**3. Results**

### **3.1 General clinical outcome results**

General clinical outcome results were available for the CHARITÉ Artificial Disc, the ProDisc-L, the Maverick Total Disc Arthroplasty System, and the FlexiCore Intervertebral Disc. However, level-1 data was only available for the CHARITÉ Artificial disc and the ProDisc-L, as the final study FDA IDE results for the Maverick Total Disc Arthroplasty System and the FlexiCore Intervertebral Disc have yet to be published.

The CHARITÉ Artificial Disc manuscripts described clinical outcomes as early as 1 year 3 and up to 13 years post-operative4. The short/medium term papers included herein typically disclosed early analyses from single sites involved in the CHARITÉ Artificial Disc IDE study comparing arthroplasty with CHARITÉ Artificial Disc vs. anterior interbody fusion with BAK cage and autograft 3, 5, 6. The complete RCT at 2-year follow-up included 205 arthroplasty and 99 fusion patients, and was thoroughly described in two manuscripts, one focused on clinical outcomes7, the other on radiographic outcomes8. Three additional medium- and long-term studies were also found: 2 papers with 10-year follow-up 4, 9 and one with an average of 6.6 year follow-up 10.

Safety and efficacy of arthroplasty was demonstrated in all short- and medium-term studies. Specifically, at 2-years post-operative, Blumenthal and McAfee reported no device-related complications and a reoperation rate of 5.4% (vs. 9.1% in the control arm). Efficacy was also demonstrated using validated disability (ODI) and pain (VAS) clinical outcomes tools. At 2 years, the reduction in ODI reached 48.5% (vs. 42.4% in the control group) and the absolute reduction in VAS reached 40.6 points (vs. 34.1 points in the control group) 7, 8.

Two of the three long-term studies confirmed these findings. Lemaire et al reported 10 year follow-up results in 100 patients. 4 This study included 54 patients operated at one level, 45 patients operated at two levels and one patient operated at 3 levels. Overall, authors reported excellent or good clinical outcomes in 90% cases. In a second long-term study, David et al presented 10-year data on 106 patients9. Only one-level surgeries were performed in this study. Excellent or good clinical outcome was obtained in 82.1% patients. Both papers thus concluded that arthroplasty was a viable option for disc degeneration.

Recently, a third, medium-term paper was published by Ross et al, describing the longterm effect of arthroplasty in 160 patients (226 CHARITÉ Artificial Discs). This paper reported a cumulative survival rate at 156 months of 35% and a mean ODI score

(CHARITÉ Artificial Disc or ProDisc-L or Maverick Total Disc Arthroplasty System or KineFlex or FlexiCore Intervertebral Disc) and (disc) and (lumbar). The search was limited to English-language papers. Preclinical, biomechanical, and review papers were excluded from the final paper selection. In addition, papers describing obsolete devices (CHARITÉ I and CHARITÉ II) were also excluded from the study. A total of 60 papers were analyzed herein and subdivided by key topic, as following: 1) General clinical outcomes; 2) Radiographic Analysis: Range of motion, heterotopic ossification and sagittal balance analyses; 3) facet and adjacent-level degeneration; 4) Revisions and revision strategies; 5) Surgical technique; 6) Complications; 7) Special patient population analyses; and 8) Health

General clinical outcome results were available for the CHARITÉ Artificial Disc, the ProDisc-L, the Maverick Total Disc Arthroplasty System, and the FlexiCore Intervertebral Disc. However, level-1 data was only available for the CHARITÉ Artificial disc and the ProDisc-L, as the final study FDA IDE results for the Maverick Total Disc Arthroplasty

The CHARITÉ Artificial Disc manuscripts described clinical outcomes as early as 1 year 3 and up to 13 years post-operative4. The short/medium term papers included herein typically disclosed early analyses from single sites involved in the CHARITÉ Artificial Disc IDE study comparing arthroplasty with CHARITÉ Artificial Disc vs. anterior interbody fusion with BAK cage and autograft 3, 5, 6. The complete RCT at 2-year follow-up included 205 arthroplasty and 99 fusion patients, and was thoroughly described in two manuscripts, one focused on clinical outcomes7, the other on radiographic outcomes8. Three additional medium- and long-term studies were also found: 2 papers with 10-year follow-up 4, 9 and

Safety and efficacy of arthroplasty was demonstrated in all short- and medium-term studies. Specifically, at 2-years post-operative, Blumenthal and McAfee reported no device-related complications and a reoperation rate of 5.4% (vs. 9.1% in the control arm). Efficacy was also demonstrated using validated disability (ODI) and pain (VAS) clinical outcomes tools. At 2 years, the reduction in ODI reached 48.5% (vs. 42.4% in the control group) and the absolute

