Resultant Joint Force Research Articles

Kinetics prediction of normal knee and undergone total knee arthroplasty during squatting based on extreme gradient boosting

Following an arthroplasty, biomechanical evaluation of the knee joint is crucial because it plays a significant role in patient rehabilitation and physician follow-up. The sixty-two subjects, consisting of 31 with normal knees and 31 who had undergone total knee arthroplasty, evaluated the kinetics of the knee joints during squatting using inverse dynamics analysis. Artificial intelligence based on the XGBoost model was also used to predict kinetics data during group squatting. The result revealed that the maximum force, moment, and quadriceps force in the normal knee were higher than in the TKA group during squatting. The maximum resultant joint force magnitude in the normal and TKA groups revealed an average of 4.35 ± 1.00 and 3.08 ± 1.20 times body weight, respectively. Kinetics of the knee joint in a normal knee significantly differed (p < 0.05) from undergoing TKA, especially in the AP-direction force. Additionally, the resultant moment that included the quadriceps muscle force in the normal group was higher than in the TKA groups. The extreme gradient boosting algorithm (XGBoost) model has prediction performance metrics, which are considered to have high correlation performance in the case of kinetics.

Monitoring of Hip Joint Forces and Physical Activity after Total Hip Replacement by an Integrated Piezoelectric Element

Resultant hip joint forces can currently only be recorded in situ in a laboratory setting using instrumented total hip replacements (THRs) equipped with strain gauges. However, permanent recording is important for monitoring the structural condition of the implant, for therapeutic purposes, for self-reflection, and for research into managing the predicted increasing number of THRs worldwide. Therefore, this study aims to investigate whether a recently proposed THR with an integrated piezoelectric element represents a new possibility for the permanent recording of hip joint forces and the physical activities of the patient. Hip joint forces from nine different daily activities were obtained from the OrthoLoad database and applied to a total hip stem equipped with a piezoelectric element using a uniaxial testing machine. The forces acting on the piezoelectric element were calculated from the generated voltages. The correlation between the calculated forces on the piezoelectric element and the applied forces was investigated, and the regression equations were determined. In addition, the voltage outputs were used to predict the activity with a random forest classifier. The coefficient of determination between the applied maximum forces on the implant and the calculated maximum forces on the piezoelectric element was R2 = 0.97 (p &lt; 0.01). The maximum forces on the THR could be determined via activity-independent determinations with a deviation of 2.49 ± 13.16% and activity-dependent calculation with 0.87 ± 7.28% deviation. The activities could be correctly predicted using the classification model with 95% accuracy. Hence, piezoelectric elements integrated into a total hip stem represent a promising sensor option for the energy-autonomous detection of joint forces and physical activities.

Video-driven simulation of lower limb mechanical loading during aquatic exercises

Understanding the mechanical demands of an exercise on the musculoskeletal system is crucial to prescribe effective training or therapeutic interventions. Yet, that knowledge is currently limited in water, mostly because of the difficulty in evaluating external resistance. Here I reconcile recent advances in 3D markerless pose and mesh estimation, biomechanical simulations, and hydrodynamic modeling, to predict lower limb mechanical loading during aquatic exercises. Simulations are driven exclusively from a single video. Fluid forces were estimated within 12.5±4.1% of the peak forces determined through computational fluid dynamics analyses, at a speed three orders of magnitude greater. In silico hip and knee resultant joint forces agreed reasonably well with in vivo instrumented implant recordings (R2=0.74) downloaded from the OrthoLoad database, both in magnitude (RMSE =251±125 N) and direction (cosine similarity = 0.92±0.09). Hip flexors, glutes, adductors, and hamstrings were the main contributors to hip joint compressive forces (40.4±12.7%, 25.6±9.7%, 14.2±4.8%, 13.0±8.2%, respectively), while knee compressive forces were mostly produced by the gastrocnemius (39.1±15.9%) and vasti (29.4±13.7%). Unlike dry-land locomotion, non-hip- and non-knee-spanning muscles provided little to no offloading effect via dynamic coupling. This noninvasive method has the potential to standardize the reporting of exercise intensity, inform the design of rehabilitation protocols and improve their reproducibility.

Unanticipated fake-and-cut maneuvers do not increase knee abduction moments in sport-specific tasks: Implication for ACL injury prevention and risk screening.

