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BackgroundBleb presence in intracranial aneurysms (IAs) is a known indication of instability and vulnerability.ObjectiveTo develop and evaluate predictive models of bleb development in IAs based on hemodynamics, geometry, anatomical location, and patient population.MethodsCross-sectional data (one time point) of 2395 IAs were used for training bleb formation models using machine learning (random forest, support vector machine, logistic regression, k-nearest neighbor, and bagging). Aneurysm hemodynamics and geometry were characterized using image-based computational fluid dynamics. A separate dataset with 266 aneurysms was used for model evaluation. Model performance was quantified by the area under the receiving operating characteristic curve (AUC), true positive rate (TPR), false positive rate (FPR), precision, and balanced accuracy.ResultsThe final model retained 18 variables, including hemodynamic, geometrical, location, multiplicity, and morphology parameters, and patient population. Generally, strong and concentrated inflow jets, high speed, complex and unstable flow patterns, and concentrated, oscillatory, and heterogeneous wall shear stress patterns together with larger, more elongated, and more distorted shapes were associated with bleb formation. The best performance on the validation set was achieved by the random forest model (AUC=0.82, TPR=91%, FPR=36%, misclassification error=27%).ConclusionsBased on the premise that aneurysm characteristics prior to bleb formation resemble those derived from vascular reconstructions with their blebs virtually removed, machine learning models can identify aneurysms prone to bleb development with good accuracy. Pending further validation with longitudinal data, these models may prove valuable for assessing the propensity of IAs to progress to vulnerable states and potentially rupturing.

Background: Implanting hardware into surgical sites increases the rate of infection associated with these sites. Without novel efforts to reduce this rate of infection, we can expect to see an incr...

To investigate the biomechanical changes in the development of scoliosis due to intervertebral disc and facet joint degeneration.We enrolled 39 cases of fresh-frozen lumbar spine specimens and underwent CT scanning and 3D reconstruction. An Osirix Dicom imaging system was to assess the degeneration of the intervertebral disc and facet joints, and mechanical loading was conducted using a spine mechanical instrument with the frequency set at plus/minus 7.5 NM, 0.005 Hz. Range of motion (ROM) and neutral zone (NZ) of 39 cadaveric lumbar spines were tested.Degeneration existed in all 39 cases of the lumbar specimens: the Cobb angle10° in 5 cases (degenerative scoliosis (DS) group), between 3° and 10° in 9 cases (pre-degenerative scoliosis (PS) group) and3° in 25 cases (no scoliosis (NS) group). The axial torsion (AT) range of motion (ROMThe AT correlated with intervertebral disc and facet joint degeneration, which might be a mechanic factor in the occurrence and development of degenerative scoliosis.

Objective: Intraoperative neurophysiological monitoring (IONM) is the use of electrophysiological methods during certain high-risk surgeries to assess the functional integrity of nerves in real time and alert the surgeon to prevent damage. However, the efficiency of IONM in current practice is limited by latency of verbal communications, inter-rater variability, and the subjective manner in which electrophysiological signals are described. Methods: In an attempt to address these shortcomings, we investigate automated classification of free-running electromyogram (EMG) waveforms during IONM. We propose a hybrid model with a convolutional neural network (CNN) component and a long short-term memory (LSTM) component to better capture complicated EMG patterns under conditions of both electrical noise and movement artifacts. Moreover, a preprocessing pipeline based on data normalization is used to handle classification of data from multiple subjects. To investigate model robustness, we also analyze models under different methods for processing of artifacts. Results: Compared with several benchmark modeling methods, CNN-LSTM performs best in classification, achieving accuracy of 89.54% and sensitivity of 94.23% in cross-patient evaluation. Conclusion: The CNN-LSTM model shows promise for automated classification of continuous EMG in IONM. Significance: This technique has potential to improve surgical safety by reducing cognitive load and inter-rater variability.

Background: Expandable cages that allow for bidirectional expansion, in both height and width, may offer benefits over traditional expandable cages or static cages. Effective stiffness must also be considered, as implants with exceedingly high stiffness may increase subsidence risk and reduce graft loading. Methods: A retrospective case series of 7 patients were assessed with computed tomography (CT) scan at the final 1-year follow-up to evaluate the interbody fusion and configuration of the expandable cage related to the endplates within the intervertebral space. CT scans were reformatted using cage9s tantalum markers as fiducials for single-plane orientation for each intervertebral cage. Device height and width at maximum in situ expansion was measured at its anterior and posterior aspects to evaluate implant deformation. The new bone volume within each cage was measured from the same CT scan data sets and by the Bridwell classification of interbody fusion. Results: The average difference between medial and lateral height measurements was 1.82 mm (±1.08) at the device9s anterior aspect and 1.41 mm (±0.98) at the posterior aspect. The average difference between medial and lateral heights was 18.55% (±9.34) anteriorly and 15.49% (±9.24) posteriorly. There was a successful fusion in all 7 patients, as evidenced by measurable bone volume in the center of each interbody cage with an average of 586.42 mm3 (±237.06). Conclusion: The authors demonstrated the feasibility of successfully using bidirectionally expandable multimaterial cages to achieve interbody fusion. These composite open-architecture cages were found to conform to each patient9s endplate configuration. The authors9 observations support the concept of material selection impacting the effective construct stiffness. The design investigated by the authors provided sufficient anterior column support and successful fusion in all patients. Level of Evidence: 4.

BACKGROUND: Expandable devices for transforaminal or posterior lumbar interbody fusion (TLIF and PLIF, respectively) may enable greater restoration of disc height, foraminal height, and stability within the interbody space than static spacers. Medial-lateral expansion may also increase stability and resistance to subsidence. This study evaluates the clinical and radiographic outcomes from early experience with a bidirectional expandable device. METHODS: This was a retrospective analysis of a continuous series of patients across 3 sites who had previously undergone TLIF or PLIF surgery with a bidirectional expandable interbody fusion device (FlareHawk, Integrity Implants, Inc) at 1 or 2 contiguous levels between L2 and S1. Outcomes included the Oswestry Disability Index (ODI), a visual analog scale (VAS) for back pain or leg pain, radiographic fusion by 1 year of follow-up, subsidence, device migration, and adverse events (AE). RESULTS: There were 58 eligible patients with radiographs for 1-year fusion assessments and 45 patients with ODI, VAS back pain, or VAS leg pain data at baseline and a mean follow-up of 4.5 months. The ODI, VAS back pain, and VAS leg pain scores improved significantly from baseline to final follow-up, with mean improvements of 14.6 ± 19.1, 3.4 ± 2.6, and 3.9 ± 3.4 points (P < .001 for each), respectively. In addition, 58% of patients achieved clinically significant improvements in ODI, 76% in VAS back pain, and 71% in VAS leg pain. By 1 year, 96.6% of patients and 97.4% of levels were considered fused. There were zero cases of device subsidence and 1 case of device migration (1.7%). There were zero device-related AEs, 1 intraoperative dural tear, and 3 subsequent surgical interventions. CONCLUSIONS: The fusion rate, improvements in patient-reported outcomes, and the AEs observed are consistent with those of other devices. The bidirectional expansion mechanism may provide other important clinical value, but further studies will be required to elucidate the unique advantages. LEVEL OF EVIDENCE: 4.

Background: Bidirectional expandable designs for lumbar interbody fusion cages are the latest iteration of expandable spacers employed to address some of the common problems inherent to static interbody fusion cages. Objective: To describe the rationales for contemporary bidirectional, multimaterial expandable lumbar interbody fusion cage designs to achieve in situ expansion for maximum anterior column support while decreasing insertion size during minimal-access surgeries. Methods: The authors summarize the current concepts behind expandable spinal fusion open architecture cage designs focusing on advanced minimally invasive spinal surgery techniques, such as endoscopy. A cage capable of bidirectional expansion in both height and width to address constrained surgical access problems was of particular interest to the authors while they analyzed the relationship between implant material stiffness and geometric design regarding the risk of subsidence and reduced graft loading. Conclusions: Biomechanical advantages of new bidirectional, multimaterial expandable interbody fusion cages allow insertion through minimal surgical access and combine the advantages of proven device configurations and advanced material selection. The final construct stiffness is sufficient to provide immediate anterior column support while accommodating reduced sizes required for minimally invasive surgery applications. Level of Evidence: 7.

