Cadaveric Testing Research Articles

A novel modeling approach for finite element human body models with high computational efficiency and stability: application in pedestrian safety analysis

The purpose of the current study was to develop and validate a finite element (FE) pedestrian model with high computational efficiency and stability using a novel modeling approach. Firstly, a novel modeling approach of using hollow structures (HS) to simulate the mechanical properties of soft tissues under impact loading was proposed and evaluated. Then, an FE pedestrian model was developed, employing this modeling approach based on the Total Human Model for Safety (THUMS) pedestrian model, named as THUMS-HS model. Finally, the biofidelity of the THUMS-HS model was validated against cadaver test data at both segment and full-body level. The results show that the proposed hollow structures can simulate the mechanical properties of soft tissues and the predictions of the THUMS-HS model show good agreement with the cadaver test data under impact loading. Simulations also prove that the THUMS-HS model has high computational efficiency and stability. The proposed modeling approach of using hollow structures to simulate the mechanical properties of soft tissues is plausible and the THUMS-HS model could be used as a valid, efficient and robust numerical tool for analysis of pedestrian safety in vehicle collisions.

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Purpose: The purpose of this study was to evaluate the capability of a detailed FE human body lower limb mode, called HALL (Human Active Lower Limb) model, in predicting real world pedestrian injuries and to investigate injury mechanism of pedestrian lower limb in vehicle collisions. Methods: Two real world vehicle-to-pedestrian crashes with detailed information were selected. Then, a pedestrian model combining the HALL model and the upper body of the 50th% Chinese dummy model and vehicle front models were developed to reconstruct the selected real world crashes, and the predictions of the simulations were analyzed together with observations from the accident data. Results: The results show that the predictions of the HALL model for pedestrian lower limb long bone fractures match well with the observation from hospital data of the real world accidents, and the predicted thresholds of bending moment for tibia and femur fracture are close to the average values calculated from cadaver test data. Analysis of injury mechanism of pedestrian lower limb in collisions indicates that the relatively sharper bumper of minivan type vehicles can produce concentrated loading to the lower leg and a high risk of tibia/fibula fracture, while the relatively sharper and lower bonnet leading edge may cause concentrate loading to the thigh and high femur fracture risk. Conclusions: The findings imply that the HALL model could be used as an effective tool for predicting pedestrian lower limb injuries in vehicle collisions and improvements to the minivan bumper and sedan bonnet leading edge should be concerned further in vehicle design.

Experimental and clinical analysis of the use of asymmetric vs symmetric polyethylene inserts in a mobile bearing total knee arthroplasty

PurposeThis study compared the effects of symmetric and asymmetric designs for mobile bearing polyethylene insert for total knee arthroplasty (TKA), both clinically and biomechanically through experimental cadaver tests. Methods303 patients implanted with a mobile bearing TKA were retrospectively analyzed up to 2-year follow-up with relative scores. The same femoral and tibial components were used for all the patients; 151 patients received a Symmetric Design (SD) insert and 152 an Asymmetric Design (AD). A biomechanical experimental test was performed to improve the comprehension of the clinical results, analyzing passive squat on 5 cadaveric knee specimens: internal-external rotations of femur and tibial insert respect to the tibia tray were analyzed in native and implanted configurations (with both symmetrical and asymmetrical inserts for each specimen). ResultsAfter surgery, patients' average flexion improved from 105° (with preoperative extension deficit of 5°), to 115° (SD-group) and 120° (AD-group) at the 2-year follow-up. There was no postoperative extension deficit. AD-group presented better ability to perform certain routines and wasn't affected by any pain, while antero-lateral pain was reported in some SD-group patients. The experimental tests returned no statistically relevant difference in tibio-femoral flexion-extension and internal-external rotations among all the three configurations tested; a statistically significant difference is found for insert-tray internal-external rotations between SD and AD configurations; in details, the AD insert showed insert-tray angles comparable to the ones found for femoral component-tibial tray, while the SD insert returned lower angular values. ConclusionClinically and biomechanically, an asymmetric mobile bearing insert could represent a valid alternative to symmetric mobile bearing insert. Level of evidenceIII, Case-control study Retrospective comparative study.

