I hurt my back in a lifting accident at work. As part of my home program, the therapist insists that I sleep with a pillow between my legs. The knees and ankles both have to be supported by this pillow. What difference does this make, really?
Even small changes in position can put pressure on the soft tissue structures of the low back. Lying on the side without a pillow to support the hips, knees, and ankles can affect the spine directly. For some patients, sidelying without support puts one or more segments of the spine in a bent or even a twisted position. When sleeping or resting for several hours in this position, the joint can be stressed.
At the same time, muscles and ligaments can be overstretched or tightened in an unsupported position. The goal is to rest or sleep with the spine in a neutral position. This avoids undue pressure or long periods in a mechanically stressful position.