Functional Spinal Unit Research Articles

Force Distribution Within Spinal Tissues During Posterior to Anterior Spinal Manipulative Therapy: A Secondary Analysis.

BackgroundPrevious studies observed that the intervertebral disc experiences the greatest forces during spinal manipulative therapy (SMT) and that the distribution of forces among spinal tissues changes as a function of the SMT parameters. However, contextualized SMT forces, relative to the ones applied to and experienced by the whole functional spinal unit, is needed to understand SMT’s underlying mechanisms.AimTo describe the percentage force distribution between spinal tissues relative to the applied SMT forces and total force experienced by the functional unit.MethodsThis secondary analysis combined data from 35 fresh porcine cadavers exposed to a simulated 300N SMT to the skin overlying the L3/L4 facet joint via servo-controlled linear motor actuator. Vertebral kinematics were tracked optically using indwelling bone pins. The functional spinal unit was then removed and mounted on a parallel robotic platform equipped with a 6-axis load cell. The kinematics of the spine during SMT were replayed by the robotic platform. By using serial dissection, peak and mean forces induced by the simulated SMT experienced by spinal structures in all three axes of motion were recorded. Forces experienced by spinal structures were analyzed descriptively and the resultant force magnitude was calculated.ResultsDuring SMT, the functional spinal unit experienced a median peak resultant force of 36.4N (IQR: 14.1N) and a mean resultant force of 25.4N (IQR: 11.9N). Peak resultant force experienced by the spinal segment corresponded to 12.1% of the total applied SMT force (300N). When the resultant force experienced by the functional spinal unit was considered to be 100%, the supra and interspinous ligaments experienced 0.3% of the peak forces and 0.5% of the mean forces. Facet joints and ligamentum flavum experienced 0.7% of the peak forces and 3% of the mean forces. Intervertebral disc and longitudinal ligaments experienced 99% of the peak and 96.5% of the mean forces.ConclusionIn this animal model, a small percentage of the forces applied during a posterior-to-anterior SMT reached spinal structures in the lumbar spine. Most SMT forces (over 96%) are experienced by the intervertebral disc. This study provides a novel perspective on SMT force distribution within spinal tissues.

Місце малоінвазивної нейрохірургії на хребетно-рухових сегментах у багатопрофільному реабілітаційному центрі

Надано 100 пацієнтів, прооперованих з приводу поперекових міжхребцевих гриж, зі стабілізацією хребетно-рухового сегмента міжтіловим титановим кейджем. Проаналізовано закономірність залежності локалізації міжхребцевої грижі від рівня хребетного стовпа, віку, статі та латералізації. Показана ефективність включення малоінвазивних нейрохірургічних операцій в умовах реабілітаційного центру.

Reaction Forces and Flexion-Extension Moments Imposed on Functional Spinal Units With Constrained and Unconstrained In Vitro Testing Systems.

A mechanical goal of in vitro testing systems is to minimize differences between applied and actual forces and moments experienced by spinal units. This study quantified the joint reaction forces and reaction flexion-extension moments during dynamic compression loading imposed throughout the physiological flexion-extension range of motion. Constrained (fixed base) and unconstrained (floating base) testing systems were compared. Sixteen porcine spinal units were assigned to both testing groups. Following conditioning tests, specimens were dynamically loaded for 1 cycle with a 1 Hz compression waveform to a peak load of 1 kN and 2 kN while positioned in five different postures (neutral, 100% and 300% of the flexion and extension neutral zone), totaling ten trials per functional spinal unit (FSU). A six degree-of-freedom force and torque sensor was used to measure peak reaction forces and moments for each trial. Shear reaction forces were significantly greater (25.5 N-85.7 N) when the testing system was constrained compared to unconstrained (p < 0.029). The reaction moment was influenced by posture (p = 0.037), particularly in C5C6 spinal units. In 300% extension (C5C6), the reaction moment was, on average, 9.9 N·m greater than the applied moment in both testing systems and differed from all other postures (p < 0.001). The reaction moment error was, on average, 0.45 N·m at all other postures. In conclusion, these findings demonstrate that comparable reaction moments can be achieved with unconstrained systems, but without inducing appreciable shear reaction forces.

