**5. Radiographic results**

Heterotopic ossification (HO) has initially been reported in the Bryan Cervical Disc Replacement (Bartels & Donk, 2005; Leung et al 2005; Solas et al, 2005) but as the literature expands, no disc arthroplasty has proven immune to this problem. (Figure 7) McAfee et al characterized the severity of HO with a simple scale, modified from lumbar disc arthroplasty findings. The scale ranged from grade 0 (no HO) to grade IV -(complete ankylosis). (McAfee et al, 2003) (Table 2) Delamarter et al described three patients that developed grade IV HO in the ProDisc-C IDE study by 24 months, with two additional patients developing grade IV HO by 48 months. Non-steroidal anti-inflammatory drugs (NSAIDs) were not part of the study protocol. Interestingly in the continued access arm of the study, in which NSAIDs were more commonly used, no patients developed ankylosis at the index level. (Delamarter et al, 2010) Mehren et al (Mehren et al, 2006) evaluated the rate of HO at two centers performing cervical disc arthroplasty. Approximately one third of patients postoperatively showed no sign of HO, while almost 20% of patients had HO that lead to restrictions in motion. Nine percent of the patients had grade IV HO, with most of the patients having had multilevel procedures. There was a difference in the overall rate of grade IV HO between the two centers, 12.8% versus 5.2%. The center with the lower HO

Murrey et al (Murrey et al, 2009) published the two year ProDisc-C IDE study. The study was structured similarly to the Prestige ST and Bryan studies, with 209 patients enrolled, 103 who underwent ProDisc-C arthroplasty and 106 who had an ACDF. Both groups showed improvement by all clinical after parameters; NDI, SF-36, VAS arm and neck pain scores and neurological success. A significant difference was in the rate of re-operation:

Delamarter et al further evaluated the ProDisc-C IDE patients as well as 136 patients who received ProDisc-C in the continued access phase of the study, with a minimum of four years follow-up. (Delamarter et al, 2010) Demographic data remained similar between the arthroplasty and ACDF groups. All clinical parameters improved equally in both groups at all follow-up periods (p<.0001). A significant difference in the study was the rate of secondary surgical procedures. At the four year follow-up point, 12 (11.3%) of the ACDF patients had additional surgery, while only three (2.9%) of the ProDisc-C patients required further procedures (p=.0292). The ACDF patients primarily required additional surgery for pseudoarthrosis at the index level; however, six (5.6%) ACDF patients had surgery at an adjacent level. Three ProDisc-C patients were converted to fusion for axial pain. No ProDisc-C patients had to have surgery at adjacent levels. In the continued access arm of the study, one ProDisc-C patient required additional surgery to reposition the implant and two were

Pimenta et al (Pimenta et al, 2007) prospectively evaluated patients undergoing the PCM cervical disc replacement. Seventy-one single-level and 69 multi-level arthroplasties were performed. While both groups improved, the multi-level patients showed improved scores compared to the single-level patients. The mean NDI improvement was better in the multilevel PCM group (p=0.021). While the overall IDE results have yet to be reported, Philips et al (Phillips et al, 2009) showed in a small set of the IDE patients that arthroplasty was viable

Heterotopic ossification (HO) has initially been reported in the Bryan Cervical Disc Replacement (Bartels & Donk, 2005; Leung et al 2005; Solas et al, 2005) but as the literature expands, no disc arthroplasty has proven immune to this problem. (Figure 7) McAfee et al characterized the severity of HO with a simple scale, modified from lumbar disc arthroplasty findings. The scale ranged from grade 0 (no HO) to grade IV -(complete ankylosis). (McAfee et al, 2003) (Table 2) Delamarter et al described three patients that developed grade IV HO in the ProDisc-C IDE study by 24 months, with two additional patients developing grade IV HO by 48 months. Non-steroidal anti-inflammatory drugs (NSAIDs) were not part of the study protocol. Interestingly in the continued access arm of the study, in which NSAIDs were more commonly used, no patients developed ankylosis at the index level. (Delamarter et al, 2010) Mehren et al (Mehren et al, 2006) evaluated the rate of HO at two centers performing cervical disc arthroplasty. Approximately one third of patients postoperatively showed no sign of HO, while almost 20% of patients had HO that lead to restrictions in motion. Nine percent of the patients had grade IV HO, with most of the patients having had multilevel procedures. There was a difference in the overall rate of grade IV HO between the two centers, 12.8% versus 5.2%. The center with the lower HO

8.5% in the ACDF group versus 1.8% in the ProDisc-C group (p= 0.033).

converted to fusion for axial neck pain.

at levels adjacent to a prior fusion.

