By now, the torn tissue is probably healed in place by fibrous tissue (scar tissue), and it's not as elastic as the original tendon tissue (sorry, the name escapes me at the moment, but you know what I mean). And because of this inferior elasticity, it's probably overloading the rest of the healthy quadriceps to carry out the function.
And honestly, you really can't "repair" scar tissue, because it's already repaired by the body. The surgery for a relatively fresh torn tendon is the stitching of the torn pieces, thus allowing the body's natural healing process to take place. Which, unfortunately, after 6 years, and if you're still able to play basketball, then the healing process is more or less complete.
Having said that, if you were to go in and have any worked done, you're only going to get more scar tissue, the surgery itself is an injury (pretty big one!). Hence why most people who go into surgery will lose some degree of range of motion.
Sorry, this may not have been what you want to hear.
I have a partially torn UCL on my left thumb from a snowboarding incident, it's been ~2 years and I doubt I'll have it repaired.
You can always consult your doctor about this, and perhaps seek out a debridement procedure to clean out some of that scar tissue/loose bodies on the quads. But again, the surgery itself is an injury, you'll risk scar tissue building elsewhere in the knee joint.
Lastly, any sort of surgery will result in a considerable lengthy lay-off, and sometimes, you'd just "lose it".