Anterior Shear Force Research Articles

Associations between lower limb muscle activation strategies and resultant multi-planar knee kinetics during single leg landings

Anterior cruciate ligament injury prevention programs purportedly improve knee joint loading through beneficial modification of lower limb neuromuscular control strategies and joint biomechanics, but little is known about how these factors relate during single-legged landings. Thus, we examined the relationship between explicit lower limb muscular pre-activity patterns and knee joint biomechanics elicited during such landings. Randomized controlled trial. Thirty-five female athletes had 3D knee joint biomechanics and lower limb EMG data recorded during a series of single-leg landings. Regression analysis assessed the relationship between pre-activity of vastus lateralis, lateral hamstring and rectus femoris with peak knee flexion angle and moment, and external anterior tibial shear force. Vastus lateralis, lateral hamstring and vastus lateralis:lateral hasmtring co-contraction assessed the relationship with knee abduction angle and moment. Greater pre-activity of rectus femoris predicted increased peak anterior tibial shear force (R(2)=0.235, b=2.41 and P=0.003) and reduced knee flexion moment (R(2)=0.131, b=-0.591, and P=0.032), while greater lateral hamstring predicted decreased peak knee flexion angle (R(2)=0.113, b=8.96 and P=0.048). No EMG pre-activity parameters were predictors (P>0.05) for knee abduction angle and moment. Current outcomes suggest reducing reliance on quadriceps activation may be beneficial during single-legged landings. It also, however, may be required for adequate joint stability during such maneuvers. Further research is needed to determine if inadequate hamstring activation, rather than elevated quadriceps activation, leads to hazardous loading during single-legged landings.

The impact of shear force magnitude on cumulative injury load tolerance: a force weighting approach for low-back shear loads

Vertebral joint fatigue life non-linearly decreases with increasing anterior shear force magnitude. Therefore, equal treatment of independent shear force exposures will underestimate low-back injury potential. This investigation developed mathematical functions for deriving appropriate weighting factors (WFs) to be applied in occupational cumulative shear force estimates. Porcine vertebral joints were repetitively loaded in shear to 20%, 40%, 60% or 80% of their calculated shear failure tolerance for 21,600 cycles or until bone failure was detected. Two WF functions were derived from mathematical relationships between sub-maximal shear force magnitude and sustained cumulative shear force to failure. These functions explained 98.2% and 88.6% of the variance in sustained cumulative shear force. Accelerated injury potential represented by WFs greater than unity was assigned to shear forces above 35.6% and 695 N. These weighting approaches will enhance sensitivity in future evaluations between exposure and lost-time/injury for detecting relationships between cumulative shear loading and low-back injury.

Hamstrings Stiffness and Landing Biomechanics Linked to Anterior Cruciate Ligament Loading.

Greater hamstrings stiffness is associated with less anterior tibial translation during controlled perturbations. However, it is unclear how hamstrings stiffness influences anterior cruciate ligament (ACL) loading mechanisms during dynamic tasks. To evaluate the influence of hamstrings stiffness on landing biomechanics related to ACL injury. Cross-sectional study. Research laboratory. A total of 36 healthy, physically active volunteers (18 men, 18 women; age = 23 ± 3 years, height = 1.8 ± 0.1 m, mass = 73.1 ± 16.6 kg). Hamstrings stiffness was quantified via the damped oscillatory technique. Three-dimensional lower extremity kinematics and kinetics were captured during a double-legged jump-landing task via a 3-dimensional motion-capture system interfaced with a force plate. Landing biomechanics were compared between groups displaying high and low hamstrings stiffness via independent-samples t tests. Hamstrings stiffness was normalized to body mass (N/m·kg-1). Peak knee-flexion and -valgus angles, vertical and posterior ground reaction forces, anterior tibial shear force, internal knee-extension and -varus moments, and knee-flexion angles at the instants of each peak kinetic variable were identified during the landing task. Forces were normalized to body weight, whereas moments were normalized to the product of weight and height. Internal knee-varus moment was 3.6 times smaller in the high-stiffness group (t22 = 2.221, P = .02). A trend in the data also indicated that peak anterior tibial shear force was 1.1 times smaller in the high-stiffness group (t22 = 1.537, P = .07). The high-stiffness group also demonstrated greater knee flexion at the instants of peak anterior tibial shear force and internal knee-extension and -varus moments (t22 range = 1.729-2.224, P < .05). Greater hamstrings stiffness was associated with landing biomechanics consistent with less ACL loading and injury risk. Musculotendinous stiffness is a modifiable characteristic; thus exercises that enhance hamstrings stiffness may be important additions to ACL injury-prevention programs.

