Kneecap Pain

 By: Erik Dalton
Every year, more and more clients come in grumbling of generalized pain around the kneecap (patella) aggravated by activities such as squatting, stair climbing, or hiking over hilly terrain. Symptoms typically worsen during prolonged knee flexion (i.e., long car rides, sitting in class or in a movie theater). Clients regularly carry with them a diagnosis of chondromalacia or patellar tendinitis. In most cases, neither of these terms accurately describes the cause of this painful condition, which remains elusive and poorly understood.

In attempting to discern the source of the client's pain, an important question is whether it primarily involves the surrounding soft tissues or the patellofemoral articulation itself. Some clinicians (including myself) tend to accumulate patella-related symptoms into a category of chondromalacia. Since most researchers agree that nerve endings are relatively not present in articular cartilage, chondromalacia shouldn't be labeled as the true anatomic cause of anterior knee pain.1 Chondromalacia is a surgical finding that signifies areas of softening of hyaline cartilage due to trauma or aberrant loading, but is not the cause of pain.

Oddly, this shiny, smooth tissue underlying the patella and covering the surface of the femoral head receives the most accolades as a knee pain generator but is possibly the least innervated of all human tissues. I don't mean to say that cartilage degeneration may not be a precursor to knee pain. Certainly, a roughened and degraded cartilaginous surface could impair mobility and joint function leading to irritation in nearby tissues. But the anatomical cause of pain in this area probably originates from compression and torsion to the richly innervated subchondral bone, infrapatellar fat pad, or medial and lateral retinacula.

Synovial "Nipping"
I've had surgeons tell me that lots of of their non-traumatic, non-specific knee pain cases have been traced to pinching of the synovial lining between the patella and femur. They speculate that accumulation of inflammatory waste products leads to increased swelling and even greater synovial "nipping." But when it comes to comprehending patellofemoral pain, no one can top this guy. In 2005, a surgeon and renowned researcher Scott F. Dye, MD, enlightened the orthopedic community in a somewhat unusual way. In a brazen experiment using no anesthesia, Dr. Dye, a long-time sufferer of patellofemoral pain, opened an incision in his affected knee adequately to insert a probe so he could test the sensitivity of various interarticular tissues. As he prodded the damaged hyaline cartilage beneath the patella, to his surprise, he found the tissue to be completely painless. {But|However|Nevertheless] when the probe contacted the joint's synovial lining, the familiar pain he had been feeling for months screamed back at him. I encourage you to review this man's outstanding work in an article, "The Pathophysiology of Patellofemoral Pain: A Tissue Homeostasis Perspective."2

Basic Biomechanics
As the knee flexes and extends, the patella moves through the trochlear groove in the distal femur. (See Figure 1) This patellar mechanism promotes leverage of the quadriceps by improving the angle of pull on the tibia. Similar to a shim (the thicker the better), the patella helps push the quadriceps tendon further away from the tibia to allow for more powerful knee extension - and powerful it is. The forces executed during knee extension exceed all other body movements. Surprisingly, much of the literature implies that the patella moves only in an up-and-down direction when, in fact, it also tilts and rotates. Imagine the massive forces the patella must endure during hill climbing or squatting. Pressures per square inch under the patella rise to more than three times the body weight when climbing a ladder and greater than eight times the body weight during a variety of stages of deep squatting...whew!
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