Background A number of minimally invasive sacroiliac (SI) joint fusion solutions for placing implants exist, with reduced post-operative pain and improved outcomes compared to open procedures. The objective of this study was to compare two MIS SI joint fusion approaches that place implants directly across the joint by comparing the ilium and sacrum bone characteristics and SI joint separation along the implant trajectories. Methods Nine cadaveric specimens (n = 9) were CT scanned and the left and right ilium and sacrum were segmented. The bone density, bone volume fraction, and SI joint gap distance were calculated along lateral and posterolateral trajectories and compared using analysis of variance between the two orientations. Results Iliac bone density, indicated by the mean Hounsfield Unit, was significantly greater for each lateral trajectory compared to posterolateral. The volume of cortical bone in the ilium was greater for the middle lateral trajectory compared to all others and for the top and bottom lateral trajectories compared to both posterolateral trajectories. Cortical density was greater in the ilium for all lateral trajectories compared to posterolateral. The bone fraction was significantly greater in all lateral trajectories compared to posterolateral in the ilium. No differences in cortical volume, cortical density, or cancellous density were found between trajectories in the sacrum. The ilium was significantly greater in density compared with the sacrum when compared irrespective of trajectory (p < 0.001). The posterolateral trajectories had a significantly larger SI joint gap than the lateral trajectories (p < 0.001). Conclusion Use of the lateral approach for minimally invasive SI fusion allows the implant to interact with bone across a significantly smaller joint space. This interaction with increased cortical bone volume and density may afford better fixation with a lower risk of pull-out or implant loosening when compared to the posterolateral approach.

Study Design: An in vitro biomechanics study. Objective: To evaluate the efficacy of triangular titanium implants in providing mechanical stabilization to a sacroiliac joint with primary and revision sized implants. Methods: Ten lumbopelvic cadaveric specimens were tested in 4 stages: intact, pubic symphysis sectioned, primary, and simulated revision. Primary treatment was performed using 3 laterally placed triangular titanium implants. To simulate revision conditions before and after bone ingrowth and ongrowth on the implants, 7.5-mm and 10.75-mm implants were randomly assigned to one side of each specimen during the simulated revision stage. A 6 degrees of freedom spinal loading frame was used to load specimens in 4 directions: flexion extension, lateral bending, axial torsion, and axial compression. Biomechanical evaluation was based on measures of sacroiliac joint rotational and translational motion. Results: Both primary and revision implants showed the ability to reduce translational motion to a level significantly lower than the intact condition when loaded in axial compression. Simulated revision conditions showed no statistically significant differences compared with the primary implant condition, with the exception of flexion-extension range of motion where motions associated with the revised condition were significantly lower. Comparison of rotational and translation motions associated with the 7.5- and 10.75-mm implants showed no significant differences between the treatment conditions. Conclusions: These results indicate that implantation of laterally placed triangular titanium implants significantly reduces the motion of a sacroiliac joint using either the primary and revision sized implants. No statistically significant differences were detected when comparing the efficacy of primary, 7.5-mm revision, or 10.75-mm revision implants.

Background Polyetheretherketone (PEEK), and more recently titanium-coated PEEK, have been given serious consideration as biomaterial design choices for spinal interbody implants. Shortcomings in these materials necessitate further innovation into materials research, for example, on polyetherketoneketone (PEKK). Common complications such as surface delamination (as with titanium coating) and lack of bone apposition (as with PEEK) indicate the need for a new material that inherently displays preferable bone growth characteristics without sacrificing structural integrity. Purpose To compare three biomaterials with respect to their osseointegrative capacity. Study Design Evaluate the in vivo material characteristics of three separate biomaterials in an ovine bone defect model: PEEK, titanium-coated PEEK (Ti-coated PEEK), and 3D printed PEKK. Biomechanical, histological and radiographic testing was the basis for evaluation and material characterization. Methods Eight ovine specimens were implanted with one of each of the three types of biomaterials tested in both left and right epicondyles using a femoral bone defect model, and were sacrificed at 8 and 16 weeks. Implants were then analyzed using a push-out method, histological staining, and various radiographic tests. Industry funding was provided for the completion of this research study, followed by an independent third party review of all relevant data for publication. Results PEKK implants demonstrated bone ingrowth, no radiographic interference, no fibrotic tissue membrane formation, significant increase in bony apposition over time, and significantly higher push-out strength compared to standard PEEK. The PEKK implant displayed bone growth characteristics comparable to Ti-coated PEEK with significant improvements in implant integrity and radiographic properties. Conclusion This study found that PEKK displayed preferable characteristics when compared to PEEK and Ti-coated PEEK, and is therefore a potential alternative to their use.

Background: Effective triage - directing patients with low back pain to appropriate treatment or correct referral - is fundamental to quality care. Without guidelines, a physician's initial decision may lead to unnecessary investigation, unneeded intervention or unwarranted consultation.Methods: To compare the functional outcomes of patients triaged by a classification based on clinical presentation with those of patients selected at the clinicians’ discretion, an insurance-owned hospital network employed forty-seven specially-trained physical therapists, working within participating primary care practices, to classify low back pain patients into specific Patterns of Pain. Between October 2017 and April 2019, the primary care physicians used this classification, derived entirely from the patient's history and physical examination, to direct subsequent treatment for 260 consecutive low back pain patients. Patients with systemic symptoms, recent substantial trauma or non-mechanical diagnoses indicative of spinal infections or possible malignancy were excluded. Functional outcome measures were spinal imaging, opioid use, length of treatment and number of visits, back-related unplanned care, frequency of spinal surgery and back-related episode cost. These were compared with a control group of 256 propensity-matched patients and, for assessing the financial impact, with a historic cohort of 111 previously treated, non-classified patients.Results: Spinal imaging: study group 24.5%; controls 42.2% (P< .001). Narcotic use: study group 4.6%; controls 13.3% (P< .001). Treatment length: study group 62.2 days; controls 74.5 days (P=.10). Treatment visits: study group 1528 visits; controls 2,046 visits (P=.003). Unplanned care: study group 1.9%; controls 12.8% (P< .001). Spine surgery: study group 15.4%; controls 26.2% (P=.005). Episode cost: study group $1453; controls $2334 (P=.005).Conclusions: A well-defined clinically-based triage system produced meaningful reductions in imaging, opioid use, treatment duration, unplanned interventions, surgery and cost of care.