Anterior tibiofemoral intersegmental forces during landing are predicted by passive restraint measures in women

BackgroundPassive restraint capabilities may influence sagittal plane knee joint mechanics during activity. This study aimed to determine if measures associated with passive restraint of anterior translation of the tibia are predictive of peak anterior knee shear force during landing. MethodsPassive restraint measures were assessed via joint arthrometry and during 40% body weight simulated weight acceptance using recreationally active students (73F, 42M; 21.8±2.9yr, 1.69±0.1m, 68.9±14.1kg). Anterior knee laxity (mm) at 133N and initial (0–20N) and terminal (100–130N) anterior stiffnesses (N/mm) were calculated from arthrometer data. Peak anterior tibial acceleration (m∙s−2) relative to the femur was assessed via electromagnetic position sensors during 40% body weight acceptance trials. Peak knee shear force was assessed during double-leg drop jumps. ResultsSex specific linear stepwise regressions revealed that in females, increasing peak tibial acceleration (5.1±1.8m·s−2) (R2∆=7.3%, P∆=0.021), increasing initial anterior stiffness (31.0±14.0N/mm) (R2∆=5.9%, P∆=0.032), and decreasing terminal anterior stiffness (43.4±17.4N/mm) (R2∆=4.9%, P∆=0.046) collectively predicted greater peak knee shear forces (66.6±12.03% BW) (multiple R2=18.1%). No male regressions were significant. ConclusionsSagittal laxity measures are associated with anterior knee shear loads during landing in females. Greater tibial acceleration during early axial load along with greater initial and lesser terminal anterior stiffnesses predicted increasing anterior knee shear forces. Future work should investigate the combined contribution of passive and active restraints to high-risk ACL biomechanics.

The relationship between proximal and distal lower limb muscle activities with time to stabilization

Abstract Introduction : Identifying factors which cause the high incidence of ACL is of great importance .The anterior shear forces are the primary mechanism of load sustained on the ACL. During exercise, the activity of muscles and position of lower limbs may increase or decrease the anterior shear force. The purpose of this study is to investigate the relationship between the activity level of some lower extremity muscles and anterior shear force during single-leg jump landing . Materials and Methods: Twenty male-students of physical education participated in this study. EMG activity of the muscles of the gluteus medius, tibialis anterior and hamstring were evaluated via Electromyography system and ground reaction force was evaluated via force plate system in jump-landing task. There was used Pearson correlation test. Results: The results indicated no significant correlation between tibialis anterior and gluteus medius muscles activity with shear force, while there was found correlation between lateral hamstring muscle activity and anterior shear force (P< 0.05 ). Conclusion: The findings of this study showed that hamstring muscle activity during single-leg jump landing acts as a supporting muscle of ACL. This increased muscle activity leads to the reduction of the load on the ACL . Keywords: Electromyography, Anterior Shear Force, Anterior Cruciate ligament, Jump-Landing task, Lower Extremity Muscles

Biomechanical Evaluation of Physeal-Sparing Fixation Methods in Tibial Eminence Fractures