Two of the three long-term studies confirmed these findings. Lemaire et al reported 10 year follow-up results in 100 patients. 4 This study included 54 patients operated at one level, 45 patients operated at two levels and one patient operated at 3 levels. Overall, authors reported excellent or good clinical outcomes in 90% cases. In a second long-term study, David et al presented 10-year data on 106 patients9. Only one-level surgeries were performed in this study. Excellent or good clinical outcome was obtained in 82.1% patients. Both papers thus concluded that arthroplasty was a viable option for disc

Recently, a third, medium-term paper was published by Ross et al, describing the longterm effect of arthroplasty in 160 patients (226 CHARITÉ Artificial Discs). This paper reported a cumulative survival rate at 156 months of 35% and a mean ODI score

reduction in VAS reached 40.6 points (vs. 34.1 points in the control group) 7, 8.

System and the FlexiCore Intervertebral Disc have yet to be published.

economics evaluations.

**3.1 General clinical outcome results** 

one with an average of 6.6 year follow-up 10.

**3. Results** 

degeneration.

improvement of 14%. Implant removal was also described in 12 patients10. These relatively poor findings were further discussed in two Letters to the Editors, which pointed out mathematical inconsistencies and overall clinical flaws in the manuscript, and further highlighted the need of proper surgical technique and patient selection for optimal clinical outcome 11, 12.

The ProDisc-L manuscripts described clinical outcomes as early as 3 months13 and up to 8.7 years post-operative 14. As described above for CHARITÉ Artificial Disc, The shortterm papers typically disclosed early findings from one or two of the sites that participated in the randomized controlled trial comparing ProDisc-L against a 360 degree fusion13, 15-21. The complete RCT at 2-year follow-up included 161 arthroplasty and 75 fusion patients 2. The long-term data included 64 patients operated at one site, of which 55 were available between 7 and 11 years post-operative, for clinical and radiographic follow-up14. All these studies concluded similarly that disc arthroplasty, at all evaluated time points, was safe and resulted in complication and/or re-operation rates comparable to those generally accepted for spinal surgery (complication rate of 9% at 8.7 years14; there were no major complications, but a reoperation rate of 3.7% at 2 years was reported2). In addition to safety, efficacy of spinal arthroplasty was also shown herein as all cases presented significant improvements in pain and disability. The final RCT data reported improvements in the arthroplasty group in Visual Analogue Scores (VAS) for pain by an average 39-mm, and in disability, as determined by the Oswestry Disability Index (ODI), by 28 points. It is worth noting, however, that the ODI tool utilized in this RCT was not the validated and widely accepted ODI methodology Version 1.0 as defined by Fairbanks et al22. In a Letter to the Editor, Fairbanks denounced the use of the so-called Oswestry Disability Index in the ProDisc-L study and thus cast doubt on the validity of the disability improvement outcomes observed herein23.

The 2 clinical data publications on the MAVERICK device were both based on the same data set of 64 patients, collected at one site24, 25. The clinical outcomes were described using the ODI Version 1.0 and VAS scores. The efficacy of arthroplasty was once again demonstrated using these tools, as ODI scores decreased by an average of 20.7 points and VAS scores by 4.4 points. As for the FlexiCore Intervertebral Disc, only one paper was recently published26. This manuscript describes the clinical outcomes of 44 patients, of which only 6 were available for 2-year follow-up. While the clinical relevance of this data may therefore be questionable, authors still concluded that the device may be safe and efficacious but that the data was not representative of the entire patient cohort.

### **3.2 Radiographic analyses: Range of motion, heterotopic ossification and sagittal balance analyses**

Radiographic evaluations such as ROM, heterotopic ossification, and sagittal balance have been broadly analyzed for the CHARITÉ Artificial Disc, the ProDisc-L, as well as the Maverick Total Disc Arthroplasty System.

