Musculoskeletal diseases are extremely common, in part because of the normal (or sometimes abnormal) stresses and abuses we subject our bodies to in the course of our daily lives but increasingly because of rising longevity in our population as well. These degenerative disorders have become societal burdens; thus, it is imperative to expand our appreciation of their etiology and acquire insights into their pathophysiology. Imaging has the ability to provide an understanding of the natural history of these ailments, and may be the microscope that enables novel observations into the common degenerative conditions that afflict the population, ultimately advancing treatment and improving our quality of life.
Cartilage
Degenerative changes of joints often begin in the cartilage. The ability of magnetic resonance (MR) to visualize, in vivo, the earliest degenerative changes in cartilage, and to follow these abnormalities sequentially, in either an animal model or a patient, has led to remarkable advances in our knowledge of the degenerative process. Recently, chondro-protective pharmaceutical agents promising to prevent the progression of degenerative joint disease have become more widely utilized, with yet more effective agents under develpment. Imaging will play a vital role in objectively ascertaining the efficacy of these therapies. We are fortunate to have recruited Dr. Ravinder Regatte from the University of Pennsylvania, a pioneer in the field of cartilage imaging. He will lead our efforts to develop new techniques focused on imaging cartilage and evaluation of therapeutic interventions. He and his colleagues have devised a novel approach to cartilage MR imaging termed T1 Rho. This is an extremely sensitive technique that facilitates the earliest detection of degenerative cartilaginous changes—a critical advance in our ability to diagnose and treat osteoarthritis.
Fig. 1: In vivo T1 Rho-weighted images of the knee and the corresponding relaxation maps of healthy (with no known abnormalities of knee) and symptomatic subjects with clinical symptoms of osteoarthritis (absence of cartilage abnormalities on radiographs). T1 Rho-weighted image (a) and a corresponding relaxation map of T1 Rho (c) for a healthy volunteer are shown. Similarly, a T1 Rho-weighted image (b) and a T1 Rho map (d) for a patient with moderately symptomatic osteoarthritis are shown. There is pronounced elevation of T1 Rho times (50–60%) in the diseased patellofemoral cartilage when compared to healthy T1 Rho values.
Tendons
We are honored to have as a member of our section Dr. Mavash Rafii, one of the world’s experts on imaging of the rotator cuff. Her understanding of the mechanisms and types of injury to the rotator cuff is widely utilized by orthopedic surgeons and rehabilitative medicine physicians caring for patients with such injuries. Dr. Zehava Rosenberg, another luminary musculoskeletal radiologist, was amongst the earliest investigators to describe the CT and MR findings of posterior tibialis tendon disorders. Our musculoskeletal section was first to apply the concept of secondary signs of tendon disorders to imaging. This component of the routine orthopedic physical exam utilizes the principle that mechanical signs can assess the functionality of supporting structures. We hypothesized that mechanical signs can be visualized by advanced imaging techniques. We have applied this concept to tendons and ligaments, particularly those of the knee and the ankle. The extensor mechanism in the knee, the Achilles tendon, the peroneal tendon, the posterior tibialis tendon, and the anterior tibialis tendon have all been studied. Our group is now exploiting T1 Rho imaging to study extremely early tendon degeneration.
As a result of this research we realized that synovitis is not only a manifestation of tendon disorders, but may accelerate the degenerative cascade in the joint at large. We have described the MR signs of synovitis in several articulations and tendon sheaths. In related research we were able to characterize the normal amount and location of fluid in various musculoskeletal structures. It is quite remarkable how variable physiologic fluid is—what is physiologic in one tendon is clearly abnormal in a different tendon. This information is essential to understand how synovitis affects the natural history of degenerative disease.
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