The contribution of E3D imaging integrated with robotic navigation: analysis of the first 80 consecutive posterior spinal fusion cases.

Eighty consecutive complex spinal robotic cases utilizing intraoperative 3D CT imaging (E3D, Group 2) were compared to 80 age-matched controls using the Excelsius robot alone with C-arm Fluoroscopic registration (Robot Only, Group 1). The demographics between the two groups were similar-severity of deformity, ASA Score for general anesthesia, patient age, gender, number of spinal levels instrumented, number of patients with prior spinal surgery, and amount of neurologic compression. The intraoperative CT scanning added several objective factors improving patient safety. There were significantly fewer complications in the E3D group with only 3 of 80 (4%) patients requiring a return to the operating room compared to 11 of 80 (14%) patients in the Robot Only Group requiring repeat surgery for implant related problems (Chi squared analysis = 5.00, p = 0.025). There was a significant reduction the amount of fluoroscopy time in the E3D Group (36 s, range 4-102 s) compared to Robot only group (51 s, range 15-160 s) (p = 0.0001). There was also shorter mean operative time in the E3D group (257 ± 59.5 min) compared to the robot only group (306 ± 73.8 min) due to much faster registration time (45 s). A longer registration time was required in the Robot only group to register each vertebral level with AP and Lateral fluoroscopy shots. The estimated blood loss was also significantly lower in Group 2 (mean 345 ± 225 ml) vs Group 1 (474 ± 397 ml) (p = 0.012). The mean hospital length of stay was also significantly shorter for Group 2 (3.77 ± 1.86 days) compared to Group 1 (5.16 ± 3.40) (p = 0.022). There was no significant difference in the number of interbody implants nor corrective osteotomies in both groups-Robot only 52 cases vs. 42 cases in E3D group.Level of evidence: IV, Retrospective review.

100 Complex posterior spinal fusion cases performed with robotic instrumentation.

Robotic navigation has been shown to increase precision, accuracy, and safety during spinal reconstructive procedures. There is a paucity of literature describing the best techniques for robotic-assisted spine surgery for complex, multilevel cases or in cases of significant deformity correction. We present a case series of 100 consecutive multilevel posterior spinal fusion procedures performed for multilevel spinal disease and/or deformity correction. 100 consecutive posterior spinal fusions were performed for multilevel disease and/or deformity correction utilizing robotic-assisted placement of pedicle screws. The primary outcome was surgery-related failure, which was defined as hardware breakage or reoperation with removal of hardware. A total of 100 consecutive patients met inclusion criteria. Among cases included, 31 were revision surgeries with existing hardware in place. The mean number of levels fused was 5.6, the mean operative time was 303 min, and the mean estimated blood loss was 469 mL. 28 cases included robotic-assisted placement of S2 alar-iliac (S2AI) screws. In total, 1043 pedicle screws and 53 S2AI screws were placed with robotic-assistance. The failure rate using survivorship analysis was 18/1043 (1.7%) and the failure rate of S2AI screws using survivorship analysis was 3/53 (5.7%). Four patients developed postoperative wound infections requiring irrigation and debridement procedures. None of the 1043 pedicle screws nor the 53 S2AI screws required reoperation due to malpositioning or suboptimal placement. This case series of 100 multilevel posterior spinal fusion procedures demonstrates promising results with low failure rates. With 1043 pedicle screws and 53 S2AI screws, we report low failure rates of 1.7% and 5.7%, respectively with zero cases of screw malpositioning. Robotic screw placement allows for accurate screw placement with no increased rate of postoperative infection compared to historical controls. Level of evidence: IV, Retrospective review.

Computer Simulated Enhancement and Planning, Robotics and Navigation With Patient Specific Implants and 3-D Printed Cages.

