Lynn SK and Noffal GJ. Frontal plane knee moments in golf: Effect of target side foot position at address. Journal of Sports Science and Medicine, 2010, 9:275-281.
This article studied the knee moments created during the golf swing in the frontal plane. The authors sought to determine the effects of modifying the foot position of the target (front) leg on the external moments (torque) on the target side knee. They studied 7 collegiate golfers hitting balls while standing with the front leg on a force plate. After a warm-up, each subject completed 5 swings with the target foot pointing straight ahead (perpendicular to target line) and 5 trials with the foot rotated 30 degrees towards the target. The order of foot positions was randomized.
Before this blog discusses the results, it is important to review knee biomechanics. External moments are torques (rotary forces) created by the movement of the body, gravity, ground reaction forces, and momentum. Motion in the frontal plane of the knee is often overlooked because it is not a motion that can be actively created in a non-weight-bearing position. Some books do not even discuss frontal plane motion of the knee. During functional weight-bearing activities, the knee goes through substantial motion in the frontal plane and is subject to large torques. Once the importance of frontal plane motion is recognized, the terms used to describe the motions can lead to confusion. Most movement practitioners know that when the knee moves inward toward the midline of the body that this position is called valgus. But the motion of the knee is called abduction because the foot is “away” from the midline. In the same way, when the knee moves outward away from the midline (varus position), this motion is called adduction because the foot is “in” relative to the knee and femur.
This study focused on the adduction moments created by the swing that cause the knee to bow out during the follow-through of the swing to the finish position. They measured the adduction moments in the two foot positions and found that the when the foot was rotated 30 degrees towards the target, the varus / adduction moments were decreased in every subject. The peak varus / adduction moment occurred slightly after ball strike. When all trials for all subjects were averaged, the reduction in knee moment was approximately 17%. The authors also compared the varus / adduction moment in golf to other studies that measured these torques in gait and climbing stairs. They noted that the knee moments in either foot position during the golf swing were greater than those experienced during the two activities of daily living.
So why does this article matter for function? First, it highlights the substantial torques on the knee in the frontal plane that can lead to knee injury and long term degeneration. Second, it raises the question: If the motion can’t be created actively by the patient / client, then what is the best way to assess the amount, control, and pain production during function? With regard to the golf swing (and many other activities) 3DMAPS® (3D Movement Analysis & Performance System) provides the most authentic way to assess knee motion in the frontal plane. The 6 Chain Reaction® Movements (also referred to as the Mobility Analysis Movements) of 3DMAPS® focus on the stance leg while motion is driven by the swinging arms and opposite leg lunges. The swinging arms create the top-down forces that drive knee motion while the foot is weight-bearing. The Same Side Lateral Chain Reaction® creates a valgus / abduction moment at the knee. The Opposite Side Lateral Chain Reaction® creates the varus / adduction moment. The frontal plane knee motion can be observed, and the presence of pain can be determined. The ability to control the movement is assessed using the Stability Analysis Movements. In addition, the contribution (or lack thereof) of the foot, hip, and trunk to the global movement can be identified. The 3DMAPS® Mobility and Stability Analysis Movements can be repeated with the foot rotated out to determine the effect on any pain or dysfunction the client might be experiencing.
Although this study was related to the golf swing, the importance of assessing the frontal plane motion at the knee with an authentic global movement cannot be overlooked for all our patients / clients, regardless of their functional status and desired activity.