Anterior-posterior Shear Forces Research Articles

Biomechanical analysis of complications following T10-Pelvis spinal fusion: A population based computational study

Proximal junctional kyphosis (PJK) and proximal junctional failure (PJF) are challenging complications of long fusion constructs for the treatment of adult spinal deformity. The objective of this study is to understand the biomechanical stresses proximal to the upper instrumentation of a T10-pelvis fusion in a large patient cohort. The pre-fusion models were subject-specific thoracolumbar spine models that incorporate the height, weight, spine curvature, and muscle morphology of 250 individuals from the Framingham Heart Study Multidetector CT Study. To create post-fusion models, the subject-specific models were further modified to eliminate motion between the intervertebral joints from T10 to the pelvis. OpenSim analysis tools were used to calculate the medial lateral shear force, anterior posterior shear force, and compressive force on the T9 vertebra during the static postures. Differences between pre-fusion and post-fusion T9 biomechanics were consistent between increased segmental mobility and unchanged segmental mobility conditions.For all static postures, compression decreased (p < 0. 0005). Anterior-posterior shear force significantly increased (p < 0. 0005) during axial twist and significantly increased (p < 0. 0005) during trunk flexion. Medial lateral shear force significantly increased (p < 0. 0005) during axial twist. This computational study provided the first use of subject-specific models to investigate the biomechanics of long spinal fusions. Patients undergoing T10-Pelvis fusion were predicted to have increased shear forces and decreased compressive force at the T9 vertebra, independent of change in segmental mobility. The computational model shows potential for the investigation of spinal fusion biomechanics to reduce the risk of PJK or PJF.

Invasiveness of decompression surgery affects modeled lumbar spine kinetics in patients with degenerative spondylolisthesis.

Introduction: The surgical treatment of degenerative spondylolisthesis with accompanying spinal stenosis focuses mainly on decompression of the spinal canal with or without additional fusion by means of a dorsal spondylodesis. Currently, one main decision criterion for additional fusion is the presence of instability in flexion and extension X-rays. In cases of mild and stable spondylolisthesis, the optimal treatment remains a subject of ongoing debate. There exist different opinions on whether performing a fusion directly together with decompression has a potential benefit for patients or constitutes overtreatment. As X-ray images do not provide any information about internal biomechanical forces, computer simulation of individual patients might be a tool to gain a set of new decision criteria for those cases. Methods: To evaluate the biomechanical effects resulting from different decompression techniques, we developed a lumbar spine model using forward dynamic-based multibody simulation (FD_MBS). Preoperative CT data of 15 patients with degenerative spondylolisthesis at the level L4/L5 who underwent spinal decompression were identified retrospectively. Based on the segmented vertebrae, 15 individualized models were built. To establish a reference for comparison, we simulated a standardized flexion movement (intact) for each model. Subsequently, we performed virtual unilateral and bilateral interlaminar fenestration (uILF, bILF) and laminectomy (LAM) by removing the respective ligaments in each model. Afterward, the standardized flexion movement was simulated again for each case and decompression method, allowing us to compare the outcomes with the reference. This comprehensive approach enables us to assess the biomechanical implications of different surgical approaches and gain valuable insights into their effects on lumbar spine functionality. Results: Our findings reveal significant changes in the biomechanics of vertebrae and intervertebral discs (IVDs) as a result of different decompression techniques. As the invasiveness of decompression increases, the moment transmitted on the vertebrae significantly rises, following the sequence intact ➝ uILF ➝ bILF ➝ LAM. Conversely, we observed a reduction in anterior-posterior shear forces within the IVDs at the levels L3/L4 and L4/L5 following LAM. Conclusion: Our findings showed that it was feasible to forecast lumbar spine kinematics after three distinct decompression methods, which might be helpful in future clinical applications.

Reverse total shoulder glenoid component inclination affects glenohumeral kinetics during abduction: a cadaveric study.

