Total Disc Replacement Devices Research Articles

Removals and Revisions of Cervical Total Disc Replacement Devices in a Consecutive Series of 1626 Patients Beginning With the First Case Experience in 2003.

Retrospective cohort study. The purpose of this study was to investigate the rate of cervical total disc replacement (TDR) device removal or revision. Cervical TDR has gained acceptance as an alternative to anterior cervical discectomy and fusion in appropriately selected patients. There have been concerns over device safety, one measure of which is subsequent surgery related to device problems. A consecutive series of 1626 patients undergoing cervical TDR from 2003 to June 2021 were included, consisting of TDRs up to 3 levels and hybrids (TDR and fusion). TDR removal or revision surgeries and reasons for these surgeries, procedures performed, and duration from index procedure were recorded. Data were analyzed to determine the removal/revision rate and factors possibly related to these events. There were 24 removals/revisions (1.48%) in the 1626 patients. Removal was performed in 23 cases (1.41%) and revision in 1 (0.06%). Among removal cases, anterior cervical discectomy and fusion was performed in 18 and TDR was replaced with another TDR in 5. Removals with fusion included 5 cases of osteolysis with/without Cutibacterium acnes , 4 device displacement/migration, 4 posterior spinal pathology, and one for each of the following: metal allergy, approach-related complications, malpositioning, subsidence, and hypermobility. The revision involved TDR repositioning 3 days after index surgery. There were 66 patients for whom a minimum of 10-year follow-up was confirmed, and none had removal/revision surgery 10 or more years after index surgery. There was no relationship between the occurrence of removal/revision and age, sex, body mass index, or physician experience (learning curve). The removal/revision rate was significantly higher in FDA trials versus postapproval (4.1% vs . 1.3%, P < 0.05). In this large consecutive series of patients, 1.48% of cervical TDRs were removed/revised. The low rate of removals/revisions over a long period of time provides support for the devices' safety. Level IV.

171. A novel monolithic 3D-printed titanium lumbar total disc replacement device results in biomechanics similar to the intact spine: a finite element study

171. A novel monolithic 3D-printed titanium lumbar total disc replacement device results in biomechanics similar to the intact spine: a finite element study

Application of PEEK in total cervical disc arthroplasty: A review

Cervical disc arthroplasty (CDA) is a surgical procedure where a degenerated or damaged cervical disc is removed and replaced with an artificial disc in levels C3/4, C4/5, C5/6, and C6/7 of the spine. Cervical disc replacement promises improvement for the patient compared to conventional fusion surgery. Commonly used disc replacement devices are Ultra-high-molecular-weight polyethylene (UHMWPE) over cobalt-chrome alloy (CoCr). The problems associated with the current total disc replacement devices are wear and the biological response to the wear debris in vivo. UHMWPE and metal wear particles can cause an inflammatory reaction and promote foreign-body granulation tissue response, leading to the implant's failure in vivo. Considering these effects, there exists a need for revising the material in CDA. Polyether ether ketone (PEEK) as an alternative material to UHMWPE has shown less wear when used as a self-mating surface in CDA. The current study reviews and reports the literature on PEEK and its composites as alternating materials for CDA.

Biocompatible liquid-crystal elastomers mimic the intervertebral disc

The hierarchical and anisotropic mechanical behavior requirement of load-bearing soft tissues limits the utility of conventional elastomeric materials as a replacement for soft-tissue materials. Liquid-crystal elastomers (LCEs) have the potential to excel in this regard owing to its unique combination of mesogenic order in an elastomeric network. In this study, the mechanical behavior of the LCEs relevant to load-bearing biomedical applications was explored. LCEs with different network orientations (i.e., mesogen alignments) were investigated by fabricating the LCEs with polydomain and monodomain configurations. The polydomain and monodomain LCEs with the same degree of network crosslinking demonstrated diverse mechanical behavior, ranging from highly stiff and elastic nature to high damping capacity, depending on the loading direction with respect to the network alignment. The LCEs were also capable of matching the anisotropic mechanical behavior of an intervertebral disc. Additional studies were conducted on the in vivo biological response of LCEs upon subcutaneous implantation, as well as on the effect of the exposure to an in vitro simulated physiological environment on the mechanical behavior. The LCEs’ mechanical response was negligibly affected when exposed to biomedically relevant conditions. Furthermore, the solid and porous LCEs did not show any adverse effect on the surrounding tissues when implanted subcutaneously in rats. The biological response allows for tissue ingrowth and helps illustrate their utility in implantable biological devices. Finally, the utility of LCEs to mimic the mechanical function of biological tissue such as intervertebral disc was demonstrated by fabricating a proof of concept total disc replacement device.

