The Functional Knee: Caught in the Middle with No Where to Hide

Posted: November 12, 2008 in Uncategorized
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Injuries to the knee are seen throughout virtually all sports and all age ranges. Have you ever wondered why the knee is the most common reason for a visit to an orthopedic surgeon? Moreover, have you ever wondered how rehabilitation and training programs could better alleviate the stresses placed on the knee? The answers lie in using Applied Functional Science to understand the chain reaction biomechanics of the two “bookend” joints of the knee – the hip and the ankle.

Although the distal femur and the proximal tibia form the primary knee joint, the other ends of these two longest bones in the body reveal the reactive nature of the knee. The knee is referred to as a reactor because it responds to drivers from above and below. These drivers can be ground reaction force, gravity, momentum, hands, feet, or often times the eyes. During initial foot contact in upright function, the ankle joint, comprised of the distal tibia and talus, create a chain reaction from the ground up that directly influences the knee via tibial and fibular motion. Similarly, the hip joint, comprised of the proximal femur and the illium, influences the knee from the top down via the femur. The three-dimensional motions of these two “bookend” joints play a significant role in determining the magnitude of stress placed on the knee. An appropriate chain reaction from these two bookend joints enables the knee to effectively dissipate significant forces. However, dysfunction at either joint can leave the knee caught in the middle with few places to go and nowhere to hide.

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A practical example of the chain reaction relationship between the ankle and the knee can be illustrated using a female beach volleyball player. Based on its attachment sites, the ACL it is placed under stress during combined knee flexion, abduction (i.e. valgus), and internal rotation. In this example, as the volleyball player approaches the net and begins to load her lower extremity to prepare for jumping, she steps in an uneven sand hole which causes her heel to abruptly evert and her talus to plantarflex and adduct. This motion of the talus influences the tibia to internally rotate and abduct. This tibial motion, if not properly decelerated, will create excessive knee internal rotation, abduction, and flexion which can directly lead to a right ACL tear. However, this motion can be properly controlled and reduce the risk of injury by muscles properly decelerating the tibia and femur. The specific tri-plane action of muscles that influence the knee are too numerous to adequately describe in this article and, therefore, will be discussed in an upcoming newsletter.

A second practical example can illustrate a situation when dysfunction at the hip is the underlying cause of patella femoral pain. Recent research has confirmed Gary Gray’s long held belief that patella femoral pain is more a track problem (femur) than a train problem (patella). Dr. Chris Powers, et al, summarized that “patellofemoral joint kinematics during weight-bearing conditions could be characterized as the femur rotating underneath the patella.”1 In another study, Dr. Powers, et al, goes on to assert that “interventions aimed at controlling hip and ankle motions may be warranted and should be considered when treating persons with patellofemoral joint dysfunction.”2

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A forty-year-old triathlete with excessive femoral internal rotation during the loading phase of gait presents lateral right knee pain while running. His knee pain can be explained by the inability of the hip external rotators, adductors, and hamstring muscles to decelerate the excessive femoral motion. The track crashing toward midline too rapidly, in effect, causes the train to derail laterally. The symptoms are present at the knee; however, through use of lower extremity chain reaction biomechanics, one can easily understand how the cause is at the hip.

These examples illustrate a few core principles of Applied Functional Science. First, joints in the body move in three planes of motion. Second, function is driven by, among other things, ground reaction force, the environment, and gravity. Third, movement at one joint will create chain reaction responses at other joints throughout the body. Lastly, function is individualized and task-specific.

Applied Functional Science requires us to understand the person, tasks, and goal(s). A thorough understanding of the chain reaction biomechanics of all three joints will assist in implementing rehabilitation and training programs that ensure that, although still caught in the middle, the knee now has two powerful friends by its side. ——-By Brett Bloom

Gray G: Functional Video Digest. Functional Manual Reaction. The Knee. v3.7

Gray G: Functional Video Digest. Patella Femoral. The Train & The Track. v2.5

1. Powers CM, Ward SR, Fredericson M, Guillet M, Shellock FG. Patellofemoral kinematics during weightbearing and non-weightbearing knee extension in persons with patellar subluxation: A preliminary study. J Orthop Sports Phys Ther. 33:677-685, 2003.

2. Powers CM. The influence of altered lower extremity kinematics on patellofemoral joint dysfunction: A theoretical perspective J Orthop Sports Phys Ther. 33:639-646, 2003

Get Strong! Stay Strong!

Chris

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