The two most popular models used in anatomical training for residents, clinicians, or surgeons are cadavers and sawbones. The former is extremely costly and difficult to attain due to cost, ethical implications, and availability, while the latter is said to not have the same tactile fidelity or mechanical properties as human bone. This study examined the potential use of 3D-printed phantoms to emulate cadaveric, human vertebrae, in hopes of acting as a future use over cadavers. In so doing, we developed 3D-printed MedPhantom®, with the intended use to offer similar tactile feel, mechanical characteristics, and visual appearance as human bone. In order to quantify tactility, a mechanical test was developed where a 5-mm diameter diamond-coated bur spinning at 75,000 RPM swept across the specimens while continuously recording the resultant forces (N) and moments (N-cm), The bur sweep motion is common in orthopedic surgery and neurosurgery. Since most 3D-prints do not offer internal, trabecular structure similar to bone, an algorithm was written to create a stochastic framework of internal mesh to mimic cancellous bone within an STL (stereolithography) file. The ranges of mesh parameters were chosen after several visits with the neurosurgeons participating in the project. In order to quantify structural combinations of wall thickness, gap sizes, and varying cylindrical radii within a print, 1000 RPM compression test with a 5-mm diamond-coated bur was performed with resultant forces (N). Two sample t-test shows statistical significance that samples are not equal to the vertebrae (p

BACKGROUND CONTEXT Osteoimmunology, the study of the relationship between the musculoskeletal system and immune system, has emerged as an important consideration in biomaterial research. Based on the current understanding of the immune system, both the innate and adaptive components, a combination of tests on current design materials in spinal implant devices may help understand potential clinical complications and thus reduce the potential adverse events associated with specific design materials. Studies involving macrophages facilitate the understanding behind the mechanism of fibrous capsule formation anecdotally reported with PEEK implants. The cell studies in combination with larger animal studies help understand the importance of appropriate choice in materials. The combination of results from three separate kinds of studies would potentially weave a better understanding of PEEK fibrous encapsulation around retrieved implanted PEEK devices. It was hypothesized that IL-1β, IL-6, and TNF-α cytokine expression levels results would be different for PEEK and a novel zeolite filled PEEK composite (ZFuze, DiFusion Technologies). PURPOSE The objective of this study was to compare the activation state of macrophages, as determined by selected gene and protein expression profiles, following in vitro exposure to PEEK zeolite and PEEK based spinal interbody devices. Similarly, the immune response measured at the local sites in a large animal study was also studied in order to determine the inflammatory response at the local implanted site. STUDY DESIGN/SETTING In vitro cell culture study in combination with a large animal functional cervical spine model. The large animal model included two instrumented levels with one level implanted with a PEEK interbody cervical cage and the alternate level implanted with a PEEK zeolite composite interbody device. OUTCOME MEASURES The levels of inflammatory cytokines interleukin-1 beta (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-α) were quantified in muscle tissue directly anterior to the index level based on the intensity of fluorescence in each slide. For cell-based study, the presence of cytokines was noted as comparable, increased, or slightly increased compared to macrophages of the M0 phenotype. METHODS Mature macrophages were exposed to the following treatments for 24 hours: complete media (M0 control), 20 ng/ml IFN-γ and 100 ng/mL lipopolysaccharide LPS (M1 control), 20 ng/mL interleukin IL-4 (M2 control). For the cytokine challenge study, cells were exposed for 6 hours to 20 ng/ml IFN-γ and 100 ng/mL LPS, washed and then placed in 10% FBS 1% P/S DMEM for 24 hours. After the incubation period at 37°C, cells were washed with sterile PBS and fixed for 30 minutes with 2% paraformaldehyde (PFA) for immunolabeling, or harvested with TRIzol lysis reagent for RNA assessment, respectively. RNA were isolated from 8 × 106 cells using the RNeasy Mini Kit according to the manufacturer's instructions. Isolated RNA concentration was subsequently determined using a NanoDrop spectrophotometer. Reverse transcription of 500 ng of RNA to cDNA were performed via a high-capacity reverse transcriptase kit according to the manufacturer's instructions. SYBR Green gene expression assays were used to determine the relative expression levels of: gapdh, inos, tnf-α, arg1, fizz1, il1β, il6, and gapdh. Skeletally mature Montadale sheep were implanted with PEEK and PEEK zeolite interbody cages at the C2-C3 and C4-C5 index levels and survived to 12 or 26 weeks, as approved by the IACUC Committee. At the time of sacrifice index level functional spinal units (FSU), major organs, lymph nodes, and muscle tissues were collected. Muscle tissue from the spinal column at the operative level was collected and used for a quantitative analysis of various inflammatory markers using immunohistochemistry techniques. Slides were prepared from these spinal tissue samples as well as positive and negative control tissues. Lymph nodes and muscle tissues distant from the surgical site were collected during necropsy and served as the positive and negative controls respectively. RESULTS In vivo expression was normalized to represent a percentage of intensity measured in the negative control. Independent T-test was performed to compare cytokine expression at both 12 and 26 week time points. Expression of IL1-β was found to be significantly lower in PEEK zeolite samples at 12 weeks (M=0.23, SD=0.28) than standard PEEK samples at 12 weeks (M=1.37, SD=0.49) t(8)=-4.582, p=0.002. PEEK zeolite composite samples were also found to have significantly lower IL1-β expression at 26 weeks (M=0.02, SD=0.009) when compared to standard PEEK samples (M=0.60, SD=0.23) t(11)=-6.667, p CONCLUSIONS The macrophage study in combination with larger animal studies help understand the importance of appropriate choice in design materials. With the above strategies in mind, it was possible to conduct in vitro and/or in vivo studies that comprehensively evaluate the macrophage response to a biomaterial. Results of the macrophage study suggest that PEEK-zeolite, but not PEEK, increases the expression at the translational level of an M2-associated marker, Fizz1. Results of protein expression data support the hypothesis that PEEK zeolite promotes a pro-repair M2-like macrophage phenotype. Similarly, the ovine study showed a novel PEEK zeolite composite elicits reduced pro-inflammatory cytokine excretion when compared to standard PEEK implants. Specifically, the tissues surrounding PEEK-zeolite composite implants had significantly lower levels of IL1-β and IL-6. These results may explain the increased bone growth observed in the pilot rabbit study and suggest the new material is well suited for clinical application including spinal implants that benefit from host bone implant apposition. FDA DEVICE/DRUG STATUS Unavailable from authors at time of publication.

Background Interbody fusion cages with integrated fixation components have become of interest due to their ability to provide enhanced post-operative stability and mitigate device migration. A recently approved anterior lumbar interbody fusion cage with integrated fixation anchors has yet to be compared in vitro to a standard polyetheretherketone cage when used in combination with an interspinous process clamp. Methods Twelve human cadaveric lumbar segments were implanted at L4–L5 with a Solus interbody cage (n = 6) or standard polyetheretherketone cage (n = 6) following Intact testing and discectomy. Each cage was subsequently evaluated in all primary modes of loading after supplementation with the following posterior constructs: interspinous process clamp, bilateral transfacet screws, unilateral transfacet screw with contralateral pedicle screws, and bilateral pedicle screws. Range of motion results were normalized to Intact, and a two-way mixed analysis of variance was utilized to detect statistical differences. Findings The Solus cage in combination with all posterior constructs provided significant fixation compared to Intact in all loading conditions. The polyetheretherketone cage also provided significant fixation when combined with all screw based treatments, however when used with the interspinous process clamp a significant reduction was not observed in lateral bending or axial torsion. Interpretation Interbody cages with integrated fixation components enhance post-operative stability within the intervertebral space, thus affording clinicians the potential to utilize less invasive methods of posterior stabilization when seeking circumferential fusion. Interspinous process clamps, in particular, may reduce peri-operative and post-operative comorbidities compared to screw based constructs. Further study is necessary to corroborate their effectiveness in vivo .

Sacroiliac joint (SIJ) dysfunction and its surgical treatment remain a controversial topic in spine surgery. Determining success after SIJ fusion may be difficult due to preexisting back pain, lumbar fusion (LF), and functional disability. We examine the utility of Oswestry Disability Index (ODI) as a measure of clinical outcomes after minimally invasive SIJ fusion. A retrospective review of 24 patients with at least 12- months follow-up. Patients were divided into two groups based on presence of previous LF. Their post-operative ODI was compared with overall satisfaction, pain reduction, and return to work status. No difference in demographics was found in patients with and without prior LF with 92% of patients reporting lower post-operative pain and 96% being satisfied. Presence of LF did not show any statistically significant differences in pain or satisfaction. However, patient with prior LF reported lower ODI than those without LF at 1-year post-operatively (P=0.015). Postoperative ODI may give a falsely pessimistic impression of outcomes in SIJ fusion patients with prior LF, and its use and limitations should be carefully considered in future studies.