Background: Tibial eminence fractures occur most commonly in skeletally immature children. Several techniques using physeal-sparing fracture fixation have been described, but their structural properties have not been evaluated. Purpose: To determine the strength and resistance to displacement of physeal-sparing techniques used to fix tibial eminence fractures. Study Design: Controlled laboratory study. Methods: Skeletally immature porcine knees were randomized into 4 treatment groups: (1) ultra–high molecular weight polyethylene suture–suture button (UHMWPE/SB), (2) suture anchor, (3) polydioxanone suture–suture button (PDS/SB), and (4) screw fixation. A prospective analysis of bone mineral density using dual-energy x-ray absorptiometry was performed on all specimens. Fracture fragments were created in a standardized manner and measured for size comparison. After fracture fixation, biomechanical testing was performed with cyclical and load-to-failure protocols by loading the tibia with an anterior shear force. Results: In load-to-failure testing, screw fixation had a significantly lower median peak failure load (186.4 N; lower quartile [LQ], 158.4 N; upper quartile [UQ], 232.6 N) than did UHMWPE/SB (465.8 N; LQ, 397.8 N; UQ, 527.8 N), suture anchors (440.5 N; LQ, 323.0 N; UQ, 562.3 N), and PDS/SB (404.3 N; LQ, 385.9 N; UQ, 415.6 N). UHMWPE/SB demonstrated a significantly higher median yield load (465.8 N; LQ, 397.8 N; UQ, 527.8 N) than did PDS/SB (306.7 N; LQ, 271.4, N; UQ, 405.7 N) and screw fixation (179.0 N; LQ, 120.2 N; UQ, 232.5 N). During cyclical testing, screw fixation demonstrated significantly lower percentage survival of specimens (0%) compared with the other groups (UHMWPE/SB, 100%; suture anchor, 78%; PDS/SB, 78%). After 1000 cycles of loading, PDS/SB fixation had significantly more median creep (6.76 mm; LQ, 6.34 mm; UQ, 8.28 mm) than did UHMWPE/SB (4.43 mm; LQ, 3.80 mm; UQ, 4.73 mm) and suture anchor fixation (3.06 mm; LQ, 2.59 mm; UQ, 4.28 mm). The lowest median stiffness was observed in the PDS/SB group (48.6 N/mm; LQ, 45.3 N/mm; UQ, 54.2 N/mm). UHMWPE/SB fixation demonstrated a significantly higher median peak failure load after cyclic testing (469.0 N; LQ, 380.6 N; UQ, 507.2 N) than did PDS/SB (237.7 N; LQ, 197.3 N; UQ, 298.3 N) and screw fixation (132.4 N; LQ, 123.7 N; UQ, 180.9 N). Suture anchor fixation had significantly more variance, as demonstrated by width of interquartile range, in peak failure load, yield load, and creep than did other techniques. Conclusion: Physeal-sparing fixation of tibial eminence fractures with UHMWPE suture–suture button is biomechanically superior to both PDS suture–suture button and a single screw at the time of surgery and provides more consistent fixation than do suture anchors. Clinical Relevance: Suture anchors provide inconsistent fixation for tibial eminence fractures.

THE RELATIONSHIP BETWEEN ACTIVITY LEVEL OF SOME LOWER EXTREMITY MUSCLE AND ANTERIOR SHEAR FORCE DURING SINGLE-LEG JUMP LANDING

چکیده مقدمه: شناسایی فاکتورهایی که باعث شیوع بالای آسیب ACL می‌شود از اهمیت زیادی برخوردار است. نیروهای برشی قدامی مکانیزم اصلی بار وارده به ACL هستند. فعالیت عضلات و پوزیشن اندام تحتانی طی فعالیت می‌تواند باعث افزایش یا کاهش نیروی برشی قدامی شود. هدف از این مطالعه بررسی ارتباط بین سطح فعالیت برخی از عضلات اندام تحتانی با نیروی برشی قدامی در حرکت پرش-فرود تک‌پا بود. مواد و روش‌ها: 20 دانشجوي پسر رشته تربیت بدنی در اين مطالعه شركت كردند. سطح فعالیت الکترومیوگرافی عضلات سرینی میانی، ساقی قدامی و همسترینگ خارجی با استفاده از دستگاه الکترومیوگرافی، و نیروی عکس‌العمل زمین با استفاده از دستگاه صفحه نيرو در حركت پرش- فرود تک پا ارزیابی شد. به منظور تجزیه و تحلیل داده­ها، از آزمون همبستگی پیرسون استفاده شد. یافته‌ها: نتایج آماری نشان داد که بین سطح فعالیت عضله ساقی قدامی و سرینی میانی با نیروی برشی قدامی ارتباط معنی داری وجود ندارد (05/0P>)، اما ارتباط معنی داری بین سطح فعالیت عضله همسترینگ خارجی با نیروی برشی قدامی یافت شد (05/0P<). نتیجه‌گیری: یافته­های این مطالعه نشان داد که فعالیت عضله همسترینگ در حین حرکت پرش- فرود تک‌پا به عنوان عضله حمایت کننده از ACL عمل می‌کند و افزایش فعالیت این عضله می‌تواند منجر به کاهش بار وارده بر ACL شود. کلیدواژه‌ها: الکترومیوگرافی، نیروی برشی قدامی، لیگامنت صلیبی قدامی، حرکت پرش- فرود، عضلات اندام تحتانی

The application of musculoskeletal modeling to investigate gender bias in non-contact ACL injury rate during single-leg landings