Motion capture evaluation of sagittal spino-pelvic biomechanics after lumbar spinal fusion.

The spine and pelvis coexist as a dynamic linked system in which spinal and pelvic parameters are correlated. Investigation of this system can inform the understanding and treatment of spinal deformity. Here, we demonstrate the use of motion capture technology to measure spine biomechanical parameters using a novel testing apparatus. Three complete cadaveric spines with skull and pelvis were mounted into a biomechanical testing apparatus. Each lumbar vertebra was monitored by motion capture cameras as the spines underwent maximal anterior and posterior pelvic tilts about two sagittal axes at a controlled speed and applied force. These axes were defined as the sacral axis which passes transversely through the ilium and S1, and the acetabular axis which passes transversely through both acetabula. The experiments were repeated after L4-L5 fusion, and then, after both L4-L5 and T12-S1 fusion with pedicle screw instrumentation. Data were collected for total range of motion and for coupled translation at each functional spinal unit (FSU). Total range of motion and coupled translation within functional spinal units (FSUs) was decreased after spinal fusion. The displacement of each individual FSU was captured and summarized along with the observed patterns under each experimental condition. Lumbar fusion decreases spinal motion in the sagittal plane in both overall ROM and individual coupled translations of lumbar vertebrae. This was demonstrated using motion capture technology which is useful for quantifying the translations of individual FSUs in a multisegmental spinal model.

Kinematic analysis of L4–L5 spinal segment with spondylolysis and different types of grade 1 spondylolisthesis: a nonlinear finite element study

Purpose: This work aimed to evaluate and characterize the motion of the fourth and fifth lumbar vertebrae functional spinal unit with spondylolysis and different types of grade 1 spondylolisthesis using the finite element method. Methods: Nine nonlinear three-dimensional finite element models were reconstructed from computed tomography scans to five educational fourth and fifth lumbar vertebrae models. The intervertebral disc was simulated in two conditions: four models with healthy discs and five models with degenerated discs. Each model consisted of two vertebrae divided into three bony parts, two endplates, an intervertebral disc and five ligaments. The flexion, extension, lateral bending and rotation loading conditions were simulated, and the ranges of motion were measured and plotted. Results: In flexion, compared to the baseline intact model, the most significant increase in the range of motion was experienced by the isthmic spondylolisthesis model, while in extension, a reduction in the range of motion was measured in both prolonged pars and unilateral pars defect and healthy disc models. In degenerated disc results, the unilateral pars defect and degenerative spondylolisthesis models had the lowest range of motion. No large differences were noticed in lateral bending results. Lastly, in axial rotation, the most significant increase in the range of motion was measured in the isthmic spondylolisthesis model, followed by the spondylolysis model and similarly, in the degenerated disc models. Conclusions: The isthmic spondylolisthesis displayed hypermobility in flexion and rotation. Moreover, the model with unilateral pars defect showed hypermobility in axial rotation only. Finally, hypomobility in all movements was noticed with the degenerative spondylolisthesis model.

Development of a Finite Element Model of the Cervical Spine and Validation of a Functional Spinal Unit

Development of a Finite Element Model of the Cervical Spine and Validation of a Functional Spinal Unit

Comparison of in vivo kinematic and radiological parameters of three cervical disc prostheses.

