The overall goal of this motion capture methodology is to provide an objective method to evaluate the movement performance quality and sensorimotor function of the upper extremity in individuals with stroke and in healthy controls. This method can help answer key questions in the field of neural rehabilitation, such as how does a stroke influence upper extremity movements and recovery and how this information can be used for selecting effective treatments. The main advantage of this technique is that specific movement deficits and recovery that might be undetected when using traditional clinical scales can be quantified in detail.
Assisting us for the demonstration of the procedure today will be Ulla-Britt Bergstrom, who is a occupation therapist working at Neural Rehabilitation Clinic at Sahlgrenska University Hospital. To set the motion capture system, mount four cameras on the wall approximately one to three meters away from the measurement area at the height of 1.5 to 2.5 meters facing the measurement area. Mount one camera on the ceiling just above the measurement area.
Placing one of the cameras on the ceiling with viewing angle over the entire measurement area was crucial for the data collection. This resulted in almost 100%successful data collection. Start the camera system.
Next, place the L-shaped calibration frame on the table with the short axis in line with the edge of the table and the long axis pointing forward. Then, open the 3-D tracking in data acquisition software. Start calibration by selecting capture, then calibrate.
Enter the calibration time of 30 seconds and click, okay. Move the wand in all directions throughout the entire measurement area above the chair and table to ensure that all five cameras capture the wand in as many orientations as possible. Accept calibration residuals below 0.5 millimeters.
Now, direct the subject, wearing a sleeveless top, to sit on a height-adjustable chair with her back against the chair's back. The upper arm should be in neutral adducted position. Rest the arm on the table and align the wrist with the edge of the table.
The knee, hip, and elbow angles should be approximately 90 degrees. Next, place the retro-reflective passive markers with double adhesive tape on the skeletal landmarks of the tested hand, wrist, elbow, right and left shoulder, thorax, and forehead. After that, place two markers on the cup.
In this procedure, place a hard plastic cup with 100 milliliters of water 30 centimeters from the table edge in the midline of the subject. Ask the subject to perform the drinking task in a comfortable, self-paced speed by one, reaching and grasping the cup. Two, lifting the cup from the table towards her mouth.
Three, taking as sip. Four, placing the cup back on the table behind a marked line. And five, returning to the initial position with the hand on the edge of the table.
It is important to encourage the patient to do the task as naturally as possible and therefore, only the three middle trials will be used for calculation of the kinematics to ensure that the patient is familiar with the testing. Make sure the subject understands the instructions and can reach the cup comfortably with the less affected arm without leaning forward. Prior to each recording, ensure the start position is correct and ask the subject to be ready.
Start the capture by selecting, start capture and give verbal instructions to tell her to start. When the subject finishes the task, stop the recording by selecting, stop. Record five trials with a short pause between each trial, starting with the less affected arm.
Check if the data acquisition reaches 95 to 100%for each identified marker. When incomplete data are detected, perform extra trials after identifying the problem and adjusting the sitting or marker positions to ensure full visibility of the markers in order to obtain at least three successful trials. This figure shows the representative velocity profile of a healthy control performing the drinking task.
A smooth bell-shaped velocity profile with one dominant peak can be seen for each movement phase, which is typical for normal movement. In contrary, this figure shows that a velocity profile of an individual with moderate stroke reveals a less smooth profile with increased number of velocity peaks. Also, the peak velocity in each movement phase is lower and the total movement time is longer.
This is the animation of the drinking task performed by a healthy control recorded in real time. The markers on the head, trunk, left arm, and two markers on the drinking cup, along with the movement trajectories are displayed. This is the same animation of an individual with stroke.
Notice the less smooth movement trajectories and increased forward movement of the trunk during the drinking task. This is an example of the same task performed by an individual with more severe motor impairment. This person also had spasticity.
The visible sub-movements indicate repetitive accelerations and decelerations signifying deficits in movement smoothness. Once mastered, this technique can be done in 10 to 15 minutes by any trained professional without specific technical qualifications. Technical expertise is however, needed to create and develop a program for the data analysis.
This procedure is particularly relevant for clinical studies due to a simple set-up with straight-forward data acquisition and analysis of an ecologically valid task. Using this method, we obtain valid, reliable, and responsive kinematics that quantify the key elements of the movement analysis in people with stroke. After it's development, this method paved the way for the researchers in the field of neural rehabilitation to explore upper extremity kinematics in general but also, specifically, during purposeful tasks such as drinking from a glass.
The key variables identified in the drinking task for people with stroke, such as movement time, smoothness, elbow angle, velocity, and compensatory trunk displacement are also recognized as central for stroke in other tasks. After watching this video, you should have a good understanding how to set up and carry out a simple and clinically feasible kinematic analysis of an upper extremity task using an optical motion capture system.
