Damage to joint cartilage inevitably leads to osteoarthritis, which causes painful bone-on-bone contact. Currently, physicians evaluate the extent of this damage to articular cartilage using x-rays or by manually feeling this tissue, but both methods are imprecise. Now, investigators at the University of Pittsburgh's department of orthopaedic surgery report their development of a probe that can accurately measure the extent of damage to articular cartilage. Details of this method, which soon could become clinically applicable, are being presented at this year's annual national meeting of the Orthopaedic Research Society in Anaheim, Calif.
"By combining ultrasound with a method to measure the amount of stress, or load, on a sample of articular cartilage, we are able to measure both the thickness and the mechanical strength of this tissue," said J. K. Suh, Ph.D., principal investigator on the study and assistant professor of orthopaedic surgery, mechanical engineering and bioengineering at the University of Pittsburgh.
"This is extremely promising, because the probe can be used arthroscopically. We could someday measure the thickness and strength of a patient's articular cartilage just before surgery to determine the extent of an injury and plan the most effective course of treatment. For instance, based on this information we might choose either to surgically repair damaged cartilage or leave it alone if damage is minor," remarked Freddie Fu, M.D., professor and chairman of the department of orthopaedic surgery.
The researchers tested the probe on 20 samples of articular cartilage taken from cow knees. The probe was equipped with an ultrasound unit to measure thickness and a load cell unit to measure the strength, or indentation stiffness, of a sample of articular cartilage. The researchers measured the difference in the speed of ultrasound waves that were passed through an uncompressed piece of cartilage versus the same piece of cartilage when slightly compressed by the probe. Using these figures, the researchers could calculate the thickness of the cartilage and correlate it exactly with its thickness as measured directly with calipers.
Next, the researchers used the load cell unit to measure indentation stiffness. They indented a sample of articular cartilage by increasing degrees, thus applying more pressure each time, and recorded the stiffness of the tissue. In this way, they could determine the health of the tissue. Some pieces of tissue they tested were previously treated with an enzyme known to chemically weaken articular cartilage in ways similar to the naturally occurring degenerative disease, osteoarthritis. Other pieces were untreated. The investigators discovered that treated articular cartilage was much weaker as measured by indentation thickness than untreated articular cartilage, thus confirming the usefulness of this approach. Moreover, the speed of an ultrasound wave was slower in enzyme-treated tissue than in normal tissue, indicating treatment-related damage.