How the knee works: Education as a treatment tool
The knee is one of the most unstable joints in the body, and for good reason. Understanding knee mechanics will help you understand movement inefficiencies, the root cause of knee pain, and hang-ups limiting your performance. For more information on different types of knee pain, be sure to check out Dr. Miller’s Blog: Knee Pain: Getting to the Root of the Problem
Knee stability comes primarily from the ligaments and muscles that cross the joint. The knee is a relatively unstable joint. To visualize why it is unstable, compare it to the hip for example. The bony structures around the hip provide stability, versus the soft tissue surrounding the knee.
The knee is comprised of three joints: the tibiofemoral joint, the patellofemoral joint, and the proximal tibiofibular joint. For our purposes, we will talk about the two weight-bearing joints: the tibiofemoral and the patellofemoral. The tibiofemoral joint is composed of the femur (thigh bone) sitting on top of the tibia (shin bone) to create the main joint that allows knee movement. The patella (knee cap) sits in a groove of the femur to create the patellofemoral joint and provides an area for muscle attachment.
The tibiofemoral joint’s job is to transmit body weight and forces up and down between the femur and tibia allowing constant energy movement. As a hinge joint the tibiofemoral joint functions like a hinge on a door, “swinging” in one direction. This allows flexion movement (bending the knee) and extension (straightening the knee). The tibiofemoral joint has a small amount of rotational movement from the shapes of the contacting surfaces and some of the soft tissues that connect the two bones. The benefit to the rotational movement is a function called the “screw home” mechanism. The tibia rotates outward about 5 degrees in the last 15 degrees of knee straightening. This means when the knee is straightened all the way the foot points outward slightly. This mechanism occurs to take the load off the thigh muscles while standing- it conserves energy.
The patellofemoral joint function is to transmit tensile forces generated by the quadriceps (thigh muscles) to the patellar tendon (the thick band just below the knee cap). The patella glides in a groove of the femur as the knee bends and straightens. Injury most commonly occurs one of two ways. First, excessive force transmitted through the joint or surrounding soft-tissues cause injury. Alternatively the direction of glide changes for the patella, most commonly from muscle imbalance, which increases friction and therefore injury.
Common knee injuries to the tibiofemoral joint include a sprain or tear to the ligaments or damage to the cartilage, know as the meniscus. Ligament injuries include the ACL (anterior cruciate ligament), MCL (medial collateral ligament), or LCL (lateral collateral ligament). Ligaments, such as the ACL, are injured when they are over-stretched in the direction they usually stop or control movement. The ACL is one of the most well-known sports injuries. The ACL’s job is to help control forward slide of the femur on the tibia as well as stop rotation; therefore it is usually injured when the knee is forced into rotation or over-extending. The MCL is commonly hurt by a force driving the knee inward since it usually stops this movement. The LCL is the opposite of MCL and is injured when the knee is forced or pushed outward.
Meniscus damage can occur independently or in combination with ligaments. A single event can cause injury to the meniscus, as in many athletic injuries. Cartilage damage occurs just as frequently, however, when worn down, “frayed” or torn over years of poor movement mechanics.
The most common injuries related to the patellofemoral joint are inflammation of the patellar tendon (tendonitis) or the fluid-filled sacs that provide padding for the moving parts of the knee (bursitis). Injuries also commonly occur due to abnormal gliding of the knee cap in its groove on the femur, usually because of muscle imbalances.
Proper knee mechanics reduce risk of injury and pain
Proper knee mechanics are important to living life with healthy knees. Using correct form while performing everyday life activities, from getting up and down the stairs, or out of a chair to weight lifting, can decrease knee pain throughout your lifetime. Proper mechanics can help prevent injury- obviously incredibly important! But remember, don’t write off the pain or past injury you are living with as something you have to live with forever. Many times correcting improper patterns can resolve long-standing issues!
Want to know if you’re using correct form? Just ask us!
For a functional examination of how you move, contact our office. We love watching the way patients move, educating them on their movement patterns and identifying the cause, or potential risks for injury. Let us help you find ways to move and feel well.