EVER wondered whether the twinge in your knee is a result of overdoing it at the gym or symptoms of something more sinister such as osteoarthritis? A laser-based test could one day give your GP a quick, cheap answer.
Osteoarthritis (OA) is a degenerative condition in which the cartilage tissue that coats joint surfaces breaks down, causing great pain as neighbouring bones crunch together. Some 20 million people in the US and 2 million in the UK have the incurable condition, for which there is no reliable lab test.
But biochemist Michael Morris at the University of Michigan, Ann Arbor, is developing a test that may be able to identify people in the early stages of OA, perhaps years before they experience any symptoms.
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Jane Tadman of the Arthritis Research Campaign in the UK says this might allow people to take measures to mitigate the condition鈥檚 effects, such as keeping their weight down to limit the pressure on their knees, and keeping physically active. Emerging therapies could also be tested on these people.
In OA, the failing cartilage allows a lubricating polymer called hyaluronic acid (HA) to leak from the joint鈥檚 synovial fluid, elevating levels in the bloodstream. Morris and his colleagues claim to have found a way to measure HA concentrations using a variation of Raman spectroscopy, a process in which incoming photons collide with the atoms in a material, and the scattered photons emerge at a different wavelength.
The shift in wavelength depends on the vibrational characteristics of the atom or molecular group that the photon strikes, revealing which chemicals are present. But it鈥檚 a very inefficient process: only one photon in 10 million is scattered this way.
鈥淭he new test might allow people to take measures to mitigate osteoarthritis鈥�
To boost the efficiency enough to detect HA, Morris used a variant of the technique called surface enhanced Raman spectroscopy (SERS), in which a 5-micrometre-thick layer of the material under analysis is deposited on a gold or silver substrate. Surface electronic effects boost the scattering by between 10,000 and 100,000 times.
Using a gold-coated SERS chip, from Mesophotonics of Southampton, UK, Morris鈥檚 team was able to measure a variety of HA concentrations in blood serum. The team will now seek approval for animal and human trials to determine how closely HA concentration is related to OA severity.
John Kirwan, a consultant rheumatologist at the Bristol Royal Infirmary in the UK, is trying to develop OA tests based on two other components of synovial fluid. While he is impressed with the Michigan team鈥檚 novel technique, he says that some people might have elevated HA levels but develop only mild OA. 鈥淲e think the best way to assess this will ultimately be to consider a combination of biomarkers alongside a patient鈥檚 genetics,鈥� he says.
