failure is likely multifactorial though evidence for osteolysis leading to aseptic loosening has become a leading cause for late failure of multiple prosthet- ics, including total hip and total knee arthroplasties [1,2]. Here we present a case of periprosthetic osteolysis in the cervical spine. Differential diagnosis for failure included periprosthetic osteolysis as well as low-grade infection. The patient had sta- ble vital signs without any laboratory evidence of infection. Following surgical resection of the prosthesis with subsequent anterior cervical corpectomy and stabilization the patient had resolution of his upper extremity pain.

The mechanism of osteolysis primarily described in the liter- ature relates to hip and knee arthroplasties [1,2]. In brief, it is believed that small particles initially detach from the prosethe- sis. Evidence from knee and hip arthroplasties suggest that small, biologically active particles are released as a result of rotational motion while larger particles are released as a result of delamination and pitting[4]. These particles lead to forma- tion of granulomatous tissue at the prosthetic-bone interface which results in increased infiltration of osteoclasts and de- creased osteoblast activity. In conjunction with increased me-

chanical stress, bone adjacent to the prostethesis is resorbed [2]. The cellular pathogenesis of periprosthetic osteolysis is largely driven by the inflammatory response to particle forma- tion. Particle complexes undergo phagocytosis by host macro- phages. This results in the release of cytokines, chemokines, and proteolytic enzymes resulting in a microenvironment that is favorable for osteoclast infiltration and activity [5,6]. Pathol- ogy sections taken from the patient presented here showed foreign body giant cell reaction as well as granulation tissue, which is consistent with the previously described cellular mechanisms of osteolysis.

Given the morbidity associated with periprosthetic osteoly- sis, increasingly durable implants continue to be developed to decrease the release of inflammatory particles. Techniques in manufacturing and sterilizing polyethylene have been shown to affect the clinical performance of implants [7]. Furthermore, there is evidence to suggest that peri-operative bisphospho- nates decrease periprosthetic inflammation and osteoclast maturation and may decrease aseptic loosening [8,9]. The M6-C disc that was used in this patient is a novel implant that incorporates an artificial annulus, made of polyethylene, sur- rounding an artificial nucleus, made of polycarbonate urethane, between two titanium plates. A sheath surrounds the artificial nucleus and annulus, which is intended to decrease debris mi- gration [10]. This disc was placed in Germany because at the time of implantation, this implant was not FDA approved in the United States. Though intended to simulate the biomechanics of human intervertebral disc, it is clear that increasingly com- plex designs can be associated with catastrophic failures.

In conclusion, we report on a rare case of periprosthetic os- teolysis following implantation of a cervical disc arthroplasty. This report stresses the importance of radiographic workup of patients with neck pain or cervical radiculopathy who have re- ceived a disc arthroplasty.

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