Angular needle tracker and stabilizer for image-guided interventions

Introduction Minimally invasive image-guided interventions have changed the face of procedural medicine. For these procedures, safety and efficacy depend on precise needle placement. Needle targeting devices help improve the accuracy of needle placement, but their use has not seen broad penetration. Some of these devices are costly and require major modifications to the clinical workflow. In this article, we developed a low-cost, disposable, and easy-to-use angulation tracking device, which was based on a redesigned commercial passive needle holder. Material and methods The new design provided real-time angulation information for needle tracking. In this design, two potentiometers were used as angulation sensors, and they were connected to two axes of the passive needle holder’s arch structure through a 3 D-printed bridge structure. A control unit included an Arduino Pro Mini, a Bluetooth module, and two rechargeable batteries. The angulation was calculated and communicated in real time to a novel developed smartphone app, where real-time angulation information was displayed for guiding the operator to position the needle to the planned angles. Results The open-air test results showed that the average errors are 1.03° and 1.08° for left–right angulation and head–foot angulation, respectively. The animal cadaver tests revealed that the novel system had an average angular error of 3.2° and a radial distance error of 3.1 mm. Conclusions The accuracy was comparable with some commercially available solutions. The novel and low-cost needle tracking device may find a role as part of a real-time precision approach to both planning and implementation of image-guided therapies.

Magnetic Resonance Image Based Computational Modeling for Anterior Cruciate Ligament Response at Low Knee Flexion Angle

Abstract A three-dimensional (3D) finite element (FE) human knee joint model developed from magnetic resonance images (MRIs) has been validated with the sets of experimental results in a normalized scale. The performance of the 3D FE knee joint model has been tested, simulating a physical experiment. The experiment provided the direct measurement of anterior cruciate ligament (ACL) strains due to the forces of quadriceps muscle force (QMF) followed by ground reaction force (GRF) at low knee flexion. Accurate and precise anatomy has been obtained from segmented MRI images. The ACL strain subject to the loading was calculated and analyzed compared with the measured data from the experimental tests. The study shows that the pre-activated ACL strain, which is measured before the application of GRF, increased nonlinearly with increasing QMF before landing. However, the total ACL strain, which is measured after both QMF and GRF applied, reaches out to the limited constant value (6%) instead of crossing the ACL failure value. These results suggest that the forces generated from QMF and GRF at low flexion may not bring ACL to a failure level as presented in the experimental tests. The results of the FE model fall into the standard deviations of the 22 cadaveric knees testing results, which represents the successful mechanical modeling of ACL and the surrounding structures of the human knee joint. The model may further be used to investigate the risks of the ACL injury.

Lower neck injury criteria for THOR and Hybrid III dummies in rear impact

Objective The objectives of the study are to derive lower-neck-injury probability curves under rear impact loading from matched pair Hybrid III and THOR dummy tests. Methods Twelve whole-body and 15 isolated head-neck rear-impact sled tests were conducted using the 2 dummies. They were positioned on a rigid seat that was attached to an acceleration sled. The dummies were positioned with the head parallel to the ground, torso against the seat back, and legs stretched such that there was no axial rotation. The acceleration pulse matched the previous in-house human cadaver tests. The 6-axis lower-neck load cell was used in both dummies. For the isolated rear-impact tests, the head-neck was excised from the dummies, and the lower-neck load cell was mounted to the top of the sled with the head parallel to the ground and such that the acceleration vector was in the rear impact mode. Lower-neck loads and lower-neck-injury criteria (LNij) were obtained using the load cell data and survival analysis was used to develop injury-assessment-risk values and curves for both dummies. The LNij criteria were determined for both dummies using the intercept value corresponding to the 90% probability level for the forces and moments. Results The lognormal and Weibull distributions were the optimal distributions for the Hybrid III and THOR devices. At the 50% risk level, the mean LNij was 1.1 and NCIS was 0.77 for the Hybrid III, and 1.5 and 0.30 for the THOR device. The quality indices were in the fair range and good range for the 2 dummies, respectively, at this risk level. Conclusions The lower neck based LNij injury assessment risk curves and reference values, IARCs and IARVs, serve as the first dataset for injury assessments, and the THOR may be a better test device for assessing injures in rear impact environments.

