In the setting of no previous trauma, and given your young age, it is unlikely that you have a meniscus problem or an internal ligament issue. The symptoms described may result from patella instability, or quadriceps mechanism weakness, which may in turn may result from a nerve compression problem in your lower back. Your best bet is to get a thorough evaluation by an orthopedic surgeon or a knee specialist who can evaluate both parts of the body and guide in the right direction

Without a history of trauma, you most likely do not have a torn MCL/PCL which may cause instability with knee flexion. More than likely your quadriceps muscle is weaker on the left which is causing the buckling. You need to perform quadriceps extension exercises to strengthen your left knee joint. After several weeks, if you do not see any improvement with weight bearing exercises, I would consult a chiropractic orthopedist or orthopedist surgeon for evaluation.

Without any trauma, I would think this most likely is a simple strain. However, I would also be concerned about a cartilage (meniscal) tear. If this does not improve, I would discuss with your doctor.

Best of luck!

You should get this examined, and likely x-rays, to find out what is going on. Meniscal tears or loose bodies won't show on x-ray, but it will rule-out more serious pathology. You don't need to necessarily have had an injury to have a mensical tear, it can be just wear and tear-related, or you may get lucky and this is just a minor sprain that will heal with rest.

I would take a conservative approach first. Go to your local chiropractor and let him evaluate your knee. He can do several orthopedic tests that gently stress the ligaments in the knee and can quite easily determine if other more expensive testing and imaging is necessary. With his expertise he will easily pinpoint the area of your problem. Your knee could be slightly misaligned. See a chiropractor that knows how to gently adjust the knee. When you call the doctors office ask the front desk if the doctor sees patients with extremities or knees problems in particular. Many chiropractors just treat the spine. However, there are chiropractors that have received special orthopedic training in knee and extremity adjusting that are extremely talented in evaluating the knee and realigning it. The ligaments in the knee give integrity to the knee joint. If they are torn the knee will lose its integrity and will not move correctly and you will have problems. The muscles animate the joint. The shape of the joint determines the way the joint moves. The knee moves like a hinge joint, like the elbow. It flexes and extends but there is very little rotation and lateral bending in the knee. Many times the Tibia can be slightly rotated and cause significant pain, loss of strength, and function in the knee. When it is adjusted the symptoms are almost instantaneously reduced. If the chiropractor doesn't feel like he can help you he should refer you to someone who can. Good luck. It is not any fun to have a painful weak knee.

There are several possible causes of pain. A good examination consisting of an MRI and depending on the referring physician, can be ordered with a contrasting agent to better identify the tear or tears. An accurate and timely diagnosis is key for the likelihood of fully restoring normal and pain-free use of the affected knee. All my best, Dr. George

If your knee gives out, or locks up. This usually can indicate a meniscus tear...yes, get it evaluated. Physical therapy can be as effective as surgery, but if it locks up, or gives out -- that is an ominious finding.

This is not my area of expertise

It is probably weak quadriceps muscles. Visit a good chiropractor who treats extremities and sports injuries.