Total disc replacement (TDR) surgery began in Europe over 20 years ago and migrated to the United States in 2000 with the first TDR Food and Drug Administration (FDA) Investigational Device Exemption (IDE) trial of the Charité III disc. Results based on the long-term follow-up from European literature have been promising so far, as have the early results from our U.S. experience.¹^–⁵ Some of the first 5-year follow-up data from the FDA IDE trial comparing the Charité disc to lumbar fusion are now available.⁶ The results show no statistically significant differences in outcome measures (visual analog scales (VAS) assessing pain and the Oswestry Disability Index) between the groups at the five-year mark, substantiating the noninferiority of the disc arthroplasty group. Additionally, the Charité patients had a statistically greater rate of part-time and full-time employment and a lower rate of long-term disability at 5years. Furthermore, the range of motion of the prosthesis, as evaluated by radiographic criteria, remained the same at 5-years compared with the 2-year data, showing preservation of motion at the surgical level.

At the time of writing of this chapter, a recently published systematic review analyzing the association of symptomatic adjacent segment disease (as distinguished from asymptomatic adjacent segment degeneration) in lumbar arthroplasty compared to arthrodesis showed that 14% of arthrodesis patients developed adjacent segment disease, compared with 1% of arthroplasty patients.⁷ Given this positive trend for arthroplasty, it is reasonable to assume that disc replacement surgery will remain a valid tool in the spine surgeon’s armamentarium and will likely become more prevalent in years to come.

There are a number of factors that influence the outcome following total disc replacement, including meticulous surgical technique and appropriate implant selection. However, as with any surgical procedure, patient selection is of utmost importance for ultimate success and reproducible results. A thorough knowledge of appropriate indications and contraindications for spinal disc arthroplasty is the key to maximizing patient safety and surgical outcome. It is the goal of this chapter to discuss these various indications and contraindications as they pertain to disc arthroplasty in the lumbar spine, with particular emphasis on older patients. It is not our intention to simply reiterate the various indications and contraindications for the multiple devices as previously published for the FDA studies. Rather, we will examine this topic from a practical standpoint, considering some of the intrinsic patient factors, surgical factors, radiographic factors, and device-specific factors that would make a patient either a favorable candidate for total disc replacement or an unfavorable one. It is still important to realize that the strict criteria set forth by the FDA for the initial studies on disc replacement were intended to maximize the expected benefit from the procedure and minimize any possible complications. Additionally, one should keep in mind that the participating surgeons for the trials were chosen in large part because of their many years of surgical experience. These surgeons were poised to climb the necessary learning curve more readily than many other surgeons who were still early in their training. Therefore, the aforementioned strict inclusion and exclusion criteria for the clinical trials should be viewed as a beacon for those surgeons embarking on the first part of the learning curve with artificial disc replacement.

When we focus our attention specifically on the aging spine, we must consider a few different scenarios. The first scenario is that of the chronologically-young patient with a physiologically aged and degenerative disc, who meets the requirements for disc arthroplasty. In this case, the prosthesis will be subjected to the normal physiologic aging process and it will be the longevity of the prosthesis that poses the ultimate challenge. One must be aware of the likely need for some type of revision procedure in the future and weigh this risk with the anticipated benefit from the surgery. Furthermore, the question must be asked whether a motion-preserving implant such as a disc arthroplasty will still provide any motion in 20 years, and what the relevance of this might be. These are questions that should be answered once more long-term data are available. The second scenario is that of the patient of more advanced age who presents for consideration of a disc arthroplasty. This scenario, as would be expected, poses a completely different set of diagnostic and treatment challenges for the spine surgeon. With advanced age, the likelihood of medical comorbidities or other physiologic contraindications to disc replacement is increased. Moreover, what happens when a disc arthroplasty is implanted in an older patient who meets all the inclusion criteria at the time of surgery, but in the years to follow develops osteoporosis or significant osteopenia? Will this have an impact on the performance of the prosthesis or dramatically increase the risk of subsidence? In this chapter, we will make a specific effort to touch upon some of the special challenges of the aging spine. It is becoming more prevalent to have patients that remain highly active well into their sixth and seventh decades and who want to be evaluated as candidates for the new technology of motion preservation.

Clinical Practice Guidelines

Indications

The established indication initially set forth by the FDA IDE studies for lumbar disc arthroplasty is severe unremitting low back pain resulting from single-level degenerative disc disease that has failed to respond to a prolonged course of conservative measures. The trial period for conservative treatment is usually defined as a minimum of 6 months, although the exact time frame itself is less important than the extent to which nonoperative management has been attempted. Nonoperative treatments should incorporate the use of various antiinflammatory, nonnarcotic, and even narcotic medications if necessary; physical therapy, including active exercise and core stabilization; chiropractic modalities; and a trial of spinal injections, including epidural injections and facet injections as appropriate. The purpose of these conservative efforts is to ensure that the patient has been afforded every opportunity to obtain a satisfactory result without surgery. We know that MRI alone is not a reliable indicator in predicting whether a degenerative-appearing disc is truly symptomatic.^8,⁹ In some cases, discography may be helpful in delineating whether the disc is responsible for the patient’s clinical symptoms. The exact role for discography as part of the clinical work-up for potential surgical candidates is not clearly established, and is still an issue of significant controversy. That being said, at our institution we incorporate the use of discography in all patients that we feel might be appropriate candidates for total disc replacement. Because the interpretation of results from discography can heavily depend on the skill of the technician performing the procedure, the established relationship between the surgeon and the physician performing the test cannot be overemphasized. In our opinion, a poorly-done discogram is worse than no discogram at all.