STUDY DESIGN: This is a retrospective cohort study. OBJECTIVES: Pre and postop Measurement Testing. This is a retrospective study of 33 consecutive interbody spacers in 21 patients who underwent pre, intra, and postoperative measurement of the middle column to determine if this would lead to more precise restoration of middle column height and spacer fit. Scaled transparencies of the pre-operative simulation of angular correction and spacer geometry could be overlayed on the post-operative imaging studies. METHODS: Multiple Observers Measurement Testing. 33 consecutive vertebral levels requiring interbody spacers for multilevel deformities had middle column height pre and post operatively measured by 3 blinded observers. The preoperative and postoperative measurements were compared using a linear regression analysis and Pearson product-moment correlation. RESULTS: Pre and postop Measurement Testing: Thirty-three interbody devices in 21 patients had pre-operative planning, simulation of cage dimensions to determine the proper cage fit which would provide for the desired correction of foraminal height and sagittal balance parameters. The simulated preoperative plan overlayed the final post-operative radiograph and was a near-perfect match in 20 of 21 patients (95.2%). Multiple Observers Measurement Testing: A Pearson product-moment correlation was run between each individual's pre-op and post-op middle column measurements. There was a strong, positive correlation between pre-operative and post-operative measurements, which was statistically significant (r = 0.903, n = 33, P < 0.001). CONCLUSIONS: This consecutive series of 33 cases demonstrated the utility of measuring the preoperative middle column length in predicting the optimal height of the spacers, intervertebral disks, and posterior vertebral body height simultaneously restoring sagittal and coronal plane alignment.

Robot for Ligament Tensioning and Assessment of Spinal Stability.

STUDY DESIGN: An in vitro human cadaveric biomechanics study. OBJECTIVE: A proof-of-concept study to quantify whether or not differences in segmental mobility associated with spinal instability could be detected by a robotic distraction system. METHODS: Testing was performed in fresh human cadaveric tissue. A prototype Robotic Middle Column Distractor was attached unilaterally to the pedicles of L3-4. Distraction forces up to 150 N were applied first in the intact state, and following discectomy of L3-4. Motions were recorded by time-indexed visual and fluoroscopic images, and analyzed to measure actual motions achieved. Functions of the robot unit were monitored during the procedure and evaluated qualitatively. RESULTS: A difference of 2.5 mm in z-axis motion was detected at 150 N load between the intact and post-discectomy states. The robot coupled with the image analysis method was able to clearly detect the difference between the intact ("stable") and post-discectomy ("unstable") spine. Data analysis of fluoroscopic images taken during the procedure showed greater motion than perceived by the investigators from qualitative review of visual data. All monitored robot functions performed within design parameters without error. CONCLUSION: The study demonstrates the feasibility and utility of utilizing an intraoperative robotic distractor to measure the amount of spinal mobility present at a level. This could lead to an important clinical tool for both diagnostic functions as well as operative assist functions.

Accuracy of Robotic-Assisted Spinal Surgery-Comparison to TJR Robotics, da Vinci Robotics, and Optoelectronic Laboratory Robotics.

BACKGROUND: The optoelectronic camera source and data interpolation serve as the foundation for navigational integrity in the robotic-assisted surgical platform. The objective of the current systematic review serves to provide a basis for the numerical disparity that exists when comparing the intrinsic accuracy of optoelectronic cameras: accuracy observed in the laboratory setting versus accuracy in the clinical operative environment. It is postulated that there exists a greater number of connections in the optoelectronic kinematic chain when analyzing the clinical operative environment to the laboratory setting. This increase in data interpolation, coupled with intraoperative workflow challenges, reduces the degree of accuracy based on surgical application and to that observed in controlled musculoskeletal kinematic laboratory investigations. METHODS: Review of the PubMed and Cochrane Library research databases was performed. The exhaustive literature compilation obtained was then vetted to reduce redundancies and categorized into topics of intrinsic optoelectronic accuracy, registration accuracy, musculoskeletal kinematic platforms, and clinical operative platforms. RESULTS: A total of 147 references make up the basis for the current analysis. Regardless of application, the common denominators affecting overall optoelectronic accuracy are intrinsic accuracy, registration accuracy, and application accuracy. Intrinsic accuracy of optoelectronic tracking equaled or was less than 0.1 mm of translation and 0.1° of rotation per fiducial. Controlled laboratory platforms reported 0.1 to 0.5 mm of translation and 0.1°-1.0° of rotation per array. There is a huge falloff in clinical applications: accuracy in robotic-assisted spinal surgery reported 1.5 to 6.0 mm of translation and 1.5° to 5.0° of rotation when comparing planned to final implant position. Total Joint Robotics and da Vinci urologic robotics computed accuracy, as predicted, lies between these two extremes-1.02 mm for da Vinci and 2 mm for MAKO. CONCLUSIONS: Navigational integrity and maintenance of fidelity of optoelectronic data is the cornerstone of robotic-assisted spinal surgery. Transitioning from controlled laboratory to clinical operative environments requires an increased number of steps in the optoelectronic kinematic chain and error potential. Diligence in planning, fiducial positioning, system registration, and intraoperative workflow have the potential to improve accuracy and decrease disparity between planned and final implant position. The key determining factors limiting navigation resolution accuracy are highlighted by this Cochrane research analysis.

