Orthopaedic surgeons find critical cells remain alive after traumatic injury

By Russell Rian / March 1-12, 2011

Orthopaedic surgeons at UT Southwestern studying what happens to joints after traumatic injuries have made some surprising discoveries about why such injuries can lead to arthritis and chronic discomfort, as well as possible future avenues to avoid years of pain.

Traumatic injuries — resulting from motor-vehicle crashes, high-impact sports injuries, or falls — often cause problems to two major joint structures; the cartilage, which provides a cushion between bones, and the bones themselves, noted Dr. Joseph Borrelli, chairman of orthopaedic surgery and lead author of the study in the Journal of Orthopaedic Research. The structures not only get worse independently over time after injuries, but also interact to compound the problem.

Dr. Joseph Borrelli

Fortunately, the researchers also discovered signs of a possible remedy. Their sports-medicine investigations demonstrated that critical cells remain alive, giving hope that these cells can be reactivated to repair damaged cartilage and potentially prevent the long-term development of post-traumatic arthritis.

“We know that the cartilage often deteriorates after injury. We thought that this was a result of the impact and of the cells being killed. But we found that the cells to a certain extent are still alive. They’re resting, sleeping, not metabolically active,” explained Dr. Borrelli, an orthopaedic trauma surgeon who has been researching the cause and effect of this specialized type of arthritis for more than a decade. “That gives us some hope that if we can somehow wake them up, stimulate them and turn them back on, that they would be able to produce the things that are necessary to salvage the cartilage.”

The discoveries, based on animal models outlined in a series of papers, may prove important for people who suffer arthritis due to a traumatic injury. Victims are typically younger, meaning arthritic pain can last decades during what are normally the most productive years of their lives. The risk of developing post-traumatic osteoarthritis ranges from 20 percent to 50 percent. Previous studies indicated that post-traumatic osteoarthritis may affect as many as 6 million people in America, or about 12 percent of all osteoarthritis sufferers, and cost up to $3 billion in direct medical expenses in addition to indirect expenses like lost wages.

Cartilage, the tissue that covers the end of bones, allows joint bones to glide over one another and helps absorb shocks. The researchers found that post-traumatic cartilage has disrupted cell activity and drastically loses proteoglycan, which is responsible for the structure’s critical shock-absorbing characteristics.

“The cells, because they’re sleeping, don’t produce any new components,” Dr. Borrelli said. “But we found that they’re alive — for at least a certain period of time after the injury — and that’s going to be our window of opportunity to salvage the cells.”

The good news is that there are some compounds that are commercially available which could re-activate these cells.

“Theoretically you could have a patient with an ankle or knee or hip fracture and not only put things back together surgically, but also begin to administer something into the joint, maybe even systemically, that could wake up these cells and thus help heal the cartilage,” Dr. Borrelli said.

In addition, researchers determined untreated cells die either from the initial impact or from mechanisms that tell the cells to kill themselves, a process called apoptosis. Again, compounds already exist that may stop that process but they need to be tested as to their effectiveness, Dr. Borrelli said.

“We have the chemicals to stimulate cell growth, and we have the chemicals to inhibit apoptosis,” he said. “If you can recognize the cells that are about to kill themselves, you could stop it. You could talk them off the ledge.”

Physicians also discovered that the bone beneath the cartilage stiffened as new bone grew after a joint injury. The underlying bone helps protect the cartilage, so if it stiffens and leads to even further deterioration. When bones deteriorate, they grind together, causing pain, stiffness, limited joint movement, swelling and tenderness.

“In this scenario, you lose part of your cartilage cushion as the cartilage deteriorates in response to the injury and you have develop a harder surface underneath so the cartilage gets doubly crunched,” Dr. Borrelli explained. “That might place greater importance in reviving the dormant cells. If they’re in a more hostile environment [as a result of a traumatic event], then it’s more important that we wake these cells up and get them back in the game.”

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Dr. Borrelli holds the Doctor Charles F. Gregory Chair in Orthopaedic Surgery.