Binds are common in ashtanga yoga. They require greater flexibility--or what may seem like very long arms.
This pose uses a warrior 2, or side angle, stance. But one arm reaches behind the back while the other extends around the front knee. The goal is to clasp the hands behind you. If this seems impossible, you can use a strap until you feel more comfortable with the balance and twist, and increase your flexibility. The longer you hold the pose, the more you will not only lengthen some muscles but strengthen others.
In my book, "From the Boxing Ring to the Ashram," I mention the value of deep twists for piriformis syndrome. This is a particularly good pose for those troubled with discomfort from that condition.
Just like with any other new diet or workout plan, consult a yoga therapist to determine what is best suited for your particular physical and emotional well-being.