Tibiofemoral Compressive Forces Research Articles

Estimation of compressive tibiofemoral force using over resistance of ankle-foot orthosis on gait.

The purpose of this study was to investigate the effect of changing the plantar flexion resistance (PFR) of an ankle-foot orthosis (AFO) on the compressive tibiofemoral force, knee muscle forces, and knee joint angle. We measured and estimated knee flexion angle, knee muscle force, and the compressive tibiofemoral force in healthy adult males. The results showed that the first peak compressive tibiofemoral force, peak knee flexion angle, and peak quadriceps muscle force increased in the strong PFR condition compared with the no-AFO condition. These results suggest that over-PFR caused various knee troubles.

Influence of hamstring activity on knee moments during loading response of gait in individuals following ACL reconstruction

Purpose: Clinically, restoration of gait mechanics following anterior cruciate ligament reconstruction (ACLr) is expected by 3 months post-surgery. However, biomechanical studies at this time consistently report the presence of reduced knee extensor moments in the surgical limb during loading response (LR). This reduction in knee loading is quantified by net joint moments (NJM) estimated using inverse dynamics and represents the minimum moment required for the given kinematics. As a result, the NJM does not consider the contribution from individual muscle groups including quadriceps and hamstrings. Thus, alterations in quadriceps or hamstrings activity could confound our interpretation of the NJM and characterization of knee loading in the surgical limb. In the presence of increased knee flexor activity, the true contribution from the knee extensors may not be reduced at all. Moreover, increased hamstring and consequential quadriceps activity could result in increased tibiofemoral compressive forces and lead to the progression of knee osteoarthritis. Thus, the purpose of this study is to compare the influence of hamstring activity on knee moments during LR between limbs in individuals post-ACLr. Methods: 17 individuals (11F, 24 ± 11 yrs) 114 ±1 7 days post-ACLr walked at 1.4 m/s. 3D kinematics (250 Hz), ground reaction forces (GRF; 1000 Hz) and anthropometrics were used to quantify sagittal plane joint kinematics and kinetics (inverse dynamics). Medial and lateral hamstring surface electromyography (EMG; 1000 Hz) was collected. Maximum voluntary isometric contractions (MVIC) were performed bilaterally. Raw EMG signals were band-pass filtered (10–500 Hz) and rectified. A 6 Hz low-pass filter was used to create a linear envelope. All data were normalized to 101 points of stance. A standard musculoskeletal SIMM (Software for Interactive Musculoskeletal Modeling) model was used to estimate knee flexor moments. Sagittal plane hip, knee, and ankle kinematics and hamstring EMG (biceps femoris long head, BFLH, and short head, BFSH, semimembranosus, SM, and semitendinosus, ST) normalized to MVIC were used as inputs. SM and BFSH activation were assumed to be the same as ST and BFLH, respectively. To account for differences in hamstring strength, the knee flexor moment from SIMM was scaled using a ratio of the subject’s maximum knee flexor torque during MVIC divided by the maximum knee flexor torque of the SIMM model in the testing position. The sum of the scaled estimated knee flexor moment and net knee moment (Visual3D) were used to estimate knee extensor torque. Moment impulses were calculated as the area under the curve from initial contact to peak knee flexion. Four successful trials were collected for the surgical (ACLr) and non-surgical (NS) limbs. Paired sample t-tests were used to compare net knee and estimated flexor and extensor moment impulses between limbs (mean ± SE); α = 0.05. Results: Net knee (P = 0.02; ACLr: −0.028 ± 0.003; NS: −0.041 ± 0.004 Nm*s/kg) and estimated extensor (P = 0.02; ACLr: −0.035 ± 0.004; NS: −0.048 ± 0.005 Nm*s/kg) moment impulses during LR were reduced in ACLr compared to NS limb. However, estimated knee flexor moment impulse (P = 0.99; ACLr:0.008 ± 0.001; NS:0.008 ± 0.001 Nm*s/kg) was not different. Conclusions: These data are consistent with the literature reporting reduced net knee loading in the surgical limb post-ACLr. When accounting for the torque-producing capabilities of the knee flexors, the estimated knee extensor moment was greater than the net moment in both limbs. The estimated knee extensor moment remained reduced in the ACLr limb compared to the NS limb in the absence of between limbs differences in SIMM estimated knee flexor moment. These data indicate that individuals do not disproportionately increase hamstring contribution to the net knee moment in the surgical knee during gait and the reduced net knee moment reflects a pattern in which the contribution of knee extensors is reduced during LR of gait.