While low back pain is one of the most prevalent, if not the most prevalent reasons for visits to physicians, a majority of patients with low back pain cannot be given a definitive diagnosis. The current standard of care for function assessment of the lumbar spine focuses on uncontrolled patient directed motion which results in increased inter-patient variability and diagnostic misclassifications. The purpose of the current paper is to compare the measurement variability of lumbar spine motion when diagnosed using measurements of intervertebral motion taken from standard flexion extension bending radiographs (FE) between uncontrolled and controlled motion and to assess the rate of diagnostic misclassification errors (false positives and false negatives) in the detection of lumbar instability. 109 patients (57 asymptomatic, 52 symptomatic) were consented in the prospective investigation. The research was designed to compare studies involving FE to controlled motion bending radiographs (CCBR) using the Vertebral Motion Analysis (VMA) within the same patient. Measurement variability was determined by the mean and standard deviation of intervertebral rotation when evaluated by 9 independent observers evaluating each of the 109 patients FE and CCBR. The resulting standard deviation of the intervertebral rotation determinations was used as the measure of variability. Sensitivity (true positive rate) and specificity (true negative rate), were constructed using asymptomatic individuals and symptomatic patients in order to determine true positive (TP) and true negative (TN) appointments. The analysis was compared to known threshold of 25° (IVR) to determine the rates of false negatives (FN) and false positive (FP) rates. Sensitivity and specificity were calculated as TP/(TP/FN) and TN/(FP+TN), respectively. There was statistical greater measurement variability in intervertebral rotation in FE when compared to CCBR (both standing and lying). When comparing measurement variability between FE and CCBR, results indicate between a 26% to 46% decrease in measurement variability under CCBR compared to FE. These findings are consistent across asymptomatic and symptomatic patients. Sensitivity measures were 6.2% (VMA 12.6%, FE 6.4%) greater in the VMA test compared to the FE. Specificity measures were 8.4% (VMA 99.1%, FE 90.7%) greater in the VMA test compared to the FE. The current standard of care for functional testing of the lumbar spine utilizes uncontrolled FE with a manual data evaluation process. Recent developments in using computerized imaging processes has improved, however there remains variability in patient bending due to the self-selected rate and position of the bending. CCBR results in a significant reduction in measurement variability of intervertebral rotation measurements. Reducing measurement variability would be expected to improve the efficacy rates of surgeries indicated for these conditions.

Object Deep brain stimulation (DBS) of the lateral hypothalamic area (LHA) has been suggested as a potential treatment for intractable obesity. The authors present the 2-year safety results as well as early efficacy and metabolic effects in 3 patients undergoing bilateral LHA DBS in the first study of this approach in humans. Methods Three patients meeting strict criteria for intractable obesity, including failed bariatric surgery, underwent bilateral implantation of LHA DBS electrodes as part of an institutional review board– and FDA-approved pilot study. The primary focus of the study was safety; however, the authors also received approval to collect data on early efficacy including weight change and energy metabolism. Results No serious adverse effects, including detrimental psychological consequences, were observed with continuous LHA DBS after a mean follow-up of 35 months (range 30–39 months). Three-dimensional nonlinear transformation of postoperative imaging superimposed onto brain atlas anatomy was used to confirm and study DBS contact proximity to the LHA. No significant weight loss trends were seen when DBS was programmed using standard settings derived from movement disorder DBS surgery. However, promising weight loss trends have been observed when monopolar DBS stimulation has been applied via specific contacts found to increase the resting metabolic rate measured in a respiratory chamber. Conclusions Deep brain stimulation of the LHA may be applied safely to humans with intractable obesity. Early evidence for some weight loss under metabolically optimized settings provides the first “proof of principle” for this novel antiobesity strategy. A larger follow-up study focused on efficacy along with a more rigorous metabolic analysis is planned to further explore the benefits and therapeutic mechanism behind this investigational therapy.

Background Disc protrusion has been proposed to be a possible cause of both pain and stenosis in the lower spine. No previous study has described the amount of disc occlusion of the spinal canal and intervertebral foramen that occurs under different loading conditions. The objective of this study was to quantitatively assess the percent occlusion of the spinal canal and intervertebral foramen by disc bulge under different loading conditions. Methods Spinal canal depth and foraminal width were measured on computed tomography–scanned images of 7 human lumbar spine specimens. In vitro disc bulge measurements were completed by use of a previously described method in which single functional spinal units were subjected to 3 separate load protocols in a spine test machine and disc bulge was recorded with an optoelectric motion system that tracked active light-emitting diodes placed on the posterior and posterolateral aspects of the intervertebral disc. Occlusion was defined as percentage of encroachment into area of interest by maximum measured disc bulge at corresponding point of interest (the spinal canal is at the posterior point; the intervertebral foramen is at the posterolateral point). Results The mean spinal canal depth and mean foraminal width were 19 4 ± mm and 5 ± 2 mm, respectively. Mean spinal canal occlusion under a 250-N axial load, ± 2.5 Nm of flexion/extension, and ± 2.5 Nm of lateral bend was 2.5% ± 1.9%, 2.5% ± 1.6%, and 1.5% ± 0.8%, respectively. Mean intervertebral foramen occlusion under a 250-N axial load, ± 2.5 Nm of flexion/extension, and ± 2.5 Nm of lateral bend was 7.8% ± 4.7%, 9.5% ± 5.7%, and 11.3% ± 6.2%, respectively. Conclusion Percent occlusion of the spinal canal and intervertebral foramen is dependent on magnitude and direction of load. Exiting neural elements at the location of the intervertebral foramen are the most vulnerable to impingement and generation of pain.

The history and rationale of posterior dynamic spinal fusion devices has been derived through the experiences with arthrodesis and devices that serve as adjuncts to such procedures. Dynamic fusion devices provide stabilization through immediate fixation while allowing load sharing. Historically, incorporating these two important concepts in surgical techniques along with the implanted devices facilitates the bone healing process. It stands to reason, spinal fusion techniques that provide immediate stabilization and simultaneously significant graft loading should have the same clinical success seen in other long bone and cervical spine arthrodesis techniques. The load-sharing capability is device-dependent and posterior dynamic constructs theoretically allow dynamic compression of the anterior column higher than that of traditional rigid rod fixation.

STUDY DESIGN Biomechanical human cadaveric cervical flexibility testing with direct load-sharing measurement. OBJECTIVE To determine if the flexibility and load-sharing characteristics of a functional spinal unit were affected by anterior treatments for cervical pathologies. SUMMARY OF BACKGROUND DATA With advancements in polymers, anterior cervical plates have used thermoplastics including recent designs from biodegradable polylactide acids. However, the difference in material properties between metal and polymer can be significant. METHODS Thirteen cervical spine specimens were subjected to 5 treatments at C4-C5. Each treatment for each specimen was subjected to multidirectional flexibility testing. The third cycle was used for treatment comparisons. RESULTS With the integrated load cell spacer, the mean range of motion for the functional spinal unit measured on average 104% + or - 40% normalized to the intact control. The mean biodegradable and titanium plate were 55% + or - 31% and 40% + or - 36%, respectively. Both plates exhibited statistically lower mean range of motions (P = 0.001 and P < 0.001) compared with spacers. The load transmitted through the interbody space was 54% + or - 20%, 43% + or - 20%, and 33% + or - 15% on average for the spacer, biodegradable, and titanium plate constructs, respectively. No statistically significant difference was detected between the biodegradable plate and spacer (P = 0.214). CONCLUSIONS From this research, a biodegradable plate offers immediate postoperative stability significantly different than spacer alone treatments but with graft load sharing that is statistically no different. Thus, the intrinsic lower native material modulus of elasticity of biodegradable polymers has biomechanical implications. However, clinical evidence, particularly for long-term outcomes, will be required in understanding the efficacy of biodegradable polymers.

