Biomechanical Impact Research Articles

Moment of inertia as a means to evaluate the biomechanical impact of pelvic organ prolapse

To present an alternative measure (moment of inertia) to describe the anatomical features of the pelvic organ prolapse. A total of 30 women (21 diagnosed as having pelvic organ prolapse and 9 as controls) were evaluated by clinical scales and magnetic resonance imaging. Imaging biometric measures were carried out. Moment of inertia, pubovisceral muscle thickness and area, and levator hiatus anterior-to-posterior and lateral measures were compared by means of non-parametric tests, as well as their correlation with demographic features of the two sample groups. Moment of inertia, muscle area and levator hiatus diameters were statistically different between patients and controls. Furthermore, they were also well correlated with prolapse-associated factors, such as the number of vaginal deliveries and age, as well as Pelvic Organ Prolapse Quantification system and imaging staging of levator ani defects. Moment of inertia can be used as a new parameter to evaluate pelvic floor damage resulting from prolapse.

Impact of Partial and complete rupture of anterior cruciate ligament on medial meniscus: A cadavaric study.

Background:The clinical relationship between medial meniscus tear and anterior cruciate ligament (ACL) rupture has been well documented. However, the mechanism of this clinical phenomenon is not exactly explained. Our aim is to investigate the biomechanical impact of partial and complete ACL rupture on different parts of medial meniscus.Materials and Methods:Twelve fresh human cadaveric knee specimens were divided into four groups: ACL intact (ACL-I), anteromedial bundle transection (AMB-T), posterolateral bundle transection (PLB-T), and ACL complete transection (ACL-T) group. Strain on the anterior horn, body part, and posterior horn of medial meniscus were measured under 200 N axial compressive tibial load at 0°, 30°, 60°, and 90° of knee flexion, respectively.Results:Compared with the control group (ACL-I), the ACL-T group had a higher strain on whole medial meniscus at 0°, 60°, and 90° of flexion. But at 30°, it had a higher strain on posterior horn of meniscus only. As to PLB-T group, strain on whole meniscus increased at full extension, while strain increased on posterior horn at 30° and on body of meniscus at 60°. However, AMB-T only brought about higher strain at 60° of flexion on body and posterior horn of meniscus.Conclusions:Similar to complete rupture, partial rupture of ACL can also trigger strain concentration on medial meniscus, especially posterior horn, which may be a more critical reason for meniscus injury associated with chronic ACL deficiency.

Biomechanical profile of the cornea in primary congenital glaucoma

The aim of our study was to investigate the biomechanical properties of the cornea in primary congenital glaucoma (PCG) and to identify the potential ocular determinants, which affect the corneal biomechanical metrics. Corneal hysteresis (CH), corneal resistance factor (CRF) and central corneal thickness (CCT) were measured in 26 patients with PCG (40 eyes) with the aid of ocular response analyser. In vivo laser-scanning confocal microscopy was used for the estimation of stromal keratocyte density (KD) and the evaluation of corneal endothelium. Twenty normal subjects (40 eyes) served as controls. Student's t-test and Pearson's correlation coefficients were used for statistical analysis. p Values <0.05 were considered statistically significant. Corneal hysteresis, CRF and CCT were significantly reduced in patients with PCG (all p < 0.05). Corneal hysteresis and CRF negatively correlated with the corneal diameter in both groups (r(1) = -0.53, r(2) = -0.66, p < 0.001 for CH and r(1) = -0.61, r(2) = -0.69, p < 0.001 for CRF). Moreover, we identified a significant correlation between CH and CRF with CCT in both groups (r(1) = 0.51, r(2) = 0.48, p < 0.001 for CH and r(1) = 0.45, r(2) = 0.44, p < 0.001 for CRF). Mean KD was significantly reduced both in the anterior and posterior corneal stroma in patients with PCG (764 ± 162 and 362 ± 112 cells/mm(2) , respectively) compared with controls (979 ± 208 and 581 ± 131 cells/mm(2) , respectively) (p < 0.001). There was no significant correlation between the keratocyte density in anterior and/or posterior stroma and CH or CRF in any group (r(1) = 0.29, r(2) = 0.31, p < 0.06). Mean endothelial cell density was also significantly reduced in PCG group (2920 ± 443 cells/mm(2) ) compared with control group (3421 ± 360 cells/mm(2) ) (p < 0.001). Pleomorphism and polymegalism were significantly increased in corneal endothelium of patients with PCG. Our results showed a significant reduction in CH and CRF in PCG. Both CH and CRF were negatively correlated with corneal diameter. A significant correlation of CH and CRF with CCT was identified in both groups. Keratocyte density was decreased in PCG, but did not have a significant impact on CH and CRF. Mean endothelial density was also decreased in PCG. Our results suggest that reduced CCT and increased corneal diameter are major ocular determinants for the modified corneal biomechanical profile in PCG, while cellular alterations in corneal stroma and endothelium have no significant biomechanical impact.