Effects of Anterior Closing Wedge Tibial Osteotomy on Anterior Cruciate Ligament Force and Knee Kinematics

Background: A certain percentage of patients undergoing anterior cruciate ligament (ACL) reconstruction will experience graft failure, and there is mounting evidence that an increased posterior tibial slope (PTS) may be a predisposing factor. Theoretically, under tibiofemoral compression force (TFC), a reduced PTS would induce less anterior tibial translation (ATT) and lower ACL force. Hypothesis: Ten-degree anterior closing wedge osteotomy of the proximal tibia will significantly reduce ACL force and alter knee kinematics during robotic testing. Study Design: Controlled laboratory study. Methods: Eleven fresh-frozen human knees were instrumented with a load cell that measured ACL force as the knee was flexing continuously from 0° to 50° under 200-N TFC as our initial testing condition, followed by the addition of the following tibial loads: 45-N anterior force (AF), 5-N·m valgus moment (VM), 2-N·m internal torque (IT), and all loads combined. ACL force and knee kinematics were recorded before and after osteotomy. Results: Osteotomy produced significant changes in the tibiofemoral position at full extension (as defined by a 2-N·m knee extension moment). This resulted in apparent knee hyperextension (9.4° ± 1.9°), posterior tibial translation (7.9 mm ± 1.6 mm), internal tibial rotation (3.2° ± 2.3°), and valgus tibial rotation (3.2° ± 1.5°). During straight knee flexion with TFC alone, osteotomy reduced ACL force to 0 N beyond 5° of flexion, and ATT was reduced between 0° and 45° (P < .05). With TFC + AF, ACL force was reduced beyond 5° of flexion, and ATT was reduced between 5° and 45° (P < .05). With TFC + VM, ACL force was less than 10 N beyond 5° of flexion, and ATT was reduced at all flexion angles (P < .05). Under the loading conditions TFC + IT and TFC + IT + AF + VM, osteotomy did not significantly change ACL force or ATT at any flexion angle. Conclusion: In general, osteotomy lowered ACL force and reduced ATT when IT was not present. The benefits of osteotomy were negated when IT was included possibly because the dominant mechanism of ACL force generation was cruciate impingement from internal winding and not ATT. Clinical Relevance: PTS-reducing osteotomy significantly decreased ACL force and reduced ATT for knee loads that did not include IT.

Patellofemoral and tibiofemoral forces during knee extension: simulations to strength training and rehabilitation exercises

Abstract Introduction: Limited evidence has been shown on ways to optimize the mechanical design of machines in order to minimize knee loads. Objective: This study compared six computer simulated models of open kinetic knee extension exercises for patellofemoral pressure and tibiofemoral forces. Methods: A musculoskeletal model of the lower limb was developed using six different cam radius to change resistive forces. A default machine, a constant cam radius, a torque-angle model, a free-weight model and two optimized models were simulated. Optimized models reduced cam radius at target knee flexion angles to minimize knee forces. Cam radius, human force, tibiofemoral compressive and shear force, and patellofemoral pressure were compared for the six models using data from five knee flexion angles. Results: Large reductions in cam radius comparing the free-weight model to other models (73-180%) were limited to the large human force for the constant cam model to other models (9-36%). Larger human force (13 -36%) was estimated to perform knee extension using a constant cam radius compared other models without large effects in knee joint forces. Conclusion: Changes in cam design effected human without a potential impact in knee loads.

