Amnion derived stem cell therapy is very popular currently.
Amnion is the inner layer of the placenta which is harvested at the time of C-section. Amnion is derived from the mother, not the newborn child, so it has no ethical considerations.
The amniotic membrane contains numerous growth factors and stem cells which can aid in healing of multiple tissues including cartilage, tendon and ligament, nerve and skin.
It is used in wound healing as well as repairing tendons because it has shown to enhance healing and reduce scarring during the healing process.
There are multiple products available due to the combination of amniotic membrane, chorionic membrane (another layer of the placenta) and umbilical cord.
Processing of these products is also important. Cryopreservation (processing by freezing) seems to preserve more of the stem cells than freeze-dried or dehydration. The products can be applied in sheets or injected in a liquid form to the injured site. You typically only need one injection.