Knee Joint Dynamics

Author: Gordana Sendić, MD ' Reviewer: Declan Tempany, BSc (Hons)
Last reviewed: October 30,
Reading time: 26 minutes

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The knee joint, scientifically termed as Articulatio genu, acts as a pivotal point connecting three primary bones: the femur, tibia, and patella. This complicated hinge joint is classified into two distinct articulations: the tibiofemoral joint and patellofemoral joint. The tibiofemoral joint occurs where the femur and tibia meet, while the patellofemoral joint involves the connection between the patella and femur.

As the largest joint within the human body, the knee joint experiences significant mechanical stress in daily activities. Its unique bone structure serves to transform flexor and extensor muscle actions into precise movements. The stability of the joint is maintained by a combination of extracapsular and intracapsular ligaments, along with muscles that traverse the joint, effectively countering the various mechanical loads encountered. Although it primarily facilitates movement along a single axis through flexion and extension, the knee also permits slight medial rotation during flexion, slight lateral rotation during "unlocking," and some rotation at full extension.

Understanding the Articular Surfaces

Exploring the Tibiofemoral Joint

The tibiofemoral joint connects the lateral and medial condyles of the distal femur with the tibial plateaus, both surfaces cushioned by a layer of hyaline cartilage. The femur's medial and lateral condyles, characterized by smooth convex surfaces, form a structure with a distinct intercondylar fossa separating them. The tibial plateaus are the concave surfaces at the proximal end of the tibia, accommodating the condyles and supporting weight distribution.

The medial tibial surface is oval-shaped, contrasting with the more circular shape of its lateral counterpart. These joint surfaces are inherently incongruent, thus menisci play a critical role in distributing femoral pressure effectively across the tibial surfaces.

Diving into the Patellofemoral Joint

The patellofemoral joint is classified as a plane joint formed by the patellar surface of the femur and the patella's posterior surface. The patella, a sesamoid bone, is secured by the quadriceps tendon and features articulating surfaces with concave distinction. This joint plays a fundamental role in biomechanical function, optimizing the quadriceps femoris muscle's mechanical advantage through a larger moment arm.

The Joint Capsule

The knee joint capsule comprises a combination of tendons and ligaments that encircle the joint, thus providing a degree of stability. The capsule is relatively thin and strategically connects to the femoral and tibial surfaces. Notable features include a gap for the popliteus tendon and fluid-filled bursae, such as the suprapatellar, prepatellar, and infrapatellar bursae, which mitigate friction during knee motion.

Knee Joint Ligaments and Menisci

Ligaments in the knee are classified as either extracapsular or intracapsular. Extracapsular ligaments, such as the patellar ligament and collateral ligaments, exist outside the joint capsule to stabilize and prevent dislocation. Conversely, intrcapsular ligaments, primarily cruciate ligaments, reside within the joint capsule.

Patellar Ligament Recognition

The patellar ligament extends from the apex of the patella to the tibial tuberosity, playing a crucial role in stabilizing the patella and facilitating knee movements.

Understanding the Collateral Ligaments

The fibular collateral ligament originates from the lateral epicondyle of the femur and secures to the fibular head, vital for knee stability during lateral forces. The tibial collateral ligament serves a similar purpose, rooting from the medial epicondyle of the femur and ensuring knee alignment.

Cruciate Ligaments Functionality

The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL), residing deep within the knee capsule, maintain joint stability during flexion and extension activities while preventing excessive movement.

Menisci Significance

These fibrocartilaginous "C" shaped structures enhance joint congruency and decrease shock. Menisci position under mechanical loads, with strategic attachments through ligaments aiding in stabilization and reducing shifting.

Innervation and Blood Supply of the Knee

The knee joint receives innervation primarily through the femoral nerve, while blood circulation is sustained through the genicular branches of various arteries, forming an extensive anastomosis to support the joint's metabolic needs.

Movement Dynamics of the Knee Joint

The knee joint facilitates flexion, extension, medial, and lateral rotations. The degree of movement can vary based on hip positioning, with passive flexion enabling additional range.

Muscles Influencing Knee Movement

Muscles working on the knee include the biceps femoris, semitendinosus, and rectus femoris, leading to effective knee flexion and extension, respectively. Their optimized engagement enables significant mobility and flexibility.

Clinical Significance of the Knee Joint

Due to its complex nature and frequent biomechanical stress, the knee joint is prone to various injuries. Common knee conditions include patellar tendinitis, ACL injuries, collateral ligament tears, and the unhappy triad, all of which can significantly impact movement and joint function.

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