Background context Surgical instrumentation used for posterior craniocervical instability has evolved from simple wiring techniques to sophisticated implant systems that incorporate multiple means of rigid fixation for the cervical spine. Polyaxial screws and lamina hooks in conjunction with occipital plating and transitional rods for caudal fixation theoretically allow for fixation points at each vertebra along the posterior aspect of the cervical spine. However, the potential for anatomical constraints to prevent intraoperative instrumentation at the desired vertebral level exists. The biomechanical implications of such “skipped segments” have not been well documented. Purpose The purpose of this study was to determine the biomechanical effects of partial three-point fixation versus sequential fixation at all levels of the cervical spine from the occiput to T1. Study design/setting Fresh frozen human cadaveric cervical spines from the occiput (CO) to T1 were prepared and mounted on a spine simulator. Motion was assessed by a three-dimensional optoelectronic motion measurement system. Kinematic data were collected and range of motion (ROM) was analyzed and reported. Methods Eight human noninstrumented intact spines (Treatment 1) were tested for baseline ROM which was subclassified into axial (CO–C2), upper subaxial (C2–C4), lower subaxial (C4–T1), and total (CO–T1) ROM. Flexion extension, lateral bending, and axial torsion testing with an applied ±3 Nm moment was conducted. The same testing protocol was performed after three-point fixation in which screws were placed at the CO, C4, and T1 (Treatment 2), and also after sequential fixation at all levels from CO through T1 (Treatment 3). Fixation was achieved using an occipital plate, 12-mm lateral mass screws for C3 through C6, and 20-mm lateral mass or pedicle screws were used for C1, C2, C7, and T1. Results Intact spine testing (Treatment 1) showed statistically significant larger ROM for all segments and for overall ROM when compared with both Treatment 2 (partial fixation CO, C4, and T1) and Treatment 3 (sequential fixation at all levels from the occiput to T1). When comparing Treatment 2 with Treatment 3, no significant difference in flexion extension ROM was detected between axial, upper subaxial, lower subaxial, and total overall ROM (p > .05). Lateral bending showed statistically significant increased ROM for Treatment 2 constructs compared with Treatment 3 constructs in total overall lateral bend ROM. For axial rotation, there was significantly increased ROM for Treatment 2 at the lower subaxial segment and total overall ROM (p Conclusions There was no statistical difference between the three-point fixation treatment group and the sequential fixation group in flexion extension bending. Lateral bending and axial rotation demonstrated an increase in total overall ROM with partial fixation compared with fixation at all levels. Axial rotation in particular showed increased mobility in the lower cervical spine for the partial fixation group. In the instance where surgeons are not able to apply sequential fixation at diseased levels, especially for the lower subaxial cervical spine, particular attention to limitation of lateral bending and axial rotation by the use of external orthotics must be considered.

OBJECTIVE Spinal stability is attributed in part to osteoligamentous structures, including the vertebral body, facets, intervertebral discs, and posterior elements. The materials in this study provide an opportunity to augment the degenerated nucleus without removing native disc material, a procedure introduced here as “fortification.” The objective of this study was to determine the effect of nucleus fortification on lumbar disc biomechanics. METHODS The authors performed in vitro analysis of human cadaveric functional spinal units (FSUs), along with characterization and quantification of movement of the units using biomechanical data in intact, disc-only, and fortified specimens. The units underwent removal of all posterior elements and annulus and were fortified by injecting a biogel into the nucleus pulposus. Each specimen was subjected to load testing, range of motion (ROM) quantification, and disc bulge measurements. Optoelectric tracking was used to quantify disc bulge. These criteria were assessed in the intact, disc-only, and fortified treatments. RESULTS Disc-only FSUs resulted in increased ROM when compared with intact and fortified conditions. Fortification of the FSU resulted in partial restoration of normal ROM in the treatment groups. Analysis of hysteresis loops showed more linear response in the fortified groups when compared with the intact and disc-only groups. CONCLUSIONS Disc nucleus fortification increases linearity and decreases ROM.

Efficient load-sharing in the spinal column relies on the proper working of the components of the Functional Spinal Unit (FSU). Due to various reasons such as trauma, ageing and diseases, these components or even the entire FSU can get degenerated or injured during a person’s lifetime. Spinal column reconstruction surgerieswere created with the aimto restore the functioning of the diseased or injured spine. Several spinal implants are available today for the surgeon to aid in this process. There are three major categories of these devices: anterior stabilization devices, posterior stabilization devices and motion preservation devices. This review highlights thein vitro researchdone on these devices,over the past five decades, to evaluate their ability to effectively share loads at the operated level of the spinal column. Some conclusions have been drawn based on this research.Dynamic anterior cervical plates are more successful at maintaining load-sharing after graft subsidence and anterior stabilization devices can be used to provide support to posterior stabilization devices during severe anterior column injuries. Motion preservation devices, specifically cervical disc prostheses and facet replacement systems,show great potential in maintaining physiologicalloads in the spinal column. Further clinical investigation of all these implants would help to identify the contributing factors for their success or failure post-surgery. It would also aid in determining the requirements of an ideal spine stabilization device which perfectly mimics the physiological load-sharing properties of the FSU and its components.

Study Design. Biomechanical in vitro human cadaveric lumbar flexibility testing with 6 sequential treatments. Objective. To compare the range of motion (ROM) of dynamic one-level posterior stabilization constructs to one-level rigid rod fixation constructs and to study the effects of extending the posterior construct to the adjacent superior level. Summary of Background Data. Patients experiencing pain and biomechanical instability at one level may also present with radiographic or other indicators of early degeneration at an adjacent level. Clearly, fusion would be warranted at the symptomatic level, but the treatment plan for the adjacent level remains controversial. Additionally, the effects on adjacent motion segments above a fusion level are currently not well understood. Methods. Thirteen fresh frozen human cadaveric lumbar spines (L1–L5) were tested in 6 modes of loading: 3 were randomized to dynamic posterior stabilization constructs and 7 to a rigid rod pedicle screw system. Each group was subjected to 6 treatments. Results. When comparing the instrumented treatments, only Treatment 6, two-level hybrid constructs, exhibited a statistically significant effect in flexion-extension bending at L2–L3 between the posterior dynamic system and rigid rod fixation (P = 0.014). Conclusion. ROM at the superior adjacent level (L2–L3) demonstrated no significant difference between intact, destabilized, one-level posterior fixation, and one-level circumferential fusion at the index level (L3–L4) when comparing posterior dynamic stabilization to rigid rod fixation. However, ROM at the superior adjacent level (L2–L3) was significantly greater for lateral bending and axial rotation when both levels (L2–L3 and L3–L4) were stabilized with a dynamic stabilization system. When thefunctional spinal units were instrumented with a two-level hybrid construct, two-level posterior instrumentation (L2–L3 and L3–L4) with a cage at the index level (L3–L4), all bending modes generated significantly greater ROM for the dynamic stabilization group at L2–L3 compared with rigid rod fixation.

Object In this study the authors present the preliminary clinical outcomes of dynamic stabilization with the Dynesys spinal system as part of a multicenter randomized prospective Food and Drug Administration (FDA) investigational device exemption (IDE) clinical trial. Methods This study included 101 patients from six IDE sites (no participants were omitted from the analysis) who underwent dynamic stabilization of the lumbar spine with the Dynesys construct. Patient participation was based on the presence of degenerative spondylolisthesis or retrolisthesis (Grade I), lateral or central spinal stenosis, and their physician's determination that the patient required decompression and instrumented fusion for one or two contiguous spinal levels between L-1 and S-1. Participants were evaluated preoperatively, postoperatively at 3 weeks, and then at 3-, 6-, and 12-month intervals. The 100-mm visual analog scale was used to score both lower-limb and back pain. Patient functioning was evaluated using the Oswestry Disability Index (ODI), and the participants' general health was assessed using the Short Form-12 questionnaire. Overall patient satisfaction was also reported. One hundred one patients (53 women and 48 men) with a mean age of 56.3 years (range 27–79 years) were included. The mean pain and function scores improved significantly from the baseline to 12-month follow-up evaluation, as follows: leg pain improved from 80.3 to 25.5, back pain from 54 to 29.4, and ODI score from 55.6 to 26.3%. Conclusions The early clinical outcomes of treatment with Dynesys are promising, with lessening of pain and disability found at follow-up review. Dynesys may be preferable to fusion for surgical treatment of degenerative spondylolisthesis and stenosis because it decreases back and leg pain while avoiding the relatively greater tissue destruction and the morbidity of donor site problems encountered in fusion. However, long-term follow-up care is still recommended.

