Most Anterior Cruciate Ligament Injuries in Professional Athletes Occur Without Contact to the Injured Knee: A Systematic Review of Video Analysis Studies.

PURPOSE: To systematically review studies utilizing video analyses to evaluate anterior cruciate ligament (ACL) injury mechanisms in athletes during sport to better understand risk factors and the potential for injury prevention. METHODS: A literature search was conducted in accordance with the 2020 PRISMA guidelines statement using SCOPUS, PubMed, Medline, and the Cochrane Central Register for Controlled Trials from database inception through June 2023. Inclusion criteria including studies reporting on ACL injury mechanisms occurring in athletes based on video analysis. Athlete demographics, injury mechanisms, position of the lower extremity, and activity at the time of injury were recorded. RESULTS: A total of 13 studies, consisting of 542 athletes, met inclusion criteria. The majority of athletes competed at the professional level (91%, n=495/542) with 79% (n=422/536) of athletes being male. The most common sports were soccer (33%, n=178/542) and American football (26%, n=140/542). The most common injury mechanism was non-contact in 42.9% (n=230/536) of athletes, followed by indirect contact (32.6%, n=175/536) and direct contact (22.4%, n=120/536). The most common position of injury was with a planted foot ( 91.7%, n=110/120), full or near full knee extension ( 84.4%, n=49/58), and axial loading ( 81.3%, n=87/107). Injuries commonly involved a deceleration/shift in momentum ( 50.4%, n=123/244) or pivoting maneuver ( 36.1%, n=77/213). At the time of injury, the knee commonly fell into valgus ( 76.8%, n=225/293) with associated internal (53.5%, n=46/86) or external tibiofemoral rotation ( 57.7%, n=101/175). CONCLUSIONS: The majority of ACL injuries, when evaluated by video analysis, involve professional athletes participating in soccer and American football. The most common injury mechanism occurred without contact with the knee in extension during a deceleration or momentum shift, with resultant valgus and rotational force across the knee. LEVEL OF EVIDENCE: IV; Systematic review of level IV studies.

The Effects of Lower Leg Compression Garments on Lower Extremity Sports Injuries, Subjective Fatigue and Biomechanical Variables: A Systematic Review with Meta-analysis.

The objective of this study was to systematically review the literature on the effect of CGs versus non-CGs (such as regular socks) or versus placebo garments on 1) the incidence of lower extremity sports injuries and 2) subjective ratings of fatigue and biomechanical variables in athletes at participating in any sport that required any level of running performance, given that fatigue-related biomechanical alterations may increase the risk of sports injuries. This study was a systematic review with meta-analyses. PubMed, Embase, CINAHL, Cochrane, PEDro, and Scopus were searched for eligible studies until 7 July 2021. Two reviewers independently assessed the risk of bias using the Cochrane Collaboration's tool for risk of bias. Meta-analyses were performed using a random-effects model. The Grades of Recommendation, Assessment, Development and Evaluation (GRADE) approach was used to assess the certainty of evidence for all outcome measures. Twenty-three studies, all with a high risk of bias, were included. Nineteen studies were used in the meta-analyses. No studies focused on the effect of CGs on the incidence of lower extremity sports injuries in athletes. Seventeen studies investigated the effect of CGs on subjective ratings of fatigue, but meta-analysis showed no difference in effectiveness between CGs versus non-CGs (such as regular socks) and versus placebo CGs (low certainty evidence). Because of heterogeneity, pooling of the results was not possible for the biomechanical variables. Nonetheless, low certainty evidence showed no effect of CGs. We identified no evidence for a beneficial or detrimental effect of lower leg CGs on the occurrence of lower extremity sports injuries, subjective ratings of fatigue, or biomechanical variables in athletes at any level of running performance. Based on the variable use of running tests, definitions used for biomechanical variables, and reporting of CG characteristics and more standardized reporting is recommended for future studies evaluating CGs.

Non-invasive in vivo study of morphology and mechanical properties of the median nerve.

