Total Disc Replacement Surgery Research Articles

An in Vivo, Three-Dimensional (3D), Functional Centers of Rotation of the Healthy Cervical Spine

ObjectiveThis study examined cervical center of rotation (COR) positions in seven postures using validated cone beam computed tomography (CBCT) combined with 3D-3D registration in healthy volunteers. MethodsCBCT scans were performed on twenty healthy volunteers in seven functional positions, constructing a three-dimensional model. Images were registered to the neutral position using 3D-3D registration, allowing analysis of kinematic differences and rotational axes. COR measurements were obtained for each segment (C2/3 to C6/7) in each posture. ResultsThe CORs of C2/3 to C6/7 were predominantly posterior (-5.3±3.8 ∼ -0.6±1.2mm) and superior (16.5±6.0 ∼ 23.6±3.2 mm) to the intervertebral disc's geometric center (GC) in flexion and extension. However, the C4/5 segment's COR was anterior to the GC (2.0±9.8 mm) during flexion and close to it in the right-left direction. During left-right twisting, the CORs of C2/3-C6/7 were posterior (-21.8±10.5 ∼-0.9±0.8 mm) and superior (3.1±7.5 ∼23.2±3.6 mm) to the GCs in anterior-posterior and superior-inferior directions, without consistent right-left directionality. During left-right bending, each segment's COR was predominantly posterior (-25.2±13.1 ∼-6.5±9.9 mm) and superior (0.3±12.5 ∼12.1±5.1 mm) to the GC in anterior-posterior and superior-inferior directions, except for the C2/3 segment, located inferiorly (-5.9 ±4.1 mm) in left bending. The right-left COR position varied across segments. ConclusionsOur findings reveal segment-specific and posture-dependent COR variations. Notably, the CORs of C3/4, C4/5, and C5/6 consistently align near the intervertebral disc's GC at different postures, supporting their suitability for total disc replacement surgery within the C3/4 to C5/6 segments.

180. Who bleeds during elective anterior lumbar surgery?

<h3>BACKGROUND CONTEXT</h3> Blood loss during elective anterior lumbar access for interbody fusion or disc replacement is a potentially major complication. Patients undergoing this surgery have a variety of co-morbidities and medication which may contribute. <h3>PURPOSE</h3> The aim of this study was to examine which factors effect intraoperative estimated blood loss (EBL) during anterior lumbar surgery. <h3>STUDY DESIGN/SETTING</h3> A prospective study of consecutive anterior retroperitoneal approaches for lumbar surgery was performed between January 2010 and November 2021, by a single vascular surgeon and a single spine surgeon. <h3>PATIENT SAMPLE</h3> All patients (n=368) underwent an anterior lumbar interbody fusion (ALIF) at L4–5 and/or L5–S1, a total disc replacement (TDR) at L4–5 and/or L5–S1, or a hybrid procedure with a TDR at L4–5 and an ALIF at L5–S1. <h3>OUTCOME MEASURES</h3> We examined the effects of patient age, sex, body mass index (BMI), low-dose aspirin (LD-ASA), operative level, prosthesis and intraoperative heparinization. <h3>METHODS</h3> The Cell Saver was used in all cases with blood loss measured and recorded by an independent autotransfusionist. Saturation probes were placed on the second toes bilaterally. Heparin was administered intravenously when the saturation meter signal lost pulsatility indicating lower limb arterial flow was interrupted. <h3>RESULTS</h3> The mean age of the 368 patients was 47 ± 13.2 yrs [95% CI = 45 – 48]; and 210 (57%) were male. BMI showed a negative association with EBL. Age showed no effect on EBL in non-heparinized patients but a negative trending correlation with EBL in heparinized patients. Continuation of LD-ASA did not significantly affect EBL. Most patients underwent an ALIF (265 patients,72%), 55 (15%) had a TDR, and 48 (13%) had a hybrid operation (with a TDR at L4–5 and an ALIF at L5–S1) and the majority (249 patients,68%) had a single-level procedure (54 (26.9%) at L4–5 and 195 (73.1%) at L5–S1) and 119 (32%) underwent a 2-level procedure (L4–5 and L5–S1). There was more than twice mean EBL with TDR (135ml) and hybrid (104ml) compared to ALIF (59ml) but were not statistically significant. Intraoperative heparinization was administered in 104 patients (28%). The total mean EBL for the heparin group (125ml) was significantly higher than for the non-heparin group (56ml) (p< 0.0004). A significant difference was observed when comparing heparin vs nonheparin patients and the procedure type. With ALIF (p < 0.002), TDR (p< 0.03) and hybrid (p< 0.02) there was a significantly higher EBL with heparinized patients compared to nonheparinized patients. <h3>CONCLUSIONS</h3> TDR showed the highest EBL across procedure types. In non-heparinized patients, older age, increasing BMI and continuation of LD-ASA were not predictors for increased EBL. However, in heparinized patients, age and BMI showed a negative correlation with increased EBL. This study suggested younger, leaner, heparinized patients who undergo TDR surgery demonstrated the highest EBL risk in anterior lumbar surgery. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

Correlation between the degree of pain relief following discoblock and short-term surgical disability outcome among patients with suspected discogenic low back pain.