Increasing hip and knee flexion during a drop-jump task reduces tibiofemoral shear and compressive forces: implications for ACL injury prevention training

ABSTRACTAlthough most ACL injury prevention programmes encourage greater hip and knee flexion during landing, it remains unknown how this technique influences tibiofemoral joint forces. We examined whether a landing strategy utilising greater hip and knee flexion decreases tibiofemoral anterior shear and compression. Twelve healthy women (25.9 ± 3.5 years) performed a drop-jump task before and after a training session (10–15 min) that emphasised greater hip and knee flexion. Peak tibiofemoral anterior shear and compressive forces were calculated using an electromyography (EMG)-driven knee model that incorporated joint kinematics, EMG and participant-specific muscle volumes and patella tendon orientation measured using magnetic resonance imaging (MRI). Participants demonstrated a decrease in peak anterior tibial shear forces (11.1 ± 3.3 vs. 9.6 ± 2.7 N · kg−1; P = 0.008) and peak tibiofemoral compressive forces (68.4 ± 7.6 vs. 62.0 ± 5.5 N · kg−1; P = 0.015) post-training. The decreased peak anterior tibial shear was accompanied by a decrease in the quadriceps anterior shear force, while the decreased peak compressive force was accompanied by decreased ground reaction force and hamstring forces. Our data provide justification for injury prevention programmes that encourage greater hip and knee flexion during landing to reduce tibiofemoral joint loading.

Bike fitting: finding an optimum between performance and overuse injuries prevention? Influence of saddle fore-aft position on knee joint forces

Background: The Union Cyclist International (UCI) regulates saddle setback - ‘ the tip of the saddle shall be a minimum of 5 cm to the rear of a vertical plane passing through the crank axis but no maximum is recommended’ - while there is no scientific rational supporting this regulation. Furthermore, the absolute value of 5 cm applies to all cyclists without accounting for cyclist’s anthropometry and, in other disciplines such as track cycling and triathlon that are not subject to this regulation, a smaller setback is often used while there is no higher prevalence of joint overuse injuries.  Purpose: The aim of this study was to investigate the effect of saddle setback on knee joint forces exhibited during cycling. A musculoskeletal modelling approach was developed and, in an attempt to identify the underlined mechanisms responsible for knee joint forces, pedal force, knee kinematics and knee muscle forces were investigated  Methods: Ten well-trained (8.5 ± 6.75 years of experience in competition and average weekly training volume 4.0 ± 0.8 hours) cyclists volunteered to participate in the study. A stationary cycle ergometer was instrumented with two six-load component force sensors that were integrated in the pedals. A 20-camera motion analysis system was used to acquire 3D kinematics. Markers data and pedal forces served as input of the model for the computation of knee joint forces that resulted from the recommended Opensim calculation steps: 1) scaling to participant’s anthropometry, 2) inverse kinematics to compute joint angles, 3) static optimisation to compute muscle forces and 4) joint reaction analysis to compute tibiofemoral forces and patellofemoral forces. Knee joint forces were normalised to pedalling cycle and the mean and peak of the 3 components of each forces were calculated. Three saddle setback conditions were compared: a Recommended condition which included values of saddle height and setback based on individual anthropometric measurements, a Backward (10% more backward) and a Forward (10% more forward) conditions. The setup of all other settings was standardised. For the three conditions, participants were instructed to perform a 3minute trial while keeping cadence (90rpm) and power (200W) constant.  Results: Results showed that the timing (~160° of pedalling cycle) of the peak of tibiofemoral compressive force remained unchanged across saddle setback conditions. Contrary to what some epidemiological studies earlier suggested this study indicates that sitting close to the handlebar (even closer than the 5 cm of the UCI regulation) was not associated with an increase of patellofemoral and tibiofemoral forces. Oppositely, sitting backward may be more detrimental as it leads to higher tibiofemoral forces (Table 1). A 15% increase was found in a ~6 cm change of saddle setback. Those results balance previous findings that reported a mechanical advantage associated with sitting more backward.  Discussion: In a whole, this study brings new insights on the underlying mechanisms of tibiofemoral force in cycling that are of importance for a safe training and for rehabilitation protocols. Indeed, results further explained that the peak joint force was linked neither to the peak of force applied to the pedal nor to the peak of quadriceps force but to the increasing of eccentric hamstring force at the end of the downstroke phase, just before the transition toward the upstroke.  Conclusions: While it was previously reported that sitting more backward increases effectiveness in steady-state pedalling, the present study would oppositely prevent for using an important saddle setback. This underlies the difficult compromise between performance and health and reflects the complexity of defining an “optimal saddle position” and establishing bike fitting guidelines. Subsequently, our results suggest that UCI recommendations (1.3.013), which only regulate the maximal forward saddle position (saddle setback > 5 cm), but neither its backward position nor saddle height, may need to be revised.