Background The influence of interbody cage positioning on clinical outcomes following lumbar interbody fusion is not well understood, though it has been hypothesized to play a significant role in stability of the treated level. The purpose of this study was to evaluate any correlations between cage placement in TLIF procedures and post-operative kinematics. Methods Thirteen patients who had previously undergone a TLIF procedure were evaluated using the Vertebral Motion Analysis (VMA) system, an automated fluoroscopic method of tracking kinematics in vivo. Upright and recumbent bending platforms were used to guide patients through a set range of motion (ROM) standing up and lying down, respectively, in both flexion-extension (FE) and lateral bending (LB). Intervertebral ROM was measured via fluoroscopic images captured sequentially throughout the movement. DICOM images acquired by the VMA system were used to calculate cage positioning. Intra-rater and inter-rater reliability of TLIF cage position were also assessed. Results Statistically significant correlations were noted between sagittal cage position and lying LB (r = -0.583, p = 0.047), and coronal cage positioning with both standing (r = 0.672, p = 0.012) and lying LB (r = 0.632, p = 0.027). Additionally, the correlation between sagittal cage position and standing FE was trending towards significance (r = -0.542, p = 0.055). Conclusions The intuitive correlation between coronal cage position and both standing and lying lateral bending ROM is supported by the data from this study, suggesting placement closer to midline is optimal for stability. Additionally, the VMA system appears to be a sensitive and repeatable means to obtain information on postoperative kinematic outcomes. Further work to establish the relationship between cage placement, these kinematic outcomes and, potentially, functional pain outcomes seems to be warranted based on the results obtained here.

Background Lumbar interbody fusion is a common treatment for a variety of spinal pathologies. It has been hypothesized that insufficient mechanical loading of the interbody graft can prevent proper fusion of the joint. The purpose of this study was to evaluate the mechanical stability and anterior column loading sharing characteristics of a posterior dynamic system compared to titanium rods in an anterior lumbar interbody fusion (ALIF) model. Methods Range of motion, interpedicular kinematics and interbody graft loading were measured in human cadaveric lumbar segments tested under a pure moment flexibility testing protocol. Results Both systems provided significant fixation compared to the intact condition and to an interbody spacer alone in flexion extension and lateral bending. No significant differences in fixation were detected between the devices. A significant decrease in graft loading was detected in flexion for the titanium rod treatment compared to spacer alone. No significant differences in graft loading were detected between the spacer alone and posterior dynamic system or between the posterior dynamic system and the titanium rod. Conclusions The results of this study indicate that the posterior dynamic system provides similar fixation compared to that of a titanium rod, however, studies designed to evaluate the efficacy of fixation in a cadaver model may not be sufficiently powered to establish differences in load sharing using the techniques described here.

STUDY DESIGN: Biomechanical analysis of the level above pars defects was performed using calf lumbar spines. OBJECTIVES: To evaluate whether complete spondylolysis contributes to the pathology of the upper adjacent motion segment to the pars defect. SUMMARY OF BACKGROUND DATA: It is well recognized that patients with spondylolysis show a higher incidence of spondylolisthesis or degenerative disc changes at the level of the pars defects. However, some authors have referred to the fact that disc damage may occur at the level above the defect and give rise to symptoms. However, no previous studies have been directed to the kinematic influence on the upper adjacent segment to pars defects. METHODS: Nine fresh-frozen calf lumbar spines were used for this study. The bony defects were created on the L4 pars articularis bilaterally. Three linear extensometers and one specially designed angular extensometer were mounted across the L3-L4 and L4-L5 motion units. Nondestructive static loads, including axial compression, flexion-extension, and axial rotation, were applied on the specimens in four different conditions as follows: 1) intact spine; 2) bilateral pars defects on the L4 laminae; 3) pars defect repair with Buck technique; and 4) pedicle screw-rod fixation at L4-L5 after removal of the interarticular screws. Testing was performed on a material testing machine (MTS 858 Bionix test system, Minneapolis, MN), and load-displacement curves were recorded with the extensometers. Each test was performed for over five full sinusoidal loading cycles, and data from the fifth cycle were collected and analyzed. RESULTS: After creating the pars interarticularis defects at L4, mobility at both the L3-L4 and L4-L5 motion units were increased in all loading conditions. The normalized range of motion (% ROM) as compared with the intact specimens showed that the pars defects increased the mobility at the upper adjacent level (L3-L4) to 106.4% in flexion-extension and to 120.1% in axial rotation; the differences were significant (P < 0.01). Consequently, the increased mobility was stabilized by applying Buck screws through the defects on both sides; however, the effect was not statistically significant. Furthermore, pedicle screw-rod fixation applied at the L4-L5 segment increased the intervertebral motion at the upper adjacent level, and % ROM in axial rotation was significantly increased to 119.2% of the intact spine (P < 0.05). Comparing the treatments' effects on the L3-L4 segment and that on L4-L5, the Buck screws restored the stability of both segments to the level of the intact spine, whereas the pedicle screw system limited the motion of L4-L5 motion and, on the contrary, increased the L3-L4 motion. CONCLUSIONS: This biomechanical study exhibited that bilateral pars interarticularis defects increased the intervertebral mobility, not only at the involved level but also at the upper adjacent level to the lysis. The increased mobility at the upper segment was reduced by the Buck screw technique. However, this was increased again by the pedicle screw system applied on the involved segment. If clinically applicable, fixation of the pars defect alone appears to cause less adjacent level mechanical stress than pedicle screw-rod motion segment fixation.

Background Pure moment testing is a common method used in cadaveric spine testing. The fundamental basis for the widespread acceptance of applying a pure moment is uniform loading along the column of the spine. To our knowledge, this protocol has not been experimentally verified on a multi–degree of freedom testing apparatus. Given its ubiquitous use in spine biomechanics laboratories, confirmation of this comparative cadaveric test protocol is paramount. Methods Group A specimens (n =13) were used to test the pure moment protocol, by use of 3 constructs that changed the number of involved vertebrae, orientation, and rigidity of the spine construct. Group B specimens (n = 6) were used to determine whether potting orientation, testing order, or degradation affected the range of motion (ROM) by use of 8 constructs. Each group was subjected to 3 cycles of flexion-extension, lateral bending, and axial torsion. The data from the third cycle were used to calculate the ROM for each method. Results Group A testing resulted in significant differences in ROM across the 3 constructs for lateral bending and axial torsion (P < .02) and trended toward a difference for flexion-extension (P = .055). Group B testing showed an increase in ROM across 8 constructs (P < .04) but no significant difference due to the orientation change. Conclusion The increased ROM across constructs observed in both groups indicates that the cause is likely the testing order or degradation of the specimens, with orientation having no observed effect. The data do not invalidate pure moment testing, and its use should persist.

BACKGROUND The efficacy of intrafacet bone dowels in promoting lumbar fusion has not been established. A recently published study indicates a low fusion rate, along with device migration. OBJECTIVE To evaluate the mechanical stability of 2 lumbar facet fixation technologies before and after repeated cyclic loading. METHODS Six human lumbar specimens were implanted with both types of allograft, one at L2-3 and the other at L4-5, on a randomized basis. All specimens were subjected to pure-moment flexibility testing before and after implantation and after 2500 and 5000 cycles of flexion-extension bending. Each specimen was scanned with computed tomography before and after cyclic loading to measure device migration. RESULTS Only dowel 1 resulted in a statistically significant reduction in flexion-extension range of motion at the treatment level. This reduction was significant at baseline testing (P = .03) and after 2500 cycles of flexion-extension loading (P = .048) but was not significant after 5000 cycles of loading. One of the bone dowels extruded posteriorly out of the joint space during baseline axial torsion flexibility testing, which was before any cyclic loading. CONCLUSION The data obtained in this study do not indicate efficacy of fixation for cylindrical bone dowels in the lumbar facet joint. Significant fixation was detected only for one of the devices and was no longer present after a relatively short duration of repeated loading. Furthermore, considerable magnitudes of device migration were detected.

