Subject-specific Musculoskeletal Model for Studying Bone Strain During Dynamic Motion

During landing, lower-body bones experience large mechanical loads and are deformed. It is essential to measure bone deformation to better understand the mechanisms of bone stress injuries associated with impacts. A novel approach integrating subject-specific musculoskeletal modeling and finite element analysis is used to measure tibial strain during dynamic movements.

The overall goal of this procedure is to create a Subject-specific Musculoskeletal Model for Bone Strain analysis. This method can help answer key questions in the biomedical engineering field such as quantifying human bone deformation during dynamic motion. The main advantage of this technique is that a non-invasive approach is implemented to study bone strength during dynamic physical activities.

Demonstrating the procedure will be Marisa Loo and Kerstyn Hall, graduate students from my laboratory. To begin this procedure perform CT scanning and anthropometric measurement on the subject. After this, place 14mm reflective markers on the participants'body as outlined in the text protocol.

Place semi rigid plastic plates with four marker clusters on the participants'thighs and shanks. After entering the subjects'information into the motion capture program, ask them to stand motionless in the center of the calibrated room with their feet shoulder width apart. Then ask them to extend their upper extremities laterally so that all of the reflective markers are well exposed to the cameras.

In the main program window, open the tools pane, click the subject preparation tab. In the subject capture section, click start to record a three second motion trial to be the static calibration trial. To begin determining the functional hip joint center, ask the participant to stand on one leg while fully extending the other leg slightly forward.

Instruct the participant to move the extended leg around the hip joint anteriorly and return to neutral. Anterior laterally and return to neutral. And then laterally and return to neutral.

After this have the participant move the same leg around the hip joint posterior laterally and return to neutral. Posteriorly and return to neutral. And then in a circumduction motion.

In the main program window, open the tools pane, click the capture tab, then in the capture section click start to record a motion trial for each functional hip motion. To begin determining the functional knee joint center, ask the participant to stand on one leg while maintaining a 30 degree hip hyperextension of the other leg. Next, instruct the participant to perform a 45 degree knee flexion with the non weight bearing leg.

Have them repeat this five times. In the capture section of the tools pane, click start to record a motion trial for each functional knee motion. Place the height adjusted wood box on an area of the floor covered by a rubber mat, making sure that it is approximately 11cm from the edges of the force plates.

Next, ask the participant to stand on top of the box. Instruct the participant to extend their dominant foot directly in front of the box, then have them shift their weight forward and step off the box. Both of the participants legs should land on the ground at the same time with each foot striking a separate force plate, ask the participant to remain standing until the motion capture of the trial is complete.

Repeat the motion capture three times to collect three motion trials for each height. First, open a motion capture software program. In the main window, go to the communications pane, click the data management tab and select one of the recorded motion trials.

Open the trial data in the program. In the tools pane, click the pipeline tab. From the current pipeline list, select the reconstruct pipeline, click the run button to start reconstruction process to obtain three dimension trajectories of the reflective markers.

Navigate to the tools pane and click the label edit tab, in the manual labeling section select individual marker names and label the corresponding 3D trajectories. When labeling is complete, click the save button on the tool bar. To begin creating a lower body skeletal model, open the multi-body dynamic simulation software program with the human body modeling plug in installed.

At the splash screen, double click the new model icon to open the model building control panel, in the anthropometric database library section of the main modeling panel, choose the generic body from the drop down list, specify the body mass, body height, gender and age. In the body configuration section of the main modeling panel click the lower body radio button, in the units drop down list select mm, kg, Newton;click the apply button in the create body measurement table section to accept the body measurements. Continue to click the apply button in the create human segment section to create a lower body skeletal base model.

To begin modeling the lower body joints, open the main menu drop down list in the main modeling panel and select joints to open the joint configuration panel. In the joint rotation element section of the joint configuration panel, click the button next for prepare model with recording joints. In the spring dampers and joint limits properties section enter the parameters for nominal joint stiffness, nominal joint damping and joint stop stiffness as shown here.

Continue to select left leg and right leg by checking corresponding radio buttons, click the apply button to accept the joint configurations. After this, open the main menu drop down list in the main modeling panel and select workflow, in the sub menus drop down list select gait and calibrate, in the joint center data section enter the participants lower body joint center file. Then click the load button to import the data and modify the locations of the joint centers, in the load static trial section enter the static calibration motion capture trial.

Click the load button to import the file and parametrize the lower body skeletal model. To begin modeling the skeletal muscles, open the main menu drop down in the main modeling panel and select soft tissues, after this open the sub menu drop down and select create base tissue set. In the muscle contract tile element section, click prepare model with recording muscle elements.

Next, in the global recording element muscle properties section, click the radio button corresponding to updated 45 muscle set then accept the default settings for muscle properties as shown here. Check the radio buttons for left leg and right leg for muscle assignments, then click the apply button to accept the configurations. In this study, a non-invasive method is used to determine tibia deformation during high impact activities.

The accuracy of the forward dynamic simulation is verified by comparing the lower body joint angles from the simulation to the corresponding joint angles as measured for motion capture data. These comparisons are completed for the ankle angle, knee angle and hip angle at all three drop heights where the vertical lines represent moments of impact. As can be seen, the simulation and experimental data largely agree, demonstrating that the simulation itself has a high degree of accuracy.

Statistical analysis software is then used to calculate the cross-correlation coefficients between the experimental and simulation joint angles at zero lag. The peak strains at the antero medial region of the mid tibial shaft are recorded while the subject lands from three different heights. The 52cm landing condition demonstrates the largest peak maximum principal, peak minimum principal and peak maximum shear strains.

The peak maximum principal strains are also seen to increase as the drop height increases. After it's development, this technique paved the way for researchers in the field of biomedical engineering, to explore mechanisms of bone stress injuries in athletes and military trainees.