To evaluate how well the degree of pain relief after discoblock predicts the disability outcome of subsequent fusion or total disc replacement (TDR) surgery, based on short-term Oswestry Disability Index (ODI) scores. We retrospectively analyzed a set of patients who had undergone discoblock and subsequent fusion or TDR surgery of the same lumbar intervertebral disc due to suspected discogenic chronic LBP between 2011 and 2018. We calculated the degree of pain relief following discoblock (ΔNRS) and the changes in both absolute and percentual ODI scores (ΔODI and ΔODI%, respectively) following fusion or TDR surgery. We analyzed the statistical significance of ΔNRS and ΔODI and the correlation (Spearman's rho) between ΔNRS and ΔODI%. The fusion and TDR group were analyzed both in combination and separately. Fifteen patients were eligible for the current study (fusion n=9, TDR n=6). ΔNRS was statistically significant in all groups, and ΔODI was statistically significant in the combined group and in the fusion group alone. The parameters of both decreased. We found a Spearman's rho of 0.57 (p=0.026) between ΔNRS and ΔODI% for the combined group. The individual Spearman's rho values were 0.85 (p=0.004) for the fusion group and 0.62 (p=0.191) for the TDR group. We suggest that discoblock is a useful predictive criterion for disability outcome prior to surgery for discogenic LBP, especially when stabilizing spine surgery is under consideration. 174/2019 (Oulu University Hospital Ethics Committee).

Rehabilitation Following Lumbar Total Disc Replacement, With a Focus on Lumbar Multifidus Morphology and Function: A Case Report and Review of the Literature

Background Lumbar total disc replacement (TDR) is an option for patients with severe low back pain from degenerative disc disease who have failed conservative treatment. Paraspinal muscles have played an important role in clinical outcomes after lumbar surgery. The purpose of this study was to investigate lumbar multifidus morphology and function in a patient following lumbar TDR and a postoperative rehabilitation exercise program. Case Presentation A 52-year-old man underwent TDR surgery at the L5-S1 level to treat his chronic low back pain, which had been present for several years and unresponsive to previous conservative management. Six weeks after the operation, the patient initiated an 8-week postoperative rehabilitation program focusing on motor control and strengthening exercises. Outcome and Follow-Up The patient experienced clinically important improvements in pain and disability, as well as improvements in lumbar multifidus size ranging from 3.17% to 13.84% and changes in thickness contraction ranging from 4.04% to 16.48%, following the postoperative rehabilitation program. However, differences in lumbar multifidus muscle morphology and function were observed when comparing the surgical site to the superior motion segment. Discussion This case report displays limited evidence regarding the effects and implementation of a motor control and strengthening exercise program following lumbar TDR. Some improvements in muscle morphology and function were observed, along with improvements in pain and disability, after the completion of the exercise program. The importance of including lumbar multifidus morphology and function in the postoperative rehabilitation of this population may warrant further research. JOSPT Cases 2022;2(1):34–41. doi:10.2519/josptcases.2022.10163

Total disc replacement alters the biomechanics of cervical spine based on sagittal cervical alignment: A finite element study

IntroductionThe correlation between cervical alignment and clinical outcome of total disc replacement (TDR) surgery is arguable. We believe that this conflict exists because the parameters that influence the biomechanics of the cervical spine are not well understood, specifically the effect of TDR on different cervical alignments.Methods:A validated osseo-ligamentous model from C2-C7 was used in this study. The C2-C7 Cobb angle of the base model was modified to represent: lordotic (−10°), straight (0°), and kyphotic (+10°) cervical alignment. The TDR surgery was simulated at the C5-C6 segment. The range of motion (ROM), intradiscal pressure, annular stresses, and facet loads were computed for all the models.Results:The ROM results demonstrated kyphotic alignment after TDR surgery to be the most mobile when compared to intact base model (41% higher in flexion–extension, 51% higher in lateral bending, and 27% higher in axial rotation) followed by straight and lordotic alignment, respectively. The annular stresses for the kyphotic alignment when compared to intact base model were higher at the index level (33% higher in flexion–extension and 48% higher in lateral bending) compared to other alignments. The lordotic model demonstrated higher facet contact forces at the index level (75% higher in extension than kyphotic alignment, 51% higher in lateral bending than kyphotic alignment, and 78% higher in axial rotation than kyphotic alignment) when compared among the three alignment models.Conclusion:Preoperative cervical alignment should be an integral part of surgical planning for TDR surgery as different cervical alignments may significantly alter the postsurgical outcomes.

