In order to appreciate, and evaluate, the possible causes of patella-femoral (PF) symptoms, movement specialists must understand the biomechanics of their client’s activities. The bone motions and joint motions of the entire lower extremity must be considered. In many cases, the opposite leg as well as the trunk must be assessed. To simplify the thought process, Gary Gray would encourage us to consider why the femur and the patella are not “getting along”.
To start, let’s look at the tri-plane anatomy of the quadriceps muscle, the patella, and the patella tendon. Because of the normal valgus alignment of the femur and tibia (Q angle) the quadriceps can not run in a straight line from origin to insertion. This angle is often erroneously cited as the cause of PF problems. Certainly this Q angle can be excessive (think dynamic rather than static), but it is rare (and abnormal) to find someone with a “straight leg”. If a Q angle is present in almost everyone, we must consider why the body was designed this way.
The quadriceps is known as a knee extensor, which infers that it is a decelerator of knee flexion. Completely true, but the emphasis on sagittal plane function masks the important role in the frontal and transverse planes. The patella articulates with the trochlear groove at the distal end of the femur. The anatomy of the trochlear groove, with the much larger lateral wall, complements the Q angle and informs us about the three-dimensional function of the knee. When the quadriceps contracts concentrically, the patella increases the moment arm that enhances the force generated. But the patella will also glide laterally, pressing against the lateral femoral condyle. It is this lateral pressure against the femur that gives the quadriceps the ability to decelerate and accelerate motions in the frontal plane and the transverse plane. This is critical during weight-bearing activities. One final point is that high levels of pressure between the femur and the patella are part of normal function. It is only when the forces and pressure exceed the symptomatic threshold of the tissues will we hear complaints from our clients.
When we return to the question of why the femur and patella are not getting along, the cause/suspect may be anywhere in the body. This blog will focus on the hip joint above and the ankle/subtalar joints below for the cause. The biomechanics of walking, running, landing, lunging, and stair climbing share a number of important features. When the heel hits the ground, there are ankle and subtalar joint motions created by gravity, ground reaction force, and momentum. The subtalar joint will pronate (evert). The ankle may plantarflex or dorsiflex. These motions start the “Chain Reaction” that moves through the knee and up to the hip. The hip will flex, adduct and internally rotate. The knee in between will flex, abduct (valgus), and internally rotate. The role of the muscles is to decelerate these motions and then accelerate the opposite motions. It is during the deceleration of the 3 knee motions and/or the acceleration of the 3 opposite motions that the femur and the patella will develop symptoms. The motions of the hip and ankle/subtalar joint can be excessive or restricted, which alters the bone motions of the femur and tibia, creating a “mis-match” and ultimately leading to the abnormal patella-femoral mechanics.
Patella-femoral symptoms can be produced during the deceleration of the landing, or the acceleration reversal of bone motions. The sagittal plane motion of knee flexion is controlled by the hip extensors and the ankle plantar flexors. The frontal and transverse plane knee motions of abduction and internal rotation (respectively) are controlled by the hip abductors and external rotators, as well as the foot muscles that decelerate eversion/pronation.
In the sagittal plane, failure of the hip extensors to control flexion of the femur, or create extension of the femur can result in symptoms. Similarly, if the calf muscles don’t slow down the forward movement of the tibia, then joint surface pressure can exceed the tolerance threshold. The Anterior Chain and the Posterior Chain of 3DMAPS will assess integrated sagittal plane function of the hip, knee, and foot simultaneously.
In the frontal plane, the adduction of the femur may be restricted or excessive. Either problem will create a mis-match with the tibia and potential symptoms. Limited eversion of the calcaneus at the subtalar joint or poor control of that eversion can produce (or add to) the same mis-match. The Same Side Lateral Chain will assess the ability to decelerate the knee abduction (valgus) and then quickly accelerate back. The Opposite Side Lateral Chain looks at the coordination of the foot, knee and hip as the knee moves into adduction (varus).
In the transverse plane, the eversion of the calcaneus is converted into internal rotation of both the tibia and the femur by the subtalar joint. External rotation of the femur and tibia is linked to supination of the subtalar joint and inversion of the calcaneus. The transverse plane is particularly important at the patella-femoral joint, and therefore often the cause of symptoms. Excessive subtalar motion and / or restricted hip internal rotation during landing can be the cause. Just as likely is the combination of restricted subtalar eversion and poor control of hip internal rotation. During the reversal of bone motion, if the femur goes through the normal external rotation, but the calcaneus does not invert, there will be serious consequences at the patella-femoral joint. The Same Side Rotational Chain and the Opposite Side Rotational Chain in 3DMAPS will indicate both the amount and timing of the motions of the foot, tibia, and femur.
In summary, to assess the “suspects” of patella-femoral pain, and identify the true cause(s) of the dysfunction, all movement specialists need a system to efficiently, and more importantly, effectively analyze movement. These movements need to be driven by lunges, accompanied by arm movements to “isolate” the problem during integrated total body tasks. Based on the description of the motions in each plane above, both the amount of motion and the ability to control that motion must be analyzed. 3DMAPS, with both mobility and stability assessments, was created for just this purpose.