A typical lead width in the Arctic can range from a couple of meters to up to six kilometers and stretch for hundreds of kilometers. They account for 2-8% of a of a given area of ocean covered in sea ice. 

Just for grins let's calculate how much area an icebreaker breaks over say a 100 km patch of ocean. The Polar Star has a beam of ~30 meters, 30*100,000 m=3,000,000 m^2. Total area in a 100 km patch of ocean is 10,000,000,000 m^2 which means an icebreaker breaks 3/100ths of a percentage point in ice area. 

Or in other words, two orders of magnitude less than the 2-8% observed lead covered area, so pretty much no effect at all.