Risk Factors for High-Grade Heterotopic Ossification After Total Disc Replacement: A Single-Center Experience of 394 Cases.

Heterotopic ossification (HO) is a common complication following total disc replacement (TDR). High-grade HO is a clinically relevant complication, however, only a few studies have evaluated risk factors for high-grade HO. To evaluate potential risk factors for HO and high-grade HO and their impact on clinical outcomes. We retrospectively reviewed patients who underwent TDR or hybrid surgery (HS) with Prestige-LP (Medtronic), Discover (Depuy), and Prodisc-C (Synthes). Clinical outcomes were assessed using Japanese Orthopaedic Association, Visual Analogue Scale, and Neck Disability Index scores. Radiological variables, including preoperative ossification, global and segmental range of motion (ROM), HO, and adjacent segment degeneration (ASD) were reviewed. A total of 394 patients were evaluated. HO and high-grade HO occurred in 67.77% and 11.17% patients, respectively. Preoperative ossification was significantly associated with the occurrence of HO (P<.001, OR: 3.507, 95%CI: 2.211-5.562) and high-grade HO (P=.019, OR: 2.176, 95%CI: 1.137-4.166). The ROM of replacement levels and C2-7 were significantly lower in the high-grade HO group compared to those without high-grade HO: (3.80° vs 10.18°, P<.001) and (42.81° vs 54.00°, P<.001), respectively. The incidence of ASD was significantly higher in patients with high-grade HO than those without high-grade HO (22.73%vs 11.14%, P=.048). Preoperative ossification was identified as a potential risk factor for HO and high-grade HO. Patients with high-grade HO had limited ROM of replacement levels and the cervical spine and had a high incidence of ASD compared to those without high-grade HO.

71. Long-term follow-up of a consecutive series with prodisc C Nova at a single institution

<h3>BACKGROUND CONTEXT</h3> Cervical total disc replacement surgery has more than two decades of experience. Device designs that feature a ball and socket mechanism with central keels, such as the original prodisc C, have been shown to perform favorably. However, a tall central keel can potentially be less than optimal for patients with shorter vertebral bodies or in multi-level cases. A variation of the prodisc C design was subsequently created, keeping the original mechanism of action but changing to shorter, tri-keel fixation. prodisc C Nova (Centinel Spine, West Chester, PA), which has one central keel cranially and two lateral keels caudally, was developed and released in Europe in 2010. <h3>PURPOSE</h3> The primary objective of this study was to evaluate the long-term clinical and radiographic outcomes. <h3>STUDY DESIGN/SETTING</h3> Prospective, consecutive series. <h3>PATIENT SAMPLE</h3> Fifty-six patients (37 Female, 19 Male) underwent total disc replacement surgery for symptomatic cervical disc disease at a single level. <h3>OUTCOME MEASURES</h3> Evaluation at each visit included patient self-assessments, eg, visual analog scale (VAS) pain and satisfaction, walking, physical and neurological examination, and radiographic evaluation. Radiographic evaluation was performed by an independent radiologic group (Medical Metrics, Houston, Texas). <h3>METHODS</h3> After failing conservative therapy, patients were evaluated for their suitability for surgical intervention of their symptomatic cervical disc degeneration. Patients underwent an anterior discectomy and total disc replacement. The clinical status of each patient was evaluated pre- and postoperatively at 6 weeks, 3 months, 6 months, 1 year and annually thereafter. <h3>RESULTS</h3> Patients were followed through 9 years postoperatively. At baseline, the average age was 48.22 ± 8.98 years and an average BMI 27.68 ± 4.78 kg/m2. VAS neck and VAS arm pain both showed statistically significant reduction from baseline by 6 weeks postop and were maintained through 9 years. VAS neck was 6.67 ±2.29 mm at baseline and 3.25 ± 3.59 mm at 9 years. VAS arm was 6.02 ±2.59 mm preoperatively and 4.00 ± 3.65 mm at 9 years. Patients reported high satisfaction and willingness to have operation again at all time points. Patients walking frequency increased by month 3 and was maintained in ≥ 75% of patients at all timepoints out to 9 years. Radiographic results showed no migration or protrusions through 9 years follow-up. One case of minor subsidence was measured after 5 years but did not require surgical intervention and had satisfactory results. One patient required reoperation at 10 months for persistent pain and required facet denervation at both cranial and caudal adjacent levels as well as index level. The disc remained intact and had good follow-up. There were no device failures. <h3>CONCLUSIONS</h3> Long-term follow-up shows that prodisc C Nova has patient-reported outcomes and radiographic results comparable to that published with prodisc C. Patients reported consistent and sustained improvement through 9 years of follow-up. Not only was pain relief achieved but functional improvement through walking was sustained. There were also no adjacent level surgeries over the 9 years, showing that maintaining motion has other potential clinical benefits beyond the index level. The change in keel fixation design did not affect patient outcomes, providing another option for some patients. <h3>FDA DEVICE/DRUG STATUS</h3> prodisc C Nova (Investigational/Not approved)

