A Pain in the … Knee

It happened when I was 15 years old. I thought I was a hotshot runner, and was sure that I would soon be breaking records on the track. Nevertheless, the apparatus in the middle of the fieldhouse intrigued me, and I wondered if I might possess other undiscovered talents. One day I decided to take a shot at the high jump. This was a few years before Dick Fosbury flopped to Olympic gold, transforming the sport forever. The event seemed straightforward: All I had to do was run to the bar, jump over it with room to spare, and land gracefully on the giant foam pillow strategically placed on the other side. Unfortunately, I failed to note the importance of aiming at the middle of the landing pad. Gathering speed, I sailed effortlessly over the bar too close to its end. Before I could congratulate myself, I had also sailed over the end of the landing pad, descending with a jolt that drove my right leg into the hard-packed dirt of the fieldhouse floor. I tried to play it cool and pretend that nothing untoward had occurred, but the explosion of pain in my knee was difficult to ignore. I didn’t appreciate the magnitude of my injury until the next day, when I awoke with a knee so tensely swollen that I could scarcely bend it. Not knowing what to expect, I limped into the office of the school doctor. After gingerly prodding my bulbous joint for a few minutes, he scribbled something on a prescription blank and told me to see Jake the athletic trainer for a course of therapy. As I hobbled down to Jake’s basement hangout, I peeked at the writing on the slip of paper clutched in my fist. The two words that stared back sounded rather impressive, although I had absolutely no idea what they meant: chondromalacia patella. This odd-sounding phrase so fascinated me that I used it for the title of an essay I was writing for English class. Years later, I would realize that the precise meaning of these words was up for debate among orthopaedic surgeons. Chondromalacia patella was often used as a catch-all term for any pain in the front of the knee. I learned that many believed that this phrase was so misused as to be meaningless and worthy of permanent interdiction. I also discovered that whether you called it chondromalacia patella, patellofemoral pain syndrome, or something else, anterior knee pain was a complaint that could send a full-grown orthopaedic surgeon fleeing the examination room in frustration. I noticed that most of my colleagues were careful not to acquire a reputation for treating anterior knee pain, lest they soon have a waiting room full of such patients, eagerly referred by other orthopaedic surgeons for miles around. The reasons for this aversion were easily discerned: the etiology of such pain was obscure, and treatment of resistant cases seemed fraught with failure. Chondromalacia patella is one of those Greek-Latin hybrids we’re so fond of in medicine. Literally meaning ‘‘soft cartilage on the knee cap,’’ it may have become popular because it reassuringly suggested an identifiable anatomic basis for a patient’s elusive symptoms. However, not all individuals with anterior knee pain have visible cartilage damage, and it remains controversial whether soft patellar cartilage alone can result in anterior knee pain. In this issue of The American Journal of Sports Medicine, a new study aims to address this question using multiple magnetic resonance imaging (MRI) techniques. Van der Heijden and colleagues compared 64 young patients with anterior knee pain with a group of 70 matched controls drawn from their friends, teammates, and colleagues. For inclusion, the patients had to experience pain or crepitus during 3 or more of the following activities: stair climbing, running, squatting, cycling, or prolonged sitting with the knee flexed. These symptoms needed to be present for at least 2 months but no longer than 2 years. Patients were excluded from the study if they had a defined pathologic condition such as osteoarthritis or tendinopathy, prior surgery, or inciting trauma. Participants were evaluated with an elaborate 3-T imaging protocol that included T1r and T2 mapping, and, for adults, delayed gadoliniumenhanced MRI of cartilage (dGEMRIC). In brief, these investigators found no difference in the cartilage-imaging parameters between the patients with anterior knee pain and their asymptomatic associates, either in the patella as a whole or in the medial and lateral subregions. They did note a consistent trend for increased T1r relaxation times in their adolescent patients in comparison with controls and acknowledged that there might be a clinically relevant difference in this parameter among adolescents that their sample size did not have the power to detect. When interpreting the implications of a clinical study, it is important to be cautious in extending its conclusions to populations that differ from the one actually included. The study of van der Heijden et al provides evidence that a set of patients can be identified with anterior knee pain in the absence of any cartilage abnormalities, or at least ones that are detectable with the described sophisticated techniques. It should not be interpreted as proving the reverse—that is, that articular cartilage damage in the patella-femoral joint cannot produce anterior knee pain. Specifically, the investigation excluded patients with osteoarthritis. Although we may not fully understand the