Introduction:Cervical total disc replacement (CTDR) is an alternative to anterior cervical discectomy and fusion for select patients that may preserve range of motion and reduce adjacent segment disease. Various CTDR prostheses are available; however, comparative data are limited. This study aimed to compare the short-term kinematic and radiological parameters of the M6-C, Mobi-C, and the CP-ESP prostheses.Methods:This retrospective cohort study included patients treated with CTDR between March 2005 and October 2020 at a single institution. Patients were included if their follow-up assessment included lateral erect and flexion/extension radiographs. The primary outcome assessed at 3-months postoperatively was range of motion, measured by the difference in functional spinal unit angle between flexion and extension.Results:A total of 131 CTDR levels (120 patients, 46.2 ± 10.1 years, 57% male) were included. Prostheses implanted included the M6-C (n = 52), Mobi-C (n = 54), and CP-ESP (n = 25). Range of motion varied significantly (8.2° ± 4.4° vs. 10.9° ± 4.7° vs. 6.1° ± 2.7°, P < 0.001). On post hoc analysis, the Mobi-C prosthesis demonstrated a significantly greater range of motion than either the M6-C prosthesis (P = 0.003) or CP-ESP (P < 0.001).Conclusion:Although the optimal range of motion for CTDR has not been established, short-term differences in the range of motion may guide the selection of CTDR prosthesis. Further studies with longer follow-up and consideration of clinical outcome measures are necessary.

Radiological Changes in Adjacent and Index Levels after Cervical Disc Arthroplasty.

PurposeThe purpose of this retrospective study was to evaluate radiological and clinical outcomes in patients undergoing cervical disc arthroplasty (CDA) for cervical degenerative disc disease. The results may assist in surgical decision-making and enable more effective and safer implementation of cervical arthroplasty.Materials and MethodsA total of 125 patients who were treated with CDA between 2006 and 2019 were assessed. Radiological measurements and clinical outcomes included the visual analogue scale (VAS), the Neck Disability Index (NDI), and the Japanese Orthopaedic Association (JOA) myelopathy score assessment preoperatively and at ≥2 years of follow-up.ResultsThe mean follow-up period was 38 months (range, 25–114 months). Radiographic data demonstrated mobility at both the index and adjacent levels, with no signs of hypermobility at an adjacent level. There was a non-significant loss of cervical global motion and range of motion (ROM) of the functional spinal unit at the operated level, as well as the upper and lower adjacent disc levels, compared to preoperative status. The cervical global and segmental angle significantly increased. Postoperative neck VAS, NDI, and JOA scores showed meaningful improvements after one- and two-level CDA. We experienced a 29.60% incidence of heterotrophic ossification and a 3.20% reoperation rate due to cervical instability, implant subsidence, or osteolysis.ConclusionCDA is an effective surgical technique for optimizing clinical outcomes and radiological results. In particular, the preservation of cervical ROM with an artificial prosthesis at adjacent and index levels and improvement in cervical global alignment could reduce revision rates due to adjacent segment degeneration.

Long-Term Clinicoradiological Outcomes of Cervical Fusion With Polyether Ether Ketone versus Cervical Disc Arthroplasty in a Double-Blinded Randomized Control Trial.

Introduction:In this double-blinded randomized controlled trial, we compare the long-term clinicoradiological effects of anterior cervical discectomy and fusion with polyether ether ketone implant (ACDF with PEEK) versus artificial cervical disc (cervical disc arthroplasty [CDA]) in patients with single and bilevel cervical degenerative disc disease (CDDD).Aims:We aimed to compare the pain scores, cervical kinematics, and radiological outcomes in patients undergoing CDA and ACDF for single and bilevel CDDD over 5 years.Settings and Design:This study was carried out from 2010 to 2019 in the Neurosurgery Department of a Tertiary Care Hospital attached to a Medical College in India.Subjects and Methods:We enrolled 30 patients in each group. Clinical and radiological assessments were carried out for all patients over a period of 5 years.Statistical Analysis Used:Wilcoxon Signed-rank test, Mann–Whitney U-test, and Fischer's exact test were used for comparing the preoperative and follow-uP values. R software version 3.6.0 was used for statistical analysis.Results:A significant improvement in the cervical range of motion, sagittal range of motion (ROM), and functional spinal unit (FSU) was observed in the CDA group at final follow-up, while the PEEK group reported a significant decrease in the ROM and FSU and the difference between the two groups was also found to be statistically significant.Conclusions:When assessed over 5 years following surgery, we found CDA to be superior with respect to ROM, FSU, overall cervical alignment, and maintenance of disc height when compared to ACDF with PEEK implant.