Wednesday, September 26, 2018 3:35 PM – 5:05 PM Preserving Spinal Motion: 89. Impact of range of motion on patient outcomes five years following lumbar TDR at L5-S1

BACKGROUND CONTEXT Total disc replacement (TDR) is an alternative to fusion that preserves index level motion. A common misconception is that L5-S1 should be fused because TDR implants do not move at this level. Previously, we reported TDR at L5-S1 preserves motion at this level 5 years postimplantation, and that mobile core devices maintained better motion than constrained core devices. This study aimed to relate clinically significant improvements in patient outcomes (VAS and ODI) to the degree of motion at the L5-S1 index level. METHODS This is a post-hoc analysis of data collected from a large, multicenter clinical trial. Eligible patients were randomly allocated (2:1) to treatment with an investigational TDR device (activL) or a control TDR device (ProDisc-L or Charite). Range of motion (ROM), back pain (VAS) and Oswestry Disability Index (ODI) scores were available at the 5-year time point for 119 patients in the investigational group and 50 patients in the control group with L5-S1 TDR. RESULTS ROM was significantly better at L5-S1 at 5 years for patients implanted with the activL device (6.6° at baseline vs. 6.7° at 5 years, NS) than it was using the control devices (6.7°at baseline vs. 4.8°at 5 years, p=.002). Average ODI and VAS scores for back pain significantly decreased at 5 years from baseline for both groups. There were no differences in ODI or VAS scores between groups at 5 years, but each incremental improvement in ROM correlated with incremental clinical improvement. The percentage of patients demonstrating clinically significant (CS) improvements in ODI and VAS back pain scores (≥ 15% from baseline) at 5 years for every two degrees of ROM at L5-S1 was determined. For patients with 0-2° of motion, 81% and 86% of activL and control patients, respectively, demonstrated a CS improvement in ODI. CS improvement in ODI was observed in all patients with 8-10o of motion at L5-S1. Similarly, an average of 81% TDR patients with 0-2° of motion at L5-S1 demonstrated CS improvements in back pain. Compared to ODI scores, CS improvement for back pain was achieved in 100% of patients at just 6-8° and 4-6° for activL and control patients, respectively. CONCLUSIONS These data show that for patients with TDR at L5-S1, a greater proportion exhibited clinically significant improvements in lower back disability and pain when there was more motion at the index level at 5 years postsurgery, suggesting motion preservation has an impact on function and pain for L5-S1 index level procedures. ActivL improved L5-S1 ROM significantly better than ProDisc-L or Charite. FDA DEVICE/DRUG STATUS ActivL, Prodisc-L, and Charite: Approved for this indication.

Thursday, September 27, 2018 8:30 AM–9:30 AM Best Papers: 107. Analysis of lumbar total disc replacement removals and revisions: a 17-year experience