The central tenet of this study was to develop, validate and apply various individualised 3D musculoskeletal models of the human body for application to single-leg landings over increasing vertical heights and horizontal distances. While contributing to an understanding of whether gender differences explain the higher rate of non-contact anterior cruciate ligament (ACL) injuries among females, this study also correlated various musculoskeletal variables significantly impacted by gender, height and/or distance and their interactions with two ACL injury-risk predictor variables; peak vertical ground reaction force (VGRF) and peak proximal tibia anterior shear force (PTASF). Kinematic, kinetic and electromyography data of three male and three female subjects were measured. Results revealed no significant gender differences in the musculoskeletal variables tested except peak VGRF (p = 0.039) and hip axial compressive force (p = 0.032). The quadriceps and the gastrocnemius muscle forces had significant correlations with peak PTASF (r = 0.85, p < 0.05 and r = − 0.88, p < 0.05, respectively). Furthermore, hamstring muscle force was significantly correlated with peak VGRF (r = − 0.90, p < 0.05). The ankle flexion angle was significantly correlated with peak PTASF (r = − 0.82, p < 0.05). Our findings indicate that compared to males, females did not exhibit significantly different muscle forces, or ankle, knee and hip flexion angles during single-leg landings that would explain the gender bias in non-contact ACL injury rate. Our results also suggest that higher quadriceps muscle force increases the risk, while higher hamstring and gastrocnemius muscle forces as well as ankle flexion angle reduce the risk of non-contact ACL injury.

Preferential Loading of the ACL Compared to the MCL during Landing: A Novel In Sim Approach Yields the Multi-Planar Mechanism of Dynamic Valgus during ACL Injury

Objectives:Strong biomechanical and epidemiologic evidence associates knee valgus collapse with isolated non-contact ACL injury. However, the predominance of isolated non-contact anterior cruciate ligament (ACL) injuries is challenging for clinicians and researchers to explain, as the medial collateral ligament (MCL) has been reported to be the primary restraint against knee valgus. The purpose of this study was to investigate the relative ACL to MCL strain patterns during physiologic simulations of a wide range of high-risk dynamic landing scenarios. We hypothesized that both knee abduction and internal tibial rotation moments would generate a disproportionate increase in ACL strain relative to MCL strain. However, the physiologic range of knee abduction and internal tibial rotation moments that produce ACL injuries would not be of sufficient magnitude to consistently compromise MCL integrity.Methods:A novel in sim approach was used to test our hypotheses. 17 cadaveric lower extremities (45 ± 7 years, 9 female & 8 male) were tested to simulate a broad range of landing conditions following a jump under anterior tibial shear, knee abduction and internal tibial rotation. Specimens were oriented to simulate lower extremity posture during ground strike while landing from a jump. Landing was simulated by applying an impulsive axial impact load (simulating ground reaction forces) under simulated muscle forces. ACL and MCL strains were quantified using DVRT displacement transducers arthroscopically placed across the ACL AM-bundle and sutured to the anterior/middle/posterior aspects of superficial MCL across the joint line. Specimens were tested until failure. Multiple paired and independent t-tests along with general linear models were used to investigate the changes in strain levels under each modes of loading. An extensively validated, detailed finite element model of the lower extremity was used to better interpret experimental findings.Results:ACL failure was generated in 15 of 17 specimens (88%). Increased anterior tibial shear force, and knee abduction and internal tibial rotation moments resulted in significantly higher ACL: MCL strain ratios (p<0.05) compared to landing under no applied external loads. Under all modes of single- and multi-planar loading, ACL: MCL strain ratio remained greater than 1.7, and relative ACL strain was significantly higher than relative MCL strain (p<0.003, Figure 1). Relative change in ACL strain was significantly greater under combined multi-planar loading compared to ACL strain under anterior tibial shear force (p=0.016), knee abduction (p=0.018) and internal tibial rotation (p<0.0005) moments alone.Conclusion:The tibiofemoral frontal plane loading mechanism has become a recent topic of debate as a contributing factor to non-contact ACL injuries. Both in vivo and video analyses studies indicate that increased knee abduction is associated with increased risk for ACL injury. The current findings demonstrates that while both the ACL and MCL resist knee valgus during landing, physiological magnitudes of the applied loads that lead to high ACL strain levels and injury were not sufficient to compromise MCL integrity. Further, these findings support multi-planar knee valgus collapse as a primary mechanism of non-contact ACL injury. This enhances our understanding of the non-contact ACL injury mechanism, and provides insight that can improve current risk screening and injury prevention strategies.