The current literature studied the median nerve (MN) at specific locations during joint motions. As only a few particular parts of the nerve are depicted, the relevant information available is limited. This experiment investigated the morphological and biomechanical properties of the MN. The effects of the shoulder and wrist motions on MN were explored as well. Eight young healthy female individuals were tested with two-dimensional ultrasound and shear wave elastography (SWE). The morphological and biomechanical properties were examined in limb position 1, with the wrist at the neutral position, the elbow extended at 180°, and the shoulder abducted at 60°. In addition, the experiment assessed the differences among the wrist, forearm, elbow, and upper arm with Friedman's test and Bonferroni post hoc analysis. Two groups of limb positions were designed to explore the effects of shoulder movements (shoulder abducted at 90° and 120°) and wrist movements (wrist extended at 45° and flexed at 45°) on the thickness and Young's modulus. Differences among the distributions of five limb positions were tested as well. The ICC3, 1 values for thickness and Young's modulus were 0.976 and 0.996, respectively. There were differences among the MN thicknesses of four arm locations in limb position 1, while Young's modulus was higher at the elbow and wrist than at the forearm and upper arm. Compared to limb position 1, only limb position 4 had an effect on MN thickness at the wrist. Both shoulder and wrist motions affected MN Young's modulus, and the stiffness variations at typical locations all showed a downward trend proximally in all. The distributions of MN thickness and Young's modulus showed fold line patterns but differed at the wrist and the pronator teres. The MN in the wrist is more susceptible to limb positions, and Young's modulus is sensitive to nerve changes and is more promising for the early diagnosis of neuropathy.

Biomechanical behavior of implant retained prostheses in the posterior maxilla using different materials: a finite element study.

BACKGROUND: The aim of this study is to evaluate the biomechanical behavior of the mesial and distal off-axial extensions of implant-retained prostheses in the posterior maxilla with different prosthetic materials using finite element analysis (FEA). METHODS: Three dimensional (3D) finite element models with three implant configurations and prosthetic designs (fixed-fixed, mesial cantilever, and distal cantilever) were designed and modelled depending upon cone beam computed tomography (CBCT) images of an intact maxilla of an anonymous patient. Implant prostheses with two materials; Monolithic zirconia (Zr) and polyetherketoneketone (PEKK) were also modeled .The 3D modeling software Mimics Innovation Suite (Mimics 14.0 / 3-matic 7.01; Materialise, Leuven, Belgium) was used. All the models were imported into the FE package Marc/Mentat (ver. 2015; MSC Software, Los Angeles, Calif). Then, individual models were subjected to separate axial loads of 300 N. Von mises stress values were computed for the prostheses, implants, and bone under axial loading. RESULTS: The highest von Mises stresses in implant (111.6 MPa) and bone (100.0 MPa) were recorded in distal cantilever model with PEKK material, while the lowest values in implant (48.9 MPa) and bone (19.6 MPa) were displayed in fixed fixed model with zirconia material. The distal cantilever model with zirconia material yielded the most elevated levels of von Mises stresses within the prosthesis (105 MPa), while the least stresses in prosthesis (35.4 MPa) were recorded in fixed fixed models with PEKK material. CONCLUSIONS: In the light of this study, the combination of fixed fixed implant prosthesis without cantilever using a rigid zirconia material exhibits better biomechanical behavior and stress distribution around bone and implants. As a prosthetic material, low elastic modulus PEKK transmitted more stress to implants and surrounding bone especially with distal cantilever.

A New Biomechanical Deformation Response Parameter: Change in Central Corneal Thickness During Air Puff Induced Corneal Deformation.

