Knee joint Lecture 7

The knee joint It is the largest joint in the body & one of the more complex joints in the body. Because it is supported and maintained entirely by muscles and ligaments with no bony stability Because it is frequently exposed to severe stresses and strains it should be no surprise that it is one of the most frequently injured joints in the body.

The knee joint ….. Joint type??? synovial hinge joint From 0 degrees of extension there are approximately 120 to 135 degrees of flexion. Joint type??? synovial hinge joint flexion and extension (0 degrees - 120 to 135 degrees of flexion). Modified hinge ????!!! Rotation  accessory motion !!! knee joint is not a true hinge because it has a rotational component. This rotation is not a free motion but an accessory motion that accompanies flexion and extension.

The knee joint ….. Roll Slide Spin All three types of arthrokinematic motions are used during knee flexion and extension ??!!!!!!! The articular surface of the femoral condyles is much greater than that of the tibial condyles. the articular surface of the femoral medial condyle is longer than that of the lateral condyle. Roll Slide Spin

The convex femoral condyles move on the concave tibial condyles, or the other way around depending upon whether it is an open- or closed-chain activity. If the femur rolled on the tibia from flexion to extension, the femur would roll off the tibia before the motion was complete. Therefore, the femur must glide posteriorly on the tibia as it rolls into extension. It should also be noted that the articular surface of the femoral medial condyle is longer than that of the lateral condyle. As extension occurs, the articular surface of the femoral lateral condyle is used up while some articular surface remains on the medial condyle. Therefore, the medial condyle of the femur must also glide posteriorly to use all of its articular surface. It is this posterior gliding of the medial condyle during the last few degrees of weight-bearing extension (closed chain action) that causes the femur to spin (rotate medially) on the tibia.

screw-home mechanism Looking at the same spin, or rotational, movement during non–weight-bearing extension Open-chain action (Non-weight-bearing)  the tibia rotates laterally on the femur  lock the knee in extension  With the knee fully extended, an individual can stand for a long time without using muscles. The knee must be “unlocked” by the femur rotating laterally on the tibia for knee flexion to occur. It is this small amount of rotation of the femur on the tibia, or vice versa, that keeps the knee from being a true hinge joint. Because this rotation is not an independent motion, it will not be considered a knee motion.

screw-home mechanism

The patellofemoral joint The posterior surface of the patella is smooth and glides over the patellar surface of the femur. It is the articulation between the femur and patella.

Patella increase the mechanical advantage (to protect the knee joint)  lengthening the moment arm  By placing the patella between the quadriceps tendon and the femur, the action line of the quadriceps muscles is farther away. Hence, the moment arm is lengthened, which allows the muscle to have greater angular force. Without the patella, the moment arm would be smaller and much of the force of the muscle would be a stabilizing force directed back into the joint. The patella’s main functions are to increase the mechanical advantage of the quadriceps muscle and to protect the knee joint. An increased mechanical advantage is achieved by lengthening the moment arm. By placing the patella between the quadriceps tendon (also called the patellar tendon) and the femur, the action line of the quadriceps muscles is farther away. Hence, the moment arm is lengthened, which allows the muscle to have greater angular force. Without the patella, the moment arm would be smaller and much of the force of the muscle would be a stabilizing force directed back into the joint.

The Q angle ( patellofemoral angle) is the angle between the quadriceps muscle, primarily the rectus femoris muscle, and the patellar tendon. It is determined by drawing a line from ASIS ??!!!to the midpoint of the patella and from the tibial tuberosity to the midpoint of the patella.  The angle formed by the intersecting of these lines represents the Q angle Although the rectus femoris attaches to the anterior inferior iliac spine (AIIS), the ASIS lies just above the AIIS and is easier to palpate.

This angle ranges from 13 to 18 degrees in normal individuals in knee extension, and tends to be greater in females!!! Why???!!! A greater angle in females is associated with the fact that females tend to have a wider pelvis. - biomechanics of patellofemoral joint are effected by patellar tendon length & the Q angle;     - q angle is increased by:            - genu valgum            - increased femoral anteversion            - external tibial torsion            - laterally positioned tibial tuberosity            - tight lateral retinaculum

Ligaments and other structures The knee is held together not by its bony structure but by ligaments and muscles. Knee Ligaments: - The cruciate ligaments - The collateral ligaments

The cruciate ligaments (cruciate means “resembling a cross” in Latin). Intra-capsular ligaments. Located between the medial and lateral condyles, the cruciates cross each other obliquely.  Anterior cruciate ligament  Posterior cruciate ligament The cruciates provide stability in the sagittal plane They are named by their attachment on the tibia. The anterior cruciate ligament attaches to the anterior surface of the tibia in the inter-condylar area just medial to the medial meniscus. It spans the knee laterally to the posterior cruciate ligament and runs in a superior and posterior direction to attach posteriorly on the lateral condyle of the femur.

Anterior cruciate ligament The posterior cruciate ligament attaches to the posterior tibia in the inter-condylar area and runs in a superior and anterior direction on the medial side of the anterior cruciate ligament. It attaches to the anterior femur on the medial condyle. To summarize these attachments, the anterior cruciate runs from anterior tibia to posterior femur, and the posterior cruciate runs from posterior tibia to anterior femur. It keeps the femur from being displaced posteriorly on the tibia/ the tibia from being displaced anteriorly on the femur It tightens during extension, preventing excessive hyperextension of the knee. When the knee is partly flexed, the anterior cruciate keeps the tibia from being moved anteriorly.

posterior cruciate ligament It keeps the femur from being displaced anteriorly on the tibia/ the tibia from being displaced posteriorly on the femur. It tightens during flexion and is injured much less frequently than the anterior cruciate ligament.

Collateral ligaments The collateral ligaments provide stability in the frontal plane. - Medial collateral ligament - Lateral collateral ligament

On the lateral side is the lateral collateral, or fibular collateral, ligament. It is a round, cordlike ligament that attaches to the lateral condyle of the femur and runs down