Stress-strain distribution in intact L4-L5 vertebrae under the influence of physiological movements: A finite element (FE) investigation

This study is aimed at finding the stress and strain distribution in functional spinal unit of L4-L5 occurring due to physiological body movements under five loading conditions, namely compression, flexion, extension, lateral bending and torsion. To this purpose, 3D finite element (FE) model has been generated using 4-noded unstructured tetrahedral elements considered both for bones and intervertebral disc, and 1D tension-only spring elements for ligaments. The analyses were performed for a compression load of 500 N and for other load cases, a moment of 10 N-m along with a preload of 500 N was applied. The model was validated against in-vitro experimental data obtained from literature and FE analysis data for a range of motion (RoM) corresponding to various loading conditions. The highest stress was predicted in the case of torsion though the angular deformation was highest in case of flexion.

Anteroposterior shear stiffness of the upper thoracic spine at quasi-static and dynamic loading rates-Anin vitro biomechanical study.

To evaluate the biomechanical properties of the upper thoracic spine in anterior-posterior shear loading at various displacement rates. Thesedata broadenour understanding of thoracic spine biomechanics and inform efforts to model the spine and spinal cord injuries. Seven T1-T2 thoracic functional spinal units were loaded non-destructively by a pure shear force up to 200 N, starting from a neutral posture. Tests were run in both posterior and anterior directions, at displacement rates of 1, 10, and 100 mm/s. The three-dimensional motion of the specimen was recorded at 1000 Hz. Individual and averaged load-displacement curves were generated and specimen stiffnesses were calculated. Due to a nonlinear response of the specimens, stiffness was defined separately for both the lower half and the upper half of the specimen range of motion. Specimens were significantly stiffer in the anterior direction than in the posterior direction, across all rates. At low displacements, the anterior stiffness averaged 230 N/mm, 76% higher than the low displacement posterior stiffness of 131 N/mm. At high displacements, anterior stiffness averaged 258 N/mm, 51% stiffer than the high displacement posterior stiffness of 171 N/mm. Shear displacement rate had a small effect on the load response, with the 100 mm/s rate causing a mildly stiffer response at low displacements in the anterior direction. Overall, the load-displacement response exhibited pseudo-quadratic behavior at 1 and 10 mm/s but became more linear at 100 mm/s. The shear stiffness in the upper thoracic spine is greatest in the anterior loading direction, being 51%-76% greater than posterior, most likely due to facet interactions. The effect of the shear displacement rate is low.

Regenerative Injection Treatments Utilizing Platelet Products and Prolotherapy for Cervical Spine Pain: A Functional Spinal Unit Approach.

BackgroundThe increasing burden of musculoskeletal disorders combined with the high utilization of opiates and the relatively limited ability of traditional approaches to satisfactorily address many of these conditions has spurred an increased interest in alternative treatments such as regenerative medicine therapies. Evidence is growing to support the use of regenerative injection treatments, including prolotherapy, platelet-rich plasma (PRP), platelet lysate (PL), and mesenchymal stromal cells. This study aims to offer a proof of concept via a case series of patients with neck pain treated using a functional spinal unit (FSU) model with combination prolotherapy, PRP, and PL injections.MethodologyA chart review identified patients with neck pain treated with a combination of cervical injections using concentrated platelets and prolotherapy.ResultsA total of 14 patients met the inclusion criteria. The average decrease in the Numeric Pain Score was 2.8 (p = 0.002). The mean decrease in the Functional Rating Index was 27.3 (p = 0.004) at 24 months. Two patients had mild adverse reactions.ConclusionsThis case series demonstrates basic safety and clinically significant improvements in patients treated for neck pain with autologous concentrated platelet products and prolotherapy utilizing an FSU treatment protocol. Additional clinical studies are warranted with a larger patient sample size and longer follow-up periods.