Optimal implant placement in reverse total shoulder arthroplasty (rTSA) remains controversial. Specifically, the optimal glenoid inclination is unknown. Therefore, a cadaveric shoulder simulator with 3-dimentional human motion specific to rTSA was used to study joint contact and muscle forces as a function of glenoid component inclination. Eight human cadaver shoulders were tested before and after rTSA implantation. Scapular plane abduction kinematics from control subjects and those with rTSA drove a cadaveric shoulder simulator with 3-dimentional scapulothoracic and glenohumeral motion. Glenoid inclination varied from -20° to +20°. Outputs included compression, superior-inferior (S/I) shear, and anterior-posterior shear forces from a 6° of freedom load cell in the joint, and deltoid and rotator cuff muscle forces. Data were evaluated with statistical parametric mapping and t-tests. Inferior glenoid inclination (-) reduced S/I shear by up to 125% relative to superior inclination, with similar compression to the neutral condition (0°). Superior inclinations (+) increased the S/I shear force by approximately the same magnitude, yet decreased compression by 25% in the most superior inclination (+20°). There were few differences in deltoid or rotator cuff forces due to inclination. Only the middle deltoid decreased by approximately 7% for the most inferior inclination (-20°). Compared with native shoulders, the neutral (0°) rTSA inclination showed reduced forces of 30%-75% in the anterior deltoid and a trend toward decreased forces in the middle deltoid. Force demands on the rotator cuff varied as a function of elevation, with a trend toward increased forces in rTSA at peak glenohumeral elevation. Inferior inclination reduces superior shear forces, without influencing compression. Superior inclination increased S/I shear, while decreasing compression, which may be a source of component loosening and joint instability after rTSA. Inferior inclination of the rTSA glenoid may reduce the likelihood of glenoid loosening by reducing the magnitude of cyclic shear and compressive loading during arm elevation activities, although this may be altered by specific-subject body habitus and motion. These factors are especially important in revision rTSA or glenoid bone grafting where there is already a 3-fold increase in glenoid baseplate loosening vs. primary rTSA.

Anatomic total shoulder glenoid component inclination affects glenohumeral kinetics during abduction: a cadaveric study.

Although typically favorable in outcome, anatomic total shoulder arthroplasty (aTSA) can require long-term revision. The most common cause for revision is glenoid loosening, which may result from eccentric cyclic forces and joint translations. "Rocking" of the glenoid component may be exacerbated by the joint geometry, such as glenoid inclination and version. Restoration of premorbid glenoid inclination may be preferable, although laboratory and computational models indicate that both superior inclination and inferior inclination have benefits. This discrepancy may arise because previous studies were limited by a lack of physiological conditions to test inclination. Therefore, a cadaveric shoulder simulator with 3-dimensional human motion was used to study joint contact and muscle forces with isolated changes in glenoid inclination. Eight human cadaveric shoulders were tested before and after aTSA. Scapular-plane abduction kinematics from human subjects were used to drive a cadaveric shoulder simulator with 3-dimensional scapulothoracic and glenohumeral motion. Glenoid inclination was varied from -10° to +20°, whereas compressive, superior-inferior shear, and anterior-posterior shear forces were collected with a 6-df load cell during motion. Outputs also included muscle forces of the deltoid and rotator cuff. Data were evaluated with statistical parametric mapping repeated-measures analysis of variance and t tests. Inferior glenoid inclination (-10°) reduced both compressive and superior-inferior shear forces vs. neutral 0° inclination by up to 40%, and even more when compared with superior inclination (P<.001). Superior inclinations (+10° and +20°) tended to increase deltoid and rotator cuff forces vs. neutral 0° inclination or inferior inclination, on the order of 20%-40% (P≤.045). All force metrics except anterior-posterior shear were lowest for inferior inclination. Most aTSA muscle forces for neutral 0° inclination were not significantly different from native shoulders and decreased 45% and 15% in the posterior deltoid and supraspinatus, respectively (P≤.003). Joint translations were similar to prior reports in aTSA patients and did not differ between any inclinations or compared with native shoulders. Joint reaction forces were similar to those observed in human subjects with instrumented aTSA implants, providing confidence in the relative magnitude of our results. Inferior inclination reduces overall forces in the shoulder. Superior inclinations increase the muscle effort required for the shoulder to achieve similar motion, thus increasing the forces exerted on the glenoid component. These results suggest that a preference toward aTSA glenoid components in inferior inclination may reduce the likelihood of glenoid loosening by reducing excessive muscle and joint contact forces.

