Your knee will heal just fine on effient but obviously a bit slower. Once clotting has started, then the process will speed up. If you had surgery on your knee 2 or 3 days ago, or longer, then it's fine to restart effient.
Effient is a very potent anticoagulantia (often called bloodthinner). When a stent is placed, you need anticoagulantia to avoid thrombosis in the stent. Dependant on the type of stent you need to be on this medication for a couple of months. For a DES stent they normally keep you on it for a whole year, as for bare metal stents(BMS) the period is much shorter. It is very risky to stop Effient before the planned end date. An in-stent-thrombosis is often deadly. Your cardiologist will tell you when it is safe to stop Effient.
Did you discuss stopping Effient with your cardiologist? If not, I would strongly advice you to contact him ASAP. Note that there are other medicine with almost the same effect that might give you less side effects like Clopidogrel and Ticagrelor.