MDCT-Based Finite Element Analysis for the Prediction of Functional Spine Unit Strength-An In Vitro Study.

(1) Objective: This study aimed to analyze the effect of ligaments on the strength of functional spine unit (FSU) assessed by finite element (FE) analysis of anatomical models developed from multi-detector computed tomography (MDCT) data. (2) Methods: MDCT scans for cadaveric specimens were acquired from 16 donors (7 males, mean age of 84.29 ± 6.06 years and 9 females, mean age of 81.00 ± 11.52 years). Two sets of FSU models (three vertebrae + two disks), one with and another without (w/o) ligaments, were generated. The vertebrae were segmented semi-automatically, intervertebral disks (IVD) were generated manually, and ligaments were modeled based on the anatomical location. FE-predicted failure loads of FSU models (with and w/o ligaments) were compared with the experimental failure loads obtained from the uniaxial biomechanical test of specimens. (3) Results: The mean and standard deviation of the experimental failure load of FSU specimens was 3513 ± 1029 N, whereas of FE-based failure loads were 2942 ± 943 N and 2537 ± 929 N for FSU models with ligaments and without ligament attachments, respectively. A good correlation (ρ = 0.79, and ρ = 0.75) was observed between the experimental and FE-based failure loads for the FSU model with and with ligaments, respectively. (4) Conclusions: The FE-based FSU model can be used to determine bone strength, and the ligaments seem to have an effect on the model accuracy for the failure load calculation; further studies are needed to understand the contribution of ligaments.

Negative biomechanical effects of large grade nuclectomy in the transforaminal endoscopic discectomy increased the risk of adjacent segment diseases: A finite element study

PurposeThe protection of articular processes (AP) in the transforaminal endoscopic discectomy (TED) was proven to optimise post-operative biomechanical environments. Published studies reported a large grade of nuclectomy leading to poor prognosis, but the underlying biomechanical mechanism was unclearly illustrated. This study aimed to investigate the changes of biomechanical environments after an in-out TED with intact AP and a large grade of nuclectomy and an out-in TED with limited foraminoplasty and a smaller grade of nuclectomy. MethodsA previously constructed and validated lumbo–sacral model was used in this study, and in-out TED with intact AP and out-in TED with limited foraminoplasty, a smaller grade of nuclectomy was simulated. Biomechanical changes in the L5–S1 segment related to the degeneration acceleration were computed under different directional loading conditions. ResultsPost-operative biomechanical changes after the out-in TED with limited foraminoplasty were slight, except for the facet contact pressure under the extension position. By contrast, significant biomechanical deterioration, both in the adjacent disc and zygapophyseal joints, is observed under extension in the model after the in-out TED with large nuclectomy. ConclusionA large grade of nuclectomy is regarded as an independent risk factor of adjacent segment disease in the caudal functional spinal unit after the in-out TED.

The Influence of Simulated Low Speed Vehicle Impacts and Posture on Passive Intervertebral Mechanics.

An in vitro biomechanics investigation exposing porcine functional spinal units (FSUs) to sudden impact loading although in a flexed, neutral, or extended posture. To investigate the combined effect of impact severity and postural deviation on intervertebral joint mechanics. To date, no in vitro studies have been conducted to explore lumbar tissue injury potential and altered mechanical properties from exposure to impact forces. Typically, after a motor vehicle collision, the cause of a reported acute onset of low back pain is difficult to identify, with potential soft tissue strain injury sites including the intervertebral disc, facet joint and highly innervated facet joint capsule ligament. Seventy-two porcine functional spinal units (36 C34, 36 C56), consisting of 2 adjacent vertebrae, ligaments, and the intervening intervertebral disc were included in the study. Each specimen was randomized to 1 of 3 experimental posture conditions (neutral, flexed, or extended) and assigned to 1 of 3 impact severities representing motor vehicle accident accelerations (4 g, 8 g, and 11 g). Before impact (pre) and after impact (post) flexion-extension and anterior-posterior shear neutral zone testing was completed. A significant two-way interaction was observed between pre-post and impact severity for flexion-extension neutral zone length and stiffness and anterior-posterior shear neutral zone length and stiffness. This was a result of increasedneutral zone range and decreased neutral zone stiffness pre-post for the highest impact severity (11 g), regardless of posture. Functional spinal units exposed to the highest severity impact (11 g) had significant neutral zone changes, with increases in joint laxity in flexion-extension and anterior-posterior shear and decreased stiffness, suggesting that soft tissue injury may have occurred. Despite observed main effects of impact severity, no influence of posture was observed.Level of Evidence: N/A.

