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Check out this joint! The inner workings of the knee

The knee is a hinge joint and is the largest in the human body. It is made up of the femur and tibia, with a smaller fibula located to the outer aspect.

Inside of knee joint

Source: aclsolutions.com

The fibula functions largely as an attachment point for ligaments. The thigh musculature consists of the quadriceps and hamstring muscles, and the lower leg contains the popliteus and gastrocnemius muscles. Flexible meniscus fibro-cartilage supports the curved femoral faces on the relatively flat tibial plateau surfaces (pictured below, click to make larger).

Front view of the knee joint

Source: datlof.com

Tougher ligaments attach the two together and consist of the outer collaterals (medial and lateral ligaments) and the inner cruciates (anterior and posterior cruciates). (Pictured below, click to make larger).

Picture of knee joint showing anterior and posterior ligaments

Source: medicinenet.com

The bony configuration of the knee provides limited support for our weight-bearing demands, therefore a complex interaction of passive and active knee stabilizers create much of our knee stability. Examples of passive stabilizers include the collateral ligaments, cruciate ligaments, menisci and joint capsule (see above image). Active stabilizers are made up of quadriceps, hamstring and lower leg muscles (see image pictured below, click to make larger). The alignment from hip to ankle is also influential in terms of active stability.

Picture of front and back view of leg muscles

Source: fitnessanddefense.com

Finally, the kneecap or patella is the largest sesamoid bone in the body and it lies within the substance of the quadriceps tendon (see image below, click to make larger).

Diagram of patella in quadriceps tendon

Source: aclsolutions.com

In the action of the patellofemoral joint (the joint formed between the kneecap and the femur, pictured below) a main concern is the pull of the muscles off the pelvis and the final insertion of the extensor mechanism onto the upper tibia. Alignment differences between men and women, or even between certain individuals, make for varying degrees of “tracking problems” when it comes to the patella.

Picture of patellofemoral joint

Source: hughston.com

If you are suffering from issues with your knee, there is no degree of training that can change the passive stabilizers of your knee. Therefore, you will probably need evaluation by your doctor for major problems that occur around the collaterals, cruciates or meniscus cartilage within the knee joint. However a personal trainer with an eye for lower extremity alignment and a creative touch can help improve your knee performance by working on your active knee stabilizers. Another activity of great importance is improving flexibility within the knee, calf and ankle for overall knee function. Caution: The lower extremity is a kinetic chain so be aware that any particular change you make in your bottom half will affect others parts in it.

About Dr. Joe McCormick

Dr. Joe McCormick, orthopaedic surgeon, provides comprehensive orthopaedic surgery care with an emphasis in joint replacement, sports-related injuries, and pediatrics. He is a fellow of the American Academy of Orthopaedic Surgeons.

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