A patient must be skeletally mature to undergo disc replacement. While many of the studies have cited an age range from 18 to 60 years of age in the inclusion criteria, the actual chronological age itself is simply a number for reference. It must be taken into account with more relevant factors such as appropriate vertebral body size to accommodate the prosthesis and adequate bone quality to support the implant, which often, but not always, can be correlated with the patient’s age. It is also the authors’ belief that disc arthroplasty technology should be reserved for those patients over the age of 25 years until further long-term data becomes available. We have been proponents of recommending bone density scans in all females older than 40 years of age and all males over 50 years of age unless other risk factors are present. The acceptable bone quality is to have a T-score of more than −1.0, based on World Health Organization criteria, meaning that there is no evidence of osteopenia. Some patients with an advanced chronological age remain physiologically young and could still be a legitimate candidate for disc arthroplasty. In fact, these are important patients to identify when we are considering the issue of the “aging spine.’ On the contrary, some patients with a younger chronological age can have medical comorbidities or poor bone quality that effectively removes them from surgical consideration. It also becomes important, particularly in the elderly population, to carefully evaluate whether motion preservation is justified compared to the alternative of fusion surgery. We do not yet have enough long-term data to make resolute conclusions regarding the proposed advantages of motion preservation in comparison with fusion as it pertains to adjacent segment disease; however, with the knowledge currently available, we can feel fairly justified in our desire to preserve motion in young patients with isolated discogenic pain. The more elderly candidates may not ultimately see the benefit of disc

Clinical Case Examples

Case 1

A 54-year-old woman presents to your clinic with complaints of severe low back pain that has progressed over the past 2 years. She has been through physical therapy focusing on core muscle strengthening and has had a trial of epidural steroid injections and various facet injections that did not improve her symptoms. She denies any radicular leg pain, but states that her low back pain is constant and is aggravated by prolonged standing, sitting, or walking. She has been on NSAIDs for the past few years, and has recently started to take narcotics because of increased pain. A complete neurological examination reveals no motor or sensory deficits. She has pain and limited motion with forward flexion of her lumbar spine. Her radiographs (Figures 55-1A and B) show normal spinal alignment with decreased disc space height at the L4-5 and L5-S1 level. No instability is present on flexion-extension views. A T2-weighted MRI (Figures 55-2A and B) reveals a dessicated L4-5 disc with preservation of hydration in the remaining lumbar discs. Given this scenario, what treatment option(s) would you discuss with this patient?

FIGURE 55-1 A and B. AP (A) and lateral (B) radiographs showing disc space narrowing at L4-5 and L5-S1.

FIGURE 55-2 Sagittal (A) and axial (B) T2-weighted MRI views showing disc dehydration and posterior bulge at the L4-5 level.

Case 2

A 56-year-old male presents to your clinic for evaluation of debilitating low back pain over the last 6 years. He reports daily pain that radiates across his low back, worse on the right side. His primary care physician sent him to physical therapy for 6 weeks, but he did not see any symptomatic improvement. He has been taking hydrocodone for the past 6 months in order to bring his pain to a tolerable level but is frustrated by the need to be on narcotic medications and wishes for something to be done surgically to address his pain. His physical examination is fairly unremarkable and he has normal motor and sensory function. His plain radiographs reveal only minimal narrowing at the L4-5 and L5-S1 levels (Figure 55-3A and B). A T2-weighted MRI reveals pronounced desiccation with a small posterior bulge, along with minimal disc desiccation at the L4-5 level (Figure 55-4). On axial MRI views, the facet joints at both levels appear normal or with minimal degenerative changes. He asks whether he is a candidate for the disc replacement surgery. What do you tell him?

FIGURE 55-3 AP (A) and lateral (B) radiographs showing only minimal disc space narrowing at L4-5 and L5-S1.

FIGURE 55-4 Sagittal T2-weighted MRI showing significant disc dessication at L5-S1 and slight desiccation at the L4-5 level.

replacement, particularly if further studies suggest that adjacent-level disease is borne out over periods of 10 years or greater.

Bertagnoli and Kumar stratified indications for disc arthroplasty into four categories based on remaining disc height, status of the facet joints, adjacent level degeneration, and stability of the posterior elements.¹⁰ The prime candidate for a disc replacement, based on their evaluation of clinical outcome in 108 patients who underwent implantation of a ProDisc II prosthesis, had at least 4 mm of remaining disc space height, no radiographic changes suggestive of facet arthritis, no adjacent level disc degeneration, and intact posterior elements.

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