Radioulnar joint reconstruction: a novel surgical technique and biomechanical assessment for chronic instability

PurposeThis study aims to describe and biomechanically evaluate a novel technique using a strip of the flexor carpi ulnaris tendon for distal radioulnar joint reconstruction.MethodsSurgical technique was thoroughly detailed, and a cadaveric biomechanical test was conducted to evaluate sagittal plane stability. Pronosupination range of motion was measured before and after the procedure. Dorsal and volar translation resistances were checked in three situations: with the uninjured triangular fibrocartilage complex, after its complete resection and after the surgical procedure.ResultsFor distal radioulnar joint translation, higher values were found both in dorsal and volar translation in situations with an injured triangular fibrocartilage complex, with means equal to 25.4 mm (SD: 9.4 mm) and 26.1 mm (SD: 8.0 mm), respectively. For intact triangular fibrocartilage complex, both dorsal and volar translations averages were 3.4 mm (SD: 0.9 mm) and 4.5 mm (SD: 1.8 mm), respectively. Finally, when evaluating dorsal and volar translations after surgical reconstruction, means were 6.3 mm (SD: 1.3 mm) and 6.8 mm (SD: 0.9 mm), respectively. Regarding supination and pronation range of motion, which ranged from 57.9 to 63.4o, there were no differences in mean and median measures, when the cadavers with intact and reconstructed triangular fibrocartilage complex were compared (p > 0.05).ConclusionPromising mechanical evaluations encourage us to hypothesize that the technique effectively reconstructs the dorsal and volar radioulnar ligaments, preserving pronosupination and maintaining the physiological characteristics of the wrist joint. Clinical comparative studies are still necessary to fully validate this procedure.Level of evidenceTherapeutic - Level V.

Effects of external crushing forces on a novel below-the-knee vascular implant.

The Tack Endovascular System® is a novel vascular implant designed to focally treat dissections with low radial force and minimal metal burden. As there are currently no approved below-the-knee (BTK) implants in the USA, a unique, 3-stage model was developed to characterize crush deformation and fracture potential of the Tack Endovascular System in BTK arteries. First, 35 Tack® implants were deployed bilaterally in the posterior tibial, anterior tibial, and peroneal arteries of 3 cadavers, and clinically relevant external forces were applied to simulate BTK crushing deformation including focal load, leg crossing, and leg bending. Intravascular ultrasound images of the implanted vessels were used to assess the magnitude of artery deformation. Outputs of the cadaver testing were input into a finite element analysis (FEA) model to determine the appropriate conditions for subsequent bench testing. Tack implants were then subjected to increasing crush forces at 30Hz for up to 650,000 cycles at 25% flat plate deformation within the worst-case FEA test condition. Crush deformation across all arteries ranged from 0% to 23.1%. The posterior tibial artery and large male cadaver exhibited the most vulnerability to external crush forces, while the small female model exhibited the most resistance. No fractures were observed during cadaver or bench testing. This study characterized deformation forces in tibial arteries during various loading conditions. Tack implants withstood the loading conditions without fracture within the limits of this ex-vivo human vascular model and in-vitro bench testing.

Accuracy of fit analysis of the patient-specific Groningen temporomandibular joint prosthesis

Total joint replacement (TJR) with a prosthesis can be indicated for patients with severe temporomandibular joint (TMJ) dysfunction. Surgical accuracy is necessary for correct translation of the preoperatively predicted functional outcome, wear, and biomechanical behaviour of the patient-specific TMJ-TJR prosthesis. This study describes the first clinical applications of the patient-specific TMJ-TJR prosthesis according to the Groningen principles (G-TMJ-TJR), which was developed and validated in a prior human cadaver test study. The aim of this study was to validate the accuracy of placement of the patient-specific G-TMJ-TJR in the clinical setting. It was hypothesized that a virtual surgical plan (VSP) combined with guided placement of the patient-specific G-TMJ-TJR would be performed as predictably and accurately as in the prior cadaver series. All patients who received a VSP-based patient-specific G-TMJ-TJR between December 2017 and March 2020 were included in this study. The accuracy analysis was based on postoperative cone beam computed tomography (CBCT) data. All 11 prostheses could be inserted using routine pre-auricular and retromandibular surgical approaches. Analysis of the VSPs and postoperative CBCTs showed an average three-dimensional deviation of 1.07mm (standard deviation 0.46mm, range 0.33–1.91mm) for all of the fossa and mandibular components. The patient-specific G-TMJ-TJR can be applied predictably and accurately in a clinical setting.