Is there a difference in the outcomes of anterior cervical discectomy and fusion among female patients with different menopausal statuses?

BackgroundThe surgical outcomes of anterior cervical discectomy and fusion (ACDF) in female patients according to menopausal status remain unclear. The objective of this study was to investigate the differences in these outcomes among female patients with different menopausal statuses.MethodsNinety-one patients undergoing single-level or consecutive two-level ACDF with a minimum 12-month postoperative follow-up were included in this study. There were 38 patients in the premenopausal group, 28 patients in the early postmenopausal group, and 25 patients in the late postmenopausal group. The clinical outcomes were evaluated by means of the neck disability index (NDI) scores, Japanese Orthopedic Association (JOA) scores, and visual analog scale (VAS) scores. Radiological parameters included cervical lordosis (CL), the functional spinal unit (FSU) angle, range of motion (ROM) of the total cervical spine, ROM of the FSU, anterior and posterior FSU height, implant subsidence, adjacent segment degeneration (ASD), and Hounsfield unit (HU) values.ResultsAll groups showed significant improvements in their JOA, VAS, and NDI scores (P < 0.05). The differences in preoperative and final follow-up CL, ROM of C2-7, FSU angle, and ROM of FSU were not statistically significant among the three groups (P > 0.05). The anterior FSU height loss rate showed a significant difference (P = 0.043), while there was no difference in the posterior FSU height loss rate (P = 0.072). The fusion rates in the early and late postmenopausal groups were consistently lower than those in the premenopausal group during the follow-up period. All patients had satisfactory outcomes at the final follow-up.ConclusionThere were no significant differences in clinical or other related outcomes of single-level or consecutive two-level ACDF in the long term among female patients with different menopausal statuses. However, the early bony fusion rates and anterior FSU height loss rates were poorer in late postmenopausal patients than in premenopausal or early postmenopausal patients. Hence, importance should be attached to the protection of late postmenopausal patients in the early postoperative period to guarantee solid bony fusion.

164. Biomechanical analysis of the endplate fixation methods of cervical total disc replacement (TDR) prostheses to shear force expulsion

