Pain at the joint line is the result of a collateral ligament or meniscus
problem (or both) until proven otherwise. Anterior knee pain
can also be due to Patello-femoral syndrome.
When did his pain begin, what was he doing at the time, and what were the initial symptoms?
Does he experience any grinding, locking, catching, or giving way of the knee?
Are there any positions that make his knee more or less comfortable?
Has he tried anything to help his pain and, if yes, has that been successful?