Weakness from injury of the medial collateral ligament (MCL) is a common cause of inner elbow problems for the throwing or pitching athlete. Sometimes rest and rehab can take care of the problem. But when pain and loss of motion and function interfere, then surgery is often the treatment of choice.
The torn or damaged MCL is replaced using donor tissue from another tendon. The palmaris longus is used most often. This tendon comes from a long, slender muscle in the wrist and forearm. Not everybody has one but if you do, you will see it by touching the pads of the thumb and little fingers and bending the wrist. If the palmaris tendon is present, a cord of tendon-like tissue will stand out along the front of the wrist.
Although other tendon grafts have been tried, they don't seem to be any better than the palmaris longus. The difference may be in the surgical technique used. Type of sutures and suture technique can result in a stiffer, stronger graft. The closer the graft approximates the normal tissue, the faster rehab and recovery can proceed.
Complications after surgery can also make a difference. If there's been any problem with infection or failure of the incision to heal, recovery can be delayed. Two holes are drilled in the bone to thread the graft through and hold it in place. Sometimes the elbow bone fractures between these two drill holes.
And there may be differences in the load or force placed on the graft during the healing phase. Too much load, too soon can cause the tissue to stretch out and fail. All other factors being the same, there are sometimes just differences between people that we can't account for. There may be no way to know why one procedure works for one athlete but not another.