Non-contact anterior cruciate ligament injuries typically occur during cutting maneuvers and are associated with high peak knee abduction moments (KAM) within early stance. To screen athletes for injury risk or quantify the efficacy of prevention programs, it may be necessary to design tasks that mimic game situations. Thus, this study compared KAMs and ranking consistency of female handball players in three sport-specific fake-and-cut tasks of increasing complexity. The biomechanics of female handball players (n = 51, mean ± SD: 66.9 ± 7.8 kg, 1.74 ± 0.06 m, 19.2 ± 3.4 years) were recorded with a 3D motion capture system and force plates during three standardized fake-and-cut tasks. Task 1 was designed as a simple pre-planned cut, task 2 included catching a ball before a pre-planned cut in front of a static defender, and task 3 was designed as an unanticipated cut with three dynamic defenders involved. Inverse dynamics were used to calculate peak KAM within the first 100 ms of stance. KAM was decomposed into the frontal plane knee joint moment arm and resultant ground reaction force. RANOVAs (α ≤ 0.05) were used to reveal differences in the KAM magnitudes, moment arm, and resultant ground reaction force for the three tasks. Spearman's rank correlations were calculated to test the ranking consistency of the athletes' KAMs. There was a significant task main effect on KAM (p = 0.02; = 0.13). The KAM in the two complex tasks was significantly higher (task 2: 1.73 Nm/kg; task 3: 1.64 Nm/kg) than the KAM in the simplest task (task 1: 1.52 Nm/kg). The ranking of the peak KAM was consistent regardless of the task complexity. Comparing tasks 1 and 2, an increase in KAM resulted from an increased frontal plane moment arm. Comparing tasks 1 and 3, higher KAM in task 3 resulted from an interplay between both moment arm and the resultant ground reaction force. In contrast to previous studies, unanticipated cutting maneuvers did not produce the highest KAMs. These findings indicate that the players have developed an automated sport-specific cutting technique that is utilized in both pre-planned and unanticipated fake-and-cut tasks.

Effects of Knee Flexion Angles on the Joint Force and Muscle Force during Bridging Exercise: A Musculoskeletal Model Simulation.

Bridging exercise is commonly used to increase the strength of the hip extensor and trunk muscles in physical therapy practice. However, the effect of lower limb positioning on the joint and muscle forces during the bridging exercise has not been analyzed. The purpose of this study was to use a musculoskeletal model simulation to examine joint and muscle forces during bridging at three different knee joint angle positions. Fifteen healthy young males (average age: 23.5 ± 2.2 years) participated in this study. Muscle and joint forces of the lumbar spine and hip joint during the bridging exercise were estimated at knee flexion angles of 60°, 90°, and 120° utilizing motion capture data. The lumbar joint force and erector spinae muscle force decreased significantly as the angle of the knee joint increased. The resultant joint forces were 200.0 ± 23.2% of body weight (%BW), 174.6 ± 18.6% BW, and 150.5 ± 15.8% BW at 60°, 90°, and 120° knee flexion angles, respectively. On the other hand, the hip joint force, muscle force of the gluteus maxims, and adductor magnus tended to increase as the angle of the knee joint increased. The resultant joint forces were 274.4 ± 63.7% BW, 303.9 ± 85.8% BW, and 341.1 ± 85.7% BW at a knee flexion angle of 60°, 90°, and 120°, respectively. The muscle force of the biceps femoris decreased significantly with increased knee flexion during the bridging exercise. In conclusion, the knee flexion position during bridging exercise has different effects on the joint and muscle forces around the hip joint and lumbar spine. These findings would help clinicians prescribe an effective bridging exercise that includes optimal lower limb positioning for patients who require training of back and hip extensor muscles.

Partial Lateral Meniscectomy Affects Knee Stability Even in Anterior Cruciate Ligament-Intact Knees.

