I tweaked my right knee playing basketball last year and now when i put pressure on it at certain angles, it just gives out. what could this be?

See your doctor...: You may have sprained, or tore a tendon or ligament. Beyond analgesics, rest, ice, compression, & elevation it is necessary to consult a physician (orthopedic) for a complete evaluation of your knee. You may need imaging studes to fully diagnose the problem.

Knee gives out: It is time to be evaluated by an orthopedic surgeon with an expertise in sports injuries. It sounds as if you may have a collateral ligament injury but there are numerous other ligament or tendon injuries that may be responsible. It is likely that an MRI will be required to confirm the diagnosis.

Ligament/meniscus: You may have injured a ligament or damaged the mediscus in your knee. First line treatment should include anti inflammatory medications, bracing, and physical therapy. If no relief within a reasonable time, an MRI is warranted to evaluate the ligaments of the knee and the menisci. Get evaluated sooner than later so that you minimize risk of further injury.