BIOMECHANICAL ANALYSIS OF SMALL DIAMETER AND SHORT DENTAL IMPLANTS

In recent years, Mini and Short dental implants became more and more popular as treatment alternatives in clinical cases with critical bony situations. So-called ‘Minis’ have a reduced diameter of about 2.5 mm and are designed to be inserted in the anterior region of the maxilla or mandible. Extremely short implants, called ‘Shorties’, have a length of 5 to 7 mm and are commonly used in the posterior region after severe bone atrophy. A profound scientific analysis of the mechanical and biomechanical impact of the reduced diameter and length of these implants has not been published yet. A combined experimental and numerical study was performed in order to determine whether ultimate dimensions with respect to length and diameter can be defined for dental implants.

An integrated framework for finite-element modeling of mitral valve biomechanics from medical images: Application to MitralClip intervention planning

Treatment of mitral valve (MV) diseases requires comprehensive clinical evaluation and therapy personalization to optimize outcomes. Finite-element models (FEMs) of MV physiology have been proposed to study the biomechanical impact of MV repair, but their translation into the clinics remains challenging. As a step towards this goal, we present an integrated framework for finite-element modeling of the MV closure based on patient-specific anatomies and boundary conditions. Starting from temporal medical images, we estimate a comprehensive model of the MV apparatus dynamics, including papillary tips, using a machine-learning approach. A detailed model of the open MV at end-diastole is then computed, which is finally closed according to a FEM of MV biomechanics. The motion of the mitral annulus and papillary tips are constrained from the image data for increased accuracy. A sensitivity analysis of our system shows that chordae rest length and boundary conditions have a significant influence upon the simulation results. We quantitatively test the generalization of our framework on 25 consecutive patients. Comparisons between the simulated closed valve and ground truth show encouraging results (average point-to-mesh distance: 1.49 ± 0.62 mm) but also the need for personalization of tissue properties, as illustrated in three patients. Finally, the predictive power of our model is tested on one patient who underwent MitralClip by comparing the simulated intervention with the real outcome in terms of MV closure, yielding promising prediction. By providing an integrated way to perform MV simulation, our framework may constitute a surrogate tool for model validation and therapy planning.

The role of the tibial slope in sustaining and treating anterior cruciate ligament injuries