<h3>BACKGROUND CONTEXT</h3> Current methods for achieving immediate endplate fixation with cervical TDR include the use of keels or spiked teeth. Nonphysiologic push-out or expulsion tests are typically used to measure the distraction force and mechanical work required to expulse the device. <h3>PURPOSE</h3> To determine the failure work and load required to expulse the upper and lower components of the 4 different cervical prostheses after undergoing multidirectional cyclic testing. Endplate configurations included single central keel, tripod keel, and spiked teeth. <h3>STUDY DESIGN/SETTING</h3> Each device was implanted in a cervical functional spinal unit (FSU) and cyclically loaded 2,000 times under physiological ranges of combined flexion/extension coupled with axial rotation at a rate of 2.5deg/s. Following cyclic testing, the specimens were disarticulated through the disc space, separated into upper and lower segments and mounted in a robotic testing platform for expulsion testing. <h3>PATIENT SAMPLE</h3> Sixteen (C4-C5) and 16 (C6-C7) FSUs were dissected from 8 male and 8 female cadaveric cervical spines with an average age of 55.9 +/- 9.7 years. Three FSUs were not usable due to poor tissue quality which reduced the sample size to 29 FSUs. <h3>OUTCOME MEASURES</h3> Shear expulsion force and distraction displacement were measured and combined to calculate the expulsion work, the resistive stiffness. The peak expulsion force was also obtained. Normality of the expulsion data was tested using the Shapiro-Wilk test (for p=0.05). If normality failed, a nonparametric Kruskal-Wallis test with Bonferroni correction was used to analyze the data between implant types. An additional test was done to compare the shear expulsion parameters between the upper and lower components of the same implant type. A similar normality test as above was used and a (2 tailed) Mann-Whitney U test was used here when normality failed. <h3>Methods</h3> Four ball and socket type cervical disc prostheses having different endplate fixation features were tested: 1. A clinically used and FDA approved single central keel (SCK), 2. A clinically used (outside the U.S.) low profile teeth (LPT) with domed endplate shape to allow a better fit in case of concave vertebral endplate, 3. A clinically used (outside the U.S.) tripod keel (TK), and 4. Small single keel (SSK). A minimum sample size of 6 implants per prosthesis type were used. Three additional TK disc prostheses and two additional LPT disc prostheses were implanted. A minimum of 6 implants per prosthesis type were used. Specimens were mounted in a robotic testing platform programmed to apply a 50N compressive load to the top surface of the disc, followed by an anterior shear force to the backside of the implant until the device was fully expulsed. <h3>Results</h3> Mean and standard deviations for peak expulsion forces were 69(41)N, 62(21)N, 110(71)N and 78(36)N, expulsion work were 321(225)Nmm, 399(161)Nmm, 463(305)Nmm, and 296(149)Nmm, and resistive stiffness were 81(61)N/mm, 44(42)Nmm, 163(207)Nmm, and 150(149)Nmm. No significant differences occurred between implant types for any of expulsion data. Further, no significant differences were found between the upper and lower components of any implant type except for the expulsion work term of the traditional central keel device (p=0.037). <h3>Conclusions</h3> The distraction failure strength of three different cervical disc prostheses was comparable to an existing FDA approved central-based keel designed disc prosthesis. <h3>FDA DEVICE/DRUG STATUS</h3> Prodisc C (Approved for this indication), Prodisc C Vivo (Investigational/Not approved), Prodisc C Nova (Investigational/Not approved), Prodisc C SK (Investigational/Not approved)

P5. Fixation stability of four different cervical disc prostheses endplate configurations