Unlike other clinical and radiographic outcomes, accurate measurement of ROM was shown to be challenging and, to some extent, subjective, as patient positioning, imaging staff training, and other factors unrelated to the actual motion potential of the spine were shown to impact final readings 27. Using ProDisc-L cases, Lim et al evaluated different methodologies and associated error margins for the measurement of ROM from

Lumbar Spinal Arthroplasty: Clinical Experience 519

well as adjacent-level discs, in order to determine whether the added motion at the index level could slow down the natural progression of the disease at the facets and the

Three long-term analyses evaluated adjacent-level degeneration, one with ProDisc-L at 8.7 years, and the other two with the CHARITÉ Artificial Disc at 10 years follow-up. In the ProDisc-L study, 24% cases developed adjacent level degeneration by the latest follow-up time point. A correlation was also found between a low range of motion and the prevalence of adjacent level degeneration: all patients with adjacent-level degeneration had a ROM l ess than 5 degrees, while only 59% of patients without adjacent-level degeneration had a ROM less than 5 degrees 36. Lemaire et al and David reported 2 (2%) and 3 (2.8%) cases of adjacent-level degeneration at the latest time point, respectively4, 9. Lemaire et al and David also disclosed 11 cases (11%) and 5 cases (4.7%) with facet

The issue of facet degeneration was also recently discussed in a short-term study. From a 13 patient case series with 12 months follow-up, Trouillier et al alluded to possible maintenance of facet joint integrity following arthroplasty with CHARITÉ Artificial Disc based on the favorable results from their series37. At the other end of the spectrum, Shim et al, at the 3-year time point, observed 36.4% and 32.0% increase in index-level facet degeneration and 19.4% and 28.6% adjacent level disc degeneration with the CHARITÉ

The issue of possible revisability of arthroplasty devices represented a key concern when the first artificial disc, the CHARITÉ Artificial Disc, was introduced to the market. As such, multiple papers have focused on this issue and provided surgical and clinical insights to

The first description of appropriate revision for a CHARITÉ Artificial Disc was presented by David38. In this single-case example, a CHARITÉ Artificial Disc was replaced at 9.5 years post-operative with another CHARITÉ Artificial Disc. The author concluded that revision of the disc with another disc could be safely and adequately performed and was thus an alternative to a revision fusion procedure. David also noted that, due to the inherent difficulty of an anterior approach, only experienced surgeons should undertake this operation. Further revision and explantation of the disc were also described by McAfee et al and Leary et al 39, 40. McAfee et al confirmed Davids experience and concluded that arthroplasty with the CHARITÉ Artificial Disc did not preclude any further procedures at the index level during primary insertion, with nearly one third being revisable to a new motion-preserving prosthesis and just over two thirds being successfully converted to ALIF and/or posterior pedicle screw arthrodesis, the original alternative procedure. Leary further implied that technical errors in position and sizing of the implant were largely to blame for further revision surgery. Finally, Punt et al reviewed 75 revision cases from the Dutch experience (estimated by the authors at approximately more than 1000 Dutch patients). In this series, patients were fused posteriorly either with removal of the disc or without removal of the disc. No statistically significant difference was observed between these 2 groups41. This paper included

adjacent-level joints.

arthrosis at the latest time point, respectively.

Artificial Disc and the ProDisc-L, respectively.

ensure appropriate approaches to revision surgery.

patients previously described by Van Ooij et al42.

**3.4 Revision and revision strategies** 

radiographic images. Specifically, Lim et al concluded that a ROM of at least 4.6 degs must be observed in order to be 95% certain that a given device had any sagittal motion at all. Similarly, changes needed to be at least 9.6 degs in ROM in order to confirm at 95% that change in motion really happened28, 29. These technical limitations might explain the inconsistent ROM data, particularly for ProDisc-L cases, found in the published literature. The flexion-extension ROM results from the 2-year RCT were determined at 7.7 degrees and 4.67 degrees and characterized as a normal ROM 2. However, at 8.7 years post-operative, Huang et al reported a ROM less than that reported in asymptomatic normal individuals, with an average motion of 3.8 degs 30. In a 2006 prospective study on 41 patients with 2 year follow-up, Leivseth et al also reported that the device fails to restore normal segmental motion, while another retrospective study on 26 patients concluded that sagittal balance and ROM significantly improved after lumbar arthroplasty31.

Less controversy was observed when reviewing ROM data for the CHARITÉ Artificial Disc. A complete manuscript was dedicated to the radiographic data of the 2-year RCT of the CHARITÉ Artificial Disc 8. In this study, arthroplasty patients had a 13.6% increase in motion from preoperative to the 2-year post-operative time point. The ROM also correlated to device placement, as poor device placement resulted in a statistically significant reduction in motion. At 10-year follow-up, David reported an average 10.1 degs ROM, a value very similar to the 10.3 degs reported by Lemaire et al in their 10-year follow-up study4, 9.

Le Huec et al published the only data available on radiographic findings after arthroplasty with the Maverick Total Disc Arthroplasty System. In their study, Le Huec et al broadened their analysis to include sagittal alignment and pelvic tilt24, 32. Using data related to 35 patients at an average 14 months post-operative, authors showed maintenance of overall lordosis and unchanged sacral and pelvic tilts, following arthroplasty.