Validation of a Patient-Specific Musculoskeletal Model for Lumbar Load Estimation Generated by an Automated Pipeline From Whole Body CT.

Background: Chronic back pain is a major health problem worldwide. Although its causes can be diverse, biomechanical factors leading to spinal degeneration are considered a central issue. Numerical biomechanical models can identify critical factors and, thus, help predict impending spinal degeneration. However, spinal biomechanics are subject to significant interindividual variations. Therefore, in order to achieve meaningful findings on potential pathologies, predictive models have to take into account individual characteristics. To make these highly individualized models suitable for systematic studies on spinal biomechanics and clinical practice, the automation of data processing and modeling itself is inevitable. The purpose of this study was to validate an automatically generated patient-specific musculoskeletal model of the spine simulating static loading tasks. Methods: CT imaging data from two patients with non-degenerative spines were processed using an automated deep learning-based segmentation pipeline. In a semi-automated process with minimal user interaction, we generated patient-specific musculoskeletal models and simulated various static loading tasks. To validate the model, calculated vertebral loadings of the lumbar spine and muscle forces were compared with in vivo data from the literature. Finally, results from both models were compared to assess the potential of our process for interindividual analysis. Results: Calculated vertebral loads and muscle activation overall stood in close correlation with data from the literature. Compression forces normalized to upright standing deviated by a maximum of 16% for flexion and 33% for lifting tasks. Interindividual comparison of compression, as well as lateral and anterior–posterior shear forces, could be linked plausibly to individual spinal alignment and bodyweight. Conclusion: We developed a method to generate patient-specific musculoskeletal models of the lumbar spine. The models were able to calculate loads of the lumbar spine for static activities with respect to individual biomechanical properties, such as spinal alignment, bodyweight distribution, and ligament and muscle insertion points. The process is automated to a large extent, which makes it suitable for systematic investigation of spinal biomechanics in large datasets.

Biomechanical joint loading mechanism of Tai Chi gait in individuals with knee osteoarthritis: A pilot simulation study

ObjectivesTai Chi (TC) has shown beneficial effects on joint function in knee osteoarthritis (OA). Biomechanical mechanisms of knee joint contact load (JCL) and muscle activations during TC are less understood. The purpose of this biomechanical simulation study was to examine JCL of TC gait, the most common used TC from and its causal interactions with muscle activations in knee OA. DesignSix knee OA and five healthy participants were recruited. Their full body motion of TC gait was collected. The JCL and muscle forces were quantified using a musculoskeletal simulation approach based on collected kinematics and kinetics. The JCL and muscle activations were compared between knee OA and healthy control group. In addition, the muscle contributions to the JCL were determined and compared between the two groups. ResultsKnee OA subjects had lower peak anterior-posterior shear forces and higher lateral shear forces than healthy control subjects during TC gait. Knee OA subjects also showed higher activations of knee flexor muscles than control subjects. Both knee extensor and flexors of the knee OA group were contributing to JCL and in the control group mainly the knee extensors. ConclusionsOur simulation results showed the JCL, muscle forces profiles, and muscle contributions to the JCL during TC gait in knee OA. The findings of this study provided a direct scientific link between JCL and muscle forces during TC gait in knee OA. This would allow us to develop more effective TC interventions for knee OA in the future.

