Ankle to Knee Pose - Double Pigeon Pose - Agnistambhasana
Seated Poses - Yin Yoga - Restorative Poses
Ankle to knee pose offers a similar stretch to both hips at the same time in a relaxed seated pose. If the lumbar spine can not be extended upwards in this or other similar seated poses it is best to work on the similar stretches of those asana in laying down or standing variations. This pose can become a deep stretch without much effort as long as the knees weight can come down towards the opposite ankle. If the knees and ankles are stacked a deep forward bend can also be taken and this could become an excellent Yin Yoga pose to hold for up to 5-10 minutes.
For "modern" bodies(who mostly sit in chairs) the pose is typically not accessible in a way that is useful. Other poses could be practiced such as One Leg Pigeon Pose, Reclined Pigeon, Warrior II, and Baddhakonasana.