Searching for strategies to reduce the mechanical demands of the sit-to-stand task with a muscle-actuated optimal control model

BackgroundThe sit-to-stand task, which involves rising unassisted from sitting on a chair to standing, is important in daily life. Many people with muscle weakness, reduced range of motion or loading-related pain in a particular joint have difficulty performing the task. How should a person suffering from such impairment best perform the sit-to-stand task and, in the case of pain in a particular joint, with reduced loading of that joint? MethodsWe developed a musculoskeletal model with reference parameter values based on properties of healthy strong subjects. The model's muscle stimulation-time input was optimized using direct collocation to find strategies that yielded successful sit-to-stand task performance with minimum ‘control effort’ for the reference set and modified sets of parameter values, and with constraints on tibiofemoral compression force. FindingsThe sit-to-stand task could be performed successfully and realistically by the reference model, by a model with isometric knee extensor forces reduced to 40% of reference, by a model with isometric forces of all muscles reduced to 45% of reference, and by the reference model with the tibiofemoral compression force constrained during optimization to 65% of the peak value in the reference condition. InterpretationThe strategies found by the model in conditions other than reference could be interpreted well on the basis of cost function and task biomechanics. The question remains whether it is feasible to teach patients with musculoskeletal impairments or joint pain to perform the sit-to-stand task according to strategies that are optimal according to the simulation model.

Muscle co-contraction during gait in individuals with articular cartilage defects in the knee

Increased muscle co-contraction during gait is common in individuals with knee pathology, and worrisome as it is known to amplify tibiofemoral compressive forces. While knees with articular cartilage defects (ACD) are more vulnerable to compressive forces, muscle co-contraction has never been reported in this population. The purpose of this study was to evaluate the extent to which individuals with ACDs in the knee demonstrate elevated quadriceps to hamstrings muscle co-contraction on the involved limb during gait compared to the uninvolved limb and to healthy controls. We also explored the impact of participant characteristics and knee impairments on co-contraction. Twenty-nine individuals with full-thickness knee ACDs (ACD group) and 19 healthy adults (control group) participated in this study. Participants performed five gait trials at self-selected speed, during which activity of the quadriceps and hamstrings muscles were collected with surface electromyography. Three-dimensional motion capture was used to define phases of gait. Quadriceps strength and self-reported outcomes were also assessed in the same session. There were no differences in quadriceps: hamstrings co-contraction between the ACD and control groups, or between the involved and uninvolved limb for the ACD group. For both ACD and control groups, co-contraction was highest in early stance and lowest in late stance. Quadriceps strength was consistently the strongest predictor of muscle co-contraction in both the ACD and the control groups, with individuals with lower strength demonstrating greater co-contraction. Further study is needed to understand the effect of increased muscle co-contraction on joint compressive forces in the presence of varied quadriceps strength.

Obesity is associated with higher absolute tibiofemoral contact and muscle forces during gait with and without knee osteoarthritis

BackgroundObesity is an important risk factor for knee osteoarthritis initiation and progression. However, it is unclear how obesity may directly affect the mechanical loading environment of the knee joint, initiating or progressing joint degeneration. The objective of this study was to investigate the interacting role of obesity and moderate knee osteoarthritis presence on tibiofemoral contact forces and muscle forces within the knee joint during walking gait. MethodsThree-dimensional gait analysis was performed on 80 asymptomatic participants and 115 individuals diagnosed with moderate knee osteoarthritis. Each group was divided into three body mass index categories: healthy weight (body mass index<25), overweight (25≤body mass index≤30), and obese (body mass index>30). Tibiofemoral anterior–posterior shear and compressive forces, as well as quadriceps, hamstrings and gastrocnemius muscle forces, were estimated based on a sagittal plane contact force model. Peak contact and muscle forces during gait were compared between groups, as well as the interaction between disease presence and body mass index category, using a two-factor analysis of variance. FindingsThere were significant osteoarthritis effects in peak shear, gastrocnemius and quadriceps forces only when they were normalized to body mass, and there were significant BMI effects in peak shear, compression, gastrocnemius and hamstrings forces only in absolute, non-normalized forces. There was a significant interaction effect in peak quadriceps muscle forces, with higher forces in overweight and obese groups compared to asymptomatic healthy weight participants. InterpretationBody mass index was associated with higher absolute tibiofemoral compression and shear forces as well as posterior muscle forces during gait, regardless of moderate osteoarthritis presence or absence. The differences found may contribute to accelerated joint damage with obesity, but with the osteoarthritic knees less able to accommodate the high loads.