A steep tibial slope may contribute to anterior cruciate ligament (ACL)-injuries, a higher degree of instability in the case of ACL insufficiency, and recurrent instability after ACL reconstruction. A better understanding of the significance of the tibial slope could improve the development of ACL injury screening and prevention programmes, might serve as a basis for individually adapted rehabilitation programmes after ACL reconstruction and could clarify the role of slope-decreasing osteotomies in the treatment of ACL insufficiency. This article summarizes and discusses the current published literature on these topics. A comprehensive review of the MEDLINE database was carried out to identify relevant articles using multiple different keywords (e.g. 'tibial slope', 'anterior cruciate ligament', 'osteotomy', and 'knee instability'). The reference lists of the reviewed articles were searched for additional relevant articles. In cadaveric studies, an artificially increased tibial slope produced an anterior shift of the tibia relative to the femur. While mathematical models additionally demonstrated increased strain in the ACL, cadaveric studies have not confirmed these findings. There is some evidence that a steep tibial slope represents a risk factor for non-contact ACL injuries. MRI-based studies indicate that a steep slope of the lateral tibial plateau might specifically be responsible for this injury mechanism. The influence of the tibial slope on outcomes after ACL reconstruction and the role of slope-decreasing osteotomies in the treatment of ACL insufficiency remain unclear. The role of the tibial slope in sustaining and treating ACL injuries is not well understood. Characterizing the tibial plateau surface with a single slope measurement represents an insufficient approximation of its three-dimensionality, and the biomechanical impact of the tibial slope likely is more complex than previously appreciated. IV.

The Effects of Screw Length on Stability of Simulated Osteoporotic Distal Radius Fractures Fixed With Volar Locking Plates

Volar plating for distal radius fractures has caused extensor tendon ruptures resulting from dorsal screw prominence. This study was designed to determine the biomechanical impact of placing unicortical distal locking screws and pegs in an extra-articular fracture model. We applied volar-locking distal radius plates to 30 osteoporotic distal radius models. We divided radiuses into 5 groups based on distal locking fixation: bicortical locked screws, 3 lengths of unicortical locked screws (abutting the dorsal cortex [full length], 75% length, and 50% length to dorsal cortex), and unicortical locked pegs. Distal radius osteotomy simulated a dorsally comminuted, extra-articular fracture. We determined each construct's stiffness under physiologic loads (axial compression, dorsal bending, and volar bending) before and after 1,000 cycles of axial conditioning and before axial loading to failure (2 mm of displacement) and subsequent catastrophic failure. Cyclic conditioning did not alter the constructs' stiffness. Stiffness to volar bending and dorsal bending forces were similar between groups. Final stiffness under axial load was statistically equivalent for all groups: bicortical screws (230 N/mm), full-length unicortical screws (227 N/mm), 75% length unicortical screws (226 N/mm), 50% length unicortical screws (187 N/mm), and unicortical pegs (226 N/mm). Force at 2-mm displacement was significantly less for 50% length unicortical screws (311 N) compared with bicortical screws (460 N), full-length unicortical screws (464 N), 75% length unicortical screws (400 N), and unicortical pegs (356 N). Force to catastrophic fracture was statistically equivalent between groups, but mean values for pegs (749 N) and 50% length unicortical (702 N) screws were 16% to 21% less than means for bicortical (892 N), full-length unicortical (860 N), and 75% length (894 N) unicortical constructs. Locked unicortical distal screws of at least 75% length produce construct stiffness similar to bicortical fixation. Unicortical distal fixation for extra-articular distal radius fractures should be entertained to avoid extensor tendon injury because this technique does not appear to compromise initial fixation. Using unicortical fixation during volar distal radius plating may protect extensor tendons without compromising fixation.

Biomechanical finite element analysis of small diameter and short dental implants: extensive study of commercial implants

In recent years, mini and short dental implants have become increasingly popular as treatment alternatives for patients in whom the bone is unsuitable for a standard implant. As yet, no detailed scientific analysis of the mechanical and biomechanical impact of the reduced diameter and length of these implants has been published. We analysed 21 commercially available implants (13 mini, eight short) with respect to material behaviour and load transfer to the alveolar bone, using finite element (FE) analysis. Following μCT scanning and geometry reconstruction, FE models of mini implants and short implants were inserted into idealised bone segments. Mini implants were analysed in the anterior mandibular jaw region at a force of 150 N under immediate loading, using a contact analysis in the FE software package Marc Mentat 2007. Short implants were inserted in posterior bone segments and analysed in the osseointegrated state at an occlusal force of 300 N. Von Mises stresses (up to 1150 MPa) in mini implants partly exceeded the ultimate strength. Implant diameter and geometry had a pronounced effect on stresses in the cortical plate (up to 266 MPa). Strains in spongy bone and stresses in cortical bone around short implants were markedly increased compared to those in standard implants. An increased risk of bone damage or implant failure may be assumed in critical clinical situations.