Introduction. Pedicle based posterior dynamic stabilization systems aim to stabilize the pathologic spine while also allowing sufficient motion to mitigate adjacent level effects. Two flexible constructs that have been proposed to act in such a manner, the Dynesys Dynamic Stabilization System and PEEK rod, have yet to be directly comparedin vitroto a rigid Titanium rod.Methods. Human lumbar specimens were tested in flexion extension, lateral bending, and axial torsion to evaluate the following conditions at L4-L5: Intact, Dynesys, PEEK rod, Titanium rod, and Destabilized. Intervertebral range of motion, interpedicular travel, and interpedicular displacement metrics were evaluated from 3rd-cycle data using an optoelectric tracking system.Results. Statistically significant decreases in ROM compared to Intact and Destabilized conditions were detected for the instrumented conditions during flexion extension and lateral bending. AT ROM was significantly less than Destabilized but not the Intact condition. Similar trends were found for interpedicular displacement in all modes of loading; however, interpedicular travel trends were less consistent. More importantly, no metrics under any mode of loading revealed significant differences between Dynesys, PEEK, and Titanium.Conclusion. The results of this study support previous findings that Dynesys and PEEK constructs behave similarly to a Titanium rodin vitro.

STUDY DESIGN Nine sheep cadaveric spines were used in this acute postoperative model. OBJECTIVES To compare the biomechanical performance of translaminar facet joint fixation techique with that of cortical screws and bioabsorbable poly-L-lactide pins and with that of rigid pedicle screw fixation in the lumbar spine. SUMMARY OF BACKGROUND DATA Among numerous posterior spine fixation techniques, pedicle screw fixation has been reported to be the most rigid construct and to provide high fusion rate. Translaminar facet joint screw fixation is an alternative to pedicle screw fixation and is the lowest profile construct that achieves stabilization. The authors have developed a new concept involving application of bioabsorbable poly-L-lactide pins to translaminar facet joint fixation. Degradation in the stiffness of the implants with time may be advantageous for fusion mass remodeling. METHODS A total of nine sheep L2-L6 cadaveric spines were used. Each intact spine was nondestructively tested in flexion-extension bending (+/- 5-Nm peak bending moment with 100-N axial compression) on a modified testing machine. Loads were applied for 10-second periods using sinusoid waveforms. After testing the intact spine, bilateral fenestration was performed between L4 and L5 and the medial aspect of the facet capsule was resected. The L4-L5 functional spinal unit was than stabilized by five methods: translaminar facet joint fixation with smooth poly-L-lactide pins; translaminar facet joint fixation with cortical screws; pedicle screw fixation with the Texas Scottish Rite Hospital system; and without instrumentation, in that order. Linear displacement of L4 inferior and L5 superior articular processes in the sagittal plain (delta facet) and L4-L5 intervertebral rotation in the sagittal plain (theta sagittal) were measured by the extensometers mounted to the spine. Ranges of motion (delta facet and theta sagittal), neutral zones, linear elastic zone stiffness, and the total energy absorption during the load-unload cycle (hysteresis) were calculated. RESULTS By resecting the facet joint capsules and ligamentum flavum, delta facet and theta sagittal were not increased significantly, whereas the increase of neutral zones and hysteresis were statistically significant. Compared with the intact spine, delta facet was significantly reduced to 41% of normal with translaminar facet joint fixation with poly-L-lactide pins, to 9% with translaminar facet joint fixation with screws, and to 11% with the Texas Scottish Rite Hospital system. Neutral zones of delta facet showed a similar pattern, and these differences were significant. Regarding linear elastic zone stiffness, translaminar facet joint fixation with screws provided a stiffer construct than did pedicle screw fixation in the flexion loading mode, whereas pedicle screw fixation yielded higher values for stiffness in extension loading. Translaminar facet joint fixation with poly-L-lactide pins increased linear elastic zone stiffness in extension loading, but the increase was less than was achieved with the other constructs. CONCLUSIONS The facet joint is the only true articulation in the lumbosacral spine. It is logical to fix this part directly to achieve spine fixation. Translaminar facet joint fixation with screws show similar biomechanical performance to pedicle screw fixation. Translaminar facet joint fixation with poly-L-lactide pins is significantly less stiff than either type of screw fixation, but it also restricts the facet joint and intervertebral motions significantly when compared with the intact spine.

Background context Traditional methods for the evaluation of in vivo spine kinematics introduce significant measurement variability. Digital videofluoroscopic techniques coupled with computer-assisted measurements have been shown to reduce such error, as well as provide detailed information about spinal motion otherwise unobtainable by standard roentgenograms. Studies have evaluated the precision of computer-assisted fluoroscopic measurements; however, a formal clinical evaluation and comparison with manual methods is unavailable. Further, it is essential to establish reliability of novel measurements systems compared with standard techniques. Purpose To determine the repeatability and reproducibility of sagittal lumbar intervertebral measurements using a new system for the evaluation of lumbar spine motion. Study design Reliability evaluation of digitized manual versus computer-assisted measurements of the lumbar spine using motion sequences from a videofluoroscopic technique. Patient sample A total of 205 intervertebral levels from 61 patients were retrospectively evaluated in this study. Outcome measures Coefficient of repeatability (CR), limits of agreement (LOA), intraclass correlation coefficient (ICC; type 3,1), and standard error of measurement. Methods Intervertebral rotations and translations (IVR and IVT) were each measured twice by three physicians using the KineGraph vertebral motion analysis (VMA) system and twice by three different physicians using a digitized manual technique. Each observer evaluated all images independently. Intra- and interobserver statistics were compiled based on the methods of Bland-Altman (CR, LOA) and Shrout-Fleiss (ICC, standard error of measurement). Results The VMA measurements demonstrated substantially more precision compared with the manual technique. Intraobserver measurements were the most reliable, with a CR of 1.53 (manual, 8.28) for IVR, and 2.20 (manual, 11.75) for IVT. The least reliable measurements were interobserver IVR and IVT, with a CR of 2.15 (manual, 9.88) and 3.90 (manual, 12.43), respectively. The ICCs and standard error results followed the same pattern. Conclusions The VMA system markedly reduced variability of lumbar intervertebral measurements compared with a digitized manual analysis. Further, computer-assisted fluoroscopic imaging techniques demonstrate precision within the range of computer-assisted X-ray analysis techniques.