Clinically Relevant Injury Patterns After an Anterior Cruciate Ligament Injury Provide Insight Into Injury Mechanisms

Background: The functional disability and high costs of treating anterior cruciate ligament (ACL) injuries have generated a great deal of interest in understanding the mechanism of noncontact ACL injuries. Secondary bone bruises have been reported in over 80% of partial and complete ACL ruptures. Purpose: The objectives of this study were (1) to quantify ACL strain under a range of physiologically relevant loading conditions and (2) to evaluate soft tissue and bony injury patterns associated with applied loading conditions thought to be responsible for many noncontact ACL injuries. Study Design: Controlled laboratory study. Methods: Seventeen cadaveric legs (age, 45 ± 7 years; 9 female and 8 male) were tested utilizing a custom-designed drop stand to simulate landing. Specimens were randomly assigned between 2 loading groups that evaluated ACL strain under either knee abduction or internal tibial rotation moments. In each group, combinations of anterior tibial shear force, and knee abduction and internal tibial rotation moments under axial impact loading were applied sequentially until failure. Specimens were tested at 25° of flexion under simulated 1200-N quadriceps and 800-N hamstring loads. A differential variable reluctance transducer was used to calculate ACL strain across the anteromedial bundle. A general linear model was used to compare peak ACL strain at failure. Correlations between simulated knee injury patterns and loading conditions were evaluated by the χ2 test for independence. Results: Anterior cruciate ligament failure was generated in 15 of 17 specimens (88%). A clinically relevant distribution of failure patterns was observed including medial collateral ligament tears and damage to the menisci, cartilage, and subchondral bone. Only abduction significantly contributed to calculated peak ACL strain at failure (P = .002). While ACL disruption patterns were independent of the loading mechanism, tibial plateau injury patterns (locations) were significantly (P = .002) dependent on the applied loading conditions. Damage to the articular cartilage along with depression of the midlateral tibial plateau was primarily associated with knee abduction moments, while cartilage damage with depression of the posterolateral tibial plateau was primarily associated with internal tibial rotation moments. Conclusion: The current findings demonstrate the relationship between the location of the tibial plateau injury and ACL injury mechanisms. The resultant injury locations were similar to the clinically observed bone bruises across the tibial plateau during a noncontact ACL injury. These findings indicate that abduction combined with other modes of loading (multiplanar loading) may act to produce ACL injuries. Clinical Relevance: A better understanding of ACL injury mechanisms and associated risk factors may improve current preventive, surgical, and rehabilitation strategies and limit the risk of ACL and secondary injuries, which may in turn minimize the future development of posttraumatic osteoarthritis of the knee.

Load Transfer Characteristics Between Posterior Spinal Implants and the Lumbar Spine Under Anterior Shear Loading

A biomechanical human cadaveric study. To determine the percentage of shear force supported by posterior lumbar spinal devices of varying stiffnesses under anterior shear loading in a degenerative spondylolisthesis model. Clinical studies have demonstrated beneficial results of posterior arthrodesis for the treatment of degenerative spinal conditions with instability. Novel spinal implants are designed to correct and maintain spinal alignment, share load with the spine, and minimize adjacent level stresses. The optimal stiffness of these spinal systems is unknown. To our knowledge, low-stiffness posterior instrumentation has not been tested under an anterior shear force, a highly relevant force to be neutralized in the clinical case of degenerative spondylolisthesis. The effects of implant stiffness and specimen condition on implant load and intervertebral motion were assessed in a biomechanical study. Fifteen human cadaveric lumbar functional spinal units were tested under a static 300 N axial compression force and a cyclic anterior shear force (5-250 N). Implants (high-stiffness [HSI]: ø 5.5-mm titanium, medium-stiffness [MSI]: ø 6.35 × 7.2-mm oblong PEEK, and low-stiffness [LSI]: ø 5.5-mm round PEEK) instrumented with strain gauges were used to calculate loads and were tested in each of 3 specimen conditions simulating degenerative changes: intact, facet instability, and disc instability. Intervertebral motions were measured with a motion capture system. As predicted, implants supported a significantly greater shear force as the specimen was progressively destabilized. Mean implant loads as a percent of the applied shear force in order of increasing specimen destabilization for the HSI were 43%, 67%, and 76%; mean implant loads for the MSI were 32%, 56%, and 77%; and mean implant loads for the LSI were 18%, 35%, and 50%. Anterior translations increased with decreasing implant stiffness and increasing specimen destabilization. Implant shear stiffness significantly affected the load sharing between the implant and the natural spine in anterior shear ex vivo. Low-stiffness implants transferred significantly greater loads to the spine. This study supports the importance of load-sharing behavior when designing new implants.

