NEW YORK (TheStreet) -- Flexion Therapeutics  (FLXN) - Get Report  stock is up by 14.27% to $12.45 on heavy trading volume on Wednesday after the company said its osteoarthritis treatment met its primary endpoint during a Phase 3 clinical trial.

The Burlington, MA-based pharmaceutical company announced Tuesday that its treatment, Zilretta, demonstrated "durable and clinically meaningful pain relief" in patients with osteoarthritis knee pain. 

Osteoarthritis is a chronic condition that occurs when the cartilage between joints break down, according to the Arthritis Foundation. About 12 million people in the U.S. were diagnosed with osteoarthritis of the knee during 2014, according to Flexion. 

Flexion is preparing to submit an FDA New Drug Application during the second half of 2016,the company said on Tuesday. 

"We believe that Zilretta has the potential to become an important new non-opioid treatment in a therapeutic area that hasn't seen meaningful innovation in many years," CEO Michael Clayman said in a statement. 

So far today, 2.15 million shares of Flexion have traded, versus the company's 30-day average of about 169,000 shares. 

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