162. Cervical total disc replacement: available implant size matters

<h3>BACKGROUND CONTEXT</h3> Multiple cervical total disc replacement (TDR) studies have found this procedure to produce outcomes noninferior or superior to anterior cervical discectomy and fusion (ACDF). While restoration of disc height of a collapsed, degenerated segment is a goal of TDR surgery, there are potential problems with over-distracting the segment with an implant. Several biomechanical studies have investigated the potential impact of prosthesis height, particularly with respect to implant sizes larger than the natural disc space height, found that increased implant height was associated with decreased range-of-motion and reduced facet overlap, possibly altering the loading of the adjacent facet joints. These changes have also been found to be possible contributing factors to the development of heterotopic ossification. With respect to implant height, one study found that in 36% of a study population, the height of the cervical disc space was less than the minimal height of available TDRs, which is generally 5 mm. <h3>PURPOSE</h3> The purposes of this study were to: 1) analyze the heights of cervical disc spaces to be replaced with a TDR; 2) measure the heights of the disc spaces adjacent to the treated level (providing insight to normal disc height), and 3) investigate the frequency of use of a smaller height TDR implant when available. <h3>STUDY DESIGN/SETTING</h3> The study was based on a post hoc analysis of data collected prospectively as part of a Food and Drug Administration (FDA) Investigational Device Exemption (IDE) trial. <h3>PATIENT SAMPLE</h3> Radiographic measurements were made from 148 patients enrolled in the trial and 16 patients who were training cases for the trial. <h3>OUTCOME MEASURES</h3> Radiographic measures used in the study included disc heights of level operated with a TDR and the heights of levels adjacent to these segments. Also, the size of the TDR implants used was recorded. <h3>Methods</h3> Radiographs were used to measure the disc heights of 164 level treated with TDR and 261 adjacent nonoperated levels from C3-4 to C6-7. All radiographic measures were performed by a central facility specializing in image assessment. For each level, the recorded disc height was the average of the anterior and posterior disc heights. To investigate the TDR implant size selected by the operating surgeon, data from the Simplify_® Cervical Artificial Disc FDA IDE trial were analyzed. The device is available in 4, 5, and 6 mm heights. The device height selected was recorded and used in the current study. Of note, the 4 mm height became available only after trial enrollment was 13% complete. <h3>Results</h3> Measurements made of the 261 levels adjacent to a degenerated level to be treated by TDR found that 55% of disc spaces had a height of 4 mm or less. Among the levels to be replaced with a TDR, 82% were less than 4 mm in height. In the FDA trial in which a 4 mm device was available, it was selected for use in 38% of patients, a 5 mm device was used in 53% and a 6 mm implant was used in 9% of patients. <h3>Conclusions</h3> This study found that many disc levels to receive a TDR had a height of <4mm. Even among the adjacent segments not being operated, 55% were of height <4 mm, suggesting that motion preserving implants of greater heights may have the potential to overdistract the disc space. In a recent FDA IDE trial, which offered a 4mm TDR implant height, this was selected in 39% of patients, suggesting surgeon preference for the smaller implant in an appreciable number of patients. Further investigation is warranted to determine if the lower height implants are related to more favorable clinical and/or radiographic results. <h3>FDA DEVICE/DRUG STATUS</h3> Simplify Cervical Disc Replacement (Approved for this indication)

Motion preservation after cervical total disc replacement surgery-fact or fiction?

Cervical disc replacement surgery aims to preserve cervical motion in younger patients who present with symptomatic degenerative cervical disc herniation and mobile facet joints. We aimed to determine the demographics, pre-operative range of motion, operative parameters, post-operative parameters, range of motion at 2-years post-operatively, in 27 patients who presented to our unit over a 6-year period who underwent cervical total disc replacement surgery. Materials and methodsWe performed a retrospective chart review of 27 patients who presented to our unit with degenerative cervical disc disease, from 01 January 2014 – 31 December 2019, who underwent cervical disc replacement surgery. The data collected included patient age; gender; mechanism of injury; clinical presentation; cervical level/s involved; description and site of the disc herniation; length of preoperative symptomatology; pre-operative cervical range of motion; length of operative procedure; volume of intra-operative blood loss; amount of immediate post-operative radiculopathy pain assessed by the visual analogue scale; complications; length of hospital stay; and cervical range of motion at 2-year follow-up. ResultsThe mean age of our subjects was 45.5 (+/-6.5) years. Regarding gender 11/27 (41%) subjects were female and 16/27 (59%) subjects were male. In terms of number of levels 21/27 (78%) subjects had single level surgery and 6/27 (22%) subjects had double level surgery. Considering age categories, patients in the 4th decade demonstrated a statistically significant increase between their pre-operative segmental range of cervical flexion and their post-operative segmental range of cervical flexion (p = 0.02). ConclusionThrough the results of our study we report that in our 27 subjects cervical total disc replacement surgery was motion preserving in 100% of our subjects at a 2-year study end point. We further report that all our subjects demonstrated some degree of increase in their segmental ranges of motion in all planes, although this was largely insignificant.

