What Causes Instability In Knee After Knee Ligament Surgery?

i was suffering from ACL Tear ( knee legament injury) since 2.5 years ( injured on 11-12-2007 ) after 1.5 year i was going from ACL Reconstruction surgery or artificial legament surgery on 05-09-2009

and on 08-07-2010 when iwas playing football i feel some instability and jurk in inside of knee, now iam thinking that my artificial legament was broken. So please suggest me that what can i do, whether i am going from again reconstruction surgery or not, if not then what can i do for become physicaly fit.