186. Comparison of a 3D printed truss-based lateral interbody device to an annular lateral interbody device for resistance to subsidence: a cadaveric study

BACKGROUND CONTEXT Endplate decortication, substantive physiologic loads and inappropriate cage design may contribute to subsidence. Severe subsidence can lead to nerve compression and pain that may require revision surgery. Additionally, lateral approaches may be more susceptible to subsidence due to indirect decompression. Additive (3D) manufacturing has enabled the creation of implants with advanced structural designs that differ in endplate contact surface topology and load distribution at the bone- implant interface as compared to traditional annular designs. PURPOSE The purpose of this study is to compare two commercially available lateral interbody devices of the same size for resistance to subsidence. One device had a truss endplate contact topology and the other had an annular structure. Additionally, the study is designed to compare subsidence in the presence and absence of endplate decortication. STUDY DESIGN/SETTING Cadaver testing using human vertebral bones. PATIENT SAMPLE N/A OUTCOME MEASURES Subsidence resistance of different interbody constructs. METHODS A total of 48 vertebral bones with bone mineral density > 1g/cm2, obtained from 8 fresh male human lumbar spines (L1-L5), were dissected, cleaned and randomized into 4 groups, which included short and long lateral titanium truss and carbon fiber annular cages. Both cages had dimensions of 18mm AP depth, 12mm height in 40mm (short) and 60mm (long). These were evaluated with both intact and decorticated vertebrae (n=6). The inferior endplate of each vertebral bone was fixed into bondo block and the potted vertebra were placed in a fixture gripped in a vice centered with the actuator of a MTS mechanical testing unit.To mimic clinical subsidence displacement, a compressive load was applied to the top endplate of each implant at a rate of 5mm/min. Load displacement at 1 and 2mm of subsidence was collected and recorded for each test combination. Two-way ANOVA with Sidak-Bonferroni Posthoc was used for multiple comparisons and analysis of statistical significance. RESULTS The subsidence resistance of the truss cage was significantly greater than the annular cage of corresponding length when tested with an intact or decorticated endplate. The resistance load was 670N vs 540N (P=0.004) at 1mm subsidence and 1200N vs 920N (p=0.002) at 2mm in short Truss versus short Annular cage. For long cages the resistance load at was 840N vs 630N in (P=0.001) at 1mm subsidence and 1650N vs 1235N in (P CONCLUSIONS The truss endplate topology demonstrated significantly better resistance to subsidence for vertebral bone with intact or decorticated endplates as compared to the same size annular cage. Improved subsidence resistance of the truss cage may be due to the distribution of load across a larger cross-sectional area at the bone/implant interface (increased line length contact; snowshoe effect) where the load is uniformly distributed across more of the interbody footprint. Although this study did not control for differences in material composition and stiffness, a separate controlled study using foam blocks demonstrated that the implant's surface contact topology played a greater role than the material and the structural modulus for resisting subsidence. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

The relationship between measures of foot mobility and subtalar joint stiffness using vibration energy with color Doppler imaging-A clinical proof-of-concept validation study.

