The surgery is to repair the patella ligament. Sanchez dislocated his knee prior to his Junior Season at USC. It is believed that this surgery will strengthen the knee and increase Sanchez's movement, as he will be able to disregard the knee brace. Recovery is expected to take two months, and he will miss some off-season work outs but will be fighting fit (hopefully) by the time training camp comes around.
We knew this was going ahead but the sooner the better. So if the timetable is right, Sanchez should be good by mid April. Voluntary work outs started on March the 17th last season, so that gives you a good indication of what he will miss. The Jets also held a mini camp between the 16th and 18th of April in 2009, so if we decide to do similar this year, Sanchez could well miss that. (I can't seem to find the off-season schedule, not sure if it has been released yet for 2010).
He should be back and at full strength ahead of any OTA's in May (May 11th was the first day of OTA's in 2009), and Training camp in July.