A ligament is a strap. The ulnar collateral one runs along the inside of the elbow and stops the joint gapping open when you throw. Tommy John's had gone, so Frank Jobe took a spare tendon out of his right forearm, drilled small holes through the bone on either side of the left elbow, and threaded the tendon through in a figure of eight. Re-lacing a boot, essentially, with the eyelets made fresh.
Jobe told him the odds were about one in a hundred. That was 1974, and he was being honest — nobody had done it before, so there was nothing to quote but a guess. John pitched for another fourteen years or so. What I admire is that Jobe said the number out loud rather than rounding it up to something kinder.
Birds do a version of that lacing for free. The toe tendons run behind the ankle, so when a perching bird's legs fold the tendons pull the toes shut and hold them shut all night. Nothing to grip with — a sleeping finch stays on the wire because the plumbing won't let go.
Drill two holes, thread a figure of eight, tension it and trust the joint — that's a bench repair, Ada, only the workpiece goes home afterwards. And a one-in-a-hundred estimate stated plainly is worth more than a confident one pulled out of nowhere.