Quantification of Tibiofemoral Shear and Compressive Loads Using an MRI-Based EMG-Driven Knee Model

The purpose of this study is to describe an MRI-based EMG-driven knee model to quantify tibiofemoral compressive and shear forces. Twelve healthy females participated. Subjects underwent 2 phases of data collection: (1) MRI assessment of the lower extremity to quantify muscle volumes and patella tendon orientation and (2) biomechanical evaluation of a drop-jump task. A subject-specific EMG-driven knee model that incorporated lower extremity kinematics, EMG, and muscle volumes and patella tendon orientation estimated from MRI was developed to quantify tibiofemoral shear and compressive forces. A resultant anterior tibial shear force generated from the ground reaction force (GRF) and muscle forces was observed during the first 30% of the stance phase of the drop-jump task. All of the muscle forces and GRF resulted in tibiofemoral compression, with the quadriceps force being the primary contributor. Acquiring subject-specific muscle volumes and patella tendon orientation for use in an EMG-driven knee model may be useful to quantify tibiofemoral forces in persons with altered patella position or muscle atrophy following knee injury or pathology.

Quadriceps and Hamstrings Coactivation During Common Therapeutic Exercises

Anterior tibial shear force and knee valgus moment increase anterior cruciate ligament (ACL) loading. Muscle coactivation of the quadriceps and hamstrings influences anterior tibial shear force and knee valgus moment, thus potentially influencing ACL loading and injury risk. Therefore, identifying exercises that facilitate balanced activation of the quadriceps and hamstrings might be beneficial in ACL injury rehabilitation and prevention. To quantify and compare quadriceps with hamstrings coactivation electromyographic (EMG) ratios during commonly used closed kinetic chain exercises. Cross-sectional study. Research laboratory. Twenty-seven healthy, physically active volunteers (12 men, 15 women; age = 22.1 ± 3.1 years, height = 171.4 ± 10 cm, mass = 72.4 ± 16.7 kg). Participants completed 9 separate closed chain therapeutic exercises in a randomized order. Surface electromyography quantified the activity level of the vastus medialis (VM), vastus lateralis (VL), medial hamstrings (MH), and biceps femoris (BF) muscles. The quadriceps-to-hamstrings (Q:H) coactivation ratio was computed as the sum of average quadriceps (VM, VL) EMG amplitude divided by the sum of average hamstrings (MH, BF) EMG amplitude for each trial. We used repeated-measures analyses of variance to compare Q:H ratios and individual muscle contributions across exercises (α = .05), then used post hoc Tukey analyses. We observed a main effect for exercise (F(3,79) = 22.6, P< .001). The post hoc Tukey analyses revealed smaller Q:H ratios during the single-limb dead lift (2.87 ± 1.77) than the single-limb squat (5.52 ± 2.89) exercise. The largest Q:H ratios were observed during the transverse-lunge (7.78 ± 5.51, P< .001), lateral-lunge (9.30 ± 5.53, P< .001), and forward-lunge (9.70 ± 5.90, P< .001) exercises. The most balanced (smallest) coactivation ratios were observed during the single-limb dead-lift, lateral-hop, transverse-hop, and lateral band-walk exercises. These exercises potentially could facilitate balanced activation in ACL rehabilitation and injury-prevention programs. They also could be used in postinjury rehabilitation programs in a safe and progressive manner.

Patellofemoral and tibiofemoral forces in cyclists and triathletes: effects of saddle height

High compressive load applied to the patellofemoral joint at great knee flexion angle (e.g. >60Âo of flexion), as usually observed in cycling may provide a link between body position on the bicycle and knee joint forces. The aim of the present study was to compare knee joint forces in different saddle heights. Right pedal force and lower limb kinematics were collected for 24 competitive cyclists and triathletes at self-selected preferred, high (-10Âo of knee flexion angle from preferred), low (+10Âo of knee flexion angle from preferred) and optimal (25Âo of knee flexion angle) saddle heights in submaximal pedalling cadence and workload trials (3.45 ± 0.6 W/kg, 90 ± 2 rpm and 163 ± 33 J). Patellofemoral compressive and tibiofemoral anterior-posterior and compressive force were computed by inverse dynamics and compared for different saddle heights via effect sizes. Patellofemoral compressive force (5-13%) and tibiofemoral compressive force (1-7%) were not substantially affected by changes in saddle height. Tibiofemoral anterior shear force decreased at low saddle heights (4-6% of the preferred height) compared to optimal (35%) and high saddle heights (53%). Greater knee flexion angles were observed for lower saddle heights (8-34%). Knee flexion angle was significantly affected by changes in saddle height, which may indicate that using joint kinematics to assess saddle height effects may be useful to anticipate overload in knee joint.