More recently, a study by Tournier comparing all three - CHARITÉ Artificial Disc, ProDisc-L and Maverick Total Disc Arthroplasty System - further refined the analyses from LeHuec on pelvic and sagittal tilt. In this study, authors found no difference in ROM between prostheses and observed maintenance of sagittal balance before and after surgery with all devices. However, modifications of the lumbar curvature were observed33.

The issue of heterotopic ossification in clinical cases of lumbar arthroplasty has been presented by McAfee et al and, more recently, by Tortolani et al34, 35. In his 2003 paper, McAfee introduced a novel method to characterize spinal heterotopic ossification. This methodology was applied by Tortolani et al in reviewing the 276 arthroplasty patients from the CHARITÉ Artificial Disc RCT (randomized and non-randomized cases). From this analysis, 4.3% cases of heterotopic ossification were noted. However, heterotopic ossification was not related to range of motion, as the authors concluded that no difference in the range of motionat 24-months post-operatively was found between the patients who had and those who did not have heterotopic ossification.

### **3.3 Facets and adjacent-level degeneration**

Facet degeneration is currently a contraindication for arthroplasty. However, a few publications have investigated the impact of arthroplasty on index-level facet joints, as

radiographic images. Specifically, Lim et al concluded that a ROM of at least 4.6 degs must be observed in order to be 95% certain that a given device had any sagittal motion at all. Similarly, changes needed to be at least 9.6 degs in ROM in order to confirm at 95% that change in motion really happened28, 29. These technical limitations might explain the inconsistent ROM data, particularly for ProDisc-L cases, found in the published literature. The flexion-extension ROM results from the 2-year RCT were determined at 7.7 degrees and 4.67 degrees and characterized as a normal ROM 2. However, at 8.7 years post-operative, Huang et al reported a ROM less than that reported in asymptomatic normal individuals, with an average motion of 3.8 degs 30. In a 2006 prospective study on 41 patients with 2 year follow-up, Leivseth et al also reported that the device fails to restore normal segmental motion, while another retrospective study on 26 patients concluded that sagittal balance and

Less controversy was observed when reviewing ROM data for the CHARITÉ Artificial Disc. A complete manuscript was dedicated to the radiographic data of the 2-year RCT of the CHARITÉ Artificial Disc 8. In this study, arthroplasty patients had a 13.6% increase in motion from preoperative to the 2-year post-operative time point. The ROM also correlated to device placement, as poor device placement resulted in a statistically significant reduction in motion. At 10-year follow-up, David reported an average 10.1 degs ROM, a value very similar to the 10.3 degs reported by Lemaire et al in their 10-year

Le Huec et al published the only data available on radiographic findings after arthroplasty with the Maverick Total Disc Arthroplasty System. In their study, Le Huec et al broadened their analysis to include sagittal alignment and pelvic tilt24, 32. Using data related to 35 patients at an average 14 months post-operative, authors showed maintenance of overall lordosis and unchanged sacral and pelvic tilts, following

More recently, a study by Tournier comparing all three - CHARITÉ Artificial Disc, ProDisc-L and Maverick Total Disc Arthroplasty System - further refined the analyses from LeHuec on pelvic and sagittal tilt. In this study, authors found no difference in ROM between prostheses and observed maintenance of sagittal balance before and after surgery with all devices. However, modifications of the lumbar curvature were

The issue of heterotopic ossification in clinical cases of lumbar arthroplasty has been presented by McAfee et al and, more recently, by Tortolani et al34, 35. In his 2003 paper, McAfee introduced a novel method to characterize spinal heterotopic ossification. This methodology was applied by Tortolani et al in reviewing the 276 arthroplasty patients from the CHARITÉ Artificial Disc RCT (randomized and non-randomized cases). From this analysis, 4.3% cases of heterotopic ossification were noted. However, heterotopic ossification was not related to range of motion, as the authors concluded that no difference in the range of motionat 24-months post-operatively was found between the patients who had and those

Facet degeneration is currently a contraindication for arthroplasty. However, a few publications have investigated the impact of arthroplasty on index-level facet joints, as

ROM significantly improved after lumbar arthroplasty31.

follow-up study4, 9.

arthroplasty.

observed33.

who did not have heterotopic ossification.

**3.3 Facets and adjacent-level degeneration** 

well as adjacent-level discs, in order to determine whether the added motion at the index level could slow down the natural progression of the disease at the facets and the adjacent-level joints.

