Winter 2006

MRI May Be Key in Treating Knee

MRI may become an important tool for diagnosing knee injuries and monitoring recovery after surgery, according to researcher Benjamin Ma, M.D. Ma is using standard MRI and MRI spectroscopy to measure knee kinematics and tissue injury. He is using MRI to look at the progress of ACL repairs and bone bruises, with the hope that use of the imaging system will lead to better surgical technique and tissue repair in the future.

The standard analytical techniques used to monitor knee kinematics after ACL repair are usually simply to manipulate the joint by hand or use the KT1000, a machine that measures knee movements and torque during flexion. "The problem with these techniques is that they give very limited information about how the ligaments and the joint surfaces are actually behaving," Ma says.

Pressure Point Maps

Instead, Ma uses a device that allows him to put the knee under stress while the patient is in an MRI scanner. "It almost simulates squatting, but the patient is lying down," Ma says.

The result is a detailed picture of how the ligaments move and how the cartilaginous surfaces of the joint slide over each other during movement. Pressure points that appear and disappear transiently as the knee moves can be mapped and measured. Such points are potentially a source of injury to the cartilage.

"In general, we repair the ACL, but don't know if that restores motion to what the meniscus likes to see," Ma says. "This really allows us to do quantitative measurements to evaluate how the repair and recovery are going."

Evidence suggests that many of the 150,000 to 200,000 people who get ACL repairs each year are at risk for later complications. ACL repairs can produce a looseness in the knee, tears in the meniscus and eventually arthritis. When ACL repairs are reviewed 10 years after the operation, researchers have found that about half the knees are not doing so well. "If you do a repair on someone who is 16, and 10 years later he is getting arthritis, that's a big concern," Ma says.

UCSF is still one of the very few medical centers using MRI to evaluate knee repairs, but Ma predicts its use will spread in the future. "If we have better monitoring, it should increase the success rate in the long run."

Researchers also should benefit because they will know more quickly if a new surgical technique is beneficial, Ma says. For instance, some orthopaedists have suggested that a "double-bundle" repair of both the ACL and PCL will be better for patients than single-bundle repairs. However, without a way to accurately monitor the knee, researchers must wait many years to know if double-bundle repairs are more successful. "With MRI, we can get quantitative data on the outcome very soon after surgery," Ma says.

Limiting Cartilage Damage

Another application of MRI is as diagnostic technology for knees exposed to trauma, but without any broken bones or torn ligaments. "In the past, we would say, 'It's not broken; you're fine,' but the cartilage could have taken a pretty good hit there," Ma says.

When one bone surface slams against the other, there can be significant cartilage damage that does not show up on X-rays. In addition, as with neural cells after stroke, cells surrounding the damaged cartilage can die through apoptosis after the injury, even though they didn't feel a direct impact. "Cartilage is also one of the slowest tissues in the body to regenerate itself, so it's very important to address the damage if possible," Ma says.

While previously there was no way to limit damage to cartilage after injury, new drugs like doxycycline and methacycline have been found to prevent apoptotic cell death in cartilage. "These are very promising results, making it more important to be able to spot the damage early," Ma says.

Ma and a few other researchers now are using a technology, MRI spectroscopy to provide an even more accurate description of tissue health in the knee. While standard MRI gives a picture of tissue density and water content, MRI spectroscopy offers a detailed picture of lipids, saturated and unsaturated fats, metabolic products and many other cellular markers. "The applications are tremendous," Ma says. "To do MRI spectroscopy you need a stronger magnet, but in a few years everyone will have access to one."

Benjamin Ma can be contacted at (415) 885-3810.

Related Information

News Releases

Program to Protect Research Participants Wins Accreditation
A UCSF program to protect research participants gained full accreditation, after a rigorous review, from the Association for the Accreditation of Human Research Protection Programs.