PURPOSE: To investigate the percent change in central corneal thickness (%ΔCCT) during air-puff-induced deformation as an indicator of corneal biomechanical response. METHODS: Forty ex vivo human eyes from forty donors were imaged using the CorVis ST at experimentally controlled intraocular pressure (IOP) of 10, 20, 30, and 40 mmHg, followed by uniaxial strip testing to calculate tensile modulus. The CorVis ST research software tracked the anterior and posterior cornea edges and determined the dynamic corneal response (DCR) parameters. Eyes were excluded if image quality or posterior tracking issues were present. Custom algorithms were used to calculate CCT during deformation using a ray-tracing method to correct for Scheimpflug and optical distortion within each image. Correlation and stepwise regression analyses between the shape-related DCR parameters and %ΔCCT were conducted. A mixed model analysis was performed to test the effect of IOP and the strongest significant predictors of the stepwise regression on %ΔCCT. The significance threshold was set to p < 0.05. RESULTS: Thirty eyes were ultimately analyzed and CCT increased significantly from the pre-deformation state to the highest concavity state at each IOP level (p < 0.001). IOP and multiple shape DCRs were found to be significantly related to %ΔCCT (p < 0.0001). The strongest predictor of %ΔCCT was integrated inverse radius (IIR) (p < 0.0001; partial R2 = 0.4772) with no other parameter having a partial R2 value greater than 0.04. The mixed model analysis showed that IIR was the sole predictor (p = 0.0098) and IOP was no longer significant as a single predictor. However, the interaction of IIR with IOP (p = 0.0023) had a significant effect on %ΔCCT. CONCLUSION: Percent change in CCT is influenced by corneal stiffness as indicated by the significant relationship with IIR. The %ΔCCT may be a potential biomarker for determining differences in corneal deformation response with corneal diseases.

Multi-scale cortical bone traits vary in females and males from two mouse models of genetic diversity.

Understanding the genetic basis of cortical bone traits can allow for the discovery of novel genes or biological pathways regulating bone health. Mice are the most widely used mammalian model for skeletal biology and allow for the quantification of traits that cannot easily be evaluated in humans, such as osteocyte lacunar morphology. The goal of our study was to investigate the effect of genetic diversity on multi-scale cortical bone traits of 3 long bones in skeletally-mature mice. We measured bone morphology, mechanical properties, material properties, lacunar morphology, and mineral composition of mouse bones from 2 populations of genetic diversity. Additionally, we compared how intrabone relationships varied in the 2 populations. Our first population of genetic diversity included 72 females and 72 males from the 8 inbred founder strains used to create the Diversity Outbred (DO) population. These 8 strains together span almost 90% of the genetic diversity found in mice (Mus musculus). Our second population of genetic diversity included 25 genetically unique, outbred females and 25 males from the DO population. We show that multi-scale cortical bone traits vary significantly with genetic background; heritability values range from 21% to 99% indicating genetic control of bone traits across length scales. We show for the first time that lacunar shape and number are highly heritable. Comparing the 2 populations of genetic diversity, we show that each DO mouse does not resemble a single inbred founder, but instead the outbred mice display hybrid phenotypes with the elimination of extreme values. Additionally, intrabone relationships (eg, ultimate force vs. cortical area) were mainly conserved in our 2 populations. Overall, this work supports future use of these genetically diverse populations to discover novel genes contributing to cortical bone traits, especially at the lacunar length scale.

Effect of material composition and thickness of orthodontic aligners on the transmission and distribution of forces: an in vitro study.

OBJECTIVES: To investigate the effects of material type and thickness on force generation and distribution by aligners. MATERIALS AND METHODS: Sixty aligners were divided into six groups (n = 10): one group with a thickness of 0.89 mm using Zendura Viva (Multi-layer), four groups with a thickness of 0.75 mm using Zendura FLX (Multi-layer), CA Pro (Multi-layer), Zendura (Single-layer), and Duran (Single-layer) sheets, and one group with a thickness of 0.50 mm using Duran sheets. Force measurements were conducted using Fuji® pressure-sensitive films. RESULTS: The lowest force values, both active and passive, were recorded for the multi-layered sheets: CA Pro (83.1 N, 50.5 N), Zendura FLX (88.9 N, 60.7 N), and Zendura Viva (92.5 N, 68.5 N). Conversely, the highest values were recorded for the single-layered sheets: Duran (131.9 N, 71.8 N) and Zendura (149.7 N, 89.8 N). The highest force was recorded at the middle third of the aligner, followed by the incisal third, and then the cervical third. The net force between the incisal and cervical thirds (FI-FC) showed insignificant difference across different materials. However, when comparing the incisal and middle thirds, the net force (FI-FM) was higher with single-layered materials. Both overall force and net force (FI-FM) were significantly higher with 0.75 mm compared to those with a thickness of 0.50 mm. CONCLUSIONS: Multi-layered aligner materials exert lower forces compared to their single-layered counterparts. Additionally, increased thickness in aligners results in enhanced retention and greater force generation. For effective bodily tooth movement, thicker and single-layered rigid materials are preferred. CLINICAL RELEVANCE: This research provides valuable insights into the biomechanics of orthodontic aligners, which could have significant clinical implications for orthodontists. Orthodontists might use this information to more effectively tailor aligner treatments, considering the specific tooth movement required for each individual patient. In light of these findings, an exchangeable protocol for aligner treatment is suggested, which however needs to be proven clinically. This protocol proposes alternating between multi-layered and single-layered materials within the same treatment phase. This strategy is suggested to optimize treatment outcomes, particularly when planning for a bodily tooth movement.

