The signing was announced on Twitter by the International Sports Agency, which represents Trusnik.
The NFLPA website also shows Trusnik now signed through 2014, with base salaries of $715,000 and $855,000 the next two seasons.
Trusnik is making $700,000 this season in the second year of the two-year contract he signed with the Dolphins as an unrestricted free agent in July of 2011.
Trusnik, who joined the Dolphins from Cleveland after being traded there by the New York Jets, has appeared in every game this season. He has been credited with only two tackles on defense but leads the Dolphins in special teams tackles with eight.
Trusnik becomes the third player scheduled to become an unrestricted free agent in 2013 to be re-signed by the Dolphins, following defensive Cameron Wake in May and punter Brandon Fields in August.
Trusnik's signing leaves the Dolphins with 10 players scheduled to become unrestricted free agents next spring, a list headed by tackle Jake Long.
The others are Reggie Bush, Randy Starks, Sean Smith, Anthony Fasano, Matt Moore, Brian Hartline, Tony McDaniel, Chris Clemons and Nate Garner.