How do You Sleep with a Knee Pillow?
Keeping a pillow between the knees adds extra comfort while sleeping. In fact, for side sleepers, people with chronic back pain and for pregnant women, knee pillow is perfect for spinal alignment. Knee pillow can also offer cushion support which helps to prevent knee-joints and back pain (which further lead to pains and aches). Some sleepers get sufficient comfort by placing any knee pillow between the knees. Nevertheless, a knee pillow differs according to the sleep position, body shape, and sleep type. The pillow that matches the natural contours of the body structure and sleeping position tend to provide utmost satisfaction and comfort while sleeping by aligning the spine in the proper way. Most knee pillows are hourglass shaped and tend to be inserted between both wedges or it is particularly knee shaped. It is primarily used by side and back sleepers. Knee pillow with high-density of memory foam pillow is mainly recommended for pain-relief solution and ultimate comfort. Alignment of Knee Pillow Apart from the sleeping position, alignment of knee pillow is very important to the shoulder, spine, and hips proper alignment. This minimizes the pressure on the spine and creates a comfortable surface to sleep on. 
If you are a back sleeper, a small pillow beneath the back of the knees reduces pressure on the spine and supports the natural curvature in the lower back. The knee pillow supports the entire structure to match the alignment with your shoulder and neck.
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Sleeping on your stomach position creates a strain on the back due to the improper spine alignment or out of position alignment. Placing a flat knee pillow beneath the pelvis area and stomach can help to uphold the spine in straight alignment. For stomach position, a pillow with flat or low sleep is more suitable to sleep.