Understanding Chronic Knee Pain Part 1 – The 'Why'
By Jennifer Lewis, Performance Physical Therapist – Athletes' Performance
Knee pain is one of the most common complaints that plague’s the active population. It is often found in the front or anterior region of the knee, and has many aliases including patello-femoral pain syndrome, patellar tracking disorder, jumper’s knee, chondromalica patellae, pre-patellar bursitis, patellar tendonitis, or patellar mal-tracking. Classic rehabilitation and treatment has targeted the site of the pain with a barrage of techniques including cross-friction massage, electric stimulation, ultrasound, and isolated strengthening of the quads/VMO to name a few. Often a course of rest, ice, and anti-inflammatories provide measured relief, but symptoms rarely are permanently eliminated. This lack of success in controlling knee pain has led professionals to look elsewhere than just at the knee for the cause of the problem, and soon thereafter, found alignment and mechanics of the hip joint and femur can also be correlated as the primary cause of dysfunction leading to their symptoms.
To understand how femoral alignment can affect the knee joint, we must discuss the muscles that attach to, and control the femur. Most are familiar with the three gluteal muscles consisting of maximus, medius, and minimus. While all three provide some amount of femoral control particularly in regards to internal and external rotation and abduction, the posterior portion of the glute medius is directly responsible for extension, external rotation and abduction of the femur on the pelvis.
Often times however, the glutes, specifically the gluteus maximus and posterior glute medius, becomes inhibited, or neurally shutdown. Synergistic dominance is defined as a condition when a muscle in a group of muscles ,that share similar actions, become more dominant and in turn, another becomes less dominant. In the case of the hip extension, the hamstrings, which are ordinarily a secondary contributor, can take on the role of a primary mover. This dominance of the hamstring can lead to the glutes becoming inhibited or less active. This can be seen when one assesses prone hip extension, and takes note of the timing in activation of the glutes versus the hamstrings. When the hamstrings are activated first before the glutes, this can create over increased dominance and strain to the hamstring due to decreased glute activation to create the hip extension. As applied to real life, consider how many runners (an activity that requires repetitive hip extension and eccentric deceleration of hip flexion) who complain of having tight or constantly strained hamstrings.
Another synergistic dominance at the hip is seen with hip abduction. Hip abduction or eccentrically controlling the hip into adduction is controlled by the glutes and the tensor fascia latae via the ilio-tibial band (TFL/ITB). Over dominance of the TFL/ITB can create inhibition or decreased activation of the glutes. This is a common reason why many people complain of having tight ITB’s, which in certain cases, because of its attachment and shared orientation and line of force with the TFL, can be a frequent source of knee pain. Also, the excessive pull of the TFL/ITB can create tibial external rotation relative to the femur – creating excessive rotational stresses at the knee.
The primary reason that the glutes are more appropriate than the hamstrings and TFL for movement and control at the hip is simple: the glutes are “one-joint” muscles whereas the hamstrings and TFL are “two-joint” muscles, meaning that they cross only one joint versus crossing two joints, respectively. To be able to achieve precision and control of movement we must use the muscles that attach closest to the proximal end. Therefore, to control the femur the glutes are mechanically in a much more advantageous position to provide solid control as opposed to the hamstrings and TFL/ITB which are long muscles and attach further distally down the leg, providing less accurate control.
One then would naturally be inclined to ask then how the glutes lose their dominance, if their main action is to control the femur at the hip. Reliance on certain muscles can come based on certain training and strengthening techniques. Traditionally, the quadriceps, hamstrings, and calves are a primary focus in the weight room for the lower body. A second important reason is the actual mechanics in the execution of movement. Even exercises like squatting where we think we are targeting the glutes, are often performed with mechanics that place the glutes into a less optimal position. People with complaints of knee pain often demonstrate similar movement patterns.
When assessing a double-leg squat, common movement impairments can include:
• An unbalanced hip/knee rhythm causing excessive flexion/extension through the knees and not enough at the hip. Often seen as forward weight shift with the knees ‘excessively’ in front of the toes. This will causes an increased force through the quadriceps and patellar tendon.
• Femoral collapse into internal rotation and adduction, which further places the glutes into an over-lengthened position.
• Limited range or use of true hip flexion mobility, which may also contribute to inefficiency of glute activation.
This now brings us to what happens mechanically when the glutes are no longer the primary movers and controllers at the hip. What is most often seen can be termed “femoral collapse”, where there is an internal rotation and adduction moment on the femur. This places even more strain on over-dominant muscles like the TFL which have an internal rotation component to them. This places the glutes into an excessively lengthened position. The principle of the length-tension relationship tells us that muscle fibers produce varying amounts of force dependent on what length they are in. Muscles that are overly shortened, or overly lengthened, such as the posterior glute med in this case and the gluteus maximus, become even less capable of producing force and being able to control the femur.
A vicious circle of poor biomechanics is created where the primary hip movers are inhibited, excessive reliance is placed on muscles that are supposed to be secondary movers, mal-alignment of the femur into the direction of internal rotation and adduction occurs that further places the posterior glute med into a lengthened and inefficient position so that it is no longer able to pull the femur into proper alignment. This poor alignment along with over-dominance of less effective muscles creates a valgus and rotational torque at the knee joint. Forces through the knee joint are then not disseminated properly, and excessive tension is placed on the soft tissue structures surrounding the knee, most often the patellar tendon.
That is why the source of the pain is not necessarily always at the site of the symptoms, and why traditional treatment and rehabilitation techniques that only address the site of the pain often fail in correcting and eliminating the problem. The source needs not only to be identified, but then corrected through the education and utilization of proper muscle function and mechanics.