The effects of a partial lateral meniscectomy on knee kinematics and forces in the lateral meniscus are critical to understand. The purpose of this study was to quantify the effects of varying sizes of partial lateral meniscectomies of the posterior horn and a total lateral meniscectomy on knee kinematics and resultant forces in the lateral meniscus. Using a robotic testing system, loads (134-N anterior tibial load + 200-N axial compression, 5-Nm internal tibial torque + 5-Nm valgus torque, and 5-Nm external tibial torque + 5-Nm valgus torque) were applied to 10 fresh-frozen cadaveric knees. The resulting joint motion and resultant forces in the lateral meniscus were determined for 4 knee states: intact, one-third and two-thirds partial lateral meniscectomies of the posterior horn, and total lateral meniscectomy. A decrease in lateral translation of the tibia (up to 166.7%) was observed after one-third partial lateral meniscectomies of the posterior horn compared with the intact knee, in response to an anterior load at all knee flexion angles tested (p < 0.05). One-third partial lateral meniscectomies of the posterior horn decreased the resultant forces in the lateral meniscus compared with the intact knee at all knee flexion angles tested in response to an anterior load (p < 0.05) and to an internal tibial torque (p < 0.05). The results of two-thirds partial lateral meniscectomies of the posterior horn were similar to those of one-third partial meniscectomies (p > 0.05). Total lateral meniscectomies further decreased the lateral translation of the tibia (up to 316.6%) compared with the intact knee in response to an anterior load (p < 0.05). The changes in joint motion and meniscal forces observed in this study after even small partial lateral meniscectomies may predispose knees to further injury. Surgeons should always consider repairing and minimizing the resection of even small lateral meniscal tears to prevent the potential deleterious effects of partial meniscectomy reported in this cadaveric study.

Prediction of the Spinal Musculoskeletal Loadings during Level Walking and Stair Climbing after Two Types of Simulated Interventions in Patients with Lumbar Disc Herniation.

Background Low back pain (LBP) continues to be a severe global healthy problem, and a lot of patients would undergo conservative or surgical treatments. However, the improving capacity of spinal load sharing during activities of daily living (ADLs) after interventions is largely unknown. The objective of this study was to quantitatively predict the improvement of spinal musculoskeletal loadings during level walking and stair climbing after two simulated interventions. Material and Methods Twenty-six healthy adults and seven lumbar disc herniation patients performed level walking and stair climbing in sequence. The spinal movement was recorded using a motion capture system. The experimental data were applied to drive a musculoskeletal model to calculate all the lumbar joint resultant forces and muscle activities of seventeen main trunk muscle groups. Rehabilitation and reconstruction were selected as the representative of conservative and surgical treatment, respectively. The spinal load sharing after rehabilitation and reconstruction was predicted by replacing the patients' spine rhythm with healthy subjects' spine rhythm and altering the center of rotation at the L5S1 level, respectively. Results During both level walking and stair climbing, the joint resultant forces of the lower lumbar intervertebral discs were predicted to reduce after the two simulated inventions. In addition, the maximum muscle activities of the most trunk muscle groups decreased after simulated rehabilitation and conversely increased after simulated reconstruction. Conclusion The predictions revealed the different compensatory responses on the spinal load sharing after two simulated interventions, severing as guidance for making preoperative planning and rehabilitation planning.

Effects of body weight support and pedal stance width on joint loading during pinnacle trainer exercise

BackgroundA pinnacle trainer is a stair climber that has a biplane exercise trajectory and an adjustable pedal stance width (PSW). A pinnacle trainer integrated with a body weight support (BWS) system can help overweight individuals or individuals with poor balance exercise safely by reducing excessive or improper joint loads, preventing training-related injuries. However, few studies have investigated the biomechanical features of the lower extremities during pinnacle trainer exercise with and without partial BWS for various PSWs. Research questionWe aimed to investigate the effects of partial BWS and PSW on the joint loading of the lower extremities during stepping on a pinnacle trainer. MethodsSeventeen healthy adults exercised on the pinnacle trainer with or without BWS using various PSWs. The joint resultant forces and joint moments of the lower extremities were calculated according to the kinematic and kinetic data measured via a motion capture system and force transducers on the pedals, respectively. ResultsThe joint resultant forces and joint moments of the lower extremities significantly decreased with increasing percentage of BWS. The internal knee adduction moment and internal hip abduction moment significantly increased with increasing PSW. For every kilogram of BWS, the joint loading of the lower extremities decreased by approximately 1% of the joint resultant forces of body weight during exercise with the pinnacle trainer. SignificanceExercise on the pinnacle trainer with partial BWS significantly reduced joint loading. Exercise with a wider pedal stance may be helpful for knee osteoarthritis rehabilitation as it produces greater internal hip abduction and internal knee adduction moments.

A parametric study of effect of experimental tibialis posterior muscle pain on joint loading and muscle forces—Implications for patients with rheumatoid arthritis?

