The Parastep I™ System is a non-invasive microcomputer-controlled functional electrical stimulation system that enables unbraced standing and short-distance walking by upper-motor-neuron-injured paraplegics and some incomplete quadriplegics. It has the capability of directing up to 6 channels of electrical stimulation, and with the aid of a specially adapted control and stability walker, it enables the user to stand from a sitting position, walk short distances, and resume a sitting position.
Functional Neuromuscular Stimulation (FNS)
FNS is a rehabilitation technology that uses low-voltage electrical impulses to evoke a peripheral nerve action potential, which in turn causes a skeletal muscle response. FNS has the potential to provide the spinal cord injured with the ability to stand and ambulate.
The excitability of nerve and muscle tissue provides the basis for the therapeutic use of FNS in spinal cord injury. When the neural pathway between the brain and individual muscles is disrupted or damaged, partial or total loss of voluntary muscle control results. However, a muscle, even when atrophied, may be reactivated and controlled through FNS by means of electrical stimulation applied to peripheral nerves below the level of injury.
How the Parastep I™ System Works
The Parastep I™ System works by delivering microcomputer-controlled electrical pulses through surface (skin-) applied electrodes to nerves and muscles, causing muscle contractions. The computer is programmed to control the sequence of muscle contractions in the lower extremities that enable the functions of sit-to-stand, right and left step, and stand-to-sit. Users are taught to initiate functions by activating commands through switch modules mounted on the walker.
The system is designed to provide up to 6 channels of stimulation (i.e., stimulate up to 3 muscle groups on each leg/side).
Stimulation of the quadriceps muscles results in knee extension, enabling the user to stand. Stimulation of the peroneal nerve in the lower extremity initiates a triple-flexion reflex response, resulting in contraction of muscles to flex the hip, knee, and ankle, which lifts the foot off the floor. Subsequent quadriceps stimulation extends the knee in preparation for heel-strike and weight bearing.
When 6 channels of stimulation are used, electrical stimulation is directed to the previously mentioned sites and to two additional electrodes on each hip. Stimulation of gluteal muscles extends the hips, contributing to stability while standing and taking steps.
The user initiates and controls the intensity of stimulation to the muscles and nerves through the keypad on the stimulator/control unit or through two switch modules mounted on the walker handle bars. The walker provides balance and stability during standing and walking.
For your guidance, the Parastep I™ System has received U.S. Food and Drug Administration (FDA) approval (#P900038) for commercial marketing following a Premarket Approval (PMA) submission and multi-center clinical trials, and has been classified as a Class III medical device. It is the only such device approved specifically for enabling appropriately selected and trained spinal cord injured individuals to stand and ambulate through the use of FNS.
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