Middle-Column Gap Balancing and Middle-Column Mismatch in Spinal Reconstructive Surgery.

BACKGROUND: Middle-column gap balancing (MCGB) is a reference measurement of the path of the posterior longitudinal ligament (PLL), which is reconstructed under tension and balanced by the combined height of the posterior one-third of the vertebral bodies and the posterior one-third of the disks, including any intervening load-sharing spacers. This measurement allows for a comparison of the ligamentous component of the middle column (PLL) with the load-sharing components (posterior one-third vertebral body + disk ). This difference gives rise to a "middle-column mismatch," which provides a linear measurement of the redundancy of the ligaments and neural elements, which relates to the correct cage, spacer, or load-bearing height, which is optimized. METHODS: For phase 1 measurement testing, 24 consecutive patients underwent reliable flexion, extension, and neutral lateral radiographic studies with a calibrated marker. The anterior, middle, and posterior columns were measured using a custom software program capable of measuring the length of curved lines specifically written for this purpose. For phase 2 measurement testing, 21 consecutive patients undergoing surgery with multilevel deformities for cervical, thoracic, and lumbar procedures had MCGB height pre- and postoperatively measured by 3 blinded observers. The preoperative and postoperative measurements were compared using a linear regression analysis and Pearson product-moment correlation. RESULTS: In phase 1 measurement testing the flexion, extension, and neutral bending radiographs of spinal segments not containing deformities showed that the middle column had the most reliable measurements of spinal axial height both in the actual measurements of change from flexion to extension (mm) and in percentage of change. In phase 2 measurement testing, a Pearson product-moment correlation was run between each individual's pre- and postoperative middle-column measurements. There was a strong positive correlation between preoperative and postoperative measurements, which was statistically significant (r = 0.983, n = 21, P < .01). CONCLUSIONS: This consecutive series of 21 deformity patients demonstrated the utility of measuring the preoperative middle-column length in predicting the optimal height of the spacers and intervertebral disks, and posterior vertebral body height, simultaneously restoring sagittal and coronal plane alignment. Key points of this study include the following: (1) Spinal balance requires optimizing spinal height, which is a curved line in order to accommodate cervical lordosis, thoracic kyphosis, and lumbar lordosis. (2) Software programs can allow measurement of the preoperative curved circuitous course of the PLL and vertebral body misalignment; this curved length is predictive of the optimal postoperative middle-column height after spinal osteotomies and intervertebral spacer insertion. (3) All 3 dimensions are important to optimize in deformity correction: sagittal plane, coronal plane, and axial spinal height.

The SPOT GRADE: A New Method for Reproducibly Quantifying Surgical Wound Bleeding.

STUDY DESIGN: Benchtop model with prospective surgeon video testing. OBJECTIVE: To create a surface bleeding severity scale, the SPOT GRADE (SG), for quantitative assessment of target bleeding site (TBS) blood loss. This is of particular interest for spinal surgery due to epidural bleeding and an inability to use diathermy and radiofrequency cautery close to nerve roots. SUMMARY OF BACKGROUND DATA: A novel apparatus perfusable at known flow rates and simulating different sized wounds was used to create movies to educate surgeons on specific degrees of bleeding. METHODS: Training (36) and testing (108) videos were created using a benchtop apparatus employing different bleeding severities based on the six-level SG (none, minimal, mild, moderate, severe, and extreme) and TBS sizes (1, 10, and 50 cm). Fourteen surgeons in four specialties (cardiothoracic, abdominal, spine, and orthopedic lower extremity) were trained and tested to evaluate SG characteristics including inter-rater and intrarater reliability. RESULTS: The interclass correlation coefficient was estimated to be 0.89840 (95% confidence interval [CI]: 0.85771, 1), whereas the intraclass correlation coefficient was estimated to be 0.93673 (95% CI: 0.89603, 1). In 98% of cases (95% CI: 0.9736, 0.9927), surgeons correctly identified eligible bleeds for a future clinical trial (scores = 1, 2, or 3) and in 91% of cases (95% CI: 0.8895, 0.9344), surgeons correctly identified noneligible bleeds (scores = 4 or 5). In 98.6% of cases (95% CI: 0.9777, 0.9945), physicians correctly identified true hemostasis (score = 0). Based upon these data the probability of a physician rating a bleed incorrectly as hemostasis (score = 0) is estimated to be 1.51% (95% CI: 0.0061, 0.0363). CONCLUSION: This SG is reproducible and reliable providing a basis for educating surgeons on TBS blood loss. It appears to be a new standard for evaluating wound blood loss. LEVEL OF EVIDENCE: 2.