Three long-term analyses evaluated adjacent-level degeneration, one with ProDisc-L at 8.7 years, and the other two with the CHARITÉ Artificial Disc at 10 years follow-up. In the ProDisc-L study, 24% cases developed adjacent level degeneration by the latest follow-up time point. A correlation was also found between a low range of motion and the prevalence of adjacent level degeneration: all patients with adjacent-level degeneration had a ROM l ess than 5 degrees, while only 59% of patients without adjacent-level degeneration had a ROM less than 5 degrees 36. Lemaire et al and David reported 2 (2%) and 3 (2.8%) cases of adjacent-level degeneration at the latest time point, respectively4, 9. Lemaire et al and David also disclosed 11 cases (11%) and 5 cases (4.7%) with facet arthrosis at the latest time point, respectively.

The issue of facet degeneration was also recently discussed in a short-term study. From a 13 patient case series with 12 months follow-up, Trouillier et al alluded to possible maintenance of facet joint integrity following arthroplasty with CHARITÉ Artificial Disc based on the favorable results from their series37. At the other end of the spectrum, Shim et al, at the 3-year time point, observed 36.4% and 32.0% increase in index-level facet degeneration and 19.4% and 28.6% adjacent level disc degeneration with the CHARITÉ Artificial Disc and the ProDisc-L, respectively.

### **3.4 Revision and revision strategies**

The issue of possible revisability of arthroplasty devices represented a key concern when the first artificial disc, the CHARITÉ Artificial Disc, was introduced to the market. As such, multiple papers have focused on this issue and provided surgical and clinical insights to ensure appropriate approaches to revision surgery.

The first description of appropriate revision for a CHARITÉ Artificial Disc was presented by David38. In this single-case example, a CHARITÉ Artificial Disc was replaced at 9.5 years post-operative with another CHARITÉ Artificial Disc. The author concluded that revision of the disc with another disc could be safely and adequately performed and was thus an alternative to a revision fusion procedure. David also noted that, due to the inherent difficulty of an anterior approach, only experienced surgeons should undertake this operation. Further revision and explantation of the disc were also described by McAfee et al and Leary et al 39, 40. McAfee et al confirmed Davids experience and concluded that arthroplasty with the CHARITÉ Artificial Disc did not preclude any further procedures at the index level during primary insertion, with nearly one third being revisable to a new motion-preserving prosthesis and just over two thirds being successfully converted to ALIF and/or posterior pedicle screw arthrodesis, the original alternative procedure. Leary further implied that technical errors in position and sizing of the implant were largely to blame for further revision surgery. Finally, Punt et al reviewed 75 revision cases from the Dutch experience (estimated by the authors at approximately more than 1000 Dutch patients). In this series, patients were fused posteriorly either with removal of the disc or without removal of the disc. No statistically significant difference was observed between these 2 groups41. This paper included patients previously described by Van Ooij et al42.

Lumbar Spinal Arthroplasty: Clinical Experience 521

result, while Zeh et al did not recommend holding back with the implantation of the device, they did suggest long-term clinical evaluations to determine the clinical impact of high ion levels in serum and also recommended discussions with patients on the potential health

The clinical outcomes for selective patient populations (e.g.; smokers, >60yr old) were discussed in multiple papers, more specifically for the ProDisc-L device. Bertagnoli et al lead these efforts with 4 publications presenting clinical data on arthroplasty with ProDisc-L in patients with: 1) single-level arthroplasty15; 2) multi-level arthroplasty16; 3) patients 60 years or older49; 4) smokers 50; and 5) arthroplasty cases adjacent to a fused level 51. While Bertagnoli et al repeatedly stated the importance of proper patient selection in each and every paper, all the results presented in these studies concluded that spinal arthroplasty with ProDisc-L successfully addressed low-back pain in these specific patient populations. Hannibal et al recently compared one- vs. two-level arthroplasty cases at the 2-year followup to try and establish whether one-level cases were experiencing greater clinical improvements as compared to the two-level cases. This hypothesis was not verified as differences in clinical improvements between one- and two-level cases were marginal 52. Yaszay et al approached the problem from a different angle and evaluated patients outcomes based on a radiographic observation, i.e.; preoperative disc height 53. Yaszay et al observed that patients with greater disc collapse experienced a greater benefit from total disc replacement, as compared to patients with less collapsed intervertebral discs. On average, patients in all of Bertagnoli et al and Yaszay et al series showed significant clinical