Influence of saddle height in 3D knee loads commuter cyclists: A statistical parametric mapping analysis

ABSTRACT This study used a statistical parametric mapping method to compare temporal patterns knee joint loads and moments in cyclists pedalling using different saddle heights. Ten recreational cyclists pedalled using three saddle heights (Preferred, High and Low) during a single session. High and Low saddle heights were determined based on dynamically measured knee flexion angles (±10° from their Preferred height). 3D angles for the hip and knee and knee moments and forces were computed using a musculoskeletal model driven by 3D full-body motion and pedal forces. Knee flexion angles presented significant differences between saddle heights for the full crank cycle, without differences for hip adduction/abduction. Patellofemoral force was less for the Preferred compared to the High and Low saddle heights and for the High compared to the Low saddle heights between ~70-160° of the crank cycle. Right tibiofemoral anterior-posterior shear force was reduced for the Preferred compared to the Low saddle heights, without significant effects for the left tibiofemoral joint (p = 0.29–1.00). Large differences in temporal patterns for knee flexion due to changes in saddle height were followed by differences in patellofemoral force mostly when low force magnitudes were being transmitted between the femur and the patella.

The relationship between neck angles and ground reaction forces in schoolchildren during backpack carriage

Summary Study aim: This study aimed to examine the effect of carrying backpacks on neck posture and ground reaction forces (GRFs) and to investigate the relationship between neck angles and GRFs during backpack carriage in schoolchildren. Material and methods: The craniohorizontal angle (CHA), craniovertebral angle (CVA), sagittal shoulder posture (SSP) and GRFs were measured in right-handed schoolchildren (14 male and 12 female) with mean age 10.17 ± 1.15 years during loaded and unloading conditions. The Qualisys motion analysis system with a force plate was used to assess the neck angles and GRFs. Results: During backpack carriage there was a significant increase in the CHA (p = 0.001), significant decrease in the CVA and SSP (p = 0.001, 0.016 respectively), no significant difference in the normalized (scaled to body weight) vertical GRFs (p &gt; 0.05), and a significant increase in the anterior braking and posterior propulsive GRFs (p = 0.035, 0.002 respectively) compared to the unloading condition. While carrying a backpack there was a moderate negative correlation between the SSP and first vertical GRF (r = –0.464) and a strong negative correlation with the second vertical GRF (r = –0.571) and the posterior propulsive GRF (r = –0.587). Conclusion: Carrying a backpack weighing 15% of the child’s body weight changes the head posture and increases the normalized value of the anterior-posterior shear force. During backpack carriage, decreasing the SSP is associated with increasing the load acceptance, thrusting and posterior propulsive forces. Increasing the shearing force may lead to development of postural abnormities. Consequently, the ideal backpack weight should be considered by parents and teachers.

Anterior cruciate ligament deficiency combined with lateral and/or medial meniscal injury results in abnormal kinematics and kinetics during level walking.

Anterior cruciate ligament injuries are commonly combined with meniscal tears. This study was performed to analyze the kinematics and kinetics of knees with anterior cruciate ligament deficiency with or without a combined medial or/and lateral meniscal injury during level walking. In all, 29 patients with unilateral anterior cruciate ligament deficiency and 15 healthy male volunteers were recruited. Among these patients, 12 had isolated unilateral anterior cruciate ligament injuries (ACLD group), 5 had combined anterior cruciate ligament and lateral meniscal injuries (ACLDL group), 5 had combined anterior cruciate ligament and medial meniscal injuries (ACLDM group), and 7 had combined anterior cruciate ligament and medial/lateral meniscal injuries (ACLDML group). A subject-specific musculoskeletal multibody dynamics model was utilized to estimate the tibiofemoral joint kinematic and kinetic behaviors based on the experimental data measured by using an optical tracking system. Regardless of the presence or absence of meniscal injury, the knees with anterior cruciate ligament deficiency exhibited significantly less extension than the control knees at the terminal stance (range of extension: ACLD, 4.84° ± 4.31°; ACLDL, 6.65° ± 5.73°; ACLDM, 5.21° ± 4.77°; ACLDML, 6.91° ± 4.30°; control, 12.35° ± 5.52°; P < 0.05). A lower extension moment and adduction moment in all anterior cruciate ligament deficiency affected knees were detected during the terminal stance when compared with control knees (P < 0.05). The ACLDML group showed significantly lower proximal-distal compressive forces and anterior-posterior shear forces (approximately 0.5-1.5 body weight; P < 0.05) compared to the other 4 groups, while the anterior-posterior and medial-lateral shear forces tended to increase in the ACLD, ACLDL, and ACLDM groups at the mid to terminal stance. Significant lower adduction-abduction and internal-external moment peaks were observed in ACLDML groups, but not in the ACLD, ACLDL and ACLDM groups. These results indicate that the combination of an anterior cruciate ligament injury and meniscal injury could alter the kinematics and kinetics of anterior cruciate ligament deficiency affected knees depending on the presence and type of the meniscal tear.