IntroductionSubtalar joint (STJ) dysfunction can contribute to movement disturbances. Vibration energy with color Doppler imaging (VECDI) may be useful for detecting STJ stiffness changes.Objectives(1) Support proof-of-concept that VECDI could detect STJ stiffness differences; (2) Establish STJ stiffness range in asymptomatic volunteers; (3) Examine relationships between STJ stiffness and foot mobility; and (4) Assess VECDI precision and reliability for examining STJ stiffness.MethodsAfter establishing cadaveric testing model proof-of-concept, STJ stiffness (threshold units, ΔTU), ankle complex passive range-of-motion (PROM) and midfoot-width-difference (MFWDiff) data were collected in 28 asymptomatic subjects in vivo. Three reliability measurements were collected per variable; Rater-1 collected on all subjects and rater-2 on the first ten subjects. Subjects were classified into three STJ stiffness groups.ResultsCadaveric VECDI measurement intra-rater reliability was 0.80. A significantly lower STJ ΔTU (p = .002) and ankle complex PROM (p < .001) was observed during the screw fixation versus normal condition. A fair correlation (r = 0.660) was observed between cadaveric ΔTU and ankle complex PROM. In vivo VECDI measurements demonstrated good intra-rater (0.76–0.84) versus poor inter-rater (-3.11) reliability. Significant positive correlations were found between STJ stiffness and both dorsum (r = .440) and posterior (r = .390) PROM. MFWDiff exhibited poor relationships with stiffness (r = .103) and either dorsum (r = .256) or posterior (r = .301) PROM. STJ stiffness ranged from 2.33 to 7.50 ΔTUs, categorizing subjects’ STJ stiffness as increased (n = 6), normal (n = 15), or decreased (n = 7). Significant ANOVA main effects for classification were found based on ΔTU (p< .001), dorsum PROM (p = .017), and posterior PROM (p = .036). Post-hoc tests revealed significant: (1) ΔTU differences between all stiffness groups (p < .001); (2) dorsum PROM differences between the increased versus normal (p = .044) and decreased (p = .017) stiffness groups; and (3) posterior PROM differences between the increased versus decreased stiffness groups (p = .044). A good relationship was found between STJ stiffness and dorsum PROM in the increased stiffness group (r = .853) versus poor, nonsignificant relationships in the normal (r = -.042) or decreased stiffness (r = -.014) groups.ConclusionPROM may not clinically explain all aspects of joint mobility. Joint VECDI stiffness assessment should be considered as a complimentary measurement technique.

Developing a heuristic relationship to predict the spinal injury during vertical impact for autonomous vehicle and bio environment

Background and objectiveRecent research and tested data suggested that spinal injuries occur more often in a frontal impact. Most of the published information is focused on the lumbar spinal injury with respect to axial compression force by varying the height of drops. Parametric studies on the lumbar spinal injury are very scanty. Therefore, the present investigation aimed to optimize the effects of drop height, torso weight and seat angle on the characterization of lumbar injury criteria MethodsA detailed finite element model of a spine with multi-segmented spinal columns is developed and validated with the experimental or cadaveric tests using CORA evaluation. Hence, Dynamic loading studies or weight drop techniques were used to characterize the effect of drop height, seat angle and torso weight of the upper body on the lumbar spinal injury during a frontal impact. Parametric simulations were carried out using response surface methodology (RSM). Test of significance (p < 0.05) on the parameters was carried out using ANOVA. Desirability Function Approach is used to optimize the parameters for better safety design. ResultsThe result shows that all the factors considered in the experiment are related to the risk of lumbar spinal injury during the frontal impact. All the factors selected, the drop height, torso weight and the seat angle were the most prominent element in determining the lumbar spinal injury. The injury increased with the increase in the posture angle of the seat. Optimal parameters were determined for the better safety of the occupants as seat angle of 105°, drop height 500 mm and torso weight of 25 kg in vehicle design. During vertical impact, posterior undergoes maximum impact in the portions of vertebra and confirmed with the patient case study fracture of vertical drop incident. ConclusionsThis research insight gives an improved understanding of the parametric influence of design alternatives to minimize the risk of lumbar spinal injury in automotive vehicles. The optimal combination of drop height and the seat angle provides futuristic view on autonomous vehicle seat design.

