In isolated injuries, I usually treat them with long knee brace with full weight bearing from day 0. I do not allow knee flexion for 3 weeks and then start knee flexion as per pain tolerance.

In poly trauma, patients, I perform percutaneus lag screw fixation at the time of fixation of other fractures.

Generally I utilize knee immobilizer locked in extension for 4 weeks...if films are ok...then allow 0-20 for 2 weeks...then 0-40 for 2 weeks then range of motion as tolerated 

Functional brace would be the treatment of preference in isolated injuries. Elderly may be benefited by a locked brace or cylinder as they need more stability. Younger could be left with limited ROM of the brace but in this case I would suggest PWB. In polytrauma patients in my experience usually the patella fractures are more complex (I have not seen any non comminuted fractures in polytrauma as they are high energy injuries) and need reconstruction, so open reduction and tension band would be more appropriate. I 

For patella fractures without displacement or with minimal displacement and extensor apparatus intact (you have to test it functionally) a cylinder cast is the best solution (a brace is possible but it needs to bee long enough and well positioned.

When there is a suspect of extensor apparatus discontinuity, an open reduction and fixation with dynamic metallic cerclage is the best solution (easy, chip, with good results)

I prefer ORIF if there is a displacement greater than 2mm. In non displaced or minimally  displaced fractures I reccomend orthosis if patient is cooperative or a cilinder cast if not. I think we must think not only in extensor apparatus damage but articular integrity toó.

In completely non-displaced patella fx's, I keep patients in a ROM brace x 3weeks locked in full extension, allowing for showers, bathing, etc.  Range of motion 0-30 at 3- 6 weeks, then progress as tolerated. 

I thank all for the useful inputs

Cylinder cast or brace (non-operative treatment) is the gold standard if the extensor mechanism is intact. This is for native patella fractures, however the treatment might change if there is a resurfaced patella from a total knee replacement.

It is not the fact that there is integrity of the extensor mechanism but the possibility of displacement of the fracture that can occure even days after the fracture. I prefere ORIF to make sure that the knee will heal in the best way.