Ankle dorsiflexion insufficiency, also known as foot drop, is a condition in which the muscles that lift the foot are weak or paralyzed, causing the foot to drag or drop when walking. This can result in difficulty lifting the front part of the foot and can cause the person to trip or stumble. Drop foot can be caused by a variety of conditions, including nerve injuries, spinal cord injuries, and certain diseases such as multiple sclerosis and ALS.