Using the CHARITÉ Artificial Disc IDE RCT patient population, sub-analyses by patient types were also published by Guyer et al and Geisler et al. Specifically, patients were stratified by age at surgery (18-45 vs. 46-60) or whether they had had prior surgery or not54, 55. In both cases, there was no difference in clinical outcome between groups, whether patients were 18-45 or 46-60, or whether patient did or did not have prior surgery. Along the same trend, Geisler et al also evaluated the clinical outcomes of those patients from the CHARITÉ Artificial Disc RCT that did not improve with arthroplasty and needed revision surgery to a fusion. These patients (7.1% of all arthroplasty cases) did not improve, despite the revision surgery, further highlighting the importance of proper patient selection, and possibly, the fact that patient selection still remains a somewhat

The impact of spinal arthroplasty on health care economics were reviewed for both the CHARITÉ Artificial Disc and the ProDisc-L. Guyer et al analyzed the costs related to a CHARITÉ Artificial Disc arthroplasty compared to: 1) an anterior fusion with autograft: 2) anterior fusion with rhBMP-2 (Infuse Bone Graft and LT-Cages) as well as 3) instrumented posterior lumbar interbody fusion. This analysis included the cost of revision surgery at the rate estimated in the published literature. Guyer et al concluded that all fusion procedures were more costly than the arthroscopy approach by 12.0% (ALIF with autograft) to 36.5%

effects of the prosthesis.

**3.7 Special patient population analyses** 

improvement following arthroplasty.

approximate science(59)56.

**3.8 Health economics evaluations** 

(ALIF with rhBMP-2 and posterior fusion)57.

### **3.5 Surgical technique**

The appropriate surgical technique with the CHARITÉ Artificial Disc as well as the ProDisc-L was presented in 2 separate publications. Geisler et al provided a detailed account of the surgical technique for the CHARITÉ Artificial Disc, and dedicated an entire section of the paper to patient selection and preoperative planning, two critical aspects of successful spinal arthroplasty43. Authors also strongly recommended the availability of a spinal access surgeon to perform the approach, especially in revision cases. Finally, appropriate midline identification and positioning of the device also represented a critical discussion point in this paper. For the ProDisc-L, Gumbs et al retrospectively reviewed 64 cases of open retroperitoneal exposures and concluded that the approach was safe and, as discussed by Geisler et al, required a multidisciplinary team, such as an orthopedic and an access or general surgeon, to minimize complication rates44.

### **3.6 Complications**

Complications from spinal arthroplasty have also been reported for all three devices. Most complications requiring revision surgery were resolved by either fusion and/or disc replacement surgery. Interestingly, the causes of these complications seemed to be devicespecific (i.e.; due to the design and/or make of the device).

For the ProDisc-L, the major complication described in the literature referred to the vertical split fracture of the vertebral body following total disc replacement. This occurrence was described by Shim et al in 2 separate cases that were not revised or treated surgically, but experienced prolonged back pain as a result45. An additional complication in the form of acquired spondylolysis was described by Schulte et al46. Authors attributed this complication to inaccurate implant size and positioning.

For the CHARITÉ Artificial Disc, the key complications were observed on the earlier devices, which were gamma sterilized in air and thus had a potential for oxidation of the core polyethylene nucleus 38. Complications due to this oxidation process were described by Van Ooij et al (and Punt et al, as this paper reiterate data from the Van Ooij patient population)41, 42. This issue was resolved with a process change in 1998 to gamma sterilization in nitrogen. In a review of the RCT patient population, Geisler et al also evaluated the rate of neurological complications in the arthroplasty group vs. fusion group. The rate of neurological complication was described as exceedingly low in both groups with no statistically significant differences between groups.

While little has been published so far on the Maverick Total Disc Arthroplasty System, one article described an early removal of the Maverick Total Disc Arthroplasty System 47. This removal was performed one year after implantation due to severe persistent back pain. Intraoperatively, gross metallosis around the articulation of the device was observed. The revision was successful and included a 360 degs fusion. Metallosis was thus cited as a potential complication for devices consisting of a metal-on-metal design. Zeh et al presented an additional potential complication: due to this metal-on-metal structure of the Maverick Total Disc Arthroplasty System, cobalt and chromium ions from the device were being released into the bloodstream 48. In this study, cobalt and chromium ions from subjects implanted with the Maverick Total Disc Arthroplasty System were evaluated and compared to ion levels in total hip arthroplasty (THA) patients. Zeh et al found that concentrations of Cr/Co measured in the serum were similar in terms of their level to the values measured in THA metal-on-metal combinations or exceed those values reported in the literature. As a