Effect of baseplate positioning on fixation of reverse total shoulder arthroplasty

BackgroundThe glenoid component in reverse total shoulder arthroplasty is recommended to be positioned inferiorly or with a downward tilt with the intention of reducing scapular notching. However, it is still unclear whether modifying the position of the glenoid prosthesis affects implant stability. The aim of this study was to determine the association between implant positioning and glenoid prosthesis fixation using Grammont reverse total shoulder arthroplasty. MethodsFour positions for the glenoid prosthesis were studied using the finite element method. The glenosphere was positioned as follows: 1) in the middle of the glenoid fossa, 2) flush with the inferior glenoid rim, 3) with an inferior overhang, 4) with a 15° inferior inclination. Bone-prosthesis micromotions and strain-induced bone adaptations were quantified during five daily activities. FindingsWhen the glenoid component was tilted inferiorly, the activities producing anterior-posterior shear forces (e.g. standing up from an armchair) caused an increase in peak micromotions. In the lateral-middle glenoid, inferior positioning caused a 64.6% reduction in bone apparent density. In the lateral-inferior glenoid, central positioning led to the most severe bone resorption, reaching 43.9%. InterpretationReducing activities which generate anterior-posterior shear forces on the shoulder joint will increase bone formation and may improve the primary stability of the implant when fixed in the position with an inferior tilt. Postoperative bone resorption is highly dependent on implant positioning. Understanding the relationship between bone resorption and implant positioning will help surgeons improve the long-term stability of reverse total shoulder arthroplasty.

Effectiveness of a vacuum lifting system in reducing spinal load during airline baggage handling

Information on spinal loading for using lift assist systems for airport baggage handling is lacking. We conducted a laboratory study to evaluate a vacuum lift system for reducing lumbar spinal loads during baggage loading/unloading tasks. Ten subjects performed the tasks using the industry average baggage weight of 14.5 kg on a typical two-shelved baggage cart with or without using the lift system (i.e. lifting technique). Repeated measures analysis of variance (2 tasks × 2 shelf heights x 2 techniques) was used. Spinal loads were estimated by an electromyography-driven biomechanical model. On average, the vacuum lift system reduced spinal compressive forces on the lumbar spine by 39% and below the 3400 N damage threshold. The system also resulted in a 25% reduction in the anterior-posterior shear force at the L5/S1 inferior endplate level. This study provides evidence for the potential to reduce spinal loads when using a vacuum lift system.

Bone Density and Cross-sectional Geometry of the Proximal Femur Are Bilaterally Elevated in Elite Cricket Fast Bowlers

The skeleton of a cricket fast bowler is exposed to a unique combination of gravitational and torsional loading in the form of substantial ground reaction forces delivered through the front landing foot, and anterior-posterior shear forces mediated by regional muscle contractions across the lumbo-pelvic region. The objectives of this study were to compare the hip structural characteristics of elite fast bowlers with recreationally active age-matched controls, and to examine unilateral bone properties in fast bowlers. Dual-energy X-ray absorptiometry of the proximal femur was performed in 26 elite male fast bowlers and 26 normally active controls. Hip structural analysis (GE Lunar; enCORE version 15.0) determined areal bone mineral density (BMD) of the proximal femur, and cross-sectional area, section modulus (Z), cross-sectional moment of inertia, and femoral strength index at the narrow region of the femoral neck. Mean femoral neck and trochanter BMD were greater in fast bowlers than in controls (p < 0.001). All bone geometry properties, except for cross-sectional moment of inertia, were superior in fast bowlers (p < 0.05) following adjustment for height and lean mass. There were no asymmetries in BMD or bone geometry when considering leg dominance of the fast bowlers (p > 0.05). Elite fast bowlers have superior bone characteristics of the proximal femur, with results inferring enhanced resistance to axial compression (cross-sectional area), and bending (Z) forces, and enhanced strength to withstand a fall impact as indicated by their higher femoral strength index. No asymmetries in hip bone properties were identified, suggesting that both torsional and gravitational loading offer significant osteogenic potential.

