An Experimental Type of Knee Surgery
Autologous Chondrocyte Implantation
Seven years ago, at a Midwest barbecue joint, two young doctors schemed over ribs and ended up planning new knees on a napkin. One of the doctors – James Cook, DVM, PhD, a veterinarian at the University of Missouri–Columbia, had grown cartilage in the lab. At the same time, an engineer from Columbia University in New York City named Clark Hong, PhD, was doing similar work, shaping and training to be ready to be implanted into a body.
Hong had read Cook’s study in the vet literature but was having trouble getting a grant to proceed because reviewers said it wouldn’t work in a living animal. Hong called Cook, and they began a collaboration that could, within the next 10 to 15 years, help ease the pain of worn-out knees in people.
Right now, Hong and Cook have created custom knee replacements for dogs. Cook takes an MRI or CT scan to create a picture of the patient’s joint. Hong creates a computer-generated model for the knee replacement and then cartilage cells are taken from the dog in much the same way as the first step in autologous chondrocyte implantation. The cells are cryopreserved (frozen) and sent with the scans and computer-generated model to researchers at the University of Missouri–Columbia, who use a milling machine to create a mold from the scans and model. Researchers eliminate any defects in the knee’s cartilage when they create the mold, essentially making a perfect replacement.
Once the mold is ready – the entire process from scans to creating the mold takes about three weeks – it takes another three weeks to create new tissue. The frozen cartilage cells are grown into a sheet of tissue and then trained to handle weight-bearing loads. The training process is equivalent to exercise, with the pressure similar to the load of walking, providing “preoperative rehab” – basically, the new cartilage tissue is put through a mechanical rehab process before being implanted back into the knee. Compared to autologous chondrocyte implantation, which requires several months on crutches before the joint can bear weight, a custom knee replacement will allows a patient to bear weight right away.
“The best a metal or plastic knee will ever be is when it is first placed inside the patient’s leg,” says Cook. “After that, it starts to deteriorate. It’s possible that the knee we are trying to create will be better in 10 years than it was when we first implanted it. Living tissue adapts to changes in its environment. It can grow and become tougher where it needs to,” says Cook.
Although the experimental procedure currently can be used on dogs, Cook says the only difference between doing the surgery in dogs and humans is size. “Honestly, making bigger replacements for humans is easier,” he says. Phase I human trials would be 6 to 8 years away, provided studies in dogs with arthritis are successful, and then it will take more time to go through Phase II and Phase III before the FDA would consider approving the procedure. But it’s an option worth watching and waiting for.