The appropriate surgical technique with the CHARITÉ Artificial Disc as well as the ProDisc-L was presented in 2 separate publications. Geisler et al provided a detailed account of the surgical technique for the CHARITÉ Artificial Disc, and dedicated an entire section of the paper to patient selection and preoperative planning, two critical aspects of successful spinal arthroplasty43. Authors also strongly recommended the availability of a spinal access surgeon to perform the approach, especially in revision cases. Finally, appropriate midline identification and positioning of the device also represented a critical discussion point in this paper. For the ProDisc-L, Gumbs et al retrospectively reviewed 64 cases of open retroperitoneal exposures and concluded that the approach was safe and, as discussed by Geisler et al, required a multidisciplinary team, such as an orthopedic and an access or

Complications from spinal arthroplasty have also been reported for all three devices. Most complications requiring revision surgery were resolved by either fusion and/or disc replacement surgery. Interestingly, the causes of these complications seemed to be device-

For the ProDisc-L, the major complication described in the literature referred to the vertical split fracture of the vertebral body following total disc replacement. This occurrence was described by Shim et al in 2 separate cases that were not revised or treated surgically, but experienced prolonged back pain as a result45. An additional complication in the form of acquired spondylolysis was described by Schulte et al46. Authors attributed this

For the CHARITÉ Artificial Disc, the key complications were observed on the earlier devices, which were gamma sterilized in air and thus had a potential for oxidation of the core polyethylene nucleus 38. Complications due to this oxidation process were described by Van Ooij et al (and Punt et al, as this paper reiterate data from the Van Ooij patient population)41, 42. This issue was resolved with a process change in 1998 to gamma sterilization in nitrogen. In a review of the RCT patient population, Geisler et al also evaluated the rate of neurological complications in the arthroplasty group vs. fusion group. The rate of neurological complication was described as exceedingly low in both groups with

While little has been published so far on the Maverick Total Disc Arthroplasty System, one article described an early removal of the Maverick Total Disc Arthroplasty System 47. This removal was performed one year after implantation due to severe persistent back pain. Intraoperatively, gross metallosis around the articulation of the device was observed. The revision was successful and included a 360 degs fusion. Metallosis was thus cited as a potential complication for devices consisting of a metal-on-metal design. Zeh et al presented an additional potential complication: due to this metal-on-metal structure of the Maverick Total Disc Arthroplasty System, cobalt and chromium ions from the device were being released into the bloodstream 48. In this study, cobalt and chromium ions from subjects implanted with the Maverick Total Disc Arthroplasty System were evaluated and compared to ion levels in total hip arthroplasty (THA) patients. Zeh et al found that concentrations of Cr/Co measured in the serum were similar in terms of their level to the values measured in THA metal-on-metal combinations or exceed those values reported in the literature. As a

**3.5 Surgical technique** 

**3.6 Complications** 

general surgeon, to minimize complication rates44.

specific (i.e.; due to the design and/or make of the device).

complication to inaccurate implant size and positioning.

no statistically significant differences between groups.

result, while Zeh et al did not recommend holding back with the implantation of the device, they did suggest long-term clinical evaluations to determine the clinical impact of high ion levels in serum and also recommended discussions with patients on the potential health effects of the prosthesis.

### **3.7 Special patient population analyses**

The clinical outcomes for selective patient populations (e.g.; smokers, >60yr old) were discussed in multiple papers, more specifically for the ProDisc-L device. Bertagnoli et al lead these efforts with 4 publications presenting clinical data on arthroplasty with ProDisc-L in patients with: 1) single-level arthroplasty15; 2) multi-level arthroplasty16; 3) patients 60 years or older49; 4) smokers 50; and 5) arthroplasty cases adjacent to a fused level 51. While Bertagnoli et al repeatedly stated the importance of proper patient selection in each and every paper, all the results presented in these studies concluded that spinal arthroplasty with ProDisc-L successfully addressed low-back pain in these specific patient populations. Hannibal et al recently compared one- vs. two-level arthroplasty cases at the 2-year followup to try and establish whether one-level cases were experiencing greater clinical improvements as compared to the two-level cases. This hypothesis was not verified as differences in clinical improvements between one- and two-level cases were marginal 52. Yaszay et al approached the problem from a different angle and evaluated patients outcomes based on a radiographic observation, i.e.; preoperative disc height 53. Yaszay et al observed that patients with greater disc collapse experienced a greater benefit from total disc replacement, as compared to patients with less collapsed intervertebral discs. On average, patients in all of Bertagnoli et al and Yaszay et al series showed significant clinical improvement following arthroplasty.

