Steven A. Olson, MD, an orthopaedic surgeon at Duke University, describes himself as a clinician with a passion for basic science. For the past 15 years, he has been studying intra-articular fractures, seeking to unlock the mysteries surrounding the processes that lead to posttraumatic arthritis (PTA).
For these efforts, he and his colleagues will be honored with the 2015 Kappa Delta Ann Doner Vaughan Award during the 2015 AAOS Annual Meeting in Las Vegas.
Inflammation plays an essential role in the development of PTA after joint injury. Applying this knowledge, Dr. Olson and colleagues have developed pharmacologic interventions that, in mice, lessened the severity of PTA after an intra-articular fracture. Now they seek to translate these findings into clinical applications for human patients.
“Since we started, we have found it useful to view the joint as an organ system,” Dr. Olson explained. “Surgeons want to put the joint back together as best as possible after a injury. We try to restore the joint with fixation. The challenge is that even when we do that perfectly, some arthritis can develop. Other times it’s just a very bad injury and we cannot make it perfect. It’s frustrating to expend time and effort, and the patient still ends up with arthritis.”
He and his colleagues sought to understand the entire process surrounding a joint injury. They noted that published research could not account for the variability of outcomes in clinical studies, specifically why arthritis developed in some accurately reduced joints, while not in some malreduced fractures.
“The quality of the reduction is important, but it doesn’t explain all the variability in the response,” Dr. Olson said. “In the literature, people were trying to do traditional things. We have tried to look at it a different way. Individual aspects of injury have been studied, but the trouble is everything happens all at once.”
His team took early cues from rheumatologists studying the issue. “They don’t really treat joint injuries. They would ask orthopaedic surgeons what is going on in the synovium, the lining tissue of the joint,” said Dr. Olson. “Surgeons were not necessarily paying attention to that. We studied it and noted a huge synovial response after a fracture. We began to realize the extent of the metabolic activity that occurs.”
One avenue of thinking about the mechanism of PTA is that fracture injury causes chondrocytes to die, leading to arthritis. “That had never been proven,” said Dr. Olson. “Our experiments found no difference in chondrocyte death after either a high-energy or a low-energy fracture.” This finding led them to begin exploring the inflammatory process.
An innovation central to their work was the development of a model of a closed intra-articular fracture in mice. This experimental model involves a closed fracture of the tibial plateau in one limb of the experimental animal, with the corresponding opposite limb serving as an internal control (Fig. 1).
From experiments using the fracture model, the researchers found that mice exhibited a “rapidly increasing synovitis within 7 days after fracture.” The extent of synovitis correlated with injury, while chondrocyte viability did not.
These experiments were done with C57BL/6 (wild-type, or “Black 6”) mice, but a fortuitous finding in another mouse strain (MRL/MpJ) helped guide the effort in a new, fruitful direction. Researchers working with the MRL mice in a different line of inquiry commonly punched holes in some of the animals’ ears to differentiate them. They noticed that these ear punches were healing with spontaneous regeneration of native fibrocartilage. Dr. Olson’s colleague, Farshid Guilak, PhD, took note of this finding, and the team embarked on comparing the injury response to fracture in these “super healer” MRL mice versus the Black 6 mice.
When the knees in the super-healer mice were broken, “lo and behold, arthritis didn’t develop,” Dr. Olson said. “That was a big step forward. From there, we did a lot of comparisons, looking at what was the same and what was different between these mice. We found that each mouse has an initial inflammatory postinjury response, but the MRL mouse, for reasons we don’t completely understand, could attenuate that response. The Black 6 mouse can’t, and PTA develops.”
This finding led to experiments that would be key in developing possible therapies. Cytokine analysis showed lower systemic (serum) levels of the proinflammatory cytokine interleukin-1alpha (IL-1α) and higher levels of the anti-inflammatory cytokines IL-4 and IL-10 in the MRL/MpJ mice. This study showed that the MRL/MpJ mouse is relatively protected from posttraumatic arthritis after intra-articular fracture and thus is a useful strain for comparison with the Black 6 in greater detail.
Noting that there are two forms of IL-1, Dr. Olson explained that the team conducted immunohistochemistry staining to localize IL-1α, IL-1β, and their receptors. “It turned out that the subchondral bone right under the joint and the synovium both contained a lot of IL-1β. We observed that the synovial fluid levels of IL-1β indicated what was a direct response of the injury, with higher levels in the injured joints. It looked like it was coming directly from the joint injury, whereas the level of IL-1α was the same in the injured joint and the noninjured joint. IL-1α increased with the injury, but in a way that suggested the increase was systemic, not just in the joint. That was a new finding.”
From this finding they tried local administration of an IL-1 receptor antagonist. “IL-1 works by the molecule binding to a receptor,” Dr. Olson explained. “In nature, there is an active receptor and a decoy receptor. The antagonist binds to the receptor and blocks the activity.”
They tried injecting the antagonist agent—a drug already approved for treating rheumatoid arthritis—into the injury site immediately following fracture in the arthritis-prone, wild-type mice. The result was reduced inflammatory changes and no development of arthritis.
They also administered the compound systemically into wild mice. This application was not beneficial and resulted in degenerative changes even more severe than no treatment alone. “It appears that the systemic blockade of inflammation affects the fracture healing, so when the fractures don’t heal, the joints do very poorly,” Dr. Olson observed.
Recently, the group used an engineered elastin-like peptide as a drug depot for more prolonged delivery in the joint. The substance is a reverse-phase compound, liquid at room temperature but a gel when heated to body temperature. This application was also successful in preventing the development of arthritis.
The researchers have also investigated a possible role for stem cells, working with cells both from the Black 6 and the MRL. “Stem cells are noted in the literature to have some anti-inflammatory properties,” Dr. Olson said. They injected stem cells into both types of mice. “It turned out that both types prevented PTA—the MRL stem cells didn’t have more regenerative capacity in this situation.”
The human phase
Dr. Olson’s group has applied to conduct a human trial using the IL-1 receptor antagonist drug, which has already shown some promise in trials with anterior cruciate ligament injuries. Although “in the larger scale of the human joint, it is unlikely that biology will ever overcome abnormal biomechanics of a severely displaced articular surface,” the authors believe that biologic therapies based on an understanding of the injury response have great potential in controlling the inflammatory process to reduce or prevent PTA.
Dr. Olson hopes his work will help foster care that involves the orthopaedic surgeon beyond management of the immediate injury. “There is reason to believe that a therapeutic intervention after injury can prevent PTA in conjunction with surgical treatment,” he said. “Clinically, most injuries that lead to arthritis are treated by orthopaedic surgeons, so we as a group need to own this. We need to be the people who study PTA, to learn more about PTA along the entire spectrum of care—from injury to repair, and in some cases to arthroplasty.”
Coauthors with Dr. Olson are Farshid Guilak, PhD, a biomedical engineer; Virginia Kraus, MD, PhD, a researcher and rheumatologist; Bridgette Furman, BS; and Janet Huebner, MS. One or more of the authors reported potential conflicts of interest; visit www.aaos.org/disclosure for more information.
Terry Stanton is a senior science writer for AAOS Now. He can be reached at firstname.lastname@example.org