You may be describing a dislocating patella (knee cap). An exam and an X-ray will be needed to diagnose the problem accurately. Two special views taken with X-rays may be used.
The first is the sunrise view. This X-ray shows the knee from up above when it's bent. You should see the patella lined up at the end of the femur (thigh bone). With a dislocating patella, the knee cap is often out to the side instead of in its natural groove. X-ray views from the front and side with the joint straight and then bent may also be ordered.
You may not be having symptoms now, but pain, crepitus, and loss of motion are common with this problem. Crepitus refers to the grating, crackling, or popping sounds and sensations felt under the skin and joints.
With chronic dislocations, the cartilage on the back of the patella starts to soften and shred. This causes a painful condition called chondromalacia.
Restoring the knee to its normal position and function may require more than a brace or splint. Surgery may be needed for some patients. Before spending money on a brace, see an orthopedic surgeon and find out what are all your treatment options.
You can begin with conservative care and see if that's all that's needed before having surgery. For some patients, a series of three or four operations are needed to correct this problem.