 One of these ligaments is the impar ligament, which attaches the navicular bone to the coffin bone (distal phalanx).Cartilage lies between the navicular bone and the coffin joint, as well as between the navicular bone and the DDF tendon.The navicular bursa - a small sac that protects the DDF and navicular bone from abrasion as the tendon slides over the area - lies between the navicular bone and the DDF tendon.