The Role of the Sutures in Biomechanical Dynamic Simulation of a Macaque Cranial Finite Element Model: Implications for the Evolution of Craniofacial Form

The global biomechanical impact of cranial sutures on the face and cranium during dynamic conditions is not well understood. It is hypothesized that sutures act as energy absorbers protecting skulls subjected to dynamic loads. This hypothesis predicts that sutures have a significant impact on global patterns of strain and cranial structural stiffness when analyzed using dynamic simulations; and that this global impact is influenced by suture material properties. In a finite element model developed from a juvenile Rhesus macaque cranium, five different sets of suture material properties for the zygomaticotemporal sutures were tested. The static and dynamic analyses produced similar results in terms of strain patterns and reaction forces, indicating that the zygomaticotemporal sutures have limited impact on global skull mechanics regardless of loading design. Contrary to the functional hypothesis tested in this study, the zygomaticotemporal sutures did not absorb significant amounts of energy during dynamic simulations regardless of loading speed. It is alternatively hypothesized that sutures are mechanically significant only insofar as they are weak points on the cranium that must be shielded from unduly high stresses so as not to disrupt vitally important growth processes. Thus, sutural and overall cranial form in some vertebrates may be optimized to minimize or otherwise modulate sutural stress and strain.

Gendermedizinische Aspekte einer Kreuzbandruptur

An injury of cruciate ligament is one the most common knee injuries. This accident happens mostly without external impact and towards the end of training and competition sessions. Women, especially athletes playing team sports ball games such as soccer or disciplines such as tennis, are affected 2 to 8 times more often than men. Anatomic, biomechanical and endocrinological differences are currently discussed as potential risk factors. In terms of prevention, biomechanical impact is of greatest importance given its influenceability through various training opportunities. Training programs including endurance aspects, strengthening knee musculature, balance as well as plyometric trainings were most effective. Further studies should focus more on concomitants of course of injuries.

Biomechanical Impact Response of the Human Chin and Manubrium

Chin-to-chest impact commonly occurs in frontal crash simulations with restrained anthropomorphic test devices (ATDs) in non-airbag situations. This study investigated the biofidelity of this contact by evaluating the impact response of both the chin and manubrium of adult post-mortem human subjects (PMHSs). The adult PMHS data were scaled to a 10-year-old (YO) human size and then compared with the Hybrid III 10YO child (HIII-10C) ATD response with the same test configurations. For both the chin and manubrium, the responses of the scaled PMHS had different characteristics than the HIII-10C ATD responses. Elevated energy impact tests to the PMHS mandible provided a mean injury tolerance value for chin impact force. Chin contact forces in the HIII-10C ATD were calculated in previously conducted HYGE sled crash simulation tests, and these contact forces were strongly correlated with the Head Injury Criterion (HIC(36 ms)). The mean injurious force from the PMHS tests corresponded to a HIC(36 ms) value that would predict an elevated injury risk if it is assumed that fractures of the chin and skull are similarly correlated with HIC(36 ms). Given the rarity of same occupant-induced chin injury in booster-seated occupants in real crash data and the disparity in chin and manubrium stiffnesses between scaled PMHS and HIII-10C ATD, the data from this study can be made use of to improve biofidelity of chin-to-manubrium contact in ATDs.

Proteoglycan 4: a dynamic regulator of skeletogenesis and parathyroid hormone skeletal anabolism.