Five-Year Follow-Up of a Prospective, Randomized Trial Comparing Two Lumbar Total Disc Replacements.

STUDY DESIGN: This was a prospective, randomized, controlled, multicenter study. OBJECTIVE: The purpose of this study was to compare outcomes of two lumbar total disc replacements (TDRs) at 5-year follow-up and report results of serum ion level analysis in a subgroup of patients receiving a metal-on-metal implant. SUMMARY OF BACKGROUND DATA: Lumbar TDR has been compared with fusion in several randomized studies, finding TDR noninferior to fusion and superior on some measures. Receiving less attention has been comparing TDR devices. Additionally, there is concern about metal-on-metal implants, with little data available for spine devices. METHODS: The study included 204 patients receiving Kineflex-L (investigational) and 190 receiving CHARITÉ (control). Outcome measure included Oswestry Disability Index, visual analog pain scales (VAS), patient satisfaction, neurological status, complications, reoperations, and a composite success score. Radiographic assessment included range of motion, subsidence, and heterotrophic ossification. In 32 investigational patients, serum ion analysis was performed for cobalt and chromium. These values were compared with Medicines and Healthcare Products Regulatory Agency values to merit monitoring total hip replacement patients for potential wear problems. RESULTS: Mean Oswestry and VAS scores in both groups improved significantly by 6 weeks and remained improved during 5-year follow-up (Oswestry Disability Index, scores in both groups were approximately 60 preoperatively vs. 20 at 2- and 5-year follow-up; P < 0.01; VAS scores improved >50% by 6 weeks and remained significantly improved; P < 0.05). Approximately 11% of both groups underwent reoperation. Radiographic analysis found segmental range of motion decreased at 3 month, then increased through 24 months, and was maintained thereafter. Serum ion level analysis found the greatest mean value at any follow-up point was less than 20% of Medicines and Healthcare Products Regulatory Agency recommended minimum value to merit monitoring hip replacement patients. CONCLUSION: This prospective, randomized study comparing two TDRs found no significant differences in outcomes during 5-year follow-up. Both provided statistically significant improvements by 6 weeks that were maintained. This results support other studies. Serum ion levels in TDR patients were well below the recommended threshold levels to merit monitoring.

Long-term Outcomes of the US FDA IDE Prospective, Randomized Controlled Clinical Trial Comparing PCM Cervical Disc Arthroplasty With Anterior Cervical Discectomy and Fusion.

