Once considered harmless by doctors, calcium crystal deposits in the knee joint actually can contribute to worsening arthritis, a new study warns.

CT scans have revealed that calcium crystals in the knee can promote joint damage, wearing away the cartilage that keeps bones from rubbing together, researchers reported recently in the journal Arthritis & Rheumatology.

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“The cartilage damage is most likely to occur in the same locations where the crystals are deposited, suggesting a localized effect,” said researcher Dr. Tuhina Neogi, a professor at the Boston University School of Medicine.

“We have also showed that these crystals can contribute to knee pain in another recently published paper,” Neogi added in a university news release. “Taken together, these findings highlight the important role of calcium crystals to structural damage and symptoms in knee osteoarthritis.”

Knee osteoarthritis affects about 34 million people in the United States and 600 million worldwide. It happens when the cartilage in the knee joint breaks down.

There are no treatments available that prevent its progression, researchers said in background notes.

Up to now, calcium crystal deposits in the knee were thought to be of no clinical consequence, and just something that happens with old age, the researchers said.

But using CT scans of nearly 1,700 patients, the team was able to detect a higher amount of deposits than previously revealed by regular X-ray imaging.

These improved scans allowed researchers to track an increased risk of cartilage damage from the deposits, including among knees that hadn’t appeared damaged in earlier imaging.

About 9% of patients in the study had these calcium deposits, researchers said. The calcium crystals were associated with a nearly 40% higher risk of cartilage breakdown.

“Now that this has been identified, we can begin to focus on identifying ways to prevent these crystal deposits from occurring, to hopefully relieve pain and limit progression of joint damage in osteoarthritis,” Neogi said.