Proteoglycan 4 (Prg4), known for its lubricating and protective actions in joints, is a strong candidate regulator of skeletal homeostasis and parathyroid hormone (PTH) anabolism. Prg4 is a PTH-responsive gene in bone and liver. Prg4 null mutant mice were used to investigate the impact of proteoglycan 4 on skeletal development, remodeling, and PTH anabolic actions. Young Prg4 mutant and wild-type mice were administered intermittent PTH(1-34) or vehicle daily from 4 to 21 days. Young Prg4 mutant mice had decreased growth plate hypertrophic zones, trabecular bone, and serum bone formation markers versus wild-type mice, but responded with a similar anabolic response to PTH. Adult Prg4 mutant and wild-type mice were administered intermittent PTH(1-34) or vehicle daily from 16 to 22 weeks. Adult Prg4 mutant mice had decreased trabecular and cortical bone, and blunted PTH-mediated increases in bone mass. Joint range of motion and animal mobility were lower in adult Prg4 mutant versus wild-type mice. Adult Prg4 mutant mice had decreased marrow and liver fibroblast growth factor 2 (FGF-2) mRNA and reduced serum FGF-2, which were normalized by PTH. A single dose of PTH decreased the PTH/PTHrP receptor (PPR), and increased Prg4 and FGF-2 to a similar extent in liver and bone. Proteoglycan 4 supports endochondral bone formation and the attainment of peak trabecular bone mass, and appears to support skeletal homeostasis indirectly by protecting joint function. Bone- and liver-derived FGF-2 likely regulate proteoglycan 4 actions supporting trabeculae formation. Blunted PTH anabolic responses in adult Prg4 mutant mice are associated with altered biomechanical impact secondary to joint failure.

Effect of PCL integrity on biomechanical features of the medial femoral condyle

Objective To explore the biomechanical function of PCL and its different bundles and examine the biomechanical impact of posterior cruciate ligament (PCL) integrity on the medial femoral condyle. Methods Twelve fresh human cadaveric knee specimens were subjected to different axial load (0-800 N) at 0°, 30°,60°, and 90°of knee flexion. Four surgical treatments were carried out for biomechanical testing: PCL intact, anterolateral bundle (ALB) rupture, posteromedial bundle (PMB) rupture and PCL rupure. During the test, strains of middle part of the medial femoral condyle were calculated. Results At O°knee flexion, increasing strain of the medial femoral condyle was detected in PMB rupture and PCL rupture under all loading conditions. No significant difference of strain of the medial femoral condyle was noted between PCL intact and ALB rupture under any loading conditions. Compared to PMB rupture, PCL rupture had not higher strain of the medial femoral condyle under all loading conditions. At 30°, 60° and 90° knee flexion, increasing strain of the medial femoral condyle was noted in ALB rupture under higher loading conditions and PCL rupture under all loading conditions. ALB rupture under lower loading conditions and PMB rupture under all loading conditions did not significantly increased strain of the medial femoral condyle. PCL rupture had higher strain of the medial femoral condyle than ALB rupture under most of loading conditions.Conclusion The data suggest that PMB is the major stabilizing bundle of PCL in full extension, ALB is the major stabilizing bundle of PCL in knee flexion, and both bundles function through the ROM in a codominant fashion. Partial and complete ruptures of PCL may have hazardous biomechanical impacts on the medial femoral condyle during normal movement. Key words: Posterior cruciate ligament; Rupture; Biomechanics

Effect of posterior cruciate ligament rupture on biomechanical features of the medial femoral condyle