BACKGROUND CONTEXT One concern expressed about lumbar total disc replacement (TDR) has been safety. One measure of safety is the need for subsequent surgery to removal or revise an implant. This may be of particular importance considering TDR removal or revision generally requires re-operation through the anterior approach with the corresponding increased risk of vascular injury. PURPOSE The purpose of this study was to analyze the incidence of, and reasons for, removal or revision of lumbar TDR devices. STUDY DESIGN/SETTING Data were collected from a multi-site spine specialty practice. PATIENT SAMPLE A consecutive series of 1,707 lumbar TDR patients, beginning with the first case experience in 2000, was reviewed to identify those undergoing re-operation for TDR removal or revision. Only patients who were at least 6 months postoperative were included. Among the 1,707 patients, the mean follow-up was 42.7 months with a median of 30 months and a maximum of 195 months. OUTCOME MEASURES The primary outcome measure was the occurrence of a surgery for the revision or removal of a lumbar TDR. METHODS For each case of device removal/revision, the reason, duration from index surgery, and procedure performed were recorded. Six different devices were used in the series. RESULTS In the series of 1,707 patients, there were 17 patients who underwent TDR removal (0.99%) and three additional patients underwent TDR revision (0.17%). The rates based on the total number of 2,023 TDR devices implanted in the 1,707 patients, were 0.89% removals and 0.15% revisions. The reasons and timing of removal/revisions were analyzed. Removals included: eight for migration and/or loosening, three developed problems after a trauma, one had vertebral body fractures (osteoporosis), one TDR was too large and replaced with smaller device, one had ongoing pain, and one had an infection seeded from a chest infection at 146 month post-TDR. Revisions included one repositioning the core (technique error), one repositioned device after displacement, and one core replacement due to wear or failure. With respect to timing, 40% of removals or revisions occurred within one month after the index surgery, and a total of 85% occurred within 2 years. Of note, 40% of the revisions/removals occurred in the first 25 TDR cases performed by individual surgeons. There were no vascular complications causing clinical sequelae during the removal or revision surgeries. CONCLUSIONS In this large patient series, 1% of lumbar TDRs were removed or revised. Only one revision was related to device failure or wear. Many of the subsequent procedures were performed within a month of implantation. Also of note, many occurred within the first 25 TDR cases for individual surgeons, suggesting a learning curve. In cases of TDR removal or revision, as with any repeat anterior spine surgery, one should be acutely aware and prepared for vascular injury should it occur. The low rate of removal or revision in this large institutional experience over a 17 year period provides support for the safety of these devices. FDA DEVICE/DRUG STATUS Charite, ProDisc-L, and activL approved for single-level use; Kineflex-L, Freedom, and Flexicore investigational; and Charite, ProDisc-L, and activL off-label for multi-level and hybrid.

Wednesday, September 26, 2018 3:35 PM – 5:05 PM Preserving Spinal Motion: 90. Seven-year outcomes of lumbar total disc replacement systems on patient lifestyle and quality of life

BACKGROUND CONTEXT Degenerative disc disease (DDD) is a potentially debilitating condition resulting in pain and decreased functional ability in patients. Lumbar total disc replacement (TDR) helps to alleviate this pain and dysfunction and potentially allows for a return to preinjury activities. PURPOSE The purpose of this study was to evaluate quality of life (QoL) at 7 years post-TDR compared to preoperative status. STUDY DESIGN/SETTING Data for the analysis were collected from a Food and Drug Administration regulated prospective, randomized study conducted at multiple sites. PATIENT SAMPLE Patients were randomly allocated (2:1) to treatment with an investigational TDR device (activL, n=218) or FDA-approved control TDR devices (ProDisc-L, n=65 or Charite, n=41). All were treated for single-level symptomatic disc degeneration unresponsive to at least 6 months of nonoperative care. OUTCOME MEASURES The primary outcome measure was the SF-36. Secondary evaluations included work status, patient satisfaction, and use of pain medication. METHODS Follow-up occurred at 6 weeks and 3, 6, 12 and 24 months and every year thereafter up to 7-years postsurgery. Data from the preoperative baseline and the 7 year follow-up are reported. RESULTS At 7 years, 77% and 73% of activL and control patients (respectively) showed improvements in mental component scores (MCS) for the SF-36 compared to baseline. Similarly, physical component scores (PCS) improved for 92% and 86% of activL and control patients at 7 years postsurgery. Clinically significant improvements in MCS and PCS scores (≥15% improvement from baseline) occurred in approximately 44% (MCS) and 62% (PCS) of all TDR patients combined at 6 weeks, increased to 61% (MCS) and 80% (PCS) at 12 months and remained constant through to 7 years. Approximately 53% of all TDR patients returned to work without restriction by 12 months, which increased to 64% and 54% for activL and control patients at 7 years. Most ActivL patients were able to return to the same workload as before their back injury at 7 years, whereas more control patients worked in sedentary jobs at 7 years than before their back injury. Patient satisfaction at 7 years postsurgery showed 97% of all TDR patients were “very satisfied” or “somewhat satisfied” with the procedure, and 93% indicated that they would “definitely” or “probably” undergo the procedure again for the same condition. 97% of ActivL and 89% of control patients indicated that the treatment was “very” or “moderately” effective in eliminating their symptoms. Decreases in the proportion of patients utilizing pain medication were noted in both groups. At baseline, 90% and 92% of ActivL and control patients were using medications for pain control, which decreased by half by 7 years. CONCLUSIONS The results of this analysis indicate that lumbar TDR is effective at helping to improve patient's quality of life, potentially facilitating return to work and reducing pain medication usage. FDA DEVICE/DRUG STATUS activL, ProDisc-L, Charite artificial discs (Approved for this indication)