Biomechanical comparison of pectoralis major repair techniques: A systematic review and meta-regression.

Background: There are many surgical techniques when repairing pectoralis major tears. However, there is no clear consensus on which repair technique is biomechanically superior. Our purpose was to perform a systematic review and meta-regression to evaluate the most biomechanically superior pectoralis major repair technique. Methods: We performed a systematic review and meta-regression of six human cadaveric biomechanical studies evaluating fixation techniques for pectoralis major repairs. The primary outcome was the ultimate failure load. Covariates included cadaveric age, bone mineral density, implants, suture, and stitch method. Meta-regression accounted for differences in variables. Results: Compared with Krackow/Bunnell stitch method, the modified Mason-Allen stitch demonstrated a decrease in ultimate failure load by 220.6 N (95% CI, -273.0 to -168.2; p = <0.001). No differences were found between Krackow/Bunnell and whipstitch. There was an increase in ultimate failure load when utilizing suture tape by 206.6 N (95% CI, 139.5-273.7, p < 0.001). Suture anchors had a decrease in ultimate failure load by 88.1 N (95% CI, -153.4 to -22.8, p = 0.008) when compared to transosseous sutures. No differences were found between transosseous sutures and unicortical buttons. Discussion: We found the combination of suture tape in a whipstitch or Krackow/Bunnell stitch utilizing transosseous sutures or unicortical buttons is the most biomechanically superior construct for pectoralis major repairs.

Exploring biomechanical variations in ankle joint injuries among Latin dancers with different stance patterns: utilizing OpenSim musculoskeletal models.

Background: Dancers represent the primary demographic affected by ankle joint injuries. In certain movements, some Latin dancers prefer landing on the Forefoot (FT), while others prefer landing on the Entire foot (ET). Different stance patterns can have varying impacts on dancers' risk of ankle joint injuries. The purpose of this study is to investigate the differences in lower limb biomechanics between Forefoot (FT) dancers and Entire foot (ET) dancers. Method: A group of 21 FT dancers (mean age 23.50 (S.D. 1.12) years) was compared to a group of 21 ET dancers (mean age 23.33 (S.D. 0.94) years), performing the kicking movements of the Jive in response to the corresponding music. We import data collected from Vicon and force plates into OpenSim to establish musculoskeletal models for computing kinematics, dynamics, muscle forces, and muscle co-activation. Result: In the sagittal plane: ankle angle (0%-100%, p < 0.001), In the coronal plane: ankle angle (0%-9.83%, p = 0.001) (44.34%-79.52%, p = 0.003), (88.56%-100%, p = 0.037), ankle velocity (3.73%-11.65%, p = 0.017) (94.72-100%, p = 0.031); SPM analysis revealed that FT dancers exhibited significantly smaller muscle force than ET dancers around the ankle joint during the stance phase. Furthermore, FT dancers displayed reduced co-activation compared to ET dancers around the ankle joint during the descending phase, while demonstrating higher co-activation around the knee joint than ET dancers. Conclusion: This study biomechanically demonstrates that in various stance patterns within Latin dance, a reduction in lower limb stance area leads to weakened muscle strength and reduced co-activation around the ankle joint, and results in increased ankle inversion angles and velocities, thereby heightening the risk of ankle sprains. Nevertheless, the increased co-activation around the knee joint in FT dancers may be a compensatory response for reducing the lower limb stance area in order to maintain stability.

Comparison of Pain Scores and Functional Outcomes of Patients Undergoing Arthroscopic Hip Labral Repair and Concomitant Capsular Repair or Plication Versus No Closure.

