Rehab & Recovery Zone!

Understanding Chronic Knee Pain Part 2 – The 'What'

By Jennifer Lewis, Performance Physical Therapist – Athletes' Performance

In Part 1 - The 'Why' we examined the various causes of knee pain and highlighted the relationship between the knee, hip and trunk. When combined, these elements make up the lower extremity kinetic chain. In any sport activity it is essential that the muscles of these regions work together in a coordinated effort in order to appropriately produce and transfer energy from the ground to the body.

Energy production begins distally in the feet and is transferred through the knees to the hip and trunk. At this point, if the athlete's desired action is running, the energy is transferred to the contra-lateral limb and returned to the ground as the athlete propels himself forward. If the athlete is an overhead thrower the energy is transferred up the kinetic chain as the distal feet remain in contact with the ground and the gluteal, back extensor and abdominal muscles amplify the force adding to the movement with a significant rotational torque.

When there is a defect in the kinetic chain, or a lack of coordination between the lower extremity musculature, that is when injury will occur. As we spoke about in Part 1, weakness of the gluteal muscles can create an increased strain on the knee at the patellofemoral joint. Repeated strain at this location during running leads to a chronic overuse injury. While weakness of proximal stabilizing musculature may be one cause of an overuse injury, poor running form, more accurately stated as improper kinetic chain coordination, is often another. The continued stress put on a proximal joint to make up, or compensate, for lack of force production in a distal joint often leads to injury. We will now take a further look into specific components that are significant contributors to the kinetic chain, and how their function or dysfunction can impact kinetic chain coordination.

As discussed in Part I, hip stability is greatly influenced by the posterior glute med and it's activation. In the event of movement impairment, many often refer to the glute med as being weak, where "weakness" would imply a lack of strength or force production by the actual muscle fibers. I would like to suggest that the glute med is not suffering from a true weakness, as much as it is inhibited, or neutrally shut down. This can be directly evidenced by significant improvements in glute function that can occur in relatively little time, often 2-3 sessions of treatment. This clinical evidence cannot be directly attributed to "strength gains", as true strength gains, or hypertrophic muscle change takes four to six weeks before gains are made.

Neural activation follows the old principle of "use it or lose it". As other muscles become more dominant, and the glutes less dominant, there are less neural pathways laid to it over time. The process of neural re-education relates to activation or "re-laying" those neural pathways back to the glutes. Initially, in an inhibited state, neural impulses are analogous to dirt roads, slow and less often used; as re-education and activation occurs, those 'dirt roads' are changed into fast-flowing freeways, with greater neural input available to the glutes. Through the process of glute activation, the muscles become re-educated allowing them to take back their role of a primary mover, and decreases over-use of the synergistically dominant muscles (hamstrings and TFL/ITB). This allows the aforementioned proper mechanical alignment which significantly reduces strain on the musculoskeletal system, as well as creates a more efficient process for the production, transfer, and return of energy that is crucial to an optimal kinetic chain.

Without argument, most would consider the core, or trunk musculature, to be the foundation in movement development, and largely has the greatest affect on every movement throughout the body. Terms such as core stability, abdominal draw-in, and neutral spine have been used for years as synononmous terms to identify the activation and stabilization of the trunk and spine, however the definitions, interpretations, and how to achieve those desired results can differ greatly. First, it is easiest to define what core stability is NOT. It is not: yoga, pilates, how many crunches or sit ups one can do, or the visible definition of six-pack abs. A stronger, functional definition of core stability is: the ability to maintain a neutral spine posture while moving the extremities in a manner that is independent of the trunk. This is imperative for proper movement and function in not only sports, but all daily activity.

For those not familiar with a neutral spine position, it is simply the natural anatomical position of the spine. And while not every person exhibits identical postures and builds, everyone has their own 'neutral' position that consists of the kyphotic and lordotic curvatures that compose the spine and pelvis. An example of core stability with a neutral spine is someone standing tall on one leg with the other leg in as much hip flexion as they can while keeping that tall posture. If one sacrifices their core stability and loses the neutral spine position into one of lumbar flexion and posterior pelvic tilt, they can certainly gain further hip flexion but have now lost the foundational stability at their core. Now, one can argue that in many daily activities, and certainly all sports, it is nearly impossible to continuously maintain a neutral spine position. While this is true, if one cannot learn to achieve and maintain good core stability in a neutral spine position, then they will not be able to develop core stability in a position that is outside of a neutral spine.

Synergistic dominance in the trunk can occur as well. Most commonly, we see a rectus abdominus dominance develop. It is one of the largest and strongest abdominal wall muscles, and is superficial depth and definition has made it quite popular. When one performs an abdominal crunch, they often can see the rectus protruding down the anterior abdomen as it contracts, as opposed to visualizing a flattening of the abdomen when the obliques and transverse abdominus are activated as well. The concern with rectus abdominus dominance is that the muscle fibers of the rectus only run longitudinally from the lower ribs to the pelvis; that means that it is only capable of controlling longitudinal motion in the sagittal plance (i.e. flexion and extension). In order to control trunk movement and stabilize in motions that involve the frontal plane (sidebending), and the transverse plane (trunk rotation), the internal and external obliques as well as the tranverse abdominus must be recruited into action.

One of the most significant contributors that factor into core stability and brings us towards progressing from painful static positions to fluid, energy-producing motions of the kinetic chain, is that of movement dissociation. Movement dissociation is the separation of movement of the extremities from the trunk itself, and cannot happen properly without a sufficient level of core stability. Movement dissociation is a principle that is crucial for the proper development of movement starting in our infantile state. Infants initially lack this separation of movement, but as we observe them learning to roll, sit, crawl, and eventually walk, we see more functional, purposeful movement and use of the extremities separate from the trunk. Movement dissociation involves one part of the body to be fixed (often the trunk) and another to move; examples include throwing a ball: the trunk has to be stable so that the arm can be mobile; and running: the trunk has to remain stable while the legs are mobile.

A lack of movement dissociation results when excessive movement occurs in an area or region of the body that should remain still, and often restricts motion in the part of the body that should be moving. This excessive motion is caused by poor core activation, and creates increased shearing forces through the body. In addition, it alters the lines of force production in certain muscles further contributing to dominance and inhibition. An example can be seen with the side-lie hip external rotation with abduction exercise. As one lies on their side, the core should remain stable so that the top leg can rotate up and away (motion occurring at the hip). With poor movement dissociation, as the top hip rotates, the pelvis rotates with it and looks much like the person is going to roll over onto their back.

Part 1 – The 'Why', had initially discussed the thoughts and theories on why chronic knee pain occurs, and the role of the glutes in providing hip stability. Part 2, "The What", introduced further information into how hip stability and glute activation are closely linked to proper core stability and the need for efficient movement dissociation.