STUDY DESIGN: Prospective, multicenter, randomized clinical trial. OBJECTIVE: To evaluate the long-term safety and effectiveness of the PCM Cervical Disc compared with anterior cervical discectomy and fusion (ACDF) in treatment of patients with symptomatic single-level degenerative spondylosis between C3-C4 and C7-T1 with or without prior cervical fusion. SUMMARY OF BACKGROUND DATA: The 2-year results of the PCM Cervical Disc trial have been reported previously. The current study reports the long-term results of the same trial. METHODS: Patients with single-level cervical spondylosis and radiculopathy with or without myelopathy unresponsive to nonoperative treatment were enrolled. The per protocol patient sample at 5 years included 293 patients (163 PCM, 130 ACDF). Adverse events and secondary surgical procedures are reported on the cohorts through current follow-up, which include 110 patients (68 PCM, 42 ACDF) at 7 years. RESULTS: At 5 years postoperative, all patient-reported outcomes-neck and arm pain visual analogue scale score, neck disability index, and general health (36-Item Short Form Health Survey physical and mental component scores: physical component summary, mental component summary)-were significantly improved from baselines in both groups, and mean scores were significantly better in the PCM group for neck disability index (P=0.001), neck pain (P=0.002), general health (Pphysical component summary=0.014; Pmental component summary=0.004), and patient satisfaction (P=0.005). PCM patients trended toward fewer 2- to 7-year device-related serious adverse events (1/214, 0.5% PCM; 2/190, 1.1% ACDF) and secondary surgical procedures (7/211, 3.3% PCM; 14/290, 7.6% ACDF). Adjacent-level degeneration was radiographically more frequent after ACDF (33.1% PCM, 50.9% ACDF; P=0.006) and was the primary indication for the increase in late-term secondary surgical procedures after ACDF. CONCLUSION: The long-term results show good clinical outcomes after ACDF and PCM arthroplasty. PCM patients showed greater improvement in neck disability index and neck pain scores with a lower rate of radiographical adjacent-level degeneration and a trend toward fewer secondary surgical procedures. These data support PCM arthroplasty to be a viable and sustainable alternative to ACDF. LEVEL OF EVIDENCE: 1.

In vitro biomechanical evaluation of four fixation techniques for distractive-flexion injury stage 3 of the cervical spine.

PURPOSE: Anterior plate fixation has been reported to provide satisfactory results in cervical spine distractive flexion (DF) injuries stages 1 and 2, but will result in a substantial failure rate in more unstable stage 3 and above. The aim of this investigation was to determine the biomechanical properties of different fixation techniques in a DF-3 injury model where all structures responsible for the posterior tension band mechanism are torn. METHODS: The multidirectional three-dimensional stiffness of the subaxial cervical spine was measured in eight cadaveric specimens with a simulated DF-3 injury at C5-C6, stabilized with four different fixation techniques: anterior plate alone, anterior plate combined with posterior wire, transarticular facet screws, and a pedicle screw-rod construct, respectively. RESULTS: The anterior plate alone did not improve stability compared to the intact spine condition, thus allowing considerable range of motion around all three cardinal axes (p > 0.05). The anterior plate combined with posterior wire technique improved flexion-extension stiffness (p = 0.023), but not in axial rotation and lateral bending. When the anterior plate was combined with transarticular facet screws or with a pedicle screws-rod instrumentation, the stability improved in flexion-extension, lateral bending, and in axial rotation (p < 0.05). CONCLUSIONS: These findings imply that the use of anterior fixation alone is insufficient for fixation of the highly unstable DF-3 injury. In these situations, the use of anterior fixation combined with a competent posterior tension band reconstruction (e.g. transarticular screws or a posterior pedicle screws-rod device) improves segmental stability.

Comparison of 2 lumbar total disc replacements: results of a prospective, randomized, controlled, multicenter Food and Drug Administration trial with 24-month follow-up.

STUDY DESIGN: This was a prospective, randomized, controlled multicenter study with 24-month follow-up. OBJECTIVE: The purpose of this study was to evaluate the safety and efficacy in a Food and Drug Administration Investigation Device Exemption of a new lumbar total disc replacement (TDR) by comparing it to an earlier TDR approved for sale. SUMMARY OF BACKGROUND DATA: Randomized trials have reported TDR to produce results similar or superior to lumbar fusion. Results for various TDRs seem to be similar, but differences in study design and outcome measures pose challenges in definitively comparing devices. The purpose of this study was to perform a direct comparison of 2 lumbar TDRs in a prospective, randomized trial. METHODS: TDR was performed in 457 patients from 21 sites (261 patients in the investigational group (Kineflex-L Disc; metal-on-metal design anchored with keels, 204 randomized and 57 nonrandomized training cases), and 196 in the control group (CHARITE artificial disc; metal with polyethylene core with teeth for anchoring; 190 randomized and 6 nonrandomized training cases). All patients were treated nonoperatively for single-level symptomatic disc degeneration for at least 6 months prior to surgery. Perioperative data were collected. Clinical outcome data were collected prospectively, as approved by the Food and Drug Administration, through 24-month follow-up. Primary outcome measures used were the Oswestry Disability Index, visual analogue scales assessing pain, patient satisfaction, and reoperations. Success was defined to be at least 15-point improvements in Oswestry Disability Index scores, no reoperation, and no major adverse events. Radiographical measures included range of motion, disc space height, and assessment for device migration, subsidence, and fusion at the TDR level. RESULTS: There were no significant differences between the groups when comparing operative time, blood loss, or length of hospital stay. Both groups improved significantly on Oswestry Disability Index and visual analogue scale scores (P < 0.01) with no differences between the groups. Success rates were similar (68.1% investigational vs. 67.4% control). At 24-month follow-up, 94.1% of the investigational group and 91.9% of controls were satisfied with outcome. Reoperation was performed in 10.3% of the investigational group and 8.4% of the control group. CONCLUSION: This prospective, randomized, controlled study comparing 2 TDRs, the first to the authors' knowledge, found the devices produced very similar clinical outcomes. Both groups improved significantly by 6 weeks postoperatively and remained improved throughout follow-up with a high patient satisfaction rate.