Background: The need for capsular closure during arthroscopic hip labral repair is debated. Purpose: To compare pain and functional outcomes in patients undergoing arthroscopic hip labral repair with concomitant repair or plication of the capsule versus no closure. Study Design: Cohort study. Methods: Outcomes were compared between patients undergoing arthroscopic hip labral repair with concomitant repair or plication of the capsule versus no closure at up to 2 years postoperatively and with stratification by age and sex. Patients with lateral center-edge angle <20°, a history of instability, a history of prior arthroscopic surgery in the ipsilateral hip, or a history of labral debridement only were excluded. Subanalysis was performed between patients undergoing no capsular closure who were propensity score matched 1:1 with patients undergoing repair or plication based on age, sex, and preoperative Modified Harris Hip Score (MHHS). We compared patients who underwent T-capsulotomy with concomitant capsular closure matched 1:5 with patients who underwent an interportal capsulotomy with concomitant capsular repair based on age, sex, and preoperative MHHS. Results: Patients undergoing capsular closure (n = 1069), compared with the no-closure group (n = 230), were more often female (68.6% vs 53.0%, respectively; P < .001), were younger (36.4 ± 13.3 vs 47.9 ± 14.7 years; P < .001), and had superior MHHS scores at 2 years postoperatively (85.8 ± 14.5 vs 81.8 ± 18.4, respectively; P = .020). In the matched analysis, no difference was found in outcome measures between patients in the capsular closure group (n = 215) and the no-closure group (n = 215) at any follow-up timepoint. No significant difference was seen between the 2 closure techniques at any follow-up timepoint. Patients with closure of the capsule achieved the minimal clinically important difference (MCID) and the patient acceptable symptom state (PASS) for the 1-year MHHS at a similar rate as those without closure (MCID, 50.3% vs 44.9%, P = .288; PASS, 56.8% vs 51.1%, P = .287, respectively). Patients with T-capsulotomy achieved the MCID and the PASS for the 1-year MHHS at a similar rate compared with those with interportal capsulotomy (MCID, 50.1% vs 44.9%, P = .531; PASS, 65.7% vs 61.2%, P = .518, respectively). Conclusion: When sex, age, and preoperative MHHS were controlled, capsular closure and no capsular closure after arthroscopic hip labral repair were associated with similar pain and functional outcomes for patients up to 2 years postoperatively.

Female Lower Body Muscle Forces: A Musculoskeletal Modeling Comparison of Back Squats, Split Squats and Good Mornings.

The aim of this study was to analyze lower leg muscle forces during strength exercises such as back squats, good mornings and split squats, with a particular emphasis on females. By focusing on females, who are more vulnerable to anterior cruciate ligament injuries, we aimed to better understand muscle engagement and its role in injury prevention. Eight participants were monitored during exercises with a barbell load of 25% of body weight and, during the back squat, an additional 50% load. The analysis was conducted using personalized musculoskeletal models, electromyography (EMG) and Vicon motion capture systems to assess various muscle groups, including the m. gluteus maximus and m. gluteus medius, as well as the hamstring and quadriceps muscles. The back squat produced the highest forces for the quadriceps muscles, particularly the rectus femoris (>25 N/kg), as well as in the back leg during the split squat (>15 N/kg). The gluteal muscles were most active during good mornings and in the front leg of the split squat, especially the m. gluteus maximus medial part (>20 N/kg). The hamstrings generated the highest muscle forces in the front leg of the split squat, with the greatest forces observed in the m. semimembranosus. Our research highlights how musculoskeletal modeling helps us to understand the relationship among muscles, joint angles and anterior cruciate ligament injury risks, especially in strength training females. The results emphasize the need for personalized exercise guidance and customized models to make strength training safer and more effective.

Design and Evaluation of a Bilateral Semi-Rigid Exoskeleton to Assist Hip Motion.