85. Incidence and resolution strategies for early onset postoperative leg pain following lumbar total disc replacement

BACKGROUND CONTEXT Lumbar total disc replacement (TDR) was introduced in the 1980s and is becoming more common. Anecdotally, there have been reports of patients reporting the onset of new leg pain following TDR surgery. To date, there has been little formal investigation into this clinical phenomenon. PURPOSE The purpose of this study was to determine the incidence of new-onset leg pain following lumbar TDR and investigate treatment strategies for this occurrence. STUDY DESIGN/SETTING This study was based on a post hoc analysis of data collected prospectively as part of an FDA IDE trial. PATIENT SAMPLE The study population was comprised of 283 patients who received ProDisc-L or activL® as part of the multicenter, randomized FDA IDE trial for the latter device. Patients were treated for symptomatic single-level disc degeneration unresponsive to at least 6 months of nonoperative care. OUTCOME MEASURES The primary outcome measures in the study were the onset of leg pain following TDR surgery and the outcomes of treatments for this condition. METHODS New onset of leg pain following TDR surgery was identified from adverse event reports collected prospectively during the trial. It was defined as leg pain beginning 0- to 4 weeks postoperatively. The treatment of these symptoms was at the operating surgeon's discretion. Treatment strategies were classified as: medication, nonoperative care, injections, and/or subsequent surgery. RESULTS New onset of postoperative leg pain occurred in 9.2% of lumbar TDR patients (26/283). The new onset pain resolved in 76.9% (20/26) of patients. Most patients (24 of 26) were treated with one or more medications, the most common of which was anticonvulsant drugs such as gabapentin or pregabalin, commonly used to treat neurogenic-type pain. Symptoms resolved in 75% of patients receiving this type of medication. Some also received narcotics and 30.8% were treated with steroids, most commonly a Medrol dose-pack. Twelve patients received other nonoperative care (PT, acupuncture, etc.) and 7 received injections. Three patients went on to have subsequent surgery, none of whom had resolution of the new onset leg pain after the additional procedure. Among the 20 patients whose new symptoms resolved, resolution occurred within 3 months in 11 patients. CONCLUSIONS Early-onset postoperative leg pain occurred in approximately 10% of lumbar TDR patients. The source of the symptoms is not clear. In the majority of patients, the new symptoms resolved, often within 3 months of onset. While challenging to definitively evaluate in this relatively small subset of patients, it appears the most effective treatment strategy is gabapentin or pregabalin. The role of other nonoperative interventions could not be discerned. Surgical re-intervention is likely unnecessary and did not lead to resolution of early onset leg pain post-TDR. FDA DEVICE/DRUG STATUS activL and ProDisc-L (Approved for this indication).

Artificial disc replacement in spine surgery.

Total disc replacement (TDR) is an innovative procedure that has gained traction in spine surgery. A large amount of data in the literature report on the short-term outcomes of TDR surgery favorably. However, surgeons remain reluctant to opt for TDR surgery due to uncertainty of long-term outcomes. Recently, long term data regarding TDR surgery has become available, with some studies showing superior outcomes to fusion surgery. The goal of this review is to synthesize and clinically contextualize the recent literature on TDR surgery. This article also provides brief discussion of the biggest challenges currently facing disc arthroplasties and the ways in which they are being tackled.

