MRI May Be Key in Assessing Knee Injuries
by Christopher Vaughan
Magnetic resonance imaging (MRI) may become an important tool for diagnosing knee injuries and monitoring recovery after surgery, according to UCSF researcher Benjamin Ma. 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 knee 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 mechanics after anterior cruciate ligament (ACL) repair usually involve simply manipulating the joint by hand or using 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 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 potential sources of injury to the cartilage. "In general, when we repair the ACL, we don't know if the operation restores motion to a state that allows the joint surfaces to work well together," 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 looseness in the knee, which may cause tears in the fragile cartilage that coats the surface of the joint, and eventually may cause 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 that uses MRI to evaluate knee repairs, but Ma predicts its use will spread in the future because the technique will lead to more successful knee repairs. "If we have better monitoring, it should increase the success rate in the long run," Ma says. Limiting Cartilage Damage
Another application of MRI is as a diagnostic technology for knees that have been 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 after the injury, even though they didn't receive the 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 minocycline have been found to prevent such 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 are now using a more advanced MRI technique called MRI spectroscopy to provide an even more accurate description of the health of tissues in the knee. While standard MRI essentially 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."
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 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 potential sources of injury to the cartilage. "In general, when we repair the ACL, we don't know if the operation restores motion to a state that allows the joint surfaces to work well together," 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 looseness in the knee, which may cause tears in the fragile cartilage that coats the surface of the joint, and eventually may cause 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 that uses MRI to evaluate knee repairs, but Ma predicts its use will spread in the future because the technique will lead to more successful knee repairs. "If we have better monitoring, it should increase the success rate in the long run," Ma says. Limiting Cartilage Damage
Another application of MRI is as a diagnostic technology for knees that have been 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 after the injury, even though they didn't receive the 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 minocycline have been found to prevent such 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 are now using a more advanced MRI technique called MRI spectroscopy to provide an even more accurate description of the health of tissues in the knee. While standard MRI essentially 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."