To investigate the biomechanical impact of rupture of the posterior cruciate ligament (PCL) and its various bundles on the medial femoral condyle. Twelve fresh human cadaveric knee specimens were divided into four groups: PCL intact, anterolateral band (ALB) rupture, posteromedial band (PMB) rupture and PCL complete rupture groups according to the purpose and order of testing. Strain in the middle of the medial femoral condyle was measured under different loads (200-800N) at 0°, 30°, 60°, and 90° of knee flexion. At 0° of knee flexion, compared with the PCL intact and ALB rupture groups, strain on the medial femoral condyle increased in the PMB rupture and PCL complete rupture groups under all loading conditions. There was no statistical difference between the PMB rupture and PCL complete rupture groups. At 30°, 60° and 90° of knee flexion, compared with the PCL intact group, increase in strain on the medial femoral condyle was noted in the ALB rupture group under higher loading conditions (600N and 800N) and PCL complete rupture group under all loading conditions. The PCL complete rupture group had higher strain on the medial femoral condyle than did the ALB rupture group under most loading conditions. At 0° of knee flexion, PMB rupture or PCL complete rupture can cause increase in strain on the medial femoral condyle. However, at 30°, 60° and 90° of knee flexion, ALB rupture or PCL complete rupture can cause increase in strain on the medial femoral condyle.

Biomechanical corneal changes induced by different flap thickness created by femtosecond laser

OBJECTIVE:To evaluate the impact of the creation of corneal flaps at different thicknesses on the biomechanical properties of swine corneas.METHOD:Twelve swine eyes were obtained to form two groups: 100 µm flap thickness and 300 µm flap thickness. Each eye was submitted to the following examinations: raster topography to investigate corneal curvature alterations, ocular response analyzer to investigate corneal hysteresis change, optical coherence tomography to measure central corneal and flap thickness and sonic wave propagation velocity as a measure of stiffness, before and immediately after flap creation. After flap amputation, surface wave velocity measurements were repeated.RESULTS:Measured flap thicknesses were statistically different for thin and thick flap groups, with an average of 108.5±6.9 and 307.8±11.5 µm respectively. Hysteresis and corneal resistance factor did not change significantly after flap creation in the thin flap group. With thicker flaps, both parameters decreased significantly from 8.0±1.0 to 5.1±1.5 mmHg and from 8.2±1.6 to 4.1±2.5 mmHg respectively. Simulated keratometry values increased in the thick flap group (from 39.5±1 D to 45.9±1.2 D) after flap creation but not in the thin flap group (from 40.6±0.6 D to 41.4±1.0 D). Regarding surface wave velocity analysis, the surgical procedures induced statistically lower results in some positions.CONCLUSION:In the experimental conditions established by this model, thicker flaps presented a greater biomechanical impact on the cornea.

Tenascin‐C and Matrix Metalloproteinase‐9 Levels in Crevicular Fluid of Teeth and Implants

The role of and interaction between bacterial infection and biomechanical impact in the development of peri-implant inflammatory processes is not clear. To determine the amount and concentration of tenascin-C (TNC) in gingival crevicular fluid (GCF) around teeth and in peri-implant sulcus fluid from healthy implants and implants with peri-implantitis, and to correlate it with matrix metalloproteinase-9 (MMP-9) levels. Seven control individuals and 18 patients with 41 implants with/without peri-implantitis were included. GCF was collected with filter strips and volumes were measured with a Periotron device. The amount of serum albumin per sample was quantified by densitometric analysis of Coomassie-stained sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Relative activity of MMP-9 was determined from the densitometry of zymograms. Amounts and concentrations of TNC were evaluated by ELISA. Relative MMP-9 activity was increased in peri-implantitis. A tendency was observed to measure higher TNC concentrations at teeth than at implants. The amount of TNC in GCF collected from healthy implant sites and the peri-implantitis sites was significantly different. Based on immunoblotting, TNC in GCF seemed degraded. In contrast to TNC, MMP-9 was significantly related to the PD and the volume of GCF. TNC is known to be induced in inflammation. The increase found in peri-implantitis was less than expected. In the context of peri-implantitis, TNC might be a marker of bone remodelling rather than inflammation and infection. A possible proteolytic degradation of TNC during peri-implantitis needs to be studied.

