The tendons in the inside were all cut and subsequently repaired, The tendons on the fingernail side survived. The rubber band pulled and held my thumb in towards the palm of my hand. I was supposed to pull my thumb straight using the undamaged tendons, then let the rubber band pull it back in to my palm. The whole thing was designed to allow the inside tendons to heal while still moving freely against the tendon sheath. I guess these normally heal into one big scar which leaves the thumb unstable.

The whole experience was fascinating. It was a pia, but still fascinating. I'm lucky to have found a doc and a therapist who really knew what they were doing.