What are the Causes of Pain Under the Kneecap?
There are many cause of pain under the kneecap and on the front part of the knee. In the past, these pain generators were generically-called either “patellofemoral chondromalacia” or “anterior knee pain.” In general, sports medicine specialists today prefer to have a diagnosis based on specific pathology. Therefore, the individual components that can lead to front knee pain are important to understand to allow for their best treatment.
What Causes Pain in the Front of the Knee?
The main structures that can cause pain in the front of the knee are the joint lining, the medial and lateral plica, the medial and lateral patellotibial ligaments, the retropatellar fat pad, and the cartilage surfaces of the patella and trochlear groove. While these are the specific anatomic structures that are involved, most sports medicine doctors will not convey these specific pathologies directly to you because of the complexity in their nomenclature. Anterior knee pain can also be present in overuse syndromes of patellar tendon (patellar tendinitis or tendinopathy) or quadriceps tendon (quadriceps tendinitis or tendinopathy).
A well-localized physical exam is important to discern the area of one’s front knee pain. Pain along the tissues that are on the inside or outside of the kneecap can be due to the joint lining or synovium being irritated or irritation of the underlying plical folds. Pain deep to the patellar tendon can be irritation of the retropatellar fat pad, scarring after injury or surgery, or thickening of the ligament that courses from the kneecap down to the tibia (the patellotibial ligaments). These are all diagnosable by direct palpation by the examiner. Similarly, pain at the top or bottom of the kneecap where the quadriceps and patellar tendons attach can also be directly palpated. In particular, patellar tendinitis is felt to be present when one has pain at this location with the knee out straight and much less pain where the knee is bent to 90 degrees.
True “chondromalacia” of the patella or trochlear groove means that there is some underlying damage of the cartilage. In effect, this is a kind term to say that one has arthritis. Shifting of the kneecap either to the inside or outside (medial or lateral) or up and down (proximal or distal) during the physical exam may elicit some crepitation and pain, which almost always indicates that there is some underlying arthritis. Similarly, the same physical examination finding can be elicited when one moves the kneecap and one has arthritis at the end of the femur, i.e., the trochlear groove.
What Causes Swelling at Front of Knee?
These anatomic locations are the most common areas of anterior knee pain. Sometimes, a generalized swelling within the knee can make these tissues irritated, while other times there is an underlying source of pathology in other locations of the knee, which causes knee swelling and makes these tissues irritated. It is important to have a thorough physical exam to determine other concurrent pathology to best make a decision as to whether one needs activity modification, physiotherapy, steroid or biologic injections, bracing (such as a patellar tendon strap), or a surgical procedure. The physical exam must be intertwined with the use of radiographs and possibly an MRI scan to best make the diagnosis and predict one’s ability to have resolution of their front knee pain.