컷팅 방향이 전방십자인대 손상 위험 요인에 미치는 영향

The purpose of this study was to identify the effects of cutting direction on the ACL injury mechanism during cutting. Eighteen subjects who has the right leg dominant were participated in this study. We used vicon and force platform. The results were as follows. First, 90°cutting showed larger joint range of motion than 0 and 45° in sagittal and frontal plane. Second, 45 and 90°degree cutting showed increased moment compared to 0° cutting in extension. And tibia external rotation moment showed in sequence(0° 45° 90°). Third, 45 and 90° cutting showed increased absorption power compared to 0°. Finally, 90° cutting showed larger than 0°in anterior shear force. The finding of this study support as the cutting direction larger there was greater risk of ACL injury in knee joint. Therefore, we think it is necessary to train the athlete about this during training season.

Biomechanical risk factors of non-contact ACL injuries: A stochastic biomechanical modeling study

Significant efforts have been made to identify modifiable risk factors of non-contact anterior cruciate ligament (ACL) injuries in male and female athletes. However, current literature on the risk factors for ACL injury are purely descriptive. An understanding of biomechanical relationship between risk and risk factors of the non-contact ACL injury is necessary to develop effective prevention programs. To compare lower extremity kinematics and kinetics between trials with and without non-contact ACL injuries and to determine if any difference exists between male and female trials with non-contact ACL injuries regarding the lower extremity motion patterns. In this computer simulation study, a stochastic biomechanical model was used to estimate the ACL loading at the time of peak posterior ground reaction force (GRF) during landing of the stop-jump task. Monte Carlo simulations were performed to simulate the ACL injuries with repeated random samples of independent variables. The distributions of independent variables were determined from in vivo laboratory data of 40 male and 40 female recreational athletes. In the simulated injured trials, both male and female athletes had significantly smaller knee flexion angles, greater normalized peak posterior and vertical GRF, greater knee valgus moment, greater patella tendon force, greater quadriceps force, greater knee extension moment, and greater proximal tibia anterior shear force in comparison to the simulated uninjured trials. No significant difference was found between genders in any of the selected biomechanical variables in the trials with simulated non-contact ACL injuries. Small knee flexion angle, large posterior GRF, and large knee valgus moment are risk factors of non-contact ACL injury determined by a stochastic biomechanical model with a cause-and-effect relationship.

Changing sagittal plane body position during single-leg landings influences the risk of non-contact anterior cruciate ligament injury

To examine the effects of different sagittal plane body positions during single-leg landings on biomechanics and muscle activation parameters associated with risk for anterior cruciate ligament (ACL) injury. Twenty participants performed single-leg drop landings onto a force plate using the following landing styles: self-selected, leaning forward (LFL) and upright (URL). Lower extremity and trunk 3D biomechanics and lower extremity muscle activities were recorded using motion analysis and surface electromyography, respectively. Differences in landing styles were examined using 2-way Repeated-measures ANOVAs (sex × landing conditions) followed by Bonferroni pairwise comparisons. Participants demonstrated greater peak vertical ground reaction force, greater peak knee extensor moment, lesser plantar flexion, lesser or no hip extensor moments, and lesser medial and lateral gastrocnemius and lateral quadriceps muscle activations during URL than during LFL. These modifications of lower extremity biomechanics across landing conditions were similar between men and women. Leaning forward while landing appears to protect the ACL by increasing the shock absorption capacity and knee flexion angles and decreasing anterior shear force due to the knee joint compression force and quadriceps muscle activation. Conversely, landing upright appears to be ACL harmful by increasing the post-impact force of landing and quadriceps muscle activity while decreasing knee flexion angles, all of which lead to a greater tibial anterior shear force and ACL loading. ACL injury prevention programmes should include exercise regimens to improve sagittal plane body position control during landing motions.

ACL Strain and Tensile Forces for Weight Bearing and Non—Weight-Bearing Exercises After ACL Reconstruction: A Guide to Exercise Selection