BIOMECHANICAL PERFORMANCE OF A MODIFIED DESIGN OF DYNAMIC CERVICAL IMPLANT COMPARED TO CONVENTIONAL BALL AND SOCKET DESIGN OF AN ARTIFICIAL INTERVERTEBRAL DISC IMPLANT: A FINITE ELEMENT STUDY

Most of the implants used for total disc replacement (TDR) surgery are designed as a ball and socket pair aimed at providing a three-dimensional unconstrained motion. However, one of the major concerns with ball and socket design is the wear of the implant which limits its life. In this study the biomechanical performance of two types of implant designs is compared — a conventional ball and socket type (Prodisc-C) and a modified design of dynamic cervical implant (DCI) using FE analysis. A 3-dimensional geometrical model of cervical spine (C1–T1) was developed using CT scan data of a middle-aged healthy male. Subsequently, using FE analysis, the ROM values were validated with the existing literature using a compressive load in combination with different physiological motions of the neck. Furthermore, FE analysis on the two implants, fitted at C5–C6 segment, showed a significant increase in the ROM of implanted segment using Prodisc and decrease in the ROM of inferior segment, but modified-DCI restored the motion of the implanted and adjacent segments. Analysis of average bone strains adjacent to the implant showed a possibility of stress shielding for Prodisc. However, higher stress distribution on the modified-DCI limited its clinical use.

Validation of Pre-operative Templating for Total Disc Replacement Surgery.

This was an analytic retrospective observational study. The aims were (1) to validate patient-specific templating process by comparing postoperative range of motion (ROM) with that predicted by the model, (2) to retrospectively determine the ideal implant size, height, configuration, and location to evaluate if the ROM achieved could have been improved, and (3) to correlate postoperative ROM and clinical outcome. Previous research revealed that after total disc replacement surgery, 34% of patients with less than 5° of postoperative ROM developed adjacent segment disease. The match between patient anatomy (size, facet orientation, disc height) and implant parameters are likely to affect postoperative ROM and clinical outcomes. Seventeen consecutive patients were implanted with 22 ProDisc-L devices between 2008 and 2015. Three-dimensional finite element (FE) models of the implanted segment were constructed from preoperative computed tomography scans and virtually implanted with the ProDisc-L implant. ROM was determined with the endpoints of facet impingement in flexion and implant contact in extension. FE templating was used to determine the optimal implant size and location. ROM was then measured directly from flexion and extension radiographs and compared to predicted ROM. Pre and postoperative Oswestry Disability Index (ODI) data were used to correlate ROM with clinical outcomes. No significant difference was found between the actual and predicted ROM. The computational templating procedure identified an optimal ROM that was significantly greater than actual ROM. The ROM in our cohort could have been improved by an average of 1.2° or 12% had a different implant size or position been used. FE analyses accurately predicted ROM in this cohort and can facilitate selection of the optimal implant size and location that we believe will increase the chance of achieving clinical success with the application of this technology.

Failure of lumbar disc surgery: management by fusion or arthroplasty?

To analyze and clarify conflicting aspects of fusion and total disc replacement (TDR) surgery in literature. Using keywords, 23 literature reviews, 41 studies accepted by "importance criteria" from the Internet, and 16 articles "published in 2018" were chosen. Altogether 80 studies. General assessment was mentioned as affirmative for TDR in 40 papers, five were negative, 24 without clear decision. Long term results TDR seven affirmative, four nondecisive. Comparison to fusion (general, ALIF, 3600, BAK cage) 18 found as better, nine equal, one nondecisive. Complications TDR 3-50%. Adjacent disc degeneration disease recognized in 14 papers, denied existence in four. Cost-benefit effective in three papers comparing to fusions, ALIF, 3600. Nonimbursement from the state mentioned as problem in three papers. Salvage surgery seven papers, rare but extremely problematic. Anterior approach 16 challenging surgery, one 10% minor, one 38.5% transient complications, one 1.8% retrograde ejaculations, one 6.6% vascular injuries, two access surgeon needed. Construct judgment two no importance, 22 wear and durability problems, two inadequate biomechanics and biomaterials, threeconstruct and lateral approach. Impact of TDR upon spine surgery is decreasing, currently is less than 2%. It is concluded that problems with anterior surgery, imbursement policy, and potential problems with salvage surgery are major reasons for loosing popularity of TDR surgery.

Strain behavior of malaligned cervical spine implanted with metal-on-polyethylene, metal-on-metal, and elastomeric artificial disc prostheses – A finite element analysis

BackgroundPostoperative alterations in cervical spine curvature (i.e. loss of lordotic angle) are frequently observed following total disc replacement surgery. However, it remains unclear whether such changes in lordotic angle are due to preoperative spinal deformities and/or prostheses design limitations. The objective of the study is to investigate strain and segmental biomechanics of the malaligned cervical spine following total disc replacement. MethodsThree disc prostheses were chosen, namely a metal-on-polyethylene, a metal-on-metal, and an elastomeric prosthesis, which feature different geometrical and material design characteristics. All discs were modelled and implanted into multi-segmental cervical spine finite element model (C3-C7) with normal, straight and kyphotic alignments. Comparative analyses were performed by using a hybrid protocol. FindingsThe results indicated that as the spine loses lordotic alignment, the prosthesis with elastomeric core tends to produce significantly larger flexion range of motion (difference up to 6.1°) than metal-on-polyethylene and metal-on-metal prostheses. In contrast, when the treated spine had normal lordotic alignment, the range of motion behaviors of different prostheses are rather similar (difference within 1.9°). Large localized strains up to 84.8% were found with the elastomeric prosthesis, causing a collapsed anterior disc space under flexion loads. InterpretationChanges in cervical spinal alignments could significantly affect the surgical-level range of motion behaviors following disc arthroplasty; the in situ performance was largely dependent on the designs of the artificial disc devices in particular to the material properties.

