Biomechanical engineer makes strides toward delaying, preventing knee injury

Courtesty of Thomas Andriacchi Knee

People position their lower extremities in variable ways when they land during running or jumping. Some may increase risk of injury.

Aging brings gray hair and wrinkles, and for many, a gradual wearing away of cartilage at the knee joint. The precise cause of cartilage breakdown, or osteoarthritis, isn't well understood, and current treatment focuses on relieving symptoms such as pain rather than on addressing the underlying disease. But that may soon change. New studies from the Stanford BioMotion Laboratory in the Department of Mechanical Engineering not only may lead to a design for walking shoes that could slow the rate of osteoarthritis progression but also may help athletes prevent knee injuries that cause chronic osteoarthritis later in life.

"Osteoarthritis progresses faster with age in some people than in others," said Thomas Andriacchi, professor in the departments of Mechanical Engineering and Orthopedic Surgery. Working with mechanical engineering graduate student David Fisher and Palo Alto Veterans Affairs Hospital orthopedic surgeon Nick Giori, he aims to address that. "We've determined that this progression is a function of the way people walk, especially how loads get transferred across the knee joint." Surgery can result in more even weight distribution over the part of the knee joint that is degenerating, but the researchers found that people who did best years after surgery walked in a way that naturally relieved stress on the knee joint, even before surgery.

"The next logical step for us was to determine whether we could intervene early and slow the progression of the disease by changing how people walk," he explained. In previous studies, his team found that training people to walk differently didn't work well. As an alternative, they've developed an experimental shoe, funded in part by Nike, that changes the load on the knee.

Andriacchi, Fisher and Giori will use this modified shoe in an upcoming study recently funded by a grant from the Department of Veterans Affairs. Volunteers will be local military veterans and people from the community who have early symptoms of osteoarthritis. "We'll give them either the modified shoe or a 'control' shoe [one that looks the same but isn't modified to change the load on the knee], and have them use the shoe for a year," Andriacchi said. "Then we'll follow the disease process in these subjects to see whether we've reduced the rate of osteoarthritis progression."

Although osteoarthritis is a common consequence of aging, it isn't confined to the senior set. Athletes who tear their anterior cruciate ligament (ACL) at age 20 are much more likely to have osteoarthritis at age 40 than at 60, even after reconstructive surgery. "This has given us insight into how loss of the ACL, which provides anterior and rotational stability to the knee, changes the mechanics of the knee joint and how that contributes to osteoarthritis as a chronic condition later in life," Andriacchi said. "With ACL injury, there's a mechanical change in the way the cartilage sustains load. Breakdown occurs more quickly because the loading is moved to a location on the cartilage that isn't conditioned to sustain high stress."

In addition to studying walking mechanics in people with early osteoarthritis, Andriacchi, along with Ajit Chaudhari and Chris Dyrby, both in the Mechanical Engineering Department, hopes to help athletes prevent ACL knee injuries and the associated early onset of osteoarthritis. Women, it turns out, are at much greater risk of ACL injury than are men in the same sport. This disparity seems to be related to the significant differences in body mass distribution between the sexes and, consequently, in how men and women land from a jump, especially in sports like volleyball or basketball.

"We've found from human experiments, in conjunction with computer simulations in the lab, that when athletes land on one leg, males tend to land with their body mass aligned over the center of the knee, whereas females land with their hip more to the outside of center," explained Andriacchi. "This is true even of elite athletes." He is seeking funding to study a cohort of male and female athletes to determine whether those that sustain a knee injury over the course of their playing season fall into a group whose injuries could have been predicted at the beginning of the season based on data showing how they land. This type of study could lead to methods for training athletes to land safely.

"The future of osteoarthritis research is prevention, and intervention to slow the rate of progression," he said. "That's where we're headed."

The BioMotion Group is currently recruiting volunteers for three studies:

  • ACL Injury: Prospective participants are adults (age 20 to 60 years) with a confirmed ACL injury or a previously reconstructed ACL. Participants will be tested in the BioMotion Lab during a series of ambulatory activities and will be given an MRI of the knee. (Contact Chris Dyrby, 650-723-5793.)
  • Knee Osteoarthritis and Shoe Design: Prospective participants are adults with a diagnosis of early-stage osteoarthritis at the knee. Participants will be followed over a period of one year while wearing an experimental shoe design. Testing will include walking and MRI of the knee. (Contact Barb Elspas, 650-493-5000, ext. 64807.)
  • Healthy Knees and Cartilage Function: Prospective participants are adults (age 20 to 69 years) not being treated for any type of knee pathology and with no history of traumatic injury to the knee. Testing will include walking and MRI of the knee. (Contact Chris Dyrby, 650-723-5793.)
  • E-mail requests for further information to

    Toniann Derion is a freelance science writer.