TRANSFORMATION & THE PATELLOFEMORAL JOINT
It’s all about the train and the track, whether your leg’s in front or in back.
Dave Armet PT, FAFS
The word transform implies a major change in form, nature, or function. Understanding the word transform helps to appreciate the transformation experienced by the body as it goes through daily activity. Within the realm of applied functional science, we can delve deeper into the appreciation of proper biomechanical reactions by looking at transformational zones (TZ’s).
The transformational zone (TZ) can simply be defined as the portion of time when the body transfers its muscular loading to muscular exploding. As the name implies, it is not a fixed point in the movement but rather a zone in which this reaction occurs. For example, the TZ for a squat is the squatted position itself. In this position the muscular loading response is being transformed to the muscular exploding. Another example is a baseball swing which has two TZ’s. The loading up position to prepare for the swing is the first TZ. The second TZ is the follow through after the explode when the act of slowing down all of the force production actually becomes another loading reaction. A final example is running or gait which also has two TZ’s. The first zone is right stride stance and the second zone is left stride stance. These are the positions when the loading response of a front leg striking the ground transforms into the explosive response preparing for the leg to push off the ground. Understanding TZ’s can help identify the actual biomechanical cause of many musculoskeletal problems. A good clinical example of utilizing TZ’s for better functional understanding can be seen with further discussion of patellofemoral joint dysfunction. To fully understand the potential causes of this symptom, it is important to not only assess the knee of the front leg in the TZ, but also the biomechanical reaction of the other TZ when the same knee has become part of the back leg.
Patellofemoral pain is commonly described in various literatures as anterior knee pain. Clinically, however, people will often describe pain that can be both anterior medial and/or anterior lateral. The symptoms sometimes fluctuate or “move” and can vary depending on their activity or sport they are currently playing. To fully understand the cause of this common symptom, we can use applied functional science and transformational zones to better appreciate patellofemoral joint mechanics not only of the front leg in gait or running but also the often overlooked back leg as well.
The evolution of better understanding the patellofemoral joint has been greatly enhanced over the years by the “train and the track” analogy popularized by Gary Gray years ago. The train (patella) travels on a track (femur) that has 27 muscles attaching to it. With all of this muscular involvement influencing the femur, it makes it easy to appreciate how much influence the femur with all of its muscular attachments has on the path of the train (patella). A femur that sets up a bad track for the patella to ride on truly becomes the source of mal-tracking issues and subsequent patellofemoral joint pain.
When the R foot hits the ground, gravity and ground reaction cause the calcaneus to evert, the tibia to internally rotate, and the femur to internally rotate. The ground up or bottom up reaction means that the R tibia will be internally rotating slightly faster than the R femur. This timing becomes vital for setting up a track for the patella to ride in effectively without getting smacked excessively by one of the femoral condyle. As this reaction continues up into the pelvis a top down reaction is created for the back left leg. The pelvis rotates to the left causing the left femur to externally rotate, followed by left tibia external rotation and eventually calcaneal inversion to prepare the foot for push off. In the back leg, the top down reaction means that the femur will be externally rotating slightly faster than the tibia once again creating the important track for the patella to ride in without getting abnormally smacked by a femoral condyle.
In the first TZ (right stride stance), if the reaction of the R front leg causes excessive or too fast of a tibial internal rotation, the femur may not be able to keep up and the patella could get smacked back into the medial femoral condyle. If the proximal lower extremity musculature doesn’t effectively decelerate the amount of femur internal rotation, it will occur too quickly which could cause the lateral femoral condyle to smack into the patella.
In the second TZ (left stride stance), the right knee of the back leg needs an effective amount of right pelvic rotation and hip extension to create the necessary external rotation of the femur to occur with enough force to drive the tibia into external rotation and eventually invert the calcaneus. Therefore, limited pelvic rotation or hip extension may not allow the femur to externally rotate with enough force to drive the tibia into external rotation. This scenario of the tibia not going through enough external rotation could cause the medial femoral condyle to smack into the patella that doesn’t get helped out of the way by the movement of the tibia. The common problem of tight hip flexors creating limited hip extension is often compensated by toe out lower extremity position and/or a medial heel whip to slacken the hip flexor musculature. Functional understanding of back leg patellofemoral joint mechanics allows better appreciation of how this common compensation and its influence on femoral/tibial rotation can be a major factor for anterior knee pain.
Another likely scenario could be ineffective front leg mechanics coupled with ineffective back leg mechanics further adding to the symptomatic irritation in both TZ’s. Using the patient’s symptomatic complaints together with functional evaluative techniques will further help our ability to create a treatment strategy that truly gets to the source of how and when the patellofemoral joint is getting irritated. We must also consider that some sports or activities, such as basketball or field hockey, might dominate with more squatting type of leg movements closer in line to front leg mechanics, while other sports or activities such as soccer, lacrosse, or running, might create more back leg movement opportunities. These movement differences might be a major factor in creating changing or variable symptoms or possibly causing a change in symptoms (better or worse) as an athlete changes to a different sport.
TZ’s are a valuable tool used to better evaluate/assess biomechanical reactions occurring specific to a daily task or sport. TZ’s combined with knowledge of applied functional science allow more specific functional understanding of human movement. With regards to anterior knee pain, understanding the knee in the front leg, and the less popularized but just as important, back leg is vital for treatment of the all too common problem of patellofemoral pain.