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How does motion analysis work?

A typical gait analysis – conducted with 12 motion capture cameras, force plates, EMG, and pressure analysis systems – will have a child walk barefoot with or without prescribed orthotics or other assistive devices. The information gathered is processed and examined by physicians (orthopedic surgeons, physiatrists, neurosurgeon etc.), physical therapists and engineers and allows physicians to recommend treatment options. These recommendations could include physical therapy, bracing options, medications and surgical procedures.

Here are the steps of a gait analysis:

1. Clinical Evaluation
When a child arrives, their height, weight, and leg measurements are taken. A physician or a physical therapist is able to measure passive joint range of motion, muscle strength, and muscle tone and selectivity.

2. Video and Photographs
Digital video of a child walking is taken to have a visual representation of how a child walks. Photographs are also taken of a child’s lower extremities and their orthotics, if they have them.

3. 3-D Motion Capture
Small reflective markers are then placed on specific areas on the body. A child is then able to walk at a comfortable pace along a 30-foot walkway. The walkway contains four force platforms.

Kinematics: From the 3-D motion capture, we are able to measure the 3-D angles of a child’s joints, including the pelvis, hip, knee and ankle. The motion of the forefoot and hindfoot can also be measured with additional markers.

Figure 1: A child with marker stickers of the lower limbs walks on the four force platforms

Figure 2

Kinetics: The force collected while a child walks across the embedded force platforms allows us to determine joint moments and powers during walking. This can show physicians how much power is generated at a specific joint

Figure 2: A computer-generated skeletal model during walking and ground reaction force acting at the ankle joint.

Figure 3

4. Dynamic electromyography
Dynamic electromyography (EMG) sensors can be used to observe muscle activity. Two different types of sensors collect data for muscles of interests – surface EMG, for superficial muscles; and fine-wire EMG, for the deeper muscles. Dynamic EMG will be analyzed together with joint motions and moments to gain a better understanding of pathological gait.

Figure 3: A child with wireless EMG sensors walks at a self-selected speed.

Figure 4

5. Dynamic plantar pressure analysis
Dynamic plantar pressure analysis shows physicians how the pressure is distributed for children's feet. This can be done in two different ways:

  • EMED pressure platform: EMED is done while the child walks barefoot across a pressure platform that measures the pressure distribution of their foot while walking.

Figure 4: A screen shot from pressure analysis data: a dynamic plantar pressure distribution (Left); Plantar contact areas, ground reaction forces, and peak pressure as a function of stance phase were recorded (Middle); Pressure distribution in multiple steps (Right)

Figure 5

  • PEDAR insole pressure: Insole sensors are placed within a child’s shoes while they are walking to measure the pressure distribution. This is helpful when a child has different orthotics.

Figure 5: A screen shot of PEDAR pressure analysis (Left); A child walks with insole pressure sensors inside orthotics and shoes (Right)

Figure 6

6. Clinical treatment recommendations
After all the testing, physicians will conduct a comprehensive review of the physical examination, gait analysis, and other clinical measurements and then suggest appropriate treatment options.

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