This study focused on designing and evaluating a bilateral semi-rigid hip exoskeleton. The exoskeleton assisted the hip joint, capitalizing on its proximity to the body's center of mass. Unlike its rigid counterparts, the semi-rigid design permitted greater freedom of movement. A temporal force-tracking controller allowed us to prescribe torque profiles during walking. We ensured high accuracy by tuning control parameters and series elasticity. The evaluation involved experiments with ten participants across ten force profile conditions with different end-timings and peak magnitudes. Our findings revealed a trend of greater reductions in metabolic cost with assistance provided at later timings in stride and at greater magnitudes. Compared to walking with the exoskeleton powered off, the largest reduction in metabolic cost was 9.1%. This was achieved when providing assistance using an end-timing at 44.6% of the stride cycle and a peak magnitude of 0.11 Nm kg-1. None of the tested conditions reduced the metabolic cost compared to walking without the exoskeleton, highlighting the necessity for further enhancements, such as a lighter and more form-fitting design. The optimal end-timing aligns with findings from other soft hip exosuit devices, indicating a comparable interaction with this prototype to that observed in entirely soft exosuit prototypes.

Biomechanical Effects of Ti-Base Abutment Height on the Dental Implant System: A Finite Element Analysis.

This study aims to analyse, using a finite element analysis, the effects of Ti-base abutment height on the distribution and magnitude of transferred load and the resulting bone microstrain in the bone-implant system. A three-dimensional bone model of the mandibular premolar section was created with an implant placed in a juxta-osseous position. Three prosthetic models were designed: a 1 mm-high titanium-base (Ti-base) abutment with an 8 mm-high cemented monolithic zirconia crown was designed for model A, a 2 mm-high Ti-base abutment with a 7 mm-high crown for model B, and a 3 mm-high abutment with a 6 mm-high crown for model C. A static load of 150 N was applied to the central fossa at a six-degree angle with respect to the axial axis of the implant to evaluate the magnitude and distribution of load transfer and microstrain. The results showed a trend towards a direct linear association between the increase in the height of the Ti-base abutments and the increase in the transferred stress and the resulting microstrain to both the prosthetic elements and the bone/implant system. An increase in transferred stress and deformation of all elements of the system, within physiological ranges, was observed as the size of the Ti-base abutment increased.

Stroke Steadiness as a Determinant Factor of Performance in 100 m Freestyle in Young Swimmers.

The classical kinematic variables in swimming are based on the calculation of mean values. Stroke steadiness determines the relationship between the duration of all consecutive strokes throughout a test. The aims of the current investigation were to examine differences in stroke-to-stroke steadiness according to swimmers' performance level on both body sides (breathing and non-breathing) and to analyse the interrelationship with kinematics during a 100 m front-crawl test. Thirty-two young, experienced swimmers voluntarily participated in the present study and were divided into two groups, national level (n = 15) and local level (n = 17), according to their competitive status within the national age-rankings. All participants performed a 100 m maximal test in a 50 m pool where they were laterally recorded. Kinematic variables such as mean velocity, stroke rate, stroke length, and stroke index, as well as long-term steadiness and short-term steadiness, were calculated. The two 50 m sections were analysed independently. Significant differences were observed between the two groups in the classical kinematic variables and in stroke steadiness (p < 0.05). In addition, stroke steadiness showed moderately high correlations with velocity (r = [-0.61-(-0.749)]) and stroke index (r = [-0.356-(-0.582)]). Maintaining a more stable inter-stroke period appears to be a determinant of performance in young, high-level national swimmers.

Do astigmatid teeth matter: a tribological review of cheliceral chelae in co-occuring mites from UK beehives.