Body-borne Loads Increase Knee Joint Contact Force During Run-to-stop Task

Running with body-borne load can cause abnormal knee joint loads, such as increased tibio-femoral compressive forces. These elevated compressive forces (i.e. knee joint contact force) may lead to knee pain, injury or disease (e.g. osteoarthritis). A sudden stop during running (i.e. run-to-stop) may exacerbate these compressive forces, particularly when impaired with body-borne load, further increasing risk of injury. Currently it is not understood if body-borne load impacts knee joint contact force during a sudden stop. PURPOSE: The purpose of this study was to determine how body-borne load impacts knee joint contact force during a run-to-stop task. METHODS: Five males (23.4 ± 3.7 yrs; 1.8 ± 0.1 m; 71.8 ± 8.1 kg) had lower limb biomechanics recorded during a run-to-stop task with three military-relevant load conditions: unloaded (UL; 6.2 kg), fighting load (FL; 20.0 kg) and approach load (AL; 40.0 kg). During the run-to-stop, participants ran 3.5 m/s ± 5% down a walkway, planted their dominant limb on an embedded force platform and stopped in a low-ready position. Kinematic and kinetic data were processed in Visual 3D during the stopping phase, from initial heel strike of the dominant limb to heel strike of non-dominant limb. Knee joint contact force, defined as the force acting on the tibial plateau parallel to the longitudinal tibial axis, was estimated using OpenSim and normalized to bodyweight. Peak knee joint contact force was quantified from the normalized data, and then subject-based means calculated and submitted to a one-way ANOVA with alpha level P<0.05 to compare the load conditions. RESULTS: Peak knee joint contact forces increased significantly with the addition of body-borne load (p = 0.025), where UL was 2.42*BW (±0.51), FL was 3.10*BW (±0.54) and AL was 3.77*BW (±0.89). Specifically, peak knee joint contact force was significantly greater during AL compared to the UL (p=0.019), but not compared to the FL load (p=0.291) or between the UL and FL loads (p=0.276). CONCLUSION: When stopping, body-borne load increases knee joint contact force, potentially causing tibio-femoral compressive forces that can lead to pain and injury. Future work is necessary to determine the specific mechanical traits needed to reduce elevated knee joint contact forces evident, particularly with heavy (40.0 kg) approach loads.

Integrating dynamic stereo-radiography and surface-based motion data for subject-specific musculoskeletal dynamic modeling

This manuscript presents a new subject-specific musculoskeletal dynamic modeling approach that integrates high-accuracy dynamic stereo-radiography (DSX) joint kinematics and surface-based full-body motion data. We illustrate this approach by building a model in OpenSim for a patient who participated in a meniscus transplantation efficacy study, incorporating DSX data of the tibiofemoral joint kinematics. We compared this DSX-incorporated (DSXI) model to a default OpenSim model built using surface-measured data alone. The architectures and parameters of the two models were identical, while the differences in (time-averaged) tibiofemoral kinematics were of the order of magnitude of 10° in rotation and 10mm in translation. Model-predicted tibiofemoral compressive forces and knee muscle activations were compared against literature data acquired from instrumented total knee replacement components (Fregly et al., 2012) and the patient׳s EMG recording. The comparison demonstrated that the incorporation of DSX data improves the veracity of musculoskeletal dynamic modeling.

Voluntary Enhanced Cocontraction of Hamstring Muscles During Open Kinetic Chain Leg Extension Exercise