Wednesday, September 26, 2018 7:35 AM–9:00 AM ePosters: P63. Pain-related safety outcomes seven years following lumbar total disc replacement in mobile core devices versus constrained core devices

BACKGROUND CONTEXT Total disc replacement (TDR) is an alterative to fusion for treating patients with disabling discogenic back pain. While several studies report significant improvements in overall back pain following TDR, some patients may experience recurring episodes of pain in the lumbar and/or lower extremities. Competing lumbar disc arthroplasty devices include a mobile core device versus a constrained core device. Long-term follow up (>7 years) from investigational device trials is now available to better assess long-term outcomes with arthroplasty with the two device types. PURPOSE To evaluate pain-related adverse events in patients 7years following single-level total disc replacement at L4–L5 or L5–S1 with either a mobile core disc (MCD) or a constrained core device (CCD) to determine if implant design is associated with increased pain serious adverse effects at 7-year follow-up. STUDY DESIGN/SETTING This post-hoc analysis of a multicenter, prospective, randomized, controlled, investigational device exemption trial included patients with symptomatic lumbar degenerative disc disease at L4–L5 or L5–S1. PATIENT SAMPLE The patients had lumbar arthroplasty surgery with either an MCD (n=218) or CCD (n=65) implant and were randomized prior to surgery in the IDE study. OUTCOME MEASURES The study reviewed events deemed to be serious adverse events in a FDA IDE study. METHODS This post-hoc analysis of a multicenter, prospective, randomized, controlled, investigational device exemption trial included patients with symptomatic lumbar degenerative disc disease at L4–L5 or L5–S1. Pain related adverse events (AE) at 7years post implantation for TDRs as a class and by device type (MCD vs. CCD) are reported. RESULTS Of the reported AEs, 23% (N=327) were categorized as pain of the lumbar and/or lower extremities: lumbar only (7%), lumbar and bilateral lower leg (5%), and lumbar and unilateral lower leg (3%). Patients presenting with AEs reported an average of two pain related AEs at 7years post-op. Of the pain related AEs, 11% were device related, 8% were procedure related and 9% were serious AEs (SAEs). Onset of the first pain related SAE occurred on average at 49days (range: 0–118 days) and 395days (range: 0–2,728 days) following CCD and MCD implantation, respectively (p=.21). Overall, the majority of pain related SAEs were classified as severe (69%). A greater proportion of patients implanted with the CCD device presented with severe SAEs (88%) compared to patients with MCD (61%; p=.17). At the 7-year follow-up, over half of the SAEs occurring in MCD patients were resolved (56%) while the SAEs in CCD patients remained mostly unresolved (75%; p=.14). CONCLUSIONS While the rate of pain related AEs were the same between patients implanted with an MCD or CCD implant, there were observed differences in the quality of SAEs between the two TDR devices. On average, the first pain related SAE in MCD patients occurred approximately 1 year after CCD patients. Furthermore, a smaller proportion of SAEs were severe and a greater proportion was resolved by the 7-year follow-up appointment with MCD versus CCD implanted patients.

Challenges and Solutions for Lumbar Total Disc Replacement Implantation.

: Long-term data are now available to support the safety and efficacy of lumbar total disc replacement (TDR). Five-year randomized and controlled trials, meta-analyses, and observational studies support a similar or lower risk of complications with lumbar TDR compared with fusion. The panel concluded that published data on commercially available lumbar TDR devices demonstrate minimal concerns with late-onset complications, and that the risk of adjacent segment degeneration and reoperations can be reduced with lumbar TDR versus fusion. Survey results of surgeon practice experiences supported the evidence, revealing a low rate of complications with TDR. Panelists acknowledged the importance of adhering to selection criteria to help minimize patient complications.

M6-C artificial disc placement.

There has been a steady evolution of cervical total disc replacement (TDR) devices over the last decade resulting in surgical technique that closely mimics anterior cervical discectomy and fusion as well as disc design that emphasizes quality of motion. The M6-C TDR device is a modern-generation artificial disc composed of titanium endplates with tri-keel fixation as well as a polyethylene weave with a polyurethane core. Although not yet approved by the FDA, M6-C has finished a pilot and pivotal US Investigational Device Exemption (IDE) study. The authors present the surgical technique for implantation of a 2-level M6-C cervical TDR device. The video can be found here: https://youtu.be/rFEAqINLRCo .

