The physio will be a lot of help. She/he will check strength, tightness and alignment. of all the muscle groups/ You may be given exercises to strengthen, loosen or align.I had treatment with massage, needles and (my favourite) ultra sound. I then had a prothesis put in my shoe which cured the knee pain. Funny but true! I try to remember to do the exercises because they have helped a lot but when you feel better my resolve is not so good. I hope you are a better patient than me!!
Welcome to the MedHelp forum!
First you have to find out whether the muscle wasting was the cause or the effect of knee locking or knee pain. Generally weakness of the inner thigh muscles and tightness of the outer thigh muscles causes the knee cap to move from its place and cause knee pain and knee locking. This could have happened in your case if you have a localized muscle wasting only. Alternatively locking of knee (say due to torn piece of cartilage or bone figments) and knee pain could have caused a localized muscle atrophy in the thigh due to less use of the muscles. The X-ray will show bone figments but if the X-ray is clear, it would be wise to get a MRI of the knee joint done. Deep tendon reflexes, electrical conductivity of nerves, and MRI may be needed for diagnosis. I do not want to scare you, but there is a possibility of muscle malignancy or muscle lymphoma. Focal inflammation of the muscle or muscle myositis can also be a cause. Involvement of a single nerve or mononeuropathy due to diabetes, vasculitis, infection (leprosy), trauma, or entrapment can also be a cause. Hence as you can see, it is important to determine whether the atrophy is the cause or the effect of knee locking and pain.
Please consult your PCP for primary examination followed by proper referral.