There is a growing body of evidence documenting loads applied to the anterior cruciate ligament (ACL) for weight-bearing and non-weight-bearing exercises. ACL loading has been quantified by inverse dynamics techniques that measure anterior shear force at the tibiofemoral joint (net force primarily restrained by the ACL), ACL strain (defined as change in ACL length with respect to original length and expressed as a percentage) measured directly in vivo, and ACL tensile force estimated through mathematical modeling and computer optimization techniques. A review of the biomechanical literature indicates the following: ACL loading is generally greater with non-weight-bearing compared to weight-bearing exercises; with both types of exercises, the ACL is loaded to a greater extent between 10° to 50° of knee flexion (generally peaking between 10° and 30°) compared to 50° to 100° of knee flexion; and loads on the ACL change according to exercise technique (such as trunk position). Squatting with excessive forward movement of the knees beyond the toes and with the heels off the ground tends to increase ACL loading. Squatting and lunging with a forward trunk tilt tend to decrease ACL loading, likely due to increased hamstrings activity. During seated knee extension, ACL force decreases when the resistance pad is positioned more proximal on the anterior aspect of the lower leg, away from the ankle. The evidence reviewed as part of this manuscript provides objective data by which to rank exercises based on loading applied to the ACL. The biggest challenge in exercise selection post-ACL reconstruction is the limited knowledge of the optimal amount of stress that should be applied to the ACL graft as it goes through its initial incorporation and eventual maturation process. Clinicians may utilize this review as a guide to exercise selection and rehabilitation progression for patients post-ACL reconstruction.

Relationship of knee shear force and extensor moment on knee translations in females performing drop landings: A biplane fluoroscopy study

Background Research has linked knee extensor moment and knee shear force to the non-contact anterior cruciate ligament injury during the landing motion. However, how these biomechanical performance factors relate to knee translations in vivo is not known as knee translations cannot be obtained with traditional motion capture techniques. The purpose of this study was to combine traditional motion capture with high-speed, biplane fluoroscopy imaging to determine relationships between knee extensor moment and knee shear force profiles with anterior and lateral tibial translations occurring during drop landing in female athletes. Methods 15 females performed drop landings from a height of 40 cm while being recorded using a high speed, biplane fluoroscopy system and simultaneously being recorded using surface marker motion capture techniques to estimate knee joint angle, reaction force and moment profiles. Findings No significant statistical relationships were observed between peak anterior or posterior knee shear force and peak anterior and lateral tibial translations; or, between peak knee extensor moment and peak anterior and lateral tibial translations. Although differences were noted in peak shear force ( P = 0.02) and peak knee extensor moment ( P < 0.001) after stratification into low and high shear force and moment cohorts, no differences were noted in anterior and lateral tibial translations (all P ≥ 0.18). Interpretation Females exhibiting high knee extensor moment and knee shear force during drop landings do not yield correspondingly high anterior and lateral tibial translations.

Trunk Neuromuscular Control is Associated with ACL Loading Mechanisms During an Athletic Cutting Task

Trunk position and postural control influence lower extremity biomechanics during athletic tasks. Triplanar loading of the knee results in high levels of stress in the anterior cruciate ligament (ACL). Excessive trunk motion has been reported during movements resulting in ACL injury. However, the relationship between trunk neuromuscular control (NMC) and triplanar knee loads during an athletic cutting task (ACT) has not been examined. PURPOSE: To investigate the relationship between a laboratory measure of trunk NMC during unstable-sitting (UST) and triplanar knee loads during an ACT. METHODS: 30 physically active subjects (15 male, 15 female, age: 20.5 ± 2.5 yrs, mass: 67.50 ± 11.39 Kg, height: 173.78 ± 9.28 cm) from the university setting participated in this study. During each 1-minute UST trial subjects were required to maintain balance atop a rigid hemisphere with their arms crossed at the chest and with their feet in contact with a footrest fixed to the unstable-sitting device. Center of pressure (CoP) sway data were collected during the UST using a forceplate. For the ACT subjects were instructed to take 3 running steps, jump over a 17 cm hurdle, and cut at 60° in the opposite direction of their dominant plant leg. Peak triplanar trunk angles and knee loads were collected using an infrared motion capture system and forceplate during the first 50% of stance time during the side-step ACT. Pearson product-moment correlation coefficients were calculated among CoP sway data and external knee loads. RESULTS: CoP sway velocity (1.34 ± 0.23 cm/s) was directly associated with anterior tibial shear force (0.114 ± 0.092) (r = 0.382, p = 0.049), and tibial external rotation moment (0.032 ±.013) (r = 0.451, p = 0.018). CoP sway area (50.29 ± 18.50 cm2) was positively associated (r = 0.548, p = 0.006) with knee flexion moment (0.115 ± 0.032). CoP sway path (81.02 ± 14.44 cm) was positively associated with knee flexion moment (r = 0.407, p = 0.032) and tibial external rotation moment (r = 0.474, p = 0.011). CONCLUSION: The results of this study provide evidence of a relationship between trunk NMC and triplanar knee loading associated with ACL injury. These relationships suggest that poor NMC of the trunk is associated with increased triplanar loading at the knee joint. Interventions with a focus on improving trunk NMC may decrease ACL injury risk.