Evaluation of Aesculap Implant Systems activl Artificial Disc for the treatment of degenerative disc disease

ABSTRACTIntroduction: A primary cause of chronic low back pain and disability is lumbar degenerative disc disease (DDD). Surgical treatments are available for DDD including fusion or lumbar total disc replacement (TDR). Lumbar TDR is performed as a motion-preserving alternative to lumbar fusion. There are several marketed lumbar TDR devices including the Aesculap Implant Systems activL Artificial Disc, Charité Artificial Disc and the ProDisc-L Total Disc Replacement.Areas covered: Considering the various surgical options by which lumbar DDD can be managed, here we evaluate the biologic and biomechanical benefits and concerns of the Aesculap activL Artificial Disc. We review the use of the activL Artificial Disc compared to other lumbar TDRs and an alternative to fusion for skeletally mature patients diagnosed with isolated, symptomatic DDD.Expert commentary: Short-term follow-up studies suggest that under the right circumstances and precise patient selection, lumbar TDR with the Aesculap activL Artificial Disc is a safe and effective alternative to lumbar fusion. Long-term clinical data will provide information about the potential for adjacent level disease, effects of implant wear, and indications for revision surgery. Future clinical and biomechanical studies, as well as device-specific long-term outcome and comparison studies, will assist surgical decision making.

Lumbar Total Disc Replacement for Discogenic Low Back Pain

A prospective, multicenter, randomized, controlled, investigational device exemption (IDE) noninferiority trial. The aim of this study was to evaluate the comparative safety and effectiveness of lumbar total disc replacement (TDR) in the treatment of patients with symptomatic degenerative disc disease (DDD) who are unresponsive to nonsurgical therapy. Lumbar TDR has been used to alleviate discogenic pain and dysfunction while preserving segmental range of motion and restoring stability. There is a paucity of data available regarding the comparative performance of lumbar TDR. Patients presenting with symptomatic single-level lumbar DDD who failed at least 6 months of nonsurgical management were randomly allocated (2:1) to treatment with an investigational TDR device (activL, n = 218) or FDA-approved control TDR devices (ProDisc-L or Charité, n = 106). The hypothesis of this study was that a composite effectiveness outcome at 2 years in patients treated with activL would be noninferior (15% delta) to that in controls. The primary composite endpoint of this study was met, which demonstrated that the activL TDR was noninferior to control TDR (P < 0.001). A protocol-defined analysis of the primary composite endpoint also confirmed that activL was superior to controls (P = 0.02). Radiographic success was higher with activL versus controls (59% vs. 43%; P < 0.01). Mean back pain severity improved by 74% with activL and 68% with controls. Oswestry Disability Index scores decreased by 67% and 61% with activL and controls, respectively. Patient satisfaction with treatment was over 90% in both groups at 2 years. Return to work was approximately 1 month shorter (P = 0.08) with activL versus controls. The rate of device-related serious adverse events was lower in patients treated with activL versus controls (12% vs. 19%; P = 0.13). Surgical reintervention rates at the index level were comparable (activL 2.3%, control 1.9%). The single-level activL TDR is safe and effective for the treatment of symptomatic lumbar DDD through 2 years. 2.

In Vivo Total Disc Replacement using Tissue-Engineered Intervertebral Discs in a Canine Model