Evaluation of compressive and shear joint forces on medial and lateral compartments in knee joint during walking before and after medial open-wedge high tibial osteotomy

The main principle of open-wedge high tibial osteotomy (HTO) is to shift the weight-bearing line of the knee joint in order to decompress the degenerated compartment and delay osteoarthritis (OA). In this study, the resultant contact forces on the medial compartment, lateral compartment, and total tibiofemoral joint were analyzed during gait for five OA patients before and after HTO in order to fully understand the effect and mechanism of HTO for the OA knee. The compressive, lateral-medial shear, and anteriorposterior shear force components of the joint force, as well as the ratio of the medial contact force to the lateral contact force, were investigated using inverse dynamic and multi-body dynamic models. Medial open-wedge HTO improved the balance of medial and lateral contact forces on the tibiofemoral joint, which demonstrated the purpose of HTO provided by clinical studies and the outcomes of a computational study. In addition to the compressive contact force, the lateral-medial shear force was also reduced during the stance phase of walking after HTO. The technology in this study provides a fundamental tool to evaluate the outcomes of HTO by considering daily and sports activities.

Weight knowledge and weight magnitude: impact on lumbosacral loading

Several factors can impact lumbosacral loads during lifting, including weight knowledge and weight magnitude. However, interaction between them has never been tested. This study investigated the interaction effect of these variables on lumbosacral forces and moments. Participants performed symmetrical lifts using three different weights. Weight knowledge involved known and unknown weight conditions. A biologically assisted dynamic model was used to calculate spinal loading parameters. Weight impacted all variables, while knowledge impacted only compression, by a moderate amount (5%), and spinal moments. Lifting a lightweight resulted in a difference of 16% and 7.2% between knowledge conditions for compression and anterior-posterior shear forces, respectively, compared with a negligible difference of < 1% when lifting a heavy weight. Increased spinal loading with light unknown weight can be attributed to increased muscular co-contraction. Weight knowledge is important to consider at low weight levels as it can increase tissue loading to values equivalent to lifting a heavier weight.

The effects of position and size of drywall on the physical demands for installers

The present study utilized an integrated biomechanical modeling approach that was previously developed by the researchers to investigate the effects of position and size of drywall on the physical demands for drywall installers. If the drywall sheets were stored vertically instead of flat, it reduced the required muscle contraction forces and joint reaction forces at the low back and shoulder approximately 8% on average during drywall installation. In particular, the L4/L5 disc compression forces and the absolute values of L4/L5 anterior-posterior shear forces decreased 6.1% and 8.5%, respectively, and at the shoulder during lifting the forces of rotator cuff muscles decreased 9.8%, and the coracohumeral ligament forces decreased 12.8%. The reaction forces at both the GH (glenohumeral) and SC (sternoclavicular) joints were reduced 7.2% and 3.6%, respectively. The larger size (e.g., 4x12 and 4x16) of drywall sheets increased the physical burden for the installers tremendously and could expose them to a higher risk of musculoskeletal injuries and disorders. In some simulations the average low back lateral shear forces increased to 1675 N and 2152 N, respectively. These forces are well above the 1000 N recommended for a single lift. These results indicated that it would be physically too difficult or even impossible for one person alone to lift bigger and heavier drywall sheets. Therefore, sound engineering (e.g., lifting tables) and/or administrative (e.g., two-person team work) solutions to handling oversized drywall sheets are strongly recommended.