Background: A number of research studies provide evidence that hamstring cocontraction during open kinetic chain knee extension exercises enhances tibiofemoral (TF) stability and reduces the strain on the anterior cruciate ligament. Purpose: To determine the possible increase in hamstring muscle coactivation caused by a voluntary cocontraction effort during open kinetic chain leg-extension exercises, and to assess whether an intentional hamstring cocontraction can completely suppress the anterior TF shear force during these exercises. Study Design: Descriptive laboratory study. Methods: Knee kinematics as well as electromyographic activity in the semitendinosus (ST), semimembranosus (SM), biceps femoris (BF), and quadriceps femoris muscles were measured in 20 healthy men during isotonic leg extension exercises with resistance (R) ranging from 10% to 80% of the 1-repetition maximum (1RM). The same exercises were also performed while the participants attempted to enhance hamstring coactivation through a voluntary cocontraction effort. The data served as input parameters for a model to calculate the shear and compressive TF forces in leg extension exercises for any set of coactivation patterns of the different hamstring muscles. Results: For R≤ 40% 1RM, the peak coactivation levels obtained with intentional cocontraction (l) were significantly higher (P < 10–3) than those obtained without intentional cocontraction (l0). For each hamstring muscle, maximum level l was reached at R = 30% 1RM, corresponding to 9.2%, 10.5%, and 24.5% maximum voluntary isometric contraction (MVIC) for the BF, ST, and SM, respectively, whereas the ratio l/l0 reached its maximum at R = 20% 1RM and was approximately 2, 3, and 4 for the BF, SM, and ST, respectively. The voluntary enhanced coactivation level l obtained for R≤ 30% 1RM completely suppressed the anterior TF shear force developed by the quadriceps during the exercise. Conclusion: In leg extension exercises with resistance R≤ 40% 1RM, coactivation of the BF, SM, and ST can be significantly enhanced (up to 2, 3, and 4 times, respectively) by a voluntary hamstring cocontraction effort. The enhanced coactivation levels obtained for R≤ 30% 1RM can completely suppress the anterior TF shear force developed by the quadriceps during the exercise. Clinical Relevance: This laboratory study suggests that leg extension exercise with intentional hamstring cocontraction may have the potential to be a safe and effective quadriceps-strengthening intervention in the early stages of rehabilitation programs for anterior cruciate ligament injury or reconstruction recovery. Further studies, including clinical trials, are needed to investigate the relevance of this therapeutic exercise in clinical practice.

The effects of childhood obesity on compressive tibiofemoral force and muscle functions during normal walking

The effects of childhood obesity on compressive tibiofemoral force and muscle functions during normal walking

The Effects of Walking Speed on Tibiofemoral Loading Estimated Via Musculoskeletal Modeling

Net muscle moments (NMMs) have been used as proxy measures of joint loading, but musculoskeletal models can estimate contact forces within joints. The purpose of this study was to use a musculoskeletal model to estimate tibiofemoral forces and to examine the relationship between NMMs and tibiofemoral forces across walking speeds. We collected kinematic, kinetic, and electromyographic data as ten adult participants walked on a dual-belt force-measuring treadmill at 0.75, 1.25, and 1.50 m/s. We scaled a musculoskeletal model to each participant and used OpenSim to calculate the NMMs and muscle forces through inverse dynamics and weighted static optimization, respectively. We determined tibiofemoral forces from the vector sum of intersegmental and muscle forces crossing the knee. Estimated tibiofemoral forces increased with walking speed. Peak early-stance compressive tibiofemoral forces increased 52% as walking speed increased from 0.75 to 1.50 m/s, whereas peak knee extension NMMs increased by 168%. During late stance, peak compressive tibiofemoral forces increased by 18% as speed increased. Although compressive loads at the knee did not increase in direct proportion to NMMs, faster walking resulted in greater compressive forces during weight acceptance and increased compressive and anterior/posterior tibiofemoral loading rates in addition to a greater abduction NMM.

Effects of workload and pedalling cadence on knee forces in competitive cyclists

Limited evidence showed that higher workload increases knee forces without effects from changes in pedalling cadence. This study assessed the effects of workload and cadence on patellofemoral and tibiofemoral joint forces using a new model. Right pedal force and lower limb joint kinematics were acquired for 12 competitive cyclists at two levels of workload (maximal and second ventilatory threshold) at 90 and 70 rpm of pedalling cadence. The maximal workload showed 18% larger peak patellofemoral compressive force PFC (large effect size, ES) than the second ventilatory threshold workload (90 rpm). In the meantime, the 90-rpm second ventilatory threshold was followed by a 29% smaller PFC force (large ES) than the 70-rpm condition. Normal and anterior tibiofemoral compressive forces were not largely affected by changes in workload or pedalling cadence. Compared to those of previous studies, knee forces normalized by workload were larger for patellofemoral (mean = 19 N/J; difference to other studies = 20–45%), tibiofemoral compressive (7.4 N/J; 20–572%), and tibiofemoral anterior (0.5 N/J; 60–200%) forces. Differences in model design and testing conditions (such as workload and pedalling cadence) may affect prediction of knee joint forces.