Biomechanical and anatomical considerations in lumbar spinous process fixation--an in vitro human cadaveric model.

BACKGROUND CONTEXT: Although multiple mechanisms of device attachment to the spinous processes exist, there is a paucity of data regarding lumbar spinous process morphology and peak failure loads. PURPOSE: Using an in vitro human cadaveric spine model, the primary objective of the present study was to compare the peak load and mechanisms of lumbar spinous process failure with variation in spinous process hole location and pullout direction. A secondary objective was to provide an in-depth characterization of spinous process morphology. STUDY DESIGN: Biomechanical and anatomical considerations in lumbar spinous process fixation using an in vitro human cadaveric model. METHODS: A total of 12 intact lumbar spines were used in the current investigation. The vertebral segments (L1-L5) were randomly assigned to one of five treatment groups with variation in spinous process hole placement and pullout direction: (1) central hole placement with superior pullout (n=10), (2) central hole placement with inferior pullout (n=10), (3) inferior hole placement with inferior pullout (n=10), (4) superior hole placement with superior pullout (n=10), and (5) intact spinous process with superior pullout (n=14). A 4-mm diameter pin was placed through the hole followed by pullout testing using a material testing system. As well, the bone mineral density (BMD) (g/cm(3)) was measured for each segment. Data were quantified in terms of anatomical dimensions (mm), peak failure loads (newtons [N]), and fracture mechanisms, with linear regression analysis to identify relationships between anatomical and biomechanical data. RESULTS: Based on anatomical comparisons, there were significant differences between the anteroposterior and cephalocaudal dimensions of the L5 spinous process versus L1-L4 (p<.05). Statistical analysis of peak load at failure of the four reconstruction treatments and intact condition demonstrated no significant differences between treatments (range, 350-500 N) (p>.05). However, a significant linear correlation was observed between peak failure load and anteroposterior and cephalocaudal dimensions (p<.05). Correlation between BMD and peak spinous processes failure load was approaching statistical significance (p=.08). 30 of 54 specimens failed via direct pullout (plow through), whereas 8 of 54 specimens demonstrated spinous process fracture. The remaining cases failed via plow through followed by fracture of the spinous process (16 of 54; 29%). CONCLUSIONS: The present study demonstrated that variation in spinous process hole placement did not significantly influence failure load. However, there was a strong linear correlation between peak failure load and the anteroposterior and cephalocaudal anatomical dimensions. From a clinical standpoint, the findings of the present study indicate that attachment through the spinous process provides a viable alternative to attachment around the spinous processes. In addition, the anatomical dimensions of the lumbar spinous processes have a greater influence on biomechanical fixation than either hole location or BMD.

The Comprehensive Biomechanics and Load-Sharing of Semirigid PEEK and Semirigid Posterior Dynamic Stabilization Systems.

Alternatives to conventional rigid fusion have been proposed for several conditions related to degenerative disc disease when nonoperative treatment has failed. Semirigid fixation, in the form of dynamic stabilization or PEEK rods, is expected to provide compression under loading as well as an intermediate level of stabilization. This study systematically examines both the load-sharing characteristics and kinematics of these two devices compared to the standard of internal rigid fixators. Load-sharing was studied by using digital pressure films inserted between an artificially machined disc and two loading fixtures. Rigid rods, PEEK rods, and the dynamic stabilization system were inserted posteriorly for stabilization. The kinematics were quantified on ten, human, cadaver lumbosacral spines (L3-S1) which were tested under a pure bending moment, in flexion-extension, lateral bending, and axial rotation. The magnitude of load transmission through the anterior column was significantly greater with the dynamic device compared to PEEK rods and rigid rods. The contact pressures were distributed more uniformly, throughout the disc with the dynamic stabilization devices, and had smaller maximum point-loading (pressures) on any particular point within the disc. Kinematically, the motion was reduced by both semirigid devices similarly in all directions, with slight rigidity imparted by a lateral interbody device.