BackgroundFoot pain and deformities are commonly encountered in patients with rheumatoid arthritis (RA). Likewise, Posterior tibial tendon dysfunction (PTTD) is commonly involved in development of foot and ankle abnormalities and has been reported with a prevalence in two-thirds of the RA patients. Research questionRedundancy in the physiological function between different muscles provides the central nervous system multiple options to perform the same movement but which muscles compensate for the impairment of the tibialis posterior (TP) muscle? And how does these changes affect ankle joint loading? MethodsExperimental and computational disciplines were applied to investigate changes in muscle forces as result of induced pain in the right TP muscle. Twelve healthy subjects were enrolled in the study. Experimental pain was induced in the TP by a single ultrasound graphically guided injection of 1 mL hypertonic saline (5.0% Sodium Chloride). The participants' gait was assessed by skin marker-based motion capture and force plates. Musculoskeletal models were used to investigate compensation mechanisms systematically in the lower under extremity when TP muscle was recruited less as a consequence of the induced pain. ResultsExperimental TP muscle pain and simulated reduced strength caused altered muscle recruitment and made the flexor digitorum longus and flexor hallucis longus muscles compensated for the impairment of the TP muscle. Further, the resultant ankle joint force was increased as the strength of the TP muscle was reduced. SignificanceThe compensation mechanism observed in the present study indicate that alterations in muscle recruitment and muscle force distribution as a result of the underlying disease inflammation itself may contribute to development of chronic foot pain and deformities in patients with RA. Further studies are required to understand the role of PTTD in occurrence of those late adverse musculoskeletal manifestations aiming at search for early preventive strategies.

Upper-limb biomechanical analysis of wheelchair transfer techniques in two toilet configurations

BackgroundUsing proper technique is important for minimizing upper limb kinetics during wheelchair transfers. The objective of the study was to 1) evaluate the transfer techniques used during toilet transfers and 2) determine the impact of technique on upper limb joint loading for two different toilet configurations. MethodsTwenty-six manual wheelchair users (23 men and 3 women) performed transfers in a side and front wheelchair-toilet orientation while their habitual transfer techniques were evaluated using the Transfer Assessment Instrument. A motion analysis system and force sensors were used to record biomechanical data during the transfers. FindingsMore than 20% of the participants failed to complete five transfer skills in the side setup compared to three skills in the front setup. Higher quality skills overall were associated with lower peak forces and moments in both toilet configurations (−0.68 < r < −0.40, p < 0.05). In the side setup, participants who properly placed their hands in a stable position and used proper leading handgrips had lower shoulder resultant joint forces and moments than participants who did not perform these skills correctly (p ≤ 0.04). In the front setup, positioning the wheelchair within three inches of the transfer target was associated with reduced peak trailing forces and moments across all three upper limb joints (p = 0.02). InterpretationTransfer skills training, making toilet seats level with the wheelchair seat, positioning the wheelchair closer to the toilet and mounting grab bars in a more ideal location for persons who do sitting pivot transfers may facilitate better quality toilet transfers.

Estimation of the Optimal Shoulder Orientation from the Viewpoint of Minimal Shoulder Joint Load in 183 Adolescent Baseball Pitchers