Influence of occupant collision state parameters on the lumbar spinal injury during frontal crash

IntroductionDeveloped a detailed finite element model of spine and validated with the experimental or cadaveric tests to gain insight on occupant safety. ObjectivesThis study evaluates the influence of occupant collision state parameters such as height of the drop, occupant seating posture (occupant posture angle) and mass of the upper body on the risk of lumbar spinal injury during a frontal crash. MethodsThis parametric evaluation utilizing response surface methodology (RSM) performed. ANOVA was used to test the significance of parameters. ResultsHigher axial force of 3547 N is observed with higher dropping distance of 1500 mm. Similarly, higher strain and energy absorption were observed for the same dropping condition respectively. ConclusionThe result shows that all the factors considered in the experiment contribute to the risk of spinal lumbar injury during the frontal crash. Among all, height of the drop and the occupant posture angle are the most significant parameters in determining the lumbar spinal injury of occupant. It is observed that the injury criteria are directly proportional to the posture angle of the seat and height of drop.

Statistics in experimental studies on the human spine: Theoretical basics and review of applications

Proper statistical analysis is essential in the research studies. In particular, as regards the in vitro testing of the lumbar spine, the criteria for the standardization have been extensively discussed but the use of statistics has not been reviewed. Unfortunately, cadaveric testing is a very difficult and complex experimental field, in which many factors such as collection times, costs, funding, personnel and logistic issues, availability of implant components, can determinate low sample sizes, with impacts on the statistical evaluation. Moreover, as in any other field, some errors can be commonly made in the choice of the most appropriate statistical tests. The present tutorial article provides a comprehensive overview of the theoretical basics of the statistical approach, focusing on the experimental testing of the lumbar spine. Reference values about adequate sample size and statistical power were provided. The use of statistics was reviewed in a selection of 20 papers, chosen among the most cited and representative contributions for the in vitro study of the lumbar spine. Overall, only 7 in 20 papers applied fully corrected procedures. The achieved power, calculated for the medium conventional level of the effect size, ranged from 0.13 to 0.99 but overall was found rather poor, below 0.6. The study also revealed that applying incorrect statistical tests and having low sample size can impact p-value and power, respectively, with consequences on the identification of the significant outcomes. We emphasize that this review is not intended as a mere critical analysis from a statistical perspective, but as a constructive investigation aimed to support the researchers in the challenging field of cadaveric testing. It is worth noting that the provided recommendations and reference values can be also accounted for experimental scenarios testing the other spine regions, either in human or in animal models.

Impact of scapular notching on glenoid fixation in reverse total shoulder arthroplasty: an in vitro and finite element study

The high incidence of scapular notching in reverse total shoulder arthroplasty (RTSA) has spurred several methods to minimize bone loss. However, up to 93% of RTSAs accompanying scapular notching have been reported to maintain good implant stability for over 10 years. This study was conducted to investigate the relationship between scapular notching and glenoid fixation in RTSA. Cadaveric testing was performed to measure the notch-induced variations in strain on the scapular surface and micromotion at the bone-prosthesis interface during arm abductions of 30°, 60°, and 90°. Finite element analysis was used to further study the bone and screw stresses as well as the bone-prosthesis micromotion in cases with a grade 4 notch during complicated arm motions. The notch resulted in an apparent increase in inferior screw stress in the root of the screw cap and at the notch-screw conjunction. However, the maximum stress (172 MPa) along the screw after notching is still much less than the fatigue strength of the titanium screw (600 MPa) under cyclic loading. The bone-prosthesis micromotion results did not present significant notch-induced variations. Scapular notching will lead to few impacts on the stability of an RTSA on the glenoid side. This finding may explain the long-term longevity of RTSA in cases of severe scapular notching. The relationship between scapular notching and weak regions along the inferior screw may explain why fractures of the inferior screw are sometimes reported in patients with RTSA clinically.