Introduction Disc degeneration in the cervical spine is a prevalent clinical predicament often requiring surgery. Anterior cervical decompression and fusion (ACDF), the most commonly performed procedure, poses risks of pseudoarthrosis, and adjacent segment disease (ASD).1,2 An emerging alternative treatment option is prosthetic total disc replacement (TDR),3 which preserves segmental mobility. Our group previously developed a biological TDR device using composite AF/NP disc-like construct with viable cells and mechanical properties analogous to the native discs in a rat tail model.4 In this study, we evaluated the in vivo efficacy of this tissue-engineered intervertebral disc (TE–IVD) in a beagle cervical model assessing radiological and histological parameters. Material and Methods TE-IVD construction: Canine-sized TE–IVDs were constructed as previously described.4 Cervical IVDs from skeletally mature beagles were separated into AF and NP tissues; component cells were isolated and cultured in vitro. Cultured NP cells were seeded with alginate, injected into a predesigned mold, and encircled with two layers of an AF cell laden collagen gel. The combined construct was kept in media for 2 weeks as the surrounding annulus fibrous aligned and contracted until required TE–IVD diameter was attained. Experimental Protocol: Overall, eight skeletally mature beagles were divided into the following two groups: the control group ( n = 2) underwent discectomy with fully resected IVDs, and the experimental group ( n = 6) underwent TE–IVD implantation postdiscectomy. Adjacent proximal segments served as internal healthy controls. Postoperative X-ray and MRI were taken at 2 and 4 weeks; disc height indices5 and NP hydration using a pre-established algorithm6 were analyzed. Beagles were humanely killed at 4 weeks for histological assessment. Results TE–IVDs were successfully implanted postdiscectomy ( Fig. 1A , B). At 2 weeks, MRIs of TE–IVDs revealed T2 high intensity with acute outer inflammation because of the surgical invasion, which faded by 4 weeks. At 4 weeks, TE–IVDs maintained position in the disc space with relatively increased T2 intensity, whereas discectomized segments manifested as black discs ( Fig. 1C , D). These findings suggest that the implanted TE–IVDs engraft in the disc space despite significant biomechanical demands of the beagle cervical environment. In fact, disc height indices of the TE–IVDs and discectomized discs were 71 and 49%, respectively, of that of healthy control discs. Likewise, MRIs revealed that NP hydration of the implanted TE–IVDs was over 70% of that of healthy discs. Histological assessments further demonstrated chondrocyte-like cell viability in the TE–IVD, abundant proteoglycan content in the extracellular matrices, and substantial integration into host tissues without signs of immune reactions. [Figure: see text] Conclusion Despite the severe local milieu of the beagle cervical spine owing to mechanical loading, our in vivo TE–IVDs when appropriately implanted, maintained their position and structure at 4 weeks. The TE–IVDs displayed dynamic adaptation to the host environment, with extracellular matrix production and cell proliferation. They further maintained disc height as well as NP hydration at 4 weeks with up to 70% viability as the normal healthy discs. References Nesterenko SO, Riley LH III, Skolasky RL. Anterior cervical discectomy and fusion versus cervical disc arthroplasty: current state and trends in treatment for cervical disc pathology. Spine 2012;37(17):1470–1474 Sugawara T, Itoh Y, Hirano Y, Higashiyama N, Mizoi K. Long term outcome and adjacent disc degeneration after anterior cervical discectomy and fusion with titanium cylindrical cages. Acta Neurochir (Wien) 2009;151(4):303–309, discussion 309 Kelly MP, Mok JM, Frisch RF, Tay BK. Adjacent segment motion after anterior cervical discectomy and fusion versus Prodisc-c cervical total disk arthroplasty: analysis from a randomized, controlled trial. Spine 2011;36(15):1171–1179 Bowles RD, Gebhard HH, Härtl R, Bonassar LJ. Tissue-engineered intervertebral discs produce new matrix, maintain disc height, and restore biomechanical function to the rodent spine. Proc Natl Acad Sci U S A 2011;108(32):13106–13111 Kim JS, Kroin JS, Li X, et al. The rat intervertebral disk degeneration pain model: relationships between biological and structural alterations and pain. Arthritis Res Ther 2011;13(5):R165 Grunert P, Hudson KD, Macielak MR, et al. Assessment of intervertebral disc degeneration based on quantitative magnetic resonance imaging analysis: an in vivo study. Spine 2014;39(6):E369–E378

Material Science in Cervical Total Disc Replacement.

Current cervical total disc replacement (TDR) designs incorporate a variety of different biomaterials including polyethylene, stainless steel, titanium (Ti), and cobalt-chrome (CoCr). These materials are most important in their utilization as bearing surfaces which allow for articular motion at the disc space. Long-term biological effects of implanted materials include wear debris, host inflammatory immune reactions, and osteolysis resulting in implant failure. We review here the most common materials used in cervical TDR prosthetic devices, examine their bearing surfaces, describe the construction of the seven current cervical TDR devices that are approved for use in the United States, and discuss known adverse biological effects associated with long-term implantation of these materials. It is important to appreciate and understand the variety of biomaterials available in the design and construction of these prosthetics and the considerations which guide their implementation.

