The knee is one of the largest and most complex joints in the body. The knee joins the femur to the tibia. The smaller bone that runs alongside the tibia is the fibula. The patella, also known as the knee-cap, is another one that makes up the knee joint. I decided to discuss this joint structure because of reoccurring knee injuries.
The Knee Joint
The knee joint is formed by the articulation of the distal end of the femur and the proximal end of the tibia. The fibula serves as an attachment site for connective tissue. The knee is a diarthrotic, hinge type joint. The two articulating ends of the tibia are encased in a capsule that lubricates the joint with synovial fluid to reduce friction. The C-shaped medial and lateral menisci serve to deepen the articulation at the superior surface of the joint. Adding to the joints stability are the two major pairs of ligaments: the cruciates and collaterals.(1) The knee is part of a chain that includes the pelvis, hip, and upper leg above, and the lower leg, ankle and foot below. All of these work together and depend on each other for function and movement.
The cruciates are name because of their cross-configuration within the joint. The anterior cruciate ligament attaches to the tibia on its anterior-superior surface, crossing through the joint from the medial side to its lateral attachment on the femur. The posterior cruciate ligament attaches on the posterior-superior aspect of the tibia, crossing diagonally and medially to its lateral attachment on the femur. These ligaments are vital in maintaining the anterior and posterior stability of the knee joint, as well as its rotary stability. The medial and lateral collateral ligaments have a stabilizing effect in the frontal plane of motion, helping to prevent sideward displacement and over rotation. The medial collateral attaches the femur to the tibia, also attaching the medial meniscus. The lateral collateral attaches the femur to the fibula but has no attachment to the lateral meniscus. The positioning of these ligaments causes slackness when flexion occurs, allowing medial and lateral rotation to take place.(2)
The knee doesn’t just bend and straighten when it moves. There is a slight rotational component in this motion. The knee muscles that go across the knee joint are the quadriceps and hamstrings. The quadriceps muscles are on the front of the knee, and the hamstrings are on the back of the knee. Flexion and extension occur in the sagittal plane of motion and internal and external rotation occurs in the horizontal plane of motion. The quadriceps muscles extend the leg at the knee and the hamstrings are primarily knee flexors.
The knee joint supports our body weight, functions to straighten or bend the lower leg, and absorbs shock. Pain free walking, squatting, and transferring require unrestricted movement. (3) The amount of movement in a joint is measured with a goniometer. Range of motion of the knee is 0 degrees of extension to 150 degrees of flexion. Functional activities require 0 to 117 degrees of motion at the knee. Common causes of decreased range of motion include arthritis, knee surgery and knee injuries. In order to prevent knee anomalies and maintain strength and flexibility in the knee joint, one should move freely and fully every day to maintain knee health and longevity.
The complexity of the knee joint and the fact that it is an active weight-bearing joint are factors in making the knee one of the most commonly injured joints. Injury can affect any of the ligaments, bursae, or tendons surrounding the knee joint. It can also affect the ligaments, cartilage, menisci and bones forming the joint. Trauma can cause injury to the ligaments on the inner portion of the knee, outer portion of the knee, or within the knee.(4) A collateral ligament injury is felt on the inner or outer portions of the knee; and is often associated with local...
References: Floyd R.T. Manual of Structural Kinesiology. 8th ed. The Knee Joint. New York: McGraw-Hill, 2012.
Grogan, Brianne. Normal Range of Motion of the Knee. August 16, 2013. Available at: http://www.livestrong.com/article/normal-range-motion-knee
Howley Edward T. and Powers Scott K. Exercise Physiology. 8th ed. Training for the Female Athlete, Children, Special Population, and the Masters Athlete. New York: McGraw-Hill, 2012.
Dahm, D. and Smith, J. MayoClinic. Fitness for Everybody. Rochester, MN: MayoClinic, 2005.
Waehner, Paige. Exercise 101-The Basic Principles of Exercise. February 16, 2012. Available at: http://www.Exercise.about.com/cs/exbeginners/a/exbasics.3.htm
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