“Most methods of reconstruction to date involve using dead bone, which heals incompletely and has a high complication rate,” Dr. Larsen said. Successfully using bone transplants that are alive – with the same shape and healing properties of the bone a patient is missing – would be a biotechnological breakthrough.
Born to Norwegian and Dutch parents, Dr. Larsen is spending a year at the Mayo Clinic’s Microvascular Research Laboratory of the Department of Orthopedics in Rochester, Minnesota. There, he is hard at work with research that aims to find a way around current obstacles. “When we use living bone from the same patient, the healing is better but there is often a huge size and strength mismatch, for example when you use the fibula to reconstruct the femur. The problem with using a living bone transplant, as opposed to a dead bone transplant, is that you need strong immunosuppression drugs to prevent the tissue from being rejected,” he said – and taking such drugs on a permanent basis represent risks that may outweigh the benefit for conditions that are not life-threatening. “When you receive a new heart or lung you are willing to take the immunosuppression, but to save your arm or leg, the risk-benefit ratio might be totally different. So what we are looking for is a way to do the living bone transplantation in such a way that your body will accept the new bone even after the immunosuppression is stopped after a time.”
The methodology to achieve this goal, is enhancing bone with a large blood vessel from the recipient, that grows into the bone and replaces the blood supply from small vessels that have been attached. By the time the immunosuppression is stopped, the blood supply to the bone is “switched” and only the original vessels are rejected by the body. The new blood vessels should survive, since they belong to the patient. “The method has worked very well in the laboratory and we have seen new bone being made a long time after immunosuppression has been stopped,” Dr. Larsen said. He is performing the study using microvascular bone transplantation on small animal models and then investigates the mechanisms of bone healing and growth after bone is transplanted with the blood vessels attached to feed it. A microscope is used to attach these blood vessels. “The vessels are usually about 0.6 millimeter in diameter and the needle and thread that we use could tie a knot through a human hair,” Dr. Larsen said.
“For the patient our research offers methods that in the future may greatly improve the results from large reconstructive surgeries. For me this is a great way to learn how to conduct a large research project and work as a team with analysts in diverse fields of medicine, from surgery to molecular biology to polymer science,” he said.