interior collagen fibrils uncoil and free up the water in and around their cells.

Crues believes that MRI goes beyond simple diagnosis, and he demonstrated how the views it provides have altered the fundamental medical approach to certain conditions. "We thought we understood these disease processes," he explained, until the subtleties and unprecedented detail of the MRI scans indicated complexities that were overlooked with previous diagnostic modalities. "One of the most common causes of knee symptoms in the population at large, especially in young women, is degenerative change in the articular cartilage of the patella [kneecap]," Crues continued. MR studies in the laboratory on this tissue revealed there are actually two layers of cartilage, usually with different water content. Studies over time of a given patient can reveal deterioration within these layers, and even a single MRI study may reveal more—since the cellular biochemistry revealed by MRI may indicate incipient damage—than would be discovered by a surgeon who cut in surgically for a look. ''Further studies need to be performed to see if the signal changes [revealed with MRI] accompany early biochemical changes" that are known to be associated with diseased cartilage; if so, predicted Crues, "early detection may lead to changes in patient behavior, or to the development of drugs to protect the cartilage."

Tears of the rotator cuff in the shoulder provide another vivid example of how MRI is revolutionizing the treatment of joints. Such tears have many different possible causes, and in the past, cutting in for repair or removal did not allow surgeons "to distinguish among the etiologies," said Crues. "A major breakthrough in understanding this disease stemmed from the surgical findings of Charles Neer, who postulated that 95 percent of rotator cuff tears were due to chronic trauma," continued Crues, caused by a congenitally abnormally shaped acromion, the bone at the top of the shoulder. Normally this bone surface is flat, but "some people are born with a congenital abnormal shape," said Crues, a kind of bony hook that often abrades and produces chronic trauma on the rotator cuff muscle laid over it. Before MRI, this process was almost unavoidable in people with the condition. Now, said Crues, we "can adequately differentiate between those patients whom surgery may help, and those" whose shoulder joint degeneration stems from other causes. Now the area can be imaged, using short TE times and T1-weighted strategies, and if the misshapen bone seems the likely cause, a quick arthroscopy to file it down will likely prevent altogether a tear that once—for lack of warning symptoms—was inevitable.

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