Cervical total disc replacement with the Mobi-C cervical artificial disc compared with anterior discectomy and fusion for treatment of 2-level symptomatic degenerative disc disease: a prospective, randomized, controlled multicenter clinical trial

Cervical total disc replacement (TDR) is intended to treat neurological symptoms and neck pain associated with degeneration of intervertebral discs in the cervical spine. Anterior cervical discectomy and fusion (ACDF) has been the standard treatment for these indications since the procedure was first developed in the 1950s. While TDR has been shown to be a safe and effective alternative to ACDF for treatment of patients with degenerative disc disease (DDD) at a single level of the cervical spine, few studies have focused on the safety and efficacy of TDR for treatment of 2 levels of the cervical spine. The primary objective of this study was to rigorously compare the Mobi-C cervical artificial disc to ACDF for treatment of cervical DDD at 2 contiguous levels of the cervical spine. This study was a prospective, randomized, US FDA investigational device exemption pivotal trial of the Mobi-C cervical artificial disc conducted at 24 centers in the US. The primary clinical outcome was a composite measure of study success at 24 months. The comparative control treatment was ACDF using allograft bone and an anterior plate. A total of 330 patients were enrolled, randomized, and received study surgery. All patients were diagnosed with intractable symptomatic cervical DDD at 2 contiguous levels of the cervical spine between C-3 and C-7. Patients were randomized in a 2:1 ratio (TDR patients to ACDF patients). A total of 225 patients received the Mobi-C TDR device and 105 patients received ACDF. At 24 months only 3.0% of patients were lost to follow-up. On average, patients in both groups showed significant improvements in Neck Disability Index (NDI) score, visual analog scale (VAS) neck pain score, and VAS arm pain score from preoperative baseline to each time point. However, the TDR patients experienced significantly greater improvement than ACDF patients in NDI score at all time points and significantly greater improvement in VAS neck pain score at 6 weeks, and at 3, 6, and 12 months postoperatively. On average, patients in the TDR group also maintained preoperative segmental range of motion at both treated segments immediately postoperatively and throughout the study period of 24 months. The reoperation rate was significantly higher in the ACDF group at 11.4% compared with 3.1% for the TDR group. Furthermore, at 24 months TDR demonstrated statistical superiority over ACDF based on overall study success rates. The results of this study represent the first available Level I clinical evidence in support of cervical arthroplasty at 2 contiguous levels of the cervical spine using the Mobi-C cervical artificial disc. These results continue to support the use of cervical arthroplasty in general, but specifically demonstrate the advantages of 2-level arthroplasty over 2-level ACDF. Clinical trial registration no.: NCT00389597 (ClinicalTrials.gov).

Delayed hypersensitivity reaction caused by metal-on-metal total disc replacement

The authors report the case of a 53-year-old woman who underwent placement of a metal-on-metal total disc replacement (TDR) device for the treatment of discogenic back pain. The initial postoperative course was normal, but 2 months after surgery she started to complain of a recurrence of pain and she progressively developed cauda equina syndrome. Radiological and biological findings showed an inflammatory polyneuropathy associated with an epidural mass. A diagnosis of cell-mediated hypersensitivity reaction (Type IV) was made after patch testing showed positive reactions for 1% cobalt chloride and chromium. A decision was made to remove the TDR device and to perform a circumferential fusion. This report is intended to inform the reader that systemic metal release and hypersensitivity reaction are possible complications of metal-on-metal TDR.

Effect of lubricants on friction in laboratory tests of a total disc replacement device

Some designs of total disc replacement devices have articulating bearing surfaces, and these devices are tested in vitro with a lubricant of diluted calf serum. It is believed that the lubricant found in total disc replacement devices in vivo is interstitial fluid that may have properties between that in Ringer's solution and diluted calf serum. To investigate the effect of lubricants, a set of friction tests were performed on a generic model of a metal against metal ball-and-socket total disc replacement device. Two devices were tested: one with a ball radius of 10 mm and other with a ball radius of 16 mm; each device had a radial clearance of 0.015 mm. A spine simulator was used to measure frictional torque for each device in axial rotation, flexion-extension and lateral bending at frequencies of 0.25-2 Hz, under 1200 N axial load. Each device was tested with two different lubricants: a solution of new born calf serum diluted with deionised water and Ringer's solution. The results showed that the frictional torque generated between the bearing surfaces was significantly higher in Ringer's solution than in diluted calf serum. The use of Ringer's solution as a lubricant provides a stringent test condition to detect possible problems. Diluted calf serum is more likely to provide an environment closer to that in vivo. However, the precise properties of the fluid lubricating a total disc replacement device are not known; hence, tests using diluted calf serum may not necessarily give the same results as those obtained in vivo.