Objectives:Adolescent baseball pitchers are prone to shoulder injury as a result of the extreme force and torque placed on the shoulder, especially tremendous joint force applies to the shoulder near ball release. In our clinical experience, shoulder pain at ball release is common complaint. Little analysis is available about the relationship between shoulder orientation and shoulder joint force at the ball release.Methods:A total of 183 adolescent baseball pitchers (14 to 18 years old) participated after providing written informed consents approved by the hospital’s institutional review board. The procedures to be performed were also explained to their parent(s). Each participant was not currently injured or recovering from an injury at time of testing.For data collection, a set of 14-mm spherical reflective markers was placed on the skin overlying 34 anatomical landmarks. Subsequently, the motion capture automatic digitizing system was used to collect 500-Hz from 7 synchronized cameras was set up around the regulation pitching mound in an indoor laboratory. After stretching and warm-up pitching, each player pitch to 5 fastball pitches. Then, the best pitch thrown for a strike was chosen for kinematic and kinetic analysis.The local coordinate systems were used to calculate 3-dimesional rotation at the shoulder using the typical Eulerian sequence. The standard inverse dynamic equation was used to estimate resultant joint force at throwing shoulder. In order to normalize data between subjects, force was expressed as percent using body weight.To estimate the optimal shoulder orientation at ball release, Rz was defined a shoulder abduction angle, which indicated zero value of shoulder superior/inferior force at ball release by linear regression analysis. Similarly-defined Ry was a shoulder horizontal adduction/abduction angle, which indicated zero value of shoulder anterior/posterior force. Afterward, 2 groups with consideration for variations of shoulder orientations at ball release were created: {A- < Rz - 5, Rz - 5 ≤ A ≤ Rz + 5, Rz + 5 < A+}, {B- < Ry - 5, Ry - 5 ≤ B ≤ Ry + 5, Ry + 5 < B+}. Because shoulder range of motion is generally measured 5 degrees intervals in the orthopaedics. Then, we employed MANOVA to investigate significant differences of averages of inferior/superior and anterior/posterior forces applied to the shoulder at ball release among 2 groups respectively.Results:Superior/inferior force was significantly correlated with shoulder abduction. Also anterior/posterior force was strongly correlated with shoulder horizontal adduction/abduction (Table1). The average superior force at A- and the average inferior force at A+ were significantly greater than that at A. Also, the average anterior force at B- and the average posterior force at B+ were significantly higher than at that B (Table 2).Conclusion:The optimal shoulder orientation for minimizing shoulder force at the instant of ball release was 80.6 degrees of shoulder abduction and 10.7 degrees of shoulder adduction. Excessive shoulder horizontal abduction can lead to SLAP lesion, internal impingement and any more pitching-related shoulder injuries has been published. The results of this study demonstrated that increasing amounts of shoulder horizontal abduction were shown to increase anterior force on the shoulder. Therefore, excessive shoulder horizontal abduction can be responsible for several pitching-related shoulder injuries from the viewpoint of shoulder joint load.Table 1.Correlation coefficient between shoulder orientation and shoulder force at ball release in 183 adolescent baseball pitchers. Shoulder force at ball release (%BW) VariablesAnterior forceCompressive forceSuperior force Ball release Shoulder abduction (°)r = -.09 (P = .233)r = .07 (P = .929)r = -.66 (P < .000) Shoulder horizontal adduction (°)r = -.85 (P < .000)r = .12 (P = .117)r = -.38 (P < .000) Ball speed (m/s)r = .26 (P < .000)r = .60 (P < .000)r = -.07 (P = .347)Table 2.The average (±SD) of shoulder force at ball release among |A-, A, A+| and |B-, B, B+| groupsShoulder force (%BW)A-(A- < Rz - 5)A(Rz - 5 < A < Rz + 5)A+(Rz + 5 < A+)Significantdifferences Ball release Anterior force15.4 ± 26.424.0 ± 20.318.4 ± 23.2NS Compressive force85.3 ± 17.890.4 ± 22.388.8 ± 15.6NS Superior force12.3 ± 14.50.1 ± 15.9-17.1 ± 15.5P < .050 for allShoulder force (%BW)B-(B- < Ry - 5)B(Ry -5 < B < Ry + 5)B+(Ry + 5 < B+)Significantdifferences Ball release Anterior force28.6 ± 17.60.2 ± 14.9-25.4 ±21.9P < .001 for all Compressive force89.3 ±17.290.9 ± 15.970.0 ± 24.0P = .009 for B vs B+P = .013 for B- vs B+ Superior force-7.4 ± 16.8-19.8 ± 18.9-19.6 ± 20.8P < .001 for B vs B-Note: Rz is 80.6 degrees of shoulder abduction and Ry is 10.7 of shoulder horizontal abduction. NS is not significant at the P < .05 level

Influence of Combinations of Shoulder, Elbow and Trunk Orientation on Elbow Joint Loads in Youth Baseball Pitchers