Wednesday, September 26, 2018 7:35 AM–9:00 AM ePosters: P64. Comparing 30-day outcomes between orthopedic surgeons and neurosurgeons in lumbar total disc replacement

BACKGROUND CONTEXT Orthopedic surgeons and neurosurgeons both perform lumbar total disc replacements (LTDR). However, there is little evidence comparing outcomes between these two specialties for LTDR. It is possible that one specialty achieves superior postoperative complication, reoperation, or readmission rates following LTDR. PURPOSE This study evaluated the: (1) demographics; (2) complications; (3) operative time; (4) length of stay; (5) reoperations; and (6) readmissions of patients following LTDR. We hypothesized that orthopedic surgeons and neurosurgeons achieve similar 30-day postoperative outcomes in complications, reoperations, and readmissions following LTDR surgery. STUDY DESIGN/SETTING Retrospective review of a prospectively collected database. PATIENT SAMPLE All patients who underwent elective lumbar total disc replacement surgery between 2008 and 2016 and were eligible for at least 30-day follow-up were identified from the National Surgical Quality Improvement Program (NSQIP) database. A total of 581 patients were identified, 42.9% of whom were treated by orthopedic surgeons and 57.1% treated by neurosurgeons. OUTCOME MEASURES Demographic information, complications, operative time, length of stay, reoperations, and readmissions. METHODS The National Surgical Quality Improvement Program (NSQIP) database was utilized to identify all elective lumbar total disc replacements performed from 2008 to 2016 by ICD-9-CM code. This cohort was grouped by surgeon specialty (orthopedic surgeon and neurosurgeon). Demographics including age, sex, race, and Charlson or Deyo score, as well as comorbidities, labs, perioperative factors, and 30-day postoperative complication, reoperation, and readmission rates were collected for all patients. The groups were then compared with univariate analysis. Regression models were developed and attempted to identify potential predictive factors for 30-day postoperative complications. RESULTS A total of 581 LTDR patients were included. 42.9% of patients were treated by orthopedic surgeons and 57.1% were treated by neurosurgeons. Orthopedic patients were younger (44.71vs. 47.51years, p=.008) and had lower rates of hypertension (26.9vs. 37.1%, p=.010). Otherwise, the groups were largely comparable in comorbidities and lab values. Orthopedic patients had comparable operative time (159.3vs. 140.0 minutes, p=.731) and but slightly longer length of stay (2.59vs. 2.26days, p=.044) compared to neurosurgery patients. The orthopedic patient group had comparable 30-day complication (6.4vs. 9.3%, p=.203), readmission (1.8vs. 5.0%, p=.052) and reoperation (0.9vs. 1.6%, p=.473) rates compared to neurosurgery patients. Regression analysis revealed patient age was the lone significant predictor for higher overall complication rate (OR 1.04, p CONCLUSIONS This study compared 30-day outcomes between orthopedic surgeons and neurosurgeons in lumbar total disc replacement patients. Neurosurgeons performed lumbar total disc replacements more often than orthopedic surgeons but their outcomes were comparable for 30-day complication, reoperation and readmission rates. Orthopedic surgery patients had slightly longer length of stay. Surgeon specialty was not a significant predictor for 30-day complication rates. Orthopedic surgeons may be under-performing lumbar total disc replacement surgeries despite similar outcomes to neurosurgeons.

Are Controversial Issues in Cervical Total Disc Replacement Resolved or Unresolved?: A Review of Literature and Recent Updates.

Since the launch of cervical total disc replacement (CTDR) in the early 2000s, many clinical studies have reported better outcomes of CTDR compared to those of anterior cervical discectomy and fusion. However, CTDR is still a new and innovative procedure with limited indications for clinical application in spinal surgery, particularly, for young patients presenting with soft disc herniation with radiculopathy and/or myelopathy. In addition, some controversial issues related to the assessment of clinical outcomes of CTDR remain unresolved. These issues, including surgical outcomes, adjacent segment degeneration (ASD), heterotopic ossification (HO), wear debris and tissue reaction, and multilevel total disc replacement (TDR) and hybrid surgeries are a common concern of spine surgeons and need to be resolved. Among them, the effect of CTDR on patient outcomes and ASD is theoretically and clinically important; however, this issue remains disputable. Additionally, HO, wear debris, multilevel TDR, and hybrid surgery tend to favor CTDR in terms of their effects on outcomes, but the potential of these factors for jeopardizing patients' safety postoperatively and/or to exert harmful effects on surgical outcomes in longer-term follow-up cannot be ignored. Consequently, it is too early to determine the therapeutic efficacy and cost-effectiveness of CTDR and will require considerable time and studies to provide appropriate answers regarding the same. For these reasons, CTDR requires longer-term follow-up data.