Biomechanical behavior of two different cervical total disc replacement designs in relation of concavity of articular surfaces: ProDisc-C® vs. Prestige-LP®

Recently, many cervical total disc replacement (TDR) devices have been introduced in a variety of designs in an attempt to recreate motion behavior of the normal cervical spine thereby to limit the progression of adjacent degeneration. The purposes of this study were to evaluate and compare the range of motion (ROM) and location of instant center of rotation (COR), and load sharing characteristics of two major products with different design concepts in cervical TAR-Prodisc-C® and Prestige-LP®. A 3-D finite element (FE) model of intact cervical spine (C3-6) was made from CT scans of a normal person and validated. Based on this model, postoperative FE models simulating TDR implantation at the C4-5 disc space were made for Prodisc-C® (Synthes Spine, Paoli, PA) and Prestige-LP® (Medtronic Sofamor Danek, Memphis, TN), respectively. These two TDR devices feature different design concepts that affect kinematics: Rotations and some translations were allowed at the articulating surface of Prestige LP® as the ‘concave down’ articulating surface is less constrained whereas only rotations were allowed with Prodisc-C® that features ball & socket articulating surface in ‘concave up’ orientation. Hybrid protocol (intact: 1Nm) with a compressive follower load of 73.6N were applied at the superior endplate of the C3 vertebral body. The inferior endplate of C6 vertebral body was constrained in all directions. At the index level, Prestige-LP® showed 15% less motion than Prodisc-C® in extension and about the same in flexion. Differences in ROM were negligible at the adjacent level. Here, the COR of Prestige-LP® was located more postero-inferiorly than that of Prodisc-C® by about 1-mm during extension at the index level. Facet load was less with Prestige-LP® by about 10% at the index level but 14% more at the adjacent level. The results of this study indicated that the biomechanical behavior of the postoperative cervical spine can be indeed influenced by the design features such as concavity orientation and extent of constraint of the articulating surfaces. Particularly, ROM and COR location as well as the facet loads at the index level and adjacent levels were more sensitive during extension. It would be interesting to note that resulting differences in facet load at the index and adjacent levels between the two designs will manifest to different clinical results in terms of postoperative facet degeneration.

Symptomatic adjacent segment disease after cervical total disc replacement: re-examining the clinical and radiological evidence with established criteria

Although several publications in the last decade have proved equality in safety and efficacy of the total disc replacement (TDR) to the anterior fusion procedure in cervical spine, the claim that TDR may reduce the incidence of adjacent segment disease (ASD) has not been corroborated by clinical evidence. We attempt to predict the true incidence of symptomatic ASD after TDR surgery in the cervical spine at one or two levels at a median follow-up period of 4 years. A total of 763 patients were screened to participate in four different Food and Drug Administration device exemption trials for artificial cervical disc replacement at three collaborating institutions. Two hundred seventy-one patients qualified and enrolled in the trials. One hundred seventy-three randomized to receive artificial disc replacement surgery, and 167 have completed a 4-year or longer follow-up. Patients experiencing cervical radiculopathy symptoms in the follow-up period were worked-up with clinical examinations, magnetic resonance imaging of the cervical spine, and other diagnostic studies. Once a clinical correlation was established with the imaging evidence of adjacent segment degeneration, a careful record was maintained to document the subsequent medical and/or surgical treatment received by these patients. Statistical analysis was performed to determine the true incidence of and factors affecting the ASD after cervical disc replacement in these patients. Twenty-six patients (15.2%) were identified to satisfy our criteria for ASD at the median follow-up of 51 months, with the annual incidence of 3.1% as calculated by life tables. The actuarial 5-year freedom from ASD rate was 71.6%±0.6%, and the mean period for freedom from ASD was 70.4±2.1 months. The incidence of symptomatic ASD after cervical TDR is 3.1% annually regardless of the patient's age, sex, smoking habits, and design of the TDR device. The presence of osteopenia and lumbar degenerative disease significantly increase the risk of developing ASD after anterior cervical surgery.

Lessons Learned After Nine-Year Follow-Up on Eight Different Lumbar Total Disc Replacement Devices

Charité prothesis has over than 20.000 patients worldwide and has been implanted since the early 1980’s. Over these years, new prostheses have been developed, differing in disc materials, biomechanical features, indications and implantation approaches. Nowadays we can be supported by literature and clinical experience.