The dentition of the chelal moveable digit in cohabiting astigmatids from UK beehives (i.e., Carpoglyphus lactis (Linnaeus), Glycyphagus domesticus (DeGeer), and Tyrophagus putrescentiae (Schrank)) is characterised for the first time using quantitative tribological measures within a 2D mechanical model. The trophic function of astigmatid chelae are reviewed in terms of macroscopic tools used by humans including hooking devices, pliers, shears, rasps and saws. Comparisons to oribatid claws and isopod dactyli are made. The overall pattern of the moveable digit form of T. putrescentiae is not just a uniformly shrunken/swollen version between the other two taxa at either the macro- or micro-scale. Mastication surface macro-roughness values are in the range of international Roughness Grade Numbers N5-N6. The moveable digit of C. lactis has low rugosity values compared to the glycyphagid and acarid (which are topographically more similar and match that roughness typical of some coral reef surfaces). C. lactis has the most plesiomorphic moveable digit form. The mastication surface of all three species as a chewing tool is distinctly ornamented despite the moveable digit of C. lactis looking like a bar-like beam. The latter has more opportunities to be a multifunctional tool behaviourally than the other two species. Little evidence of any differences in the 'spikiness' of any 'toothiness' is found. Some differences with laboratory cultured specimens are found in C. lactis and possibly T. putrescentiae suggesting where selection on the digit may be able to occur. The chelal surface of T. putrescentiae has been deformed morphologically during evolution the most, that of C. lactis the least. Repeated localised surface differentiation is a feature of the moveable digit in G. domesticus compared to the likely more concerted changes over certain nearby locations in T. putrescentiae. An impactful chelal teeth design is present in G. domesticus but this is more equivocal in T. putrescentiae. Pockets within the mastication surface of the glycyphagid (and to some extent for the acarid) may produce foodstuff crunch forces of the scale of the chelal tips of oribatids. The moveable digit dentition of G. domesticus is adapted to shred foodstuff (like a ripsaw) more than that of the grazing/shearing dentition of T. putrescentiae. The collecting 'picker' design of C. lactis posterior teeth matches the size of Bettsia alvei hyphae which attacks hive-stored pollen. Detritus accumulated in chelal digit gullets through a sawing action matches the smallest observed ingested material. The dentition of C. lactis should produce less friction when moving through food material than G. domesticus. C. lactis is the most hypocarnivorous and may 'skim' through fluids when feeding. Astigmatid teeth do matter. The three commensal species can avoid direct competition. Future work is proposed in detail.

Pioneering a chick embryo model to explore the intrauterine etiology of developmental dysplasia of the hip in oligohydramnios conditions.

OBJECTIVE: To explore the impact of oligohydramnios on fetal movement and hip development, given its association with developmental dysplasia of the hip (DDH) but unclear mechanisms. METHODS: Chick embryos were divided into four groups based on the severity of oligohydramnios induced by amniotic fluid aspiration (control, 0.2 mL, 0.4 mL, 0.6 mL). Fetal movement was assessed by detection of movement and quantification of residual amniotic fluid volume. Hip joint development was assessed by gross anatomic analysis, micro-computed tomography (micro-CT) for cartilage assessment, and histologic observation at multiple time points. In addition, a subset of embryos from the 0.4 mL aspirated group underwent saline reinfusion and subsequent evaluation. RESULTS: Increasing volumes of aspirated amniotic fluid resulted in worsening of fetal movement restrictions (e.g., 0.4 mL aspirated and control group at E10: frequency difference -7.765 [95% CI: -9.125, -6.404]; amplitude difference -0.343 [95% CI: -0.588, -0.097]). The 0.4 mL aspirated group had significantly smaller hip measurements compared to controls, with reduced acetabular length (-0.418 [95% CI: -0.575, -0.261]) and width (-0.304 [95% CI: -0.491, -0.117]) at day E14.5. Histological analysis revealed a smaller femoral head (1.084 ±â€¯0.264 cm) and shallower acetabulum (0.380 ±â€¯0.106 cm) in the 0.4 mL group. Micro-CT showed cartilage matrix degeneration (13.6% [95% CI: 0.6%, 26.7%], P = 0.043 on E14.5). Saline reinfusion resulted in significant improvements in the femoral head to greater trochanter (0.578 [95% CI: 0.323, 0.833], P = 0.001). CONCLUSIONS: Oligohydramnios can cause DDH by restricting fetal movement and disrupting hip morphogenesis in a time-dependent manner. Timely reversal of oligohydramnios during the fetal period may prevent DDH.

Can lower-limb exoskeletons support sit-to-stand motions in frail elderly without crutches? A study combining optimal control and motion capture.

