State officials say Andrew Steen, the Highway Patrol trooper injured Wednesday in an incident in Sioux Falls, underwent successful surgery early Thursday to relieve pressure on his brain.

Patrol Superintendent Col. Craig Price says the 34-year-old trooper remains in critical condition at Sanford Medical Center in Sioux Falls.

Doctors say the surgery was not uncommon with head injuries such as those Steen received.

Steen, an eight-year-veteran of the Patrol, was struck by a vehicle in the line of duty following an attempted traffic stop that escalated into a pursuit ending in the area of 57th Street and Western Avenue.

Price says a benefit fund, titled the Trooper Andrew Steen Benefit Fund, has been set up at Wells Fargo, and donations may be made at any Wells Fargo institution.