Age-Related Stability for Artificial Disc Fixators Inserted into a Lumbar Vertebra: Finite Element Analysis

The objective of this research was to analyze age-related stability at 20, 40, 60, and 80 years of age for two artificial disc fixators inserted into the L3 lumbar vertebra after total disc replacement (TDR) surgery. To precisely analyze the lumbar vertebra, elastic moduli of the cortex verified by load contributions between two materials were used. The stress shielding problem was solved using a p-element. For a wedge-type of Charite III and a plate-type of ProDisc L, these two models and the aging L3 lumbar were created. Decreasing disc loads applied to the aging vertebra. Based on this, load-analysis of the trabecular bone for supporting the artificial disc with fixators was performed every 20 years. The results showed as follows: 1) The ultimate loads resulting in maximal stresses and strains of the plate shape after TDR showed a reduction of about 72 and 79%, respectively, compared with healthy vertebral bodies; 2) The decreasing width of the physiological loads greatly influenced the increase and decrease of stress and strain; 3) Both fixtators were involved in low back pain and were limited to less than 800 N at 80 years old; therefore, it was predicted that continued treatment would be needed.

Heterotopic Ossification After Cervical Total Disc Replacement at 7 Years-Prevalence, Progression, Clinical Implications, and Risk Factors.

Heterotopic ossification (HO) is a known risk following cervical total disc replacement (CTDR) surgery, but the cause and effect of HO are not well understood. Reported HO rates vary, and few studies are specifically designed to report HO. The effects on outcomes, and the risk factors for the development of HO have been hypothesized and reported in small-population, retrospective analyses, using univariate statistics. Posthoc, multiple-phase analysis of radiographic, clinical, and demographic data for CTDR as it relates to HO was performed. HO was radiographically graded for 164 one-level and 225 two-level CTDR patients using the McAfee and Mehren system. Analysis was performed to correlate HO grades to clinical outcomes and to evaluate potential risk factors for the development of HO using demographics and baseline clinical measures. At 7 years, 1-level clinically relevant HO grades were 17.6% grade 3 and 11.1% grade 4. Two-level clinically relevant HO grades, evaluated using the highest patient grade, were 26.6% grade 3 and 10.8% grade 4. Interaction between HO and time revealed significance for neck disability index (NDI; P = .04) and Visual Analog Scale (VAS) neck pain (P = .02). When analyzed at each time point NDI was significant at 48-84 months and VAS neck at 60 months. For predictors 2 analyses were run; odds ratios indicated follow-up visit, male sex, and preoperative VAS neck pain are related to HO development, whereas hazard ratios indicated male sex, obesity, endplate coverage, levels treated, and preoperative VAS neck pain. This is the largest study to report HO rates, and related outcomes and risk factors. To develop an accurate predictive model, further large-scale analyses need to be performed. Based on the results reported here, clinically relevant HO should be more accurately described as motion-restricting HO until a definitive link to outcomes has been established.

Artificial Total Disc Replacement Versus Fusion for Lumbar Degenerative Disc Disease: An Update Systematic Review and Meta-Analysis.

To conduct an updated systematic review and meta-analysis to compare the efficacy and safety between total disc replacement (TDR) and fusion surgery for lumbar degenerative disc disease (LDDD). We comprehensively searched meta-analyses comparing TDR with fusion through the PubMed, Embase, and Cochrane Library databases. Only randomized controlled trials (RCTs) were selected and collected. The end of the retrieval time was June 2017. Two authors independently extracted the data from the studies after assessing their quality. The statistical software STATA version 12.0 was used to analyze the data. A total of seven RCTs (1706 patients) were included in our analysis. The patients in the TDR group had significantly improved. A greater percentage of these patients were satisfied with the surgery concerning Oswestry disability index, visual analog scale score, and complication rate. In addition, the clinical success in the TDR group was greater than that in the fusion group. Meanwhile, the TDR group had shorter operative time and hospital stay. However, there was no clinical significance regarding blood loss, work status, and reoperation rate between the two groups. Our current updated meta-analysis suggests that TDR could be an alternative treatment for LDDD, since it yielded better clinical success and patient satisfaction, shorter hospital stay and operative time, less pain, and lower complication rates than lumbar fusion.