InMotion Study Finds Knee Pain Solutions

By Scott Shepard| The Daily News| April 8, 2008

Boning up

When a person picks a popcorn hull from their teeth it typically leads to better feeling gums. Remove a 15-inch metal rod from the lower leg, however, and the pain does not go away.

Figuring out why that is became an engineering mystery last fall at the InMotion Musculoskeletal Institute. The answers were a major topic of discussion last month when orthopedic surgeons from all over the world gathered in San Francisco for the annual meeting of the American Academy of Orthopaedic Surgeons.

Ruxi Marinescu, manager of the InMotion biomechanics laboratory, did an experiment looking into the problem. She presented her findings last month at the San Francisco meeting.

Surgeons were equally impressed with how InMotion was able to move from asking the question to getting an answer in a matter of months - lightning speed for medical research. Plus, InMotion now has an information foundation that can be applied to new projects.

"This project was very innovative in that it looked at a previously unexplored possible cause for anterior knee pain after nailing of the tibia," said physician Hassan R. Mir, an orthopedic resident at the University of Tennessee Health Science Center and Campbell Clinic. "This is a difficult clinical problem in that anterior knee pain is a common occurrence after nailing of tibia fractures."

Relief needed

A nail is a titanium rod placed inside a broken bone to provide strength and stability. In the case of the tibia, in the lower leg, a surgeon will drill a hole through the top of the bone at the knee to place the nail. But half of all those patients will experience intense, ongoing knee pain, Mir said. In the most drastic cases the nail is removed, but that only provides relief to half the patients.

So after surviving major trauma from something such as a motorcycle crash, followed by experiencing a painful surgery and recovery, there's a 25 percent chance that a person will live with chronic pain - every step - the rest of his or her life.

That's where the work started for Marinescu. She often attends the Tuesday morning trauma reports at The Regional Medical Center at Memphis and noticed surgeon Thomas Russell, a UTHSC professor and an orthopedic surgeon at The Med, spoke each week about knee pain in patients with a nail. He's co-inventor of the Russell-Taylor nail, which is manufactured by Smith & Nephew Inc. It is designed to be faster and more accurate than other nails.

"Dr. Russell came to InMotion to discuss tibia problems and he got very excited," Marinescu said.

Having fun

Marinescu set up an experiment using mechanical engineering software intended for designing machine parts. It makes sense, she said, because the knee is a machine with multiple interactive parts, and each component is subject to its own stresses.

"This is ideal, applying what we already know about mechanical engineering to the bone," she said. "It was fun calling Customer Support and trying to explain to them what we were doing with their software."

Marinescu developed virtual models of a normal tibia, one with a nail and a third with the nail removed. She took 177 CT scans of each version, in cross sections, so changes could be studied throughout the bone. Each CT slice had to go through its own series of calculations; each slice involving the nail was processed twice.

It's a very vigorous approach, Marinescu said. Scientists often have an idea of what they will see and that can inject invisible bias. She said her goal was to structure things so the results are proven by the mathematics.

"A tibia with a nail is very challenging; it has properties very different from normal bone," Marinescu said. "I had to be very careful about the interface between nail and bone."

What she found, she said, is a nail distorts bone very slightly, but enough to redistribute the pressure points inside the knee, leading to pain. What surprised everyone was that the distortion appears to be permanent in many cases, even after the nail is removed.

What's next?

As a thoughtful experiment, the project did not try to answer the next question, but only identify the source of the pain. It's up to the scientist-surgeons to deploy this knowledge, Marinescu said.

"Future clinical implications could be to make surgical technique adjustments in nail insertion, or to fill the bone void left after nail removal in hopes of alleviating knee pain," Mir said.

With a reliable, confirmed database it's now possible to study new ideas in virtual reality, and then take the best outcomes into the clinic, he said. Some possible solutions include changes in the configuration of screws that hold the nail in place, or perhaps changing the insertion depth of the nail.

The beauty of the database, Mir said, is that any modification will change the way the bones move, so those changes can be evaluated and compared to normal bones.

"Once I validated the virtual model, I can test whatever values you want; if you have a clinical problem, I can use my model," Marinescu said. "When you are working with human bones or animals, you want to minimize your use of those."

She already has been approached to submit an article on the study to a peer-review journal. In the universe of medical research, being published - and criticized by experts worldwide - is the standard for validation.

Another outcome from the study, Marinescu said, is the critical role played by researchers such as Russell, who have daily patient contact and bring that insight into the research lab. Seeing the results,

Mir and his peers already are watching for new clinical problems that can be addressed.