**5. Radiographic results** 

Fig. 7. Lateral flexion radiography- implanted ProDisc-C with heterotopic ossification, preserved motion.

Cervical Disc Arthroplasty 511

typical particles in large joint arthroplasties. Anderson studied local and remote wear debris and the subsequent inflammatory response using an *in vivo* caprine model with implanted Bryan arthroplasties. Sacrificed animals at up to twelve months showed an increase in extracellular wear debris. No apparent inflammatory response was seen locally

Clinically, there have been scattered case reports of osteolysis after cervical disc arthroplasty implantation. Tumialan and Gluf reported on a 30-year-old man who underwent a ProDisc-C arthroplasty at C5-6. (Tumialan & Gluf, 2011) He had an uneventful postoperative course until he developed worsening neck pain at nine months. Repeat imaging studies by 15 months showed a progressive osteolysis process in the vicinity of the superior endplate and keel. Work-up for infection was negative. The patient underwent explantation of the arthroplasty and conversion to a fusion. The implant was studied after removal and no defects or unusual wear was noted. The authors hypothesized that the most likely cause of the osteolysis was an immune mediated process. Longer study periods are needed to determine the significance of wear changes and the rate of osteolysis of cervical disc

Cervical disc arthroplasty has been one of the most closely scrutinized surgical procedures in the last decade. Short-term prospective clinical studies show cervical disc arthroplasty to be at least the equivalent of ACDF for degenerative pathology. There is some evidence that cervical disc arthroplasty may play a role in diminishing adjacent segment disease. However, the long-term efficacy and safety of cervical disc arthroplasty await further

[1] Amevo B, Worth D, Bogduk N. (1991) Instantaneous axis of rotation of the typical

[2] Anderson PA, Sasso RC, Rouleau JP et al. (2004) The Bryan Cervical Disc: wear

[3] Bailey R, Badgely C. (1960) Stabilization of the cervical spine by anterior fusion. *Journal of* 

[4] Barbargallo GM, Corbino LA, Olindo G, et al. (2010) Heterotopic ossification in cervical

[5] Bartels RH, Donk R. (2005) Fusion around cervical disc prosthesis: Case report.

[7] Bohlman HH, Emery SE, Goodfellow DB, et al. (1993) Robinson anterior cervical

properties and early clinical results. *Spine Journal*, 4(6): 5303-5309

*Bone and Joint Surgery Am,* 42(4): 565-594

[6] Bogduk N, Mercer S. (2000) *Clinical Biomechanics,* 15(9): 633-648

cervical motion segments: a study in normal volunteers. *Clinical Biomechanics* Vol.

disc arthroplasty: Is it clinically relevant? *Evidence-Based Spine Care Journal,*

discectomy and arthrodesis for cervical radiculopathy: long term follow-up of one hundred and twenty-two patients. *Journal of Bone and Joint Surgery Am*, 75: 1298-

or distally in these animals.

arthroplasty.

**7. Conclusions** 

clinical studies.

**8. References** 

6: pp. 111-117

1(1):15-20

1307

*Neurosurgery,* 57:E194

rate routinely prescribed NSAID use postoperatively. Yi et al (Yi et al, 2010) studied the rate of HO according to the arthroplasty type. They found the following HO rates: Bryan 21.0%, Mobi-C (LDR Medical, Troyes, France) 52.5% and ProDisc-C 71.4%. The only two patients that developed grade IV HO were in the Bryan group. All patients routinely received postoperative NSAIDs.


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HO indicates Heterotopic ossification

(modified from McAfee et al, 2003)

Table 2. Characterisation of the Different Grades of Heterotopic Ossification (HO) in Total Cervical Disc Replacement

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In all the clinical studies evaluating cervical disc arthroplasty and HO, there has been no correlation between the development of HO and the clinical results. Barbargallo et al (Barbargallo et al, 2010) specifically looked at this aspect of cervical disc arthroplasty. They found an overall rate of HO development of 42% and no difference in the functional scores in patients with or without HO. Segmental range of motion of ≥ 3° was preserved in 93.8% of patients with HO.
