A tailbone wound sits directly under the weight of anyone lying on their back, over bone with very little padding, and that is the heart of the problem.
Pressure sores form where skin covers bony areas with less tissue under the skin to pad the area, including the buttocks and the back. Too much pressure on the skin for too long reduces blood flow to the area. Without enough blood to nourish the skin, the skin can die and a sore may form.
The sacrum — the medical name for the area at the base of the spine — matters in one specific situation. Debridement (removing dead tissue) may not be appropriate for dry and intact eschars with no clinical evidence of underlying infection. One example is an unstageable pressure ulcer with an intact eschar at the sacrum, buttock, or heel, because the intact eschar serves as a natural covering over the skin defect underneath.
That is worth knowing if a hard, dark covering on a tailbone wound is being left alone. It can be a decision rather than an oversight. A sore covered in dead skin also cannot be staged at all, because the dead skin makes it hard to tell how deep the sore is.
What can change is the loading. Change positions often — about every 2 hours in bed, every 15 minutes in a wheelchair. Use pillows, foam cushions, booties or mattress pads chosen with a provider. Do not use donut-shaped or ring-shaped cushions, which reduce blood flow to the area and may cause sores. Avoid slipping or sliding when moving, and avoid positions that put pressure on the sore.
Moisture is a factor at this site in particular. Not being able to control your bladder or bowels makes a pressure sore more likely. Use a moisture barrier to protect the area from bodily fluids if needed, and ask your provider which type.
And the stage decides who treats it. Stage I or II sores will often heal if cared for carefully; most stage III and IV sores will be treated by your provider. A wound that has not started to heal in 2 weeks, or not completely healed in 6, is called non-healing, and pressure sores are first among the types treated at a wound care center.