<h3>BACKGROUND CONTEXT</h3> Motion preservation devices have become increasingly popular in the treatment of spinal pathologies that require biomechanical support following removal of the degenerated tissue. As these devices continue to be developed to treat multiple adjacent diseased spinal levels, like the use of multiple disc prostheses or placement of a disc prosthesis adjacent to a fused level, in-depth biomechanical data that supports these established surgical methods are needed. <h3>PURPOSE</h3> To assess immediate stability of four cervical disc prostheses under low endurance multidirectional cyclic loading conditions in a cadaveric cervical spine model. <h3>STUDY DESIGN/SETTING</h3> Each prosthesis was implanted in a cervical functional spinal unit (FSU) and cyclically loaded 2000 times under physiological ranges of combined flexion/extension coupled with axial rotation at a rate of 2.5deg/s. <h3>PATIENT SAMPLE</h3> There were 16 (C4-C5) and 16 (C6-C7) FSUs dissected from eight male and eight female cadaveric cervical spines with an average age of 55.9 +/- 9.7 years. Three FSUs were not usable due to poor tissue quality which reduced the sample size to 29 FSUs. <h3>OUTCOME MEASURES</h3> A one-way repeated measures ANOVA with a Student Newman-Keuls test was used to compare differences in the combined motion data. Anteroposterior endplate migration of both the upper and lower implant components was measured after 20, 250, 500, 1,000, 1,500 and 2,000 cycles. Tests were stopped if implant component migration exceeded 3mm or endplate fracture was observed, and migrations less than 0.3mm were defined as clinically stable. <h3>METHODS</h3> Four cervical disc prostheses that had a similar ball and socket type articulation mechanism but varying endplate fixation features were tested: 1. A clinically used and FDA-approved single central keel (SCK). 2. A clinically used (outside the U.S.) low profile teeth (LPT) with domed endplate shape to allow a better fit in case of concave vertebral endplate. 3. A clinically used (outside the U.S.) tripod keel (TK) and 4. Small single keel (SSK). A minimum sample size of six implants per prosthesis type were used. Three additional TK disc prostheses and two additional LPT disc prostheses were implanted. Specimens were cyclically tested 2,000 times at a rate of 2.5deg/s to an end limit of 1.5Nm in flexion or extension coupled with 1.5Nm of right and left axial rotation resulting in a total applied moment of 2.25Nm. A one-way repeated measures ANOVA with a Student Newman-Keuls test was used to compare differences in the combined motion data. Anteroposterior endplate migration of both the upper and lower implant components was measured after 20, 250, 500, 1,000, 1,500, and 2,000 cycles. Tests were stopped if implant component migration exceeded 3mm or endplate fracture was observed, and migrations less than 0.3mm were defined as clinically stable. <h3>RESULTS</h3> No statistical difference was found between the combined (flexion plus extension) sagittal plane range of motion or the combined (left plus right) axial motion. All but one of the specimen migration values were below 0.3mm. Upper prosthesis component migration ranged between 0.02mm and 0.08mm and between 0.01mm and 0.04mm for the lower components. No significant differences occurred between the upper components or the lower prosthesis components of any implant type. <h3>CONCLUSIONS</h3> Three different low profile endplate fixation designs for a cervical disc were found to provide comparable immediate holding strength to an existing FDA-approved central-based keel design. <h3>FDA DEVICE/DRUG STATUS</h3> Prodisc C (Approved for this indication), Prodisc C Vivo (Investigational/Not approved), Prodisc C Nova (Investigational/Not approved), Prodisc C SK (Investigational/Not approved).

P9. A distraction-based bench top protocol for the evaluation of growing rod concepatients

P9. A distraction-based bench top protocol for the evaluation of growing rod concepatients

Evaluation and Validation of Thorax Model Responses: A Hierarchical Approach to Achieve High Biofidelity for Thoracic Musculoskeletal System.

As one of the most frequently occurring injuries, thoracic trauma is a significant public health burden occurring in road traffic crashes, sports accidents, and military events. The biomechanics of the human thorax under impact loading can be investigated by computational finite element (FE) models, which are capable of predicting complex thoracic responses and injury outcomes quantitatively. One of the key challenges for developing a biofidelic FE model involves model evaluation and validation. In this work, the biofidelity of a mid-sized male thorax model has been evaluated and enhanced by a multi-level, hierarchical strategy of validation, focusing on injury characteristics, and model improvement of the thoracic musculoskeletal system. At the component level, the biomechanical responses of several major thoracic load-bearing structures were validated against different relevant experimental cases in the literature, including the thoracic intervertebral joints, costovertebral joints, clavicle, sternum, and costal cartilages. As an example, the thoracic spine was improved by accurate representation of the components, material properties, and ligament failure features at tissue level then validated based on the quasi-static response at the segment level, flexion bending response at the functional spinal unit level, and extension angle of the whole thoracic spine. At ribcage and full thorax levels, the thorax model with validated bony components was evaluated by a series of experimental testing cases. The validation responses were rated above 0.76, as assessed by the CORA evaluation system, indicating the model exhibited overall good biofidelity. At both component and full thorax levels, the model showed good computational stability, and reasonable agreement with the experimental data both qualitatively and quantitatively. It is expected that our validated thorax model can predict thorax behavior with high biofidelity to assess injury risk and investigate injury mechanisms of the thoracic musculoskeletal system in various impact scenarios. The relevant validation cases established in this study shall be directly used for future evaluation of other thorax models, and the validation approach and process presented here may provide an insightful framework toward multi-level validating of human body models.