Even though you place a knee pillow between your knees, it’s not usually knee or leg pain that stands to benefit from the extra support; Dr. Abraham says knee pillows work the best for back pain. This is because a pillow placed between the knees promotes proper spinal alignment, keeping your knees, hips, and back in a straight line. Maintaining an improperly aligned spine for prolonged periods of time—by slouching in a recliner, hunching over in your desk chair, or lying down without the right support—can increase back pain, per the Mayo Clinic, so your posture, even while sleeping, is important. However, knee pillows can also reduce sciatic nerve pain as well as knee, leg, and hip pain.