Biomechanical analysis for five fixation techniques of Pauwels-III fracture by finite element modeling

Background and objectivesThere are many fixation methods for Pauwels- III fracture, the most common implants are Locking Plate (LP), Dynamic Hip Screw (DHS), Multiple Lag Screw (MLS), and mixed fixture (DHS+MLS) implants, the common procedure is HemiArthroplasty (HA). However, how these fixtures biomechanically function is not clear. The aims of this study are to compare the mechanical behaviors of these five implants by finite element modeling and determinate the most suitable procedure for individuals with Pauwels- III fractures. MethodsWe gathered 20 sets of femur images from CT scans in the *.dicom format first, and then processed them by using reverse engineering software programs, such as Mimics, Geomagic Studio, UG-8, Pro-Engineer and HyperMesh. Finally, we assembled and analyzed the five types of fixture models, the LP, DHS, MLS, DHS+LS and HA models, by AnSys. ResultsThese numerical models of Pauwels III fractures, including fixators and a simulative HA, were validated by a previous study and a cadaver test. Our analytical findings include the following: the displacements of all fixtures were between 0.3801 and 1.0834 mm, and the differences were not statistically significantly different; the resulting average peaks in stress were e(Ha) = 43.859 ≤ d(LP) = 60.435 ≤ b(MLS) = 68.678 < c(LS+DHS) = 98.478 < a(DHS) = 248.595 in Mpa, indicating that the stress of DHS and DHS+LS are greater than those of LP, HA and MLS, while the last 3 models were not significantly different. ConclusionsTo optimize the treatment for Pauwels III factures clinically, HA and LP should be proposed.

Validation and sensitivity of model-predicted proximal tibial displacement and tray micromotion in cementless total knee arthroplasty under physiological loading conditions

The initial fixation of cementless tibial trays after total knee arthroplasty is crucial to bony ingrowth onto the porous surface of the implants, as micromotion magnitudes exceeding 150 μm may inhibit bone formations and limit fixation. Experimental measurement of the interface micromotions is still very challenging. Thus, previous studies investigated micromotions at the bone-tray interface via finite element methods, but few performed direct validation via in vitro cadaveric testing under physiological loading conditions. Additionally, previous models were validated by solely considering relative displacements of the marker couples placed around the tray-bone interface. In this paper, we present an experimental-computational validation framework for investigating micromotions at the tray-bone interface under physiological conditions. Three cadaveric specimens were implanted with cementless rotating-platform implants and tested under gait, deep knee bending, and stair descent loads. Corresponding subject-specific finite element models were developed and used to predict the marker (tray-bone) relative displacements and tibial surface displacements. Experimental measurements were used to validate model estimations. Subsequent sensitivity analyses were performed on implantation and friction parameters to represent model uncertainties.The models appropriately differentiated between locations, activities, and specimens. The average root-mean-square (RMS) differences and correlations between measured marker relative displacements and predictions from the ‘best-matching’ models were 13.1 μm and 0.86. RMS differences and correlations between measured surface displacements and predictions were 78.9 μm and 0.84. Full-field interface micromotions were investigated and compared with predicted marker relative displacements. The marker relative displacements underestimated the actual interface micromotions. Initial tray-bone alignment in anterior-posterior, flexion-extension, and varus-valgus degrees of freedom have a considerable impact on the interface micromotions. The validated cadaveric models can be further used for pre-clinical assessments of new TKR tray design. The outcomes of the sensitivity analyses provide further insights into reducing interface micromotions via clinical techniques.

Biomechanics of prophylactic tethering for proximal junctional kyphosis: effects of cyclic loading on tether strength and failure properties.

Biomechanical evaluation of woven polyester tethers. To quantify changes in tether elongation, stiffness, and failure characteristics after cyclic loading. Ligamentous augmentation is gaining interest as a technique to prevent proximal junctional kyphosis (PJK) in adult spinal fusions. There are a lack of data regarding the effects of cyclic loading on polyester tether mechanical properties. Tether stretch may lead to loss of stabilization and increased risk of tether failure. Biomechanical data are needed to determine the effects of cyclic loading on tether integrity. Testing was done in two materials: (1) a synthetic cortical bone composite to determine baseline mechanical properties, and (2) nine cadaveric L1 spinous processes. 5mm woven polyester tethers were looped through 2.5mm holes drilled in each material. First, five tethers were tested directly to failure in the synthetic bone to establish baseline failure properties. Next, tethers were tested at one of the three cyclic load ranges [5%, 25%, and 50% (n = 5 each) of baseline failure] for 1000 cycles and then loaded to failure. Cadaveric tests were done at the 25% range and compared to synthetic bone tests at the same range. Cadaveric failure tests were classified as either tether failure or spinous process bone failure. Greater cyclic loading range had a significant effect on tether loop elongation, increased stiffness, and decreased ultimate tensile force. Among the cadaveric failure tests, 56% resulted in tether failure and the remaining 44% resulted in bone failure. Polyester tethers stretch significantly when loaded to physiological ranges. Anticipation of tether stretch may be an important consideration for a tethering strategy to prevent PJK. Improved understanding of tether material properties can provide guidance for the evaluation of clinical outcomes associated with techniques to reduce the risk of PJK caused by ligamentous laxity. Biomechanical study.