Combining Epidemiology and Biomechanics in Sports Injury Prevention Research

Several important methodological issues need to be considered when designing sports injury case-control studies. Major design goals for case-control studies include the accounting for prior injury risk exposure, and optimal definitions of both cases and suitable controls are needed to ensure this. This article reviews methodological aspects of published sports injury case-control studies, particularly with regard to the selection of controls. It argues for a new approach towards selecting controls for case-control studies that draws on an interface between epidemiological and biomechanical concepts. A review was conducted to identify sport injury case-control studies published in the peer-review literature during 1985-2008. Overall, 32 articles were identified, of which the majority related to upper or lower extremity injuries. Matching considerations were used for control selection in 16 studies. Specific mention of application of biomechanical principles in the selection of appropriate controls was absent from all studies, including those purporting to evaluate the benefits of personal protective equipment to protect against impact injury. This is a problem because it could lead to biased conclusions, as cases and controls are not fully comparable in terms of similar biomechanical impact profiles relating to the injury incident, such as site of the impact on the body. The strength of the conclusions drawn from case-control studies, and the extent to which results can be generalized, is directly influenced by the definition and recruitment of cases and appropriate controls. Future studies should consider the interface between epidemiological and biomechanical concepts when choosing appropriate controls to ensure that proper adjustment of prior exposure to injury risk is made. To provide necessary guidance for the optimal selection of controls in case-control studies of interventions to prevent sports-related impact injury, this review outlines a new case-control selection strategy that reflects the importance of biomechanical considerations, which ensures that controls are selected based on the presence of the same global injury mechanism as the cases. To summarize, the general biomechanical principles that should apply to the selection of controls in future case-control studies are as follows: (i) each control must have been exposed to the same global injury mechanism as the case, (e.g. head impact, fall onto outstretched arm); and (ii) intrinsic (individual) factors (e.g. age, sex, skill level) that might modify the person's response to the relevant biomechanical loads are adjusted when either selecting the controls or are in the analysis phase. The same considerations for control selection apply to other study designs such as matched cohort studies or case-crossover studies.

The effect of design parameters of dynamic pedicle screw systems on kinematics and load bearing: an in vitro study

As an alternative treatment for chronic back pain due to disc degeneration motion preserving techniques such as posterior dynamic stabilization (PDS) has been clinically introduced, with the intention to alter the load transfer and the kinematics at the affected level to delay degeneration. However, up to the present, it remains unclear when a PDS is clinically indicated and how the ideal PDS mechanism should be designed to achieve this goal. Therefore, the objective of this study was to compare different PDS devices against rigid fixation to investigate the biomechanical impact of PDS design on stabilization and load transfer in the treated and adjacent cranial segment. Six human lumbar spine specimens (L3-L5) were tested in a spine loading apparatus. In vitro flexibility testing was performed by applying pure bending moments of 7.5 Nm without and with additional preload of 400 N in the three principal motion planes. Four PDS devices, "DYN" (Dynesys(®), Zimmer GmbH, Switzerland), "DSS™" (Paradigm Spine, Wurmlingen, Germany), and two prototypes of dynamic rods, "LSC" with a leaf spring, and "STC" with a spring tube (Aesculap AG, Tuttlingen, Germany), were tested in comparison to a rigid fixation device S(4) (Aesculap AG, Tuttlingen, Germany) "RIG", to the native situation "NAT" and to a defect situation "DEF" of the specimens. The instrumented level was L4-L5. The tested PDS devices comprising a stiffness range for axial stiffness of 10 N/mm to 230 N/mm and for bending stiffness of 3 N/mm to 15 N/mm. Range of motion (ROM), neutral zone (NZ), and intradiscal pressure (IDP) were analyzed for all instrumentation steps and load cases of the instrumented and non-instrumented level. In flexion, extension, and lateral bending, all systems, except STC, showed a significant reduction of ROM and NZ compared to the native situation (p < 0.05). Furthermore, we found no significant difference between DYN and RIG (p > 0.1). In axial rotation, only DSS and STC reduced the ROM significantly (p < 0.005) compared to the native situation, whereas DYN and LSC stayed at the level of the native intersegmental rotation (p > 0.05). A correlation was found between axial stiffness and intersegmental stabilization in the sagittal and frontal plane, but not in the transversal plane where intersegmental stabilization is mainly governed by the systems' ability to withstand shear loads. Furthermore, we observed the systems' capacity to reduce IDP in the treated segment. The adjacent segment does not seem to be affected by the stiffness of the fixation device under the described loading conditions.