Epidural application of spinal instrumentation particulate wear debris: a comprehensive evaluation of neurotoxicity using an in vivo animal model.

OBJECT: The introduction and utilization of motion-preserving implant systems for spinal reconstruction served as the impetus for this basic scientific investigation. The effect of unintended wear particulate debris resulting from micromotion at spinal implant interconnections and bearing surfaces remains a clinical concern. Using an in vivo rabbit model, the current study quantified the neural and systemic histopathological responses following epidural application of 11 different types of medical-grade particulate wear debris produced from spinal instrumentation. METHODS: A total of 120 New Zealand White rabbits were equally randomized into 12 groups based on implant treatment: 1) sham (control), 2) stainless steel, 3) titanium alloy, 4) cobalt chromium alloy, 5) ultra-high molecular weight polyethylene (UHMWPe), 6) ceramic, 7) polytetrafluoroethylene, 8) polycarbonate urethane, 9) silicone, 10) polyethylene terephthalate, 11) polyester, and 12) polyetheretherketone. The surgical procedure consisted of a midline posterior approach followed by resection of the L-6 spinous process and L5-6 ligamentum flavum, permitting interlaminar exposure of the dural sac. Four milligrams of the appropriate treatment material (Groups 2-12) was then implanted onto the dura in a dry, sterile format. All particles (average size range 0.1-50 µm in diameter) were verified to be endotoxin free prior to implantation. Five animals from each treatment group were sacrificed at 3 months and 5 were sacrificed at 6 months postoperatively. Postmortem analysis included epidural cultures and histopathological assessment of local and systemic tissue samples. Immunocytochemical analysis of the spinal cord and overlying epidural fibrosis quantified the extent of proinflammatory cytokines (tumor necrosis factor-α, tumor necrosis factor-ß, interleukin [IL]-1α, IL-1ß, and IL-6) and activated macrophages. RESULTS: Epidural cultures were negative for nearly all cases, and there was no evidence of particulate debris or significant histopathological changes in the systemic tissues. Gross histopathological examination demonstrated increased levels of epidural fibrosis in the experimental treatment groups compared with the control group. Histopathological evaluation of the epidural fibrous tissues showed evidence of a histiocytic reaction containing phagocytized inert particles and foci of local inflammatory reactions. At 3 months, immunohistochemical examination of the spinal cord and epidural tissues demonstrated upregulation of IL-6 in the groups in which metallic and UHMWPe debris were implanted (p < 0.05), while macrophage activity levels were greatest in the stainless-steel and UHMWPe groups (p < 0.05). By 6 months, the levels of activated cytokines and macrophages in nearly all experimental cases were downregulated and not significantly different from those of the operative controls (p > 0.05). The spinal cord had no evidence of lesions or neuropathology. However, multiple treatments in the metallic groups exhibited a mild, chronic macrophage response to particulate debris, which had diffused intrathecally. CONCLUSIONS: Epidural application of spinal instrumentation particulate wear debris elicits a chronic histiocytic reaction localized primarily within the epidural fibrosis. Particles have the capacity to diffuse intrathecally, eliciting a transient upregulation in macrophage/cytokine activity response within the epidural fibrosis. Overall, based on the time periods evaluated, there was no evidence of an acute neural or systemic histopathological response to the materials included in the current project.

A prospective, randomized, controlled clinical investigation comparing PCM cervical disc arthroplasty with anterior cervical discectomy and fusion. 2-year results from the US FDA IDE clinical trial.