Ground reaction force estimation using an insole-type pressure mat and joint kinematics during walking

Kinetic analysis of walking requires joint kinematics and ground reaction force (GRF) measurement, which are typically obtained from a force plate. GRF is difficult to measure in certain cases such as slope walking, stair climbing, and track running. Nevertheless, estimating GRF continues to be of great interest for simulating human walking. The purpose of the study was to develop reaction force models placed on the sole of the foot to estimate full GRF when only joint kinematics are provided (Type-I), and to estimate ground contact shear forces when both joint kinematics and foot pressure are provided (Type-II and Type-II-val). The GRF estimation models were attached to a commercial full body skeletal model using the AnyBody Modeling System, which has an inverse dynamics-based optimization solver. The anterior–posterior shear force and medial–lateral shear force could be estimated with approximate accuracies of 6% BW and 2% BW in all three methods, respectively. Vertical force could be estimated in the Type-I model with an accuracy of 13.75% BW. The accuracy of the force estimation was the highest during the mid-single-stance period with an average RMS for errors of 3.10% BW, 1.48% BW, and 7.48% BW for anterior–posterior force, medial–lateral force, and vertical force, respectively. The proposed GRF estimation models could predict full and partial GRF with high accuracy. The design of the contact elements of the proposed model should make it applicable to various activities where installation of a force measurement system is difficult, including track running and treadmill walking.

Diagnostic Value of Knee Arthrometry in the Prediction of Anterior Cruciate Ligament Strain During Landing

Background: Previous studies have indicated that higher knee joint laxity may be indicative of an increased risk of anterior cruciate ligament (ACL) injuries. Despite the frequent clinical use of knee arthrometry in the evaluation of knee laxity, little data exist to correlate instrumented laxity measures and ACL strain during dynamic high-risk activities. Purpose/Hypotheses: The purpose of this study was to evaluate the relationships between ACL strain and anterior knee laxity measurements using arthrometry during both a drawer test and simulated bipedal landing (as an identified high-risk injurious task). We hypothesized that a high correlation exists between dynamic ACL strain and passive arthrometry displacement. The secondary hypothesis was that anterior knee laxity quantified by knee arthrometry is a valid predictor of injury risk such that specimens with greater anterior knee laxity would demonstrate increased levels of peak ACL strain during landing. Study Design: Controlled laboratory study. Methods: Twenty cadaveric lower limbs (mean age, 46 ± 6 years; 10 female and 10 male) were tested using a CompuKT knee arthrometer to measure knee joint laxity. Each specimen was tested under 4 continuous cycles of anterior-posterior shear force (±134 N) applied to the tibial tubercle. To quantify ACL strain, a differential variable reluctance transducer (DVRT) was arthroscopically placed on the ACL (anteromedial bundle), and specimens were retested. Subsequently, bipedal landing from 30 cm was simulated in a subset of 14 specimens (mean age, 45 ± 6 years; 6 female and 8 male) using a novel custom-designed drop stand. Changes in joint laxity and ACL strain under applied anterior shear force were statistically analyzed using paired sample t tests and analysis of variance. Multiple linear regression analyses were conducted to determine the relationship between anterior shear force, anterior tibial translation, and ACL strain. Results: During simulated drawer tests, 134 N of applied anterior shear load produced a mean peak anterior tibial translation of 3.1 ± 1.1 mm and a mean peak ACL strain of 4.9% ± 4.3%. Anterior shear load was a significant determinant of anterior tibial translation (P < .0005) and peak ACL strain (P = .04). A significant correlation (r = 0.52, P < .0005) was observed between anterior tibial translation and ACL strain. Cadaveric simulations of landing produced a mean axial impact load of 4070 ± 732 N. Simulated landing significantly increased the mean peak anterior tibial translation to 10.4 ± 3.5 mm and the mean peak ACL strain to 6.8% ± 2.8% (P < .0005) compared with the prelanding condition. Significant correlations were observed between peak ACL strain during simulated landing and anterior tibial translation quantified by knee arthrometry. Conclusion: Our first hypothesis is supported by a significant correlation between arthrometry displacement collected during laxity tests and concurrent ACL strain calculated from DVRT measurements. Experimental findings also support our second hypothesis that instrumented measures of anterior knee laxity predict peak ACL strain during landing, while specimens with greater knee laxity demonstrated higher levels of peak ACL strain during landing. Clinical Relevance: The current findings highlight the importance of instrumented anterior knee laxity assessments as a potential indicator of the risk of ACL injuries in addition to its clinical utility in the evaluation of ACL integrity.