With the global geriatric population expected to reach 1.5 billion by 2050, different assistive technologies have been developed to tackle age-associated movement impairments. Lower-limb robotic exoskeletons have the potential to support frail older adults while promoting activities of daily living, but the need for crutches may be challenging for this population. Crutches aid safety and stability, but moving in an exoskeleton with them can be unnatural to human movements, and coordination can be difficult. Frail older adults may not have the sufficient arm strength to use them, or prolonged usage can lead to upper limb joint deterioration. The research presented in this paper makes a contribution to a more detailed study of crutch-less exoskeleton use, analyzing in particular the most challenging motion, sit-to-stand (STS). It combines motion capture and optimal control approaches to evaluate and compare the STS dynamics with the TWIN exoskeleton with and without crutches. The results show trajectories that are significantly faster than the exoskeleton's default trajectory, and identify the motor torques needed for full and partial STS assistance. With the TWIN exoskeleton's existing motors being able to support 112 Nm (hips) and 88 Nm (knees) total, assuming an ideal contribution from the device and user, the older adult would need to contribute a total of 8 Nm (hips) and 50 Nm (knees). For TWIN to provide full STS assistance, it would require new motors that can exert at least 121 Nm (hips) and 140 Nm (knees) total. The presented optimal control approaches can be replicated on other exoskeletons to determine the torques required with their mass distributions. Future improvements are discussed and the results presented lay groundwork for eliminating crutches when moving with an exoskeleton.

Biomechanics-mediated endocytosis in atherosclerosis.

Biomechanical forces, including vascular shear stress, cyclic stretching, and extracellular matrix stiffness, which influence mechanosensitive channels in the plasma membrane, determine cell function in atherosclerosis. Being highly associated with the formation of atherosclerotic plaques, endocytosis is the key point in molecule and macromolecule trafficking, which plays an important role in lipid transportation. The process of endocytosis relies on the mobility and tension of the plasma membrane, which is sensitive to biomechanical forces. Several studies have advanced the signal transduction between endocytosis and biomechanics to elaborate the developmental role of atherosclerosis. Meanwhile, increased plaque growth also results in changes in the structure, composition and morphology of the coronary artery that contribute to the alteration of arterial biomechanics. These cross-links of biomechanics and endocytosis in atherosclerotic plaques play an important role in cell function, such as cell phenotype switching, foam cell formation, and lipoprotein transportation. We propose that biomechanical force activates the endocytosis of vascular cells and plays an important role in the development of atherosclerosis.

Kinematic performance of a novel temporomandibular joint replacement prosthesis under bite-force conditions in dogs and cats.

OBJECTIVE: To evaluate the kinematics and stability of the temporomandibular joint (TMJ) of cats and dogs with and without a TMJ replacement (TMJR) prosthesis under simulated bite forces and mouth opening. ANIMALS: Sixteen cadaver skulls from domestic cats (n = 8) and medium- to large-breed dogs (n = 8). METHODS: Intact TMJs were tested. Following condylectomy and coronoidectomy, the skulls were fitted with a TMJR prosthesis unilaterally and retested. Prosthesis was similarly implanted in the contralateral TMJ in 4 cats and 4 dogs before retesting. Left and right bite motions were evaluated before bite contact to peak bite force (200 N in dogs, 63 N in cats). Mouth opening motion was recorded. Mandibular displacement under load was evaluated in 3 orthogonal planes. Maximal displacement was compared between TMJR groups and native TMJ. Prosthesis-bone motion of the temporal and mandibular components was evaluated during simulated bites and mouth opening. RESULTS: TMJR resulted in joint motion not demonstrably different from the native TMJ, with the ability to fully open and close the mouth and with minimal laterotrusion. The TMJR prosthesis demonstrated similar stability after unilateral and bilateral replacement during bite force and with an open mouth. Mean implant-bone motion during bite simulations for the temporal and mandibular TMJR components was ≤ 60 µm in cats and ≤ 30 µm in dogs. CLINICAL RELEVANCE: A novel TMJR can be implanted and allows normal jaw motion. Joint stability is maintained after TMJR implantation in the TMJ of dogs and cats TMJ that is devoid of muscular support.

Feasibility study of femur bone with continuum model.

It is known that the geometric structures of bones are very complex. This has made researchers unable to model them with the continuum approach and suffice to model them with simulation or experimental tests. Undoubtedly, provide a simple and accurate continuum model for studying bones is always desirable. In this article, as the first serious endeavour, a suggested beam model is investigated to see whether it is suitable for modelling femur bones or not. If this model gives an acceptable answer, it can be a link to the continuum theories for beams. In other words, the approximated beam model can be formulated with continuum approach to study femur bone. For feasibility study of the approximated model for femur bones, both static and dynamic analysis of them are investigated and compared. It is found that in most cases for vibration analysis, the suggested model has acceptable results but in static analysis, the mean difference between the results is about 16%. This research is hoped to be the first serious step in this category.