After ACL reconstruction, finding small motions that cause big problems

Posted on 30. Aug, 2012 by in Academic Departments, Healthcare and Medicine, Issues, Mechanical Engineering, Research, Students, Summer: Annual Report

Jarred Kaiser

The researchers use MRI to take images of the ACL at different points in a continuous cycle in which a subject flexes and extends the knee against an external load to simulate walking. Photo: Mark Riechers.

People who tear their anterior cruciate ligament, a ligament in the knee that provides stability to the connection between the tibia and femur, usually must opt for a complete ACL reconstruction with a portion of another ligament.

However, about 90 percent of people who undergo reconstructive ACL surgery develop osteoarthritis—knee pain, swelling and stiffness—within 20 years. Many of these people first injured their ACLs as young athletes, which means that in their 40s or 50s, they’re facing debilitating knee pain that often only a total joint replacement can fix.

Mechanical Engineering Associate Professor Darryl Thelen and graduate student Jarred Kaiser (pictured) think the reason for this lies in tiny changes to knee motion following ACL reconstructive surgery. Over a person’s lifetime, knee cartilage fibers align to support precise distributions of different types of forces. So, even small changes after a surgery essentially could turn the knee against itself, damaging the cartilage by stressing it in places and ways it can’t handle.

The team is overcoming one major challenge—how to image the knee’s real-time motion in three dimensions without extremely specialized equipment or large amounts of radiation—by adapting MRI techniques currently used by cardiac researchers. Working with Medical Physics Assistant Professor Oliver Wieben, Thelen and Kaiser use the MRI to take images at different points in a continuous cycle in which a subject flexes and extends the knee against an external load (pictured) to simulate walking. By combining images from many cycles, they gain a clear, 3-D video of a single cycle.

So far, they’ve found that the knee can move dramatically differently after an ACL reconstruction, even when an orthopedist might not detect any irregularity. Along with Radiology Associate Professor Rick Kijowski and Orthopedics Assistant Professor Geoffrey Baer, they’re imaging subjects before and after ACL reconstruction and tracking how specific changes in motion correlate to early indicators of osteoarthritis—which can emerge within a year or two of surgery—in the knee cartilage. Thelen hopes his research can help form guidelines for surgery that lead to more normal motion, reduce wear on knee cartilage, and decrease the chance of osteoarthritis.

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