Trunk Kinematics under Sudden Loading Impact when Adopting Different Foot Postures

The purpose of this study was to explore the effect of foot posture on trunk biomechanical responses when experiencing sudden external loading. Fifteen subjects were recruited to perform a series of sudden loading tasks using three different foot postures with two levels of weight. Our results showed that sudden external loading generated the smallest impact when subjects adopted “Staggered Stance”. Compared with “Wide Stance”, “Staggered Stance” significantly decreased the increment of trunk flexion angle, increment of L5/S1 joint moment, and peak L5/S1 joint anterior-posterior shear force by 21.5%, 6.5%, and 22.5%, respectively. Compared with “Narrow Stance”, the decreases were 15.1%, 3.2%, and 16.2% respectively. Heavier load weight resulted in larger spinal impact. The interaction effect between foot posture and magnitude of the load was not significant. The findings of this study could be used in reducing the risk of low back pain when dealing with sudden loading.

Kinetics of Badminton Lunges in Four Directions

The lunge is the most fundamental skill in badminton competitions. Fifteen university-level male badminton players performed lunge maneuvers in four directions, namely, right-forward, left-forward, right-backward, and left-backward, while wearing two different brands of badminton shoes. The test compared the kinetics of badminton shoes in performing typical lunge maneuvers. A force plate and an insole measurement system measured the ground reaction forces and plantar pressures. These measurements were compared across all lunge maneuvers. The left-forward lunge generated significantly higher first vertical impact force (2.34 ± 0.52 BW) than that of the right-backward (2.06 ± 0.60 BW) and left-backward lunges (1.78 ± 0.44 BW); higher second vertical impact force (2.44 ± 0.51 BW) than that of the left-backward lunge (2.07 ± 0.38 BW); and higher maximum anterior-posterior shear force (1.48 ± 0.36 BW) than that of the left-backward lunge (1.18 ± 0.38 BW). Compared with other lunge directions, the left-forward lunge showed higher mean maximum vertical impact anterior-posterior shear forces and their respective maximum loading rates, and the plantar pressure at the total foot and heel regions. Therefore, the left-forward lunge is a critical maneuver for badminton biomechanics and related footwear research because of the high loading magnitude generated during heel impact.

Relative performances of artificial neural network and regression mapping tools in evaluation of spinal loads and muscle forces during static lifting

Two artificial neural networks (ANNs) are constructed, trained, and tested to map inputs of a complex trunk finite element (FE) model to its outputs for spinal loads and muscle forces. Five input variables (thorax flexion angle, load magnitude, its anterior and lateral positions, load handling technique, i.e., one- or two-handed static lifting) and four model outputs (L4–L5 and L5–S1 disc compression and anterior–posterior shear forces) for spinal loads and 76 model outputs (forces in individual trunk muscles) are considered. Moreover, full quadratic regression equations mapping input–outputs of the model developed here for muscle forces and previously for spine loads are used to compare the relative accuracy of these two mapping tools (ANN and regression equations). Results indicate that the ANNs are more accurate in mapping input–output relationships of the FE model (RMSE= 20.7N for spinal loads and RMSE= 4.7N for muscle forces) as compared to regression equations (RMSE= 120.4N for spinal loads and RMSE=43.2N for muscle forces). Quadratic regression equations map up to second order variations of outputs with inputs while ANNs capture higher order variations too. Despite satisfactory achievement in estimating overall muscle forces by the ANN, some inadequacies are noted including assigning force to antagonistic muscles with no activity in the optimization algorithm of the FE model or predicting slightly different forces in bilateral pair muscles in symmetric lifting activities. Using these user-friendly tools spine loads and trunk muscle forces during symmetric and asymmetric static lifts can be easily estimated.