**8. Arthroplasty benefits**

Numerous IDE studies have shown the benefits of arthroplasty over fusion, particularly in the cervical spine. In addition to being motion sparing, arthroplasty's perhaps greater value is in the reduction of adjacent segment breakdown. Several studies have shown lower rates of ASD in patients having undergone arthroplasty compared to their ACDF cohorts. The Secure-C study showed a 4x greater risk of having adjacent segment surgery in the ACDF group.

Lower rates of adjacent segment surgery, not only benefit patients could lower total health care costs. Ironically, this advantage has not been a motivating factor in insurance approval. The author spoke with the Medical Director of one major health insurance provider extolling the benefits of arthroplasty for a 24-year-old patient for whom a single-level ACDF was already approved. In an attempt to get authorization for an artificial disc at C5–6, I said, "I am fighting to get paid less for an operation that will potentially save the patient another surgery and in the end save you money on all accounts." Their response was, "We don't care. Our data shows most patients will change insurance carriers in the next five or six years and that doesn't help us." (Jason Highsmith, personal communication January 2009.)

Another potential benefit of this reduction of ASD is the ability to only operate on a symptomatic or freshly herniated level and leave other levels with some pathology untreated. In the past, there was a tendency to fuse everything that was

### *Cervical Arthroplasty DOI: http://dx.doi.org/10.5772/intechopen.102964*

abnormal, which of course exacerbates adjacent segment breakdown. This singlelevel approach for arthroplasty may lead to lower future costs.

ACDF patients had a higher reoperation rate at the index level in most of the IDE studies. Patients underwent a revision for nonunion as well as hardware revisions for screw pullout and plate fracture. One possible explanation is that most surgeons in the IDE study were highly skilled with ACDF procedures and took more time with the ACA procedure with better carpentry and decompression.

One explanation for this is that with arthroplasty there is only one active surface the articulating surface, whereas in ACDF there are two active surfaces of fusion to account for. Because of the need for additional decompression and resection of the uncovertebral joint, more care may be taken during ACA procedures.

Another positive factor for arthroplasty is certainly patient demand and satisfaction. The nomenclature of fusion is rarely a welcome term in clinical practice. At the same time, some patients with significant facet arthropathy or spondyloarthropathy come wanting disc replacement as the latest innovation regardless of their underlying pathology.

One limitation of the early studies was that the control group consisted of allograft spacers with a four-screw on-lay construct. While this was no doubt standard of care at the time these studies were initiated, and potentially still is, new options exist. Stand-alone devices with a cage and integrated plating are an easier construct to implant than a four screw on-lay plates.

While the clinical inclusion criteria for arthroplasty have been fairly stable over the last 20 years, the trend clinically has been more aggressive in indications. Initially, the ideal candidate was a less than 40-year-old patient with a solitary fresh disc, minimal adjacent segment disease, and little spondylosis. Now we are seeing older patients with more chronic disc issues, absent of facet pathology, undergoing arthroplasty. Based on my experience as a principal investigator for three IDE studies, we are seeing arthroplasty being offered to a broader spectrum of patients as surgeons become more comfortable with the procedure (**Figures 5** and **6**).

### **Figure 5.**

*Sagittal T2 MRI of a 38-year-old woman with worsening neck pain and radiculopathy. Note multi-level cervical disc herniations with cord impingement. Given her age, nerve impingement, isolated soft tissue pathology, and failure of conservative care patient was an ideal candidate for three-level cervical arthroplasty.*

### **Figure 6.**

*Post-op lateral cervical spine x-ray demonstrating some restoration of lordosis and Orthofix M-6 arthroplasty devices at C3–4, C4–5, and C5–6.*

### **9. Pearls**

Early in the Globus Secure-C study [40], we observed some heterotopic ossification in spite of oral NSAIDs. This led many surgeons to try additional measures to reduce this phenomenon. Several surgeons sealed the anterior edges of the adjoining bodies with bone wax, particularly where the anterior longitudinal ligament was denuded from the bone. Anecdotally, this appeared to reduce the incidence of HO.

In my experience, I've had a lower rate of autofusion by incorporating the same technique along the uncovertebral joints. The proximity of neighboring bone in this area after aggressive decompression puts it at risk for heterotopic bone formation. As such I seal the areas of decorticated bone with a thin layer of bone wax even into the joint.

Many devices have keels or teeth that provide initial fixation. I often "set" the implant into the neighboring bone by compressing the implant using the Caspar pins in compression. This helps reduce overdistraction of the facets as well.

When using a keel-based implant such as ProDisc, I recommend using the mill rather than chiseling. There have been case reports [41, 42] of fractures of the vertebral body using the chisel even in the low-profile Prestige-LP [43]. Similar findings have occurred in lumbar cases with ProDisc-L. [44] where there is no milling rig available. Concern over fractures like these should be even greater in multilevel cases [45]. Interestingly, all of these cases used the bone chisels to make the keel cut. While there is no data to support the use of the milling bit, it appears to be a less invasive option (**Figure 7**).

**Figure 7.**

*Long keels on the Centinel spine ProDisc-C illustrate the intervening vertebral body compromise in patients with short vertebral bodies.*