Objectives:Shoulder and elbow pain in youth baseball pitchers is a well-recognized phenomenon. Common problems in pitching mechanics that can lead to injury begin with stride foot contact. The purpose of this study was to address the relationships between the combinations of shoulder, elbow and trunk orientation at the instant of stride foot contact and elbow joint loads in youth baseball pitchers.Methods:A total of 143 Japanese male youth baseball pitchers participated in this study after providing written informed consents approved by the hospital’s institutional review board. The procedures to be performed were also explained to their parent(s) or legal guardian(s). Each participant was not currently injured or recovering from an injury at time of testing. For data collection of baseball pitching, a set of 14-mm spherical reflective markers was placed on the skin overlying 34 anatomical landmarks determined. Subsequently, a motion capture three-dimensional automatic digitizing system was used to collect 500-Hz from 7 charge-coupled-device synchronized cameras was set up around the regulation pitching mound in an indoor laboratory. After performing a preparation routine of stretching and warm-up pitching, each player pitch to 5 fastball pitches off the pitching mound to a catcher at the regulation distance of 16 m for youth pitchers. The best pitch thrown for a strike was chosen for kinematic and kinetic analysis. The local coordinate systems were used to calculate 3-dimesional rotation at the trunk, shoulder and elbow using the typical Eulerian sequence. Afterward, the standard inverse dynamic equation was used to estimate resultant joint forces and torques at throwing shoulder and elbow. In order to normalize data between subjects, forces and torques were expressed as percent using body weight and height. A multiple regression analysis was carried out to assess the combined effects of shoulder (external rotation, abduction and horizontal adduction), elbow (pronation and extension) and trunk (extension, contralateral tilt, rotation) orientation at SFC and the onset time of trunk rotation on elbow joint loads at SFC. The onset time of trunk rotation was defined as the event in which the magnitude of trunk rotation begins to decrease from tis maximum value.Results:The peak medial force of the elbow was significant correlated with the peak internal rotation torque of the shoulder and the peak varus torque of the elbow (Figure 1). The medial force of the elbow at SFC was significantly correlated with the peak medial force of the elbow (r = .41, p < .001). The adjusted multiple R2 value was 0.45, indicating that over 45% of the variance in the medial force of the elbow at SFC was explained by the regression equation. The standard error of estimate was 4.34. All 3 of the regression variables were significant and are shown in Table 1.Conclusion:The combinations of the greater external rotation of the shoulder, contralateral trunk tilt and elbow extension at SFC may have an indirect influence on the peak medial force on the elbow (Table 1). Then the peak elbow varus torque and shoulder internal rotation torque lead to increase as a result of these. These biomechanical data provide a scientific basis for clinicians, athletes, and coaches to establish methods to prevent pitching-related injuries and improve pitching mechanics.

Sensitivity of lumbar spine loading to anatomical parameters

Musculoskeletal simulations of lumbar spine loading rely on a geometrical representation of the anatomy. However, this data has an inherent inaccuracy. This study evaluates the influence of defined geometrical parameters on lumbar spine loading utilising five parametrised musculoskeletal lumbar spine models for four different postures. The influence of the dimensions of vertebral body, disc, posterior parts of the vertebrae as well as the curvature of the lumbar spine was studied. Additionally, simulations with combinations of selected parameters were conducted. Changes in L4/L5 resultant joint force were used as outcome variable. Variations of the vertebral body height, disc height, transverse process width and the curvature of the lumbar spine were the most influential.These parameters can be easily acquired from X-rays and should be used to morph a musculoskeletal lumbar spine model for subject-specific approaches with respect to bone geometry. Furthermore, the model was very sensitive to uncommon configurations and therefore, it is advised that stiffness properties of discs and ligaments should be individualised.

Muscle forces and activation patterns in the spine during spine stabilization exercise using a whole body tilt device

The objective of the study was to investigate the effect of 3-D stabilization exercise using a whole body tilt device. A musculoskeletal (MS) model of the whole body was developed, and used to calculate the forces in the spine, assisted by EMG measurement. The inverse dynamics was solved using the MS model of the whole body with the input data of the eight different directions of the tilt: anterior (A), posterior (P), anterior right (AR), posterior right (PR), anterior left (AL), posterior left (PL), right (R), and left (L), replicating the tilting directions of the whole body device. The anterior and posterior directions of tilt mainly induced superficial back and front muscle activations, respectively. However, deep muscles, such as the semispinalis and mulifidi, were activated in all directions of tilt. The joint resultant forces in the right and left direction of tilt were the least; but some higher activations and more diverse recruitments of muscles were demanded. In the present investigation, 3-D stabilization exercise can provide considerable muscle activation and exercise effect, with the minimum perturbation of structure. Therefore, the proposed direction of tilt can be used to strengthen the targeted muscles, depending on the patient’s muscle conditions.

