There are actually quite a few things that can cause symptoms as you described them. Given the location of your knee (along the lateral or outside aspect), there can be problems inside the joint (intra-articular) or something coming from outside the joint (extra-articular).
To get an accurate assessment, you’ll need an examination by a qualified health care professional such as an orthopedic surgeon, sports physician, or physical therapist. The examiner takes a patient history with standard questions about possible injuries or trauma to the knee.
He or she will ask the patient questions what makes it better, what makes it worse, and are there any other symptoms? Conducting a physical examination and performing specific tests help in sorting out what could be causing the problem.
X-rays may be ordered and all possibilities are considered. The most common problem causing this type of clinical presentation is a lateral meniscus tear. The meniscus is a thick U-shaped piece of cartilage inside the knee joint.
But there can be other causes coming from outside the joint mimicking a meniscal tear. These would be considered extra-articular and include: 1) iliotibial band syndrome (ITBS), 2) proximal tibiofibular joint instability, 3) snapping tendons (either the biceps femoris or the popliteus tendons), and 4) peroneal nerve compression or inflammation.
The treatment required for the best results depends on the underlying cause. That’s why finding out which of these specific disorders is present is the first step. Early identification and intervention can often prevent chronic, long-term problems from developing.