Significant advances have been made in the field of spine biomechanics with the introduction of continuous testing machines and new testing protocols. [1] Despite all the technological achievements, range of motion (RoM) continues to be the only widely agreed upon, standardized metric for data analysis. In load-controlled flexibility testing, displacement is typically recorded over three loading cycles between established limits in specific modes of loading. The first two cycles are intended for preconditioning, and the data from the third cycle is used for analysis. [2] Plotting displacement versus load defines the hysteresis inherent to the motion segment.Copyright © 2012 by ASME

The subtle effects of motion preservation devices are comparatively more difficult to detect based wholly on the range of motion (RoM) parameter, despite the historical success in characterizing fixation devices. Additional approaches such as descriptive facet techniques, i.e., facet translations analysis, and newly defined metrics, i.e., interpedicular displacement (ID) must first be established, verified and standardized. Ideally, more complete biomechanical parameters would facilitate clinical understanding of specific new devices. The recent focus in our lab has been to measure the RoM in conjunction with other parameters, including ID, to more completely characterize a lumbar spine treated with a posterior dynamic systems (PDS). Furthermore, understanding the construct and which components dominate overall tissue response is important for PDS systems.Copyright © 2012 by ASME

Facet articulation in the human lumbar spine has not been thoroughly characterized with regard to the effects of degeneration or surgical intervention. Kozanek et al. investigated the translation and rotation of the facets in 11 healthy adult subjects during maximal voluntary bending [1]. Li et al. used the same measurement technique on a cohort of 10 patients with degenerative disc disease (DDD) and found some significant differences in facet motion compared to a cohort of healthy patients [2]. Jegapragasan et al. investigated facet translations in intact lumbar spines in vitro and found the technique of facet translation analysis (FTA) to yield significantly different results compared to a similar analysis based on a vertebral body based coordinate system [3]. This abstract describes the application of this FTA technique in evaluating a posterior dynamic stabilization (PDS) system.Copyright © 2012 by ASME

Back pain is the second most common reason for physician visits in the United States, and affects up to 84 percent of patients at some point in their lives (Deyo & Tsui-Wu 1987). For many patients, neck and back pain is often due to injury or spinal instability through trauma, disease or degeneration. This can cause impingement of neural structures resulting in pain, numbness, or weakness. Also, this can be a consequence of changes in the vertebral bodies or degenerative changes in the intervertebral cartilaginous discs. Treatment of such disorders may require surgery if the pain or neurologic symptoms prove to be intractable to conservative treatments such as physical therapy or pain medications.

Study Design. In vitro flexibility testing of the lumbar spine. Objective. The goal of this study was to evaluate a motion-preserving posterior dynamic stabilization (PDS) implant based on newly defined parameters describing interpedicular kinematics. Summary of Background Data. PDS implants have been designed as either motion-preserving or adjunct-to-fusion devices to treat various degenerative spinal pathologies. The ambiguity of design and evaluation goals and the inability of traditional biomechanical parameters to appropriately describe the behavior of PDS devices in vitro have served as the impetus to develop kinematic parameters more specific to this class of device. Methods. Flexibility testing of 6 fresh-frozen human lumbar spines was conducted before and after destabilization of the index level (L4–L5). Testing under the same protocol was repeated after treatment at the index level with a 1-level PDS device, extension of the device to the adjacent inferior level (L5–S1), and treatment with a hybrid construct consisting of the PDS implant at L4–L5 and rigid fixation at L5–S1. The kinematic response was recorded using an optoelectric tracking system and reported in terms of intervertebral range of motion (ROM) and newly developed parameters describing interpedicular motion. Results. Based on ROM and interpedicular kinematics, the devices implanted at L4–L5 provide significant but not differing stabilization in flexion-extension with implantation after a significant destabilization procedure. Interpedicular kinematic results indicate that the 2-level construct contributes to significantly more motion at L5–S1 compared with rigid fixation. This result was not detected when evaluated by the ROM metric. Conclusion. Those involved in the design and evaluation of PDS devices may benefit from evaluation of interpedicular kinematics. Evaluating intervertebral motion from the perspective of the pedicle screw allows for a direct and intuitive translation between in vitro test results and design parameters. Furthermore, these parameters may provide additional clinical insight into the biomechanics of the healthy and pathological spine. The study presented indicates that this approach may be more sensitive in detecting differences in implant motion between PDS devices.

The use of ultrasonic technology for bone removal offers the potential advantages over the use of traditional hand instruments or cutting burrs of more precise bone resection and reduced soft-tissue injury. While the use of modified ultrasonic aspirators has been described for bone removal in spinal surgery, none of these instruments has been systematically examined to evaluate safety and efficacy. Thus, we compared laminectomies using traditional instruments, and traditional instruments with an ultrasonic osteotome, in an ovine model. We used a combination of clinical examination, intra-operative and post-operative neuromonitoring and histological analysis to evaluate safety. The secondary endpoint of efficiency was assessed by examining operative times. No significant difference was found between groups in neurophysiology or the Tarlov clinical rating scale. Histology revealed inflammatory or reparative changes in 6/8 experimental animals and 2/4 control animals with a single section in an experimental animal revealing focal nerve root disruption and mild axonal loss. A single durotomy was noted in both the control and experimental groups. Operative time for the experimental group was significantly shorter than the operative time for the control group.

Background context The three-joint-complex, which includes the two facet joints and the intervertebral disc, significantly directs the movement of the lumbar spine. When studying the biomechanics of this complex, kinematics have traditionally been measured relative to a vertebral body-based reference frame. Recently, a facet-based reference system has been used to describe the same motions, but relative to the facets. Purpose To describe in-plane and out-of-plane motion during flexion-extension (FE), lateral bending (LB), and axial rotation (AR) in the lumbar facets of cadaveric spines. Study design Biomechanical in vitro study. Methods Seven fresh-frozen and noninstrumented human cadaveric lumbar spines from L1 to sacrum were tested in FE, AR, and LB. Three coordinate systems were assigned to each vertebral body from L1 to L5: one corresponding to the vertebral body reference frame (X, Y, Z) and two corresponding to the left and right facet reference frames (A, B, C). The facet-based reference frame was aligned to each facet surface to provide descriptions of in-plane (articulation) and out-of-plane (separation) motion. For each of the three modes of loading, the magnitude of the translational range of motion (ROM) vector was calculated for the three reference frames. Results During FE, there was a significant difference in the magnitude of the translational ROM vector of the right facet as compared with the vertebral body at L1–L2. During AR, there was a significant difference between the magnitude of translational ROM vector at L2–L3, L3–L4, L4–L5, and L1–L2 trended toward significance. During LB, there was a significant difference in the magnitude of the translational ROM vector at L1–L2, L2–L3, L3–L4, and L4–L5. Conclusions A facet-based reference frame accounts for variations in facet orientation and provides a valuable characterization of facet articulation and separation that is not possible to derive from translations in a vertebral body–based reference frame.

Bow hunter's stroke is a rare symptomatic vertebrobasilar insufficiency in which vertebral artery (VA) is mechanically occluded during head rotation. Various pathologic conditions have been reported as causes of bow hunter's stroke. However, bow hunter's stroke caused by facet hypertrophy of C1-2 has not been reported. A 71-year-old woman presented with symptoms of vertebrobasilar insufficiency. Spine computed tomography showed massive facet hypertrophy on the left side of C1-2 level. A VA angiogram with her head rotated to the right revealed significant stenosis of left VA. C1-2 posterior fixation and fusion was performed to prevent serious neurologic deficit from vertebrobasilar stroke.

The biomechanics of facet kinematics is an important consideration for the native and pathologic spine. Moreover when evaluating new implants and techniques designed for motion preservation from either an anterior or posterior approach, the facet joint complex requires measurement techniques that do not violate the joint integrity to accurately characterize the contributions to the overall functional spinal unit response. Three-dimensional modeling of the lumbar spine can be used to derive a wealth of data beyond range of motion without invasive procedures. We have developed a method to apply kinematic data to rigid body models of each vertebral body reconstructed from high resolution CT scans. The method described has been shown to reduce registration errors from previous techniques. To portray the robustness of this method, we have computationally defined the articular surfaces of the L3-L4 facet joint and tracked minimum distance (MD) between each surface. The MD between intact and rigid rod instrumented conditions has been compared. The application of the rigid rod construct has shown to constrain the facet surfaces spatially closer than in the intact condition.

Facets make up two of the three joints within the three joint complex found in any given FSU.[1] The methods currently discussed in the literature relevant to facet measurements have employed suboptimal methods of characterizing the facet and the effects from various treatments. A noncontacting, nondisruptive method of facet measurements is needed in order to fully understand the role of the intact facet joint. Articulation, characterized by facet proximity with facet joint capsules kept intact may be an important method in determining facet response.Copyright © 2009 by ASME