ANALYSIS OF THE EFFECTS OF SPINE STABILIZATION EXERCISES USING A WHOLE BODY TILT DEVICE ON MUSCLE FORCES IN THE SPINE

The objective of the study was to investigate the effects of 3D stabilization exercises using a whole body tilt device on forces in the trunk, such as individual muscle forces and activation patterns, maximum muscle activities and spine loads. For this sake, a musculoskeletal (MS) model of the whole body was developed, and an inverse dynamics analysis was performed to predict the forces on the spine. An EMG measurement experiment was conducted to validate the muscle forces and activation patterns. The MS model was rotated and tilted in eight different directions: anterior (A), posterior (P), anterior right (AR), posterior right (PR), anterior left (AL), posterior left (PL), right (R) and left (L), replicating the directions of the 3D spine balance exercise device, as performed in the experiment. The anterior directions of the tilt primarily induced the activation of long and superficial back muscles and the posterior directions activated the front muscles. However, deep muscles, such as short muscles and multifidi, were activated in all directions of the tilt. The resultant joint forces in the right and left directions of the tilt were the least among the directions, but higher muscle activations and more diverse muscle recruitments than other positions were observed. Therefore, these directions of tilt may be suitable for the elderly and rehabilitation patients who require muscle strengthening with less spinal loads. In the present investigation, it was shown that 3D stabilization exercises could provide considerable muscle exercise effects with a minimum perturbation of structure. The results of this study can be used to provide safety guidelines for muscle exercises using this type of tilting device. Therefore, the proposed direction of tilt can be used to strengthen targeted muscles, depending on the patients' muscular condition.

A neural network approach for determining gait modifications to reduce the contact force in knee joint implant

There is a growing interest in non-surgical gait rehabilitation treatments to reduce the loading in the knee joint. In particular, synergetic kinematic changes required for joint offloading should be determined individually for each subject. Previous studies for gait rehabilitation designs are typically relied on a “trial-and-error” approach, using multi-body dynamic (MBD) analysis. However MBD is fairly time demanding which prevents it to be used iteratively for each subject.This study employed an artificial neural network to develop a cost-effective computational framework for designing gait rehabilitation patterns. A feed forward artificial neural network (FFANN) was trained based on a number of experimental gait trials obtained from literature. The trained network was then hired to calculate the appropriate kinematic waveforms (output) needed to achieve desired knee joint loading patterns (input). An auxiliary neural network was also developed to update the ground reaction force and moment profiles with respect to the predicted kinematic waveforms. The feasibility and efficiency of the predicted kinematic patterns were then evaluated through MBD analysis.Resuls showed that FFANN-based predicted kinematics could effectively decrease the total knee joint reaction forces. Peak values of the resultant knee joint forces, with respect to the bodyweight (BW), were reduced by 20% BW and 25% BW in the midstance and the terminal stance phases. Impulse values of the knee joint loading patterns were also decreased by 17% BW*s and 24%BW*s in the corresponding phases. The FFANN-based framework suggested a cost-effective forward solution which directly calculated the kinematic variations needed to implement a given desired knee joint loading pattern. It is therefore expected that this approach provides potential advantages and further insights into knee rehabilitation designs.

Increased horizontal shoulder abduction is associated with an increase in shoulder joint load in baseball pitching

Soft tissues of the shoulder undergoes substantial stresses due to humeral head movement, and this may contribute to throwing shoulder injuries in baseball pitchers. Prevention and management of throwing shoulder injuries critically rely on reduction of shear force at the shoulder joint. However, the amount and direction of the force applied to the shoulder during the throwing motion have not been clarified. The purpose of this study was to analyze forces applied to the shoulder during a baseball pitch. We performed biomechanical analysis of 213 baseball pitchers of various ages and skilllevels. Throwing motion was analyzed with a 3-dimensional motion capture system. The Eulerangle sequence was adopted to describe angular values of the upper arm relative to the trunk for shoulder rotation, and inverse dynamics was used to estimate the resultant joint forces at the shoulder. There was a significant relation between horizontal abduction/adduction angle and resultant anterior/posterior force at the point of maximum external rotation (MER) (r=-0.63, P<.01), whereby increased horizontal abduction was associated with increased resultant anterior force. There was a significant but weak correlation between abduction/adduction angle and superior/inferior force at MER (r=0.24, P<.01). Comparison among the groups with variable ages and skill levels showed larger horizontal abduction and smaller external rotation angles at MER in the adult amateur player group, whereas normalized compression force and internal rotation torque values at MER were smaller in the junior high school- and elementary school-aged groups. These results suggest that excessive horizontal abduction at MER increases anterior shear force in the shoulder and may lead to shoulder injuries. Focusing on reducing horizontal abduction at MER in the throwing motion may be key to preventing and managing shoulder injuries in baseball pitchers.

