**6. Complications**

All of the large clinical series published on cervical disc arthroplasty have not reported any severe neurological injuries, such as quadriplegia. The rate of revision surgery at the index level has been acceptably low. None of the cervical disc arthroplasty series have had implants removed for infection.

Concerns of wear debris and local and remote inflammatory changes in cervical disc arthroplasty have been expressed. *In vitro* wear tests have been submitted to the United States FDA as part of the clinical approval process. Generally, wear debris volume has been in the range of 10% of that produced by large joint arthroplasties. Anderson et al (Anderson et al 2004) published *in vitro* wear testing on the Bryan Cervical Disc Replacement using a custom cervical spine simulator on six disc assemblies. At 10 million cycles, the mean mass loss was 1.76% and a mean height loss of 0.75%. At 40 million cycles there was an 18% mass loss. Wear particles were elliptical in shape and larger than

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

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

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

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%

All of the large clinical series published on cervical disc arthroplasty have not reported any severe neurological injuries, such as quadriplegia. The rate of revision surgery at the index level has been acceptably low. None of the cervical disc arthroplasty series have had

Concerns of wear debris and local and remote inflammatory changes in cervical disc arthroplasty have been expressed. *In vitro* wear tests have been submitted to the United States FDA as part of the clinical approval process. Generally, wear debris volume has been in the range of 10% of that produced by large joint arthroplasties. Anderson et al (Anderson et al 2004) published *in vitro* wear testing on the Bryan Cervical Disc Replacement using a custom cervical spine simulator on six disc assemblies. At 10 million cycles, the mean mass loss was 1.76% and a mean height loss of 0.75%. At 40 million cycles there was an 18% mass loss. Wear particles were elliptical in shape and larger than

Grade I HO is detectable in front of the vertebral body but not in the

Grade II HO is growing in to the disc space. Possible affection of the

Grade IV Complete fusion of the treated segment without movement

Grade III Bridging ossifications which still allow movement of the

postoperative NSAIDs.

Grade 0 No HO present

prosthesis

anatomic interdiscal space

function of the prosthesis

HO indicates Heterotopic ossification

in flexion/extension

(modified from McAfee et al, 2003)

Cervical Disc Replacement

of patients with HO.

**6. Complications** 

implants removed for infection.

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 or distally in these animals.

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 arthroplasty.