Biomechanical Influence of Disk Properties on the Load Transfer of Healthy and Degenerated Disks Using a Poroelastic Finite Element Model

Spine degeneration is a pathology that will affect 80% of the population. Since the intervertebral disks play an important role in transmitting loads through the spine, the aim of this study was to evaluate the biomechanical impact of disk properties on the load carried by healthy (Thompson grade I) and degenerated (Thompson grades III and IV) disks. A three-dimensional parametric poroelastic finite element model of the L4/L5 motion segment was developed. Grade I, grade II, and grade IV disks were modeled by altering the biomechanical properties of both the annulus and nucleus. Models were validated using published creep experiments, in which a constant compressive axial stress of 0.35 MPa was applied for 4 h. Pore pressure (PP) and effective stress (S(E)) were analyzed as a function of time following loading application (1 min, 5 min, 45 min, 125 min, and 245 min) and discal region along the midsagittal profile for each disk grade. A design of experiments was further implemented to analyze the influence of six disk parameters (disk height (H), fiber proportion (%F), drained Young's modulus (E(a),E(n)), and initial permeability (k(a),k(n)) of both the annulus and nucleus) on load-sharing for disk grades I and IV. Simulations of grade I, grade III, and grade IV disks agreed well with the available published experimental data. Disk height (H) had a significant influence (p<0.05) on the PP and S(E) during the entire loading history for both healthy and degenerated disk models. Young's modulus of the annulus (E(a)) significantly affected not only S(E) in the annular region for both disk grades in the initial creep response but also S(E) in the nucleus zone for degenerated disks with further creep response. The nucleus and annulus permeabilities had a significant influence on the PP distribution for both disk grades, but this effect occurred at earlier stages of loading for degenerated than for healthy disk models. This is the first study that investigates the biomechanical influence of both geometrical and material disk properties on the load transfer of healthy and degenerated disks. Disk height is a significant parameter for both healthy and degenerated disks during the entire loading. Changes in the annulus stiffness, as well as in the annulus and nucleus permeability, control load-sharing in different ways for healthy and degenerated disks.

Comparison of Hybrid III Child Test Dummies to Pediatric PMHS in Blunt Thoracic Impact Response

The limited availability of pediatric biomechanical impact response data presents a significant challenge to the development of child dummies. In the absence of these data, the development of the current generation of child dummies has been driven by scaling of the biomechanical response requirements of the existing adult test dummies. Recently published pediatric blunt thoracic impact response data provide a unique opportunity to evaluate the efficacy of these scaling methodologies. However, the published data include several processing anomalies and nonphysical features. These features are corrected by minimizing instrumentation and processing error to improve the fidelity of the individual force-deflection responses. Using these data, biomechanical impact response corridors are calculated for a 3-year-old child and a 6-year-old child. These calculated corridors differ from both the originally published postmortem human subject (PMHS) corridors and the impact response requirements of the current child dummies. Furthermore, the response of the Hybrid III 3-year-old test dummy in the same impact condition shows a similar deflection but a significantly higher force than the 3-year-old corridor. The response of the Hybrid III 6-year-old dummy, on the other hand, correlates well with the calculated 6-year-old corridor. The newly developed 3-year-old and 6-year-old blunt thoracic impact response corridors can be used to define data-driven impact response requirements as an alternative to scaling-driven requirements.