Influence of model complexity and problem formulation on the forces in the knee calculated using optimization methods

BackgroundPredictions of the forces transmitted by the redundant force-bearing structures in the knee are often performed using optimization methods considering only moment equipollence as a result of simplified knee modeling without ligament contributions. The current study aimed to investigate the influence of model complexity (with or without ligaments), problem formulation (moment equipollence with or without force equipollence) and optimization criteria on the prediction of the forces transmitted by the force-bearing structures in the knee.MethodsTen healthy young male adults walked in a gait laboratory while their kinematic and ground reaction forces were measured simultaneously. A validated 3D musculoskeletal model of the locomotor system with a knee model that included muscles, ligaments and articular surfaces was used to calculate the joint resultant forces and moments, and subsequently the forces transmitted in the considered force-bearing structures via optimization methods. Three problem formulations with eight optimization criteria were evaluated.ResultsAmong the three problem formulations, simultaneous consideration of moment and force equipollence for the knee model with ligaments and articular contacts predicted contact forces (first peak: 3.3-3.5 BW; second peak: 3.2-4.2 BW; swing: 0.3 BW) that were closest to previously reported theoretical values (2.0-4.0 BW) and in vivo data telemetered from older adults with total knee replacements (about 2.8 BW during stance; 0.5 BW during swing). Simultaneous consideration of moment and force equipollence also predicted more physiological ligament forces (< 1.0 BW), which appeared to be independent of the objective functions used. Without considering force equipollence, the calculated contact forces varied from 1.0 to 4.5 BW and were as large as 2.5 BW during swing phase; the calculated ACL forces ranged from 1 BW to 3.7 BW, and those of the PCL from 3 BW to 7 BW.ConclusionsModel complexity and problem formulation affect the prediction of the forces transmitted by the force-bearing structures at the knee during normal level walking. Inclusion of the ligaments in a knee model enables the simultaneous consideration of equations of force and moment equipollence, which is required for accurately estimating the contact and ligament forces, and is more critical than the adopted optimization criteria.

Effect of centers of rotation on spinal loads and muscle forces in total disk replacement of lumbar spine

The placement of artificial disks can alter the center of rotation and kinematic pattern; therefore, forces in the spine during the motion will be affected as a result. The relationship between the location of joint center of artificial disks and forces in the spinal components is not investigated. A musculoskeletal model of the spine was developed, and three location cases of center of rotation were investigated varying 5 mm anteriorly and posteriorly from the default center. Resultant joint forces, ligament forces, facet forces, and muscle forces for each case were predicted during sagittal motion. No considerable difference was observed for joint force (maximum 14%). Anterior shift of center of rotation induced the most ligament forces (200 N) and facet forces (130 N) among the three cases. Posterior and anterior shifts of centers of rotation from the default location caused considerable changes in muscle forces, respectively: 108% and 70% of increase in multifidi muscle and 157% and 187% of increase in short segmental muscle. This study showed that the centers of rotation due to the design and the surgical placement of artificial disk can affect the kinetic results in the spine.

Effect of ligament stiffness on spinal loads and muscle forces in flexed positions

Ligaments assist muscles in stabilizing the spine within physiological ranges of motion by limiting the displacements, but the role of ligaments in spinal loads and muscle force distribution remains unknown. The purpose of this study was to investigate the effect of different stiffness on joint resultant forces and muscle forces in different flexed positions. For this study, five ligament stiffness sets were determined from the literature and applied to a musculoskeletal spine model. The dimensions of the model were adjusted according to subjects in the in vivo experiments used for validation, and spinal loads and muscle forces were determined during flexed positions. The differences between the spinal loads due to different ligament stiffnesses were insignificant (maximum difference 12%). However, the different ligament stiffnesses showed a strong effect on individual muscle forces. Among the short muscles, lumbar multifidi exerted only 65 N without ligaments but the force increased up to 254 N due to adding the maximum ligament stiffness. However, the load in the erector spinae was significantly decreased (30%). The results of this study showed that in addition to long and superficial muscles, ligaments also played an important role in stabilizing the spine in flexed positions.