Using the CHARITÉ Artificial Disc IDE RCT patient population, sub-analyses by patient types were also published by Guyer et al and Geisler et al. Specifically, patients were stratified by age at surgery (18-45 vs. 46-60) or whether they had had prior surgery or not54, 55. In both cases, there was no difference in clinical outcome between groups, whether patients were 18-45 or 46-60, or whether patient did or did not have prior surgery. Along the same trend, Geisler et al also evaluated the clinical outcomes of those patients from the CHARITÉ Artificial Disc RCT that did not improve with arthroplasty and needed revision surgery to a fusion. These patients (7.1% of all arthroplasty cases) did not improve, despite the revision surgery, further highlighting the importance of proper patient selection, and possibly, the fact that patient selection still remains a somewhat approximate science(59)56.

### **3.8 Health economics evaluations**

The impact of spinal arthroplasty on health care economics were reviewed for both the CHARITÉ Artificial Disc and the ProDisc-L. Guyer et al analyzed the costs related to a CHARITÉ Artificial Disc arthroplasty compared to: 1) an anterior fusion with autograft: 2) anterior fusion with rhBMP-2 (Infuse Bone Graft and LT-Cages) as well as 3) instrumented posterior lumbar interbody fusion. This analysis included the cost of revision surgery at the rate estimated in the published literature. Guyer et al concluded that all fusion procedures were more costly than the arthroscopy approach by 12.0% (ALIF with autograft) to 36.5% (ALIF with rhBMP-2 and posterior fusion)57.

Lumbar Spinal Arthroplasty: Clinical Experience 523

revisions were often found to be associated with technical errors, such as errors in

This critical importance of proper technique was in fact described in the 2 technique papers discussed herein. Both these publications stressed the importance of proper patient

Three types of major complications were described or foreseen in the current literature: 1) vertebral body split due to the ProDisc-L keel design; 2) oxidation of the core polymer nucleus, a problem specific to first generation CHARITÉ I prosthesis; and 3) metallosis and long-term impact of metal ions in the body. While the issue of metallosis and metal ions still needs to be thoroughly investigated, the problems related to vertebral body split only occurred once in the published literature, and as such, may represent a rare occurrence, and that of core oxidation, has been since resolved with new sterilization techniques following which core oxidation of the polymer nucleus is not observed. Thus, possible complications

Finally, low rates of complication and adverse event were observed for most of all analyzed patients. For the ProDisc-L, smokers as well as patients 60 years of age seemed to experience similar benefit from the procedure. In all these studies, however, authors reiterated the importance of proper patient selection, thus concluding that, while all analyzed patient types experienced clinical benefit from the procedure, specific care must be given to only

Finally, no technology is sustainable in today's market place if its cost is prohibitive. Thus, the impact of arthroplasty on health economics was also investigated. Both, the CHARITÉ Artificial Disc and the ProDisc-L study came up at a lower cost than their fusion controls, whether potential revision costs were included or not. No data on cost exists yet for the

The typical diseased lumbar segment considered for artificial disc technologies at L4-L5 or L5-S1 has advanced degenerative disc disease with loss of vertical height and lordosis, dehydration changes, adjacent Modic endplate changes, and little motion on dynamic studies (see Figure 1). The natural progression of degenerative disease disc limits the joint mobility and this biomechanical fact places more forces on the adjacent levels then in the normal situation. The artificial lumbar disc, by restoring normal motion, height, and lordosis, will decrease the forces on the adjacent levels. Thus, theoretically, levels adjacent to a dynamically stabilized level may have beneficial effects compared to the natural history of the unoperated degenerative state. Clearly some patients will benefit from the decreased force on the adjacent vertebral level(s) following a dynamic stabilization (arthroplasty) compared to a static stabilization (fusion). Estimates of the rate and groups of patients at maximum benefit will need to await long-term clinical follow up studies with lumbar arthroplasty devices similar to the hip and knee arthroplasty registries. Also, although a dynamically stabilized level can be converted to a fusion, a fused level cannot be converted to a dynamic joint. Thus, artificial technology can be thought of as a definitive procedure for the vast majority of patients that can be converted to a fusion if the pain and functional goals are not met or degenerative changes occur in the posterior elements and the

Maverick Total Disc Arthroplasty System and the FlexiCore Intervertebral Disc.

selection, a recurrent theme in almost all arthroplasty discussions.

related to devices with metal-on-poly designs seem to be fairly limited.

positioning or sizing of the implant.

operate on appropriate patients.

arthrodesis level is believed to be the pain generator.

**5. TDR surgery** 

A similar analysis by Levin et al evaluated the costs of 1- and 2-level arthroplasty vs. 360 degs fusion. This study did not include possible needs for revisions. Nevertheless, one-level arthroplasty cases were found to be less costly than one-level fusions (\$35,592 for arthroplasty vs. \$46,280 for 360 deg fusion) while two-level cases were similar for both groups (\$55,524 for arthroplasty vs. \$56,823 for fusion)58.