Kinematics and dynamics of pedestrian head ground contact: A cadaver study

Pedestrians struck by vehicles are generally injured by the primary vehicle contact but also the secondary ground contact. However, experimental evidence for ground contact injuries is limited. Here we report on six staged cadaver tests at 20–30 km/h with passenger cars/vans in which we recorded the whole process from first pedestrian contact until after the end of the ground contact is complete using high-speed video and accelerometers mounted in the cadavers. Results show distinct phases for pedestrian flight and ground contact in addition to the already established vehicle contact phases. No skull fractures were observed in any of the tests. However, for the speed range tested, the linear and angular head injury risk (evaluated using HIC/3ms & BrIC respectively) is generally higher from the ground contact compared to the vehicle contact. Although not yet clearly understood, angular head injury risk during ground contact is higher for the 20 km/h tests compared to the 30 km/h tests. A good comparison was observed with respect to previously predicted ground contact mechanisms and head impact speeds from multibody modelling. These results emphasize the importance of ground related injuries to pedestrians when struck by vehicles at speeds of 20–30 km/h and provide a unique dataset for computational model validation of pedestrian ground contact.

Preclinical Evaluation of the Versius Surgical System, a New Robot-assisted Surgical Device for Use in Minimal Access Renal and Prostate Surgery

BackgroundMinimal access surgery (MAS) is well-established in urological surgery. However, MAS is technically demanding and associated with a prolonged learning curve. Robot-assisted laparoscopy has made progress in overcoming these challenges. ObjectiveThe aim of this study was to evaluate the feasibility of a new robot-assisted surgical system (the Versius Surgical System; CMR Surgical, Cambridge, UK) for renal and prostate procedures in a preclinical setting, at the IDEAL-D phase 0. Design, setting, and participantsCadaveric sessions were conducted to evaluate the ability of the system to complete all surgical steps required for a radical nephrectomy, prostatectomy, and pelvic lymph node dissection. A live animal (porcine) model was also used to assess the surgical device in performing radical nephrectomy safely and effectively. Procedures were performed by experienced renal and prostate surgeons, supported by a full operating room team. Outcome measurements and statistical analysisSurgical access and reach were evaluated by the lead surgeon using a visual analogue scale. The precise surgical steps conducted to make the assessment that the procedures could be completed fully were recorded, as well as instruments used (including manual laparoscopic instruments) and endoscope angle. Results and limitationsIn total, all 24 procedures were completed successfully in cadavers by eight different lead surgeons. Positioning of the ports and bedside units reflected the lead surgeon’s preferred laparoscopic set-up and enabled good surgical access and reach, as quantified by a median visual analogue score of ≥6.5. Radical nephrectomies performed in pigs were all completed successfully, with no device- or non–device-related intraoperative complications recorded. Testing in human cadavers and pig models balances the bias introduced by each model; however, it is impossible to completely replicate the experience and performance of the robot for surgery in live humans. ConclusionsThis is the first preclinical assessment of the Versius Surgical System for renal and prostate procedures. The safety and effectiveness of the system have been demonstrated and warrant progressive assessment in a clinical setting utilising the IDEAL-D framework. Patient summaryIn this report, we looked at the usability of a new robot-assisted surgical device for renal and prostate surgery by testing the system in cadavers and pigs. We found that a number of different surgeons and operating team personnel were able to use the system to successfully complete the procedures under evaluation. We conclude that the system is ready to be tested in live human studies.