STUDY DESIGN: Prospective, multicenter, randomized Food and Drug Administration approved investigational device exemption clinical trial. OBJECTIVE: To evaluate the safety and effectiveness of the PCM Cervical Disc compared with anterior cervical discectomy and fusion (ACDF) in the treatment of patients with degenerative spondylosis and neurological symptoms at 1 level between C3-C4 and C7-T1. SUMMARY OF BACKGROUND DATA: Cervical disc arthroplasty in the treatment of symptomatic cervical spondylosis has been studied in other series. The PCM Cervical Disc is a nonconstrained motion-sparing alternative to ACDF. METHODS: Patients 18 to 65 years of age with single-level symptomatic cervical spondylosis with radiculopathy and/or myelopathy unresponsive to nonoperative treatment were enrolled, including patients with prior nonadjacent or adjacent single-level fusions. The per-protocol patient sample at 2 years included 342 patients (189 PCM, 153 ACDF). Longitudinal outcomes were comparatively evaluated. RESULTS: At 2 years postoperatively, clinical measures-neck and arm pain visual analogue scale, Neck Disability Index (NDI), SF-36, and neurological status-were significantly improved from preoperative baselines in both groups. Mean NDI score at 2 years was significantly lower in PCM group (P = 0.029). There were no statistical differences between groups in rates of surgery-related serious adverse events (5.6% PCM, 7.4% ACDF) or secondary surgical procedures (5.2% PCM, 5.4% ACDF). Patients with PCM reported lower dysphagia scores (8.8/100 vs. 12.1/100; P = 0.045) and higher patient satisfaction (82.8/100 vs. 81.4/100). Overall success, a composite endpoint including minimum 20% NDI improvement, no major complications, no neurological worsening, no secondary surgical procedures, and meeting radiographical criteria of motion for PCM and fusion for ACDF, was significantly greater in the PCM group (75.1% vs. 64.9%; P = 0.020). CONCLUSION: The treatment of symptomatic single-level cervical spondylosis with PCM achieves clinical outcomes that are at least equivalent to ACDF while maintaining motion. At 2 years, patients with PCM had lower NDI scores, statistically lower rate of prolonged dysphagia, greater patient satisfaction, and superior overall success.

Multilevel extreme lateral interbody fusion (XLIF) and osteotomies for 3-dimensional severe deformity: 25 consecutive cases.

BACKGROUND: This is a retrospective review of 25 patients with severe lumbar nerve root compression undergoing multilevel anterior retroperitoneal lumbar interbody fusion and posterior instrumentation for deformity. The objective is to analyze the outcomes and clinical results from anterior interbody fusions performed through a lateral approach and compare these with traditional surgical procedures. METHODS: A consecutive series of 25 patients (78 extreme lateral interbody fusion [XLIF] levels) was identified to illustrate the primary advantages of XLIF in correcting the most extreme of the 3-dimensional deformities that fulfilled the following criteria: (1) a minimum of 40° of scoliosis; (2) 2 or more levels of translation, anterior spondylolisthesis, and lateral subluxation (subluxation in 2 planes), causing symptomatic neurogenic claudication and severe spinal stenosis; and (3) lumbar hypokyphosis or flat-back syndrome. In addition, the majority had trunks that were out of balance (central sacral vertical line ≥2 cm from vertical plumb line) or had sagittal imbalance, defined by a distance between the sagittal vertical line and S1 of greater than 3 cm. There were 25 patients who had severe enough deformities fulfilling these criteria that required supplementation of the lateral XLIF with posterior osteotomies and pedicle screw instrumentation. RESULTS: In our database, with a mean follow-up of 24 months, 85% of patients showed evidence of solid arthrodesis and no subsidence on computed tomography and flexion/extension radiographs. The complication rate remained low, with a perioperative rate of 2.4% and postoperative rate of 12.2%. The lateral listhesis and anterior spondylolisthetic subluxation were anatomically reduced with minimally invasive XLIF. The main finding in these 25 cases was our isolation of the major indication for supplemental posterior surgery: truncal decompensation in patients who are out of balance by 2 cm or more, in whom posterior spinal osteotomies and segmental pedicle screw instrumentation were required at follow up. No patients were out of sagittal balance (sagittal vertical line <3 cm from S1) postoperatively. Segmental instrumentation with osteotomies was also more effective for restoration of physiologic lumbar lordosis compared with anterior stand-alone procedures. CONCLUSIONS: This retrospective study supports the finding that clinical outcomes (coronal/sagittal alignment) improve postoperatively after minimally invasive surgery with multilevel XLIF procedures and are improved compared with larger extensile thoracoabdominal anterior scoliosis procedures.