Imaging Modalities for Osteoarthritis
In MRI, gadolinium contrast can be given intravenously or intra-articularly, said Dr. Guermazi. Intravenous contrast is useful for evaluating synovitis and differentiating it from effusions. Intra-articular contrast is useful for evaluating cartilage and meniscal lesions.
Among the several downsides of MRI are its cost and the time needed to acquire the images and to interpret them. MRIs of the knee or hip are acquired with the patient in a lying down or supine position; however, physiologically, the knee is probably best understood when those joints are bearing weight.
CT
CT is widely available and generally less expensive than MRI. Unlike dual-energy x-ray absorptiometry, CT imaging can provide information about volumetric density of the bone via changes in the periarticular density, Dr. Hunter said.
The chosen modality may depend on the joint to be imaged, said Dr. Guermazi. In the case of OA of the facet joints, osteophytosis and bone are better viewed with CT than MRI. However, much other information is lost. Although meniscal and anterior/posterior cruciate ligament lesions can be seen on contrast CT, bone marrow lesions cannot.
Ultrasound
“Intra-articular steroids appear to reduce the extent of inflammation in joints. That can be appreciated on ultrasound,” said Dr. Hunter. Ultrasound can also be used to guide the injection of corticosteroids. “Some of the therapies that are being developed are likely to be intra-articular, and ultrasound may be helpful in guiding the needle to the right spot.”
Ultrasound also is being used in some clinical trials to visualize synovitis, according to Dr. Guermazi. “I think it's promising, especially if you use Doppler and can see vascularity.” Doppler ultrasound can be used to identify and monitor active synovitis, after treatment.
Ultrasound is also able to assess the effect of biologic drugs—currently in testing for OA—on synovitis.
Ultrasound is inexpensive, but “it's very operator dependent,” said Dr. Guermazi. “Ultrasound tends to be used more widely outside the United States, where MRI may not be so readily available.”
Ultrasound allows visualization of ligaments, muscles, and tendons, but not bone, and it can visualize only tissues close to the skin and near the probe.
Therapy
Research into potential OA therapies now focuses on tissues that are likely to play a role symptomatically and structurally, rather than just concentrating on cartilage. Just as bBiologic drugs have made huge inroads in RA, “we're right at the cusp of that” with OA, said Dr. Guermazi. When “therapies do become available, the ability to identify OA in the early stages will be very important.”
X-rays can supply information about the structural progression of underlying disease, as evidenced by the osteophytic changes, subchondral bone sclerosis, and absence of joint space seen in an anteroposterior radiograph of the left knee in a 65-year-old woman with secondary arthritis at 9 years after treated fractures (at left). A lateral view (at right) confirms severe tibiofemoral OA and shows severe patellofemoral OA with large posterior femoral condyles (arrowhead) and tibial plateaus (arrow) not seen on the anteroposterior view.
Sagittal fat-suppressed proton density-weighted MRI shows diffuse cartilage loss of the lateral central weight-bearing tibia and femur. Also seen are a central lateral femur bone marrow lesion (arrow) and a small tibiofibular ganglion cyst (arrowhead).
CT can visualize volumetric density. Medial narrowing plus subchondral medial tibiofemoral bone sclerosis (arrows) and cystic changes are seen on coronal reformatted CT.
Source Images courtesy Dr. Ali Guermazi