Selective contribution of each hamstring muscle to anterior cruciate ligament protection and tibiofemoral joint stability in leg-extension exercise: a simulation study

A biomechanical model was developed to simulate the selective effect of the co-contraction force provided by each hamstring muscle on the shear and compressive tibiofemoral joint reaction forces, during open kinetic-chain knee-extension exercises. This model accounts for instantaneous values of knee flexion angle [Formula: see text], angular velocity and acceleration, and for changes in magnitude, orientation, and application point of external resistance. The tibiofemoral shear force (TFSF) largely determines the tensile force on anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL). Biceps femoris is the most effective hamstring muscle in decreasing the ACL-loading TFSF developed by quadriceps contractions for [Formula: see text]. In this range, the semimembranosus generates the dominant tibiofemoral compressive force, which enhances joint stability, opposes anterior/posterior tibial translations, and protects cruciate ligaments. The semitendinosus force provides the greatest decreasing gradient of ACL-loading TFSF for [Formula: see text], and the greatest increasing gradient of tibiofemoral compressive force for [Formula: see text]. However, semitendinosus efficacy is strongly limited by its small physiological section. Hamstring muscles behave as a unique muscle in enhancing the PCL-loading TFSF produced by quadriceps contractions for [Formula: see text]. The levels of hamstrings co-activation that suppress the ACL-loading TFSF considerably shift when the knee angular acceleration is changed while maintaining the same level of knee extensor torque by a concurrent adjustment in the magnitude of external resistance. The knowledge of the specific role and the optimal activation level of each hamstring muscle in ACL protection and tibiofemoral stability are fundamental for planning safe and effective rehabilitative knee-extension exercises.

Joint Torques and Joint Reaction Forces During Squatting With a Forward or Backward Inclined Smith Machine

We developed a biomechanical model to determine the joint torques and loadings during squatting with a backward/forward-inclined Smith machine. The Smith squat allows a large variety of body positioning (trunk tilt, foot placement, combinations of joint angles) and easy control of weight distribution between forefoot and heel. These distinctive aspects of the exercise can be managed concurrently with the equipment inclination selected to unload specific joint structures while activating specific muscle groups. A backward (forward) equipment inclination decreases (increases) knee torque, and compressive tibiofemoral and patellofemoral forces, while enhances (depresses) hip and lumbosacral torques. For small knee flexion angles, the strain-force on the posterior cruciate ligament increases (decreases) with a backward (forward) equipment inclination, whereas for large knee flexion angles, this behavior is reversed. In the 0 to 60 degree range of knee flexion angles, loads on both cruciate ligaments may be simultaneously suppressed by a 30 degree backward equipment inclination and selecting, for each value of the knee angle, specific pairs of ankle and hip angles. The anterior cruciate ligament is safely maintained unloaded by squatting with backward equipment inclination and uniform/forward foot weight distribution. The conditions for the development of anterior cruciate ligament strain forces are clearly explained.

The Application of Computer Musculoskeletal Modeling and Simulation to Investigate Compressive Tibiofemoral Force and Muscle Functions in Obese Children

This study aimed to utilize musculoskeletal modelling and simulation to investigate the compressive tibiofemoral force and individual muscle function in obese children. We generated a 3D muscle-driven simulation of eight obese and eight normal-weight boys walking at their self-selected speed. The compressive tibiofemoral force and individual muscle contribution to the support and progression accelerations of center of mass (COM) were computed for each participant based on the subject-specific model. The simulated results were verified by comparing them to the experimental kinematics and EMG data. We found a linear relationship between the average self-selected speed and the normalized peak compressive tibiofemoral force (R 2 = 0.611). The activity of the quadriceps contributed the most to the peak compressive tibiofemoral force during the stance phase. Obese children and nonobese children use similar muscles to support and accelerate the body COM, but nonobese children had significantly greater contributions of individual muscles. The obese children may therefore adopt a compensation strategy to avoid increasing joint loads and muscle requirements during walking. The absolute compressive tibiofemoral force and muscle forces were still greater in obese children. The long-term biomechanical adaptations of the musculoskeletal system to accommodate the excess body weight during walking are a concern.

Increased Hip and Knee Flexion During Landing Decreases Tibiofemoral Compressive Forces in Women Who Have Undergone Anterior Cruciate Ligament Reconstruction

Background: Those who have undergone anterior cruciate ligament reconstruction (ACLR) have been shown to exhibit increased muscle co-contraction, decreased knee flexion, and elevated tibiofemoral compressive forces. Elevated tibiofemoral compressive forces may be associated with the high risk of developing knee osteoarthritis in this population. Purpose: To examine whether muscle co-contraction and tibiofemoral compressive forces in women after undergoing ACLR can be reduced through the use of a landing strategy that emphasizes greater hip and knee flexion. Study Design: Controlled laboratory study. Methods: Ten female recreational athletes who had previously undergone ACLR participated in this study. Participants performed a single-legged drop-land task before and after a training session that encouraged them to use greater hip and knee flexion during landing. Peak tibiofemoral compressive forces before and after training were estimated using an electromyography (EMG)–driven knee model that incorporated joint kinematics, EMG, and subject-specific muscle volumes and patellar tendon orientation estimated from magnetic resonance imaging. A co-contraction index (CCI) was calculated to quantify the level of co-contraction between knee flexor and extensor muscles. Results: After training, peak hip and knee flexion as well as hip and knee flexion excursions increased significantly. Additionally, participants demonstrated a significant decrease after training in the areas of muscle co-contraction (CCI [mean ± SD], 0.28 ± 0.10 vs 0.18 ± 0.05; P < .001) and peak tibiofemoral compressive force (97.3 ± 8.0 vs 91.3 ± 10.2 N·kg−1; P = .044). Conclusion: Increased muscle co-contraction as well as elevated tibiofemoral compressive loads observed in individuals following ACLR can be reduced by using a landing strategy that encourages greater hip and knee flexion. Clinical Relevance: The findings of the current study provide useful information for the growth of rehabilitation and/or intervention programs aimed to decrease knee joint loading to prevent or delay the development of knee osteoarthritis in those who have undergone ACLR.

Paper 217: Posterior Stabilized TKA's are Less Sensitive to Implantation Tightness than PCL-Retaining Designs: A Biomechanical Study

Restricted range of motion or excessive laxity are potential complications of total knee arthroplasty (TKA). In contrast patients demand more function for daily activities. To achieve a good function after TKA is important but the aim for all patients should be a better flexion to kneel, work and live without restrictions. Hence the present study was to investigate the effects of implantation tightness on soft tissue strain during passive range of motion. Fourteen fresh frozen cadaver knee joints mounted in a passive flexion rig. Passive flexion was applied to the tibia in 15 deg increments from 0 to 150 deg of flexion. Tibiofemoral force and ligament strain of the medial and lateral collateral ligaments were measured using a custom-built force platform inserted beneath the polyethylene inlay. The standard implantation technique and two variations (2 mm tighter, 2 mm looser) were tested for four prosthesis types: fixed-bearing PCL-retaining (with and without PCL) (PFC), mobile-bearing PCL-sacrificing (LCS), posterior-stabilised (PS), posterior-stabilised with HiFlex femoral component (HF). As expected all prostheses showed a significant increase in tibiofemoral force at full extension when implantation tightness was increased. By comparison in the midrange between 15-90 deg the tibiofemoral force dropped down and was independent of variation in implantation tightness in all designs. Beyond 90 deg the fixed bearing design (PFC) and in the LCS knee were sensitive on implantation tightness. In contrast the two posterior stabilised prosthesis types (PS and HF) showed a different pattern of tibiofemoral force during flexion, with low force throughout the range of motion. As a result in full extension and deep flexion both the PFC prosthesis and the LCS knee represent sensitive designs when considering implantation tightness. Whereas posterior stabilised knee implants are associated with lower tibiofemoral force during the range of motion and more forgiving designs in relation to implantation tightness. The data also suggest that soft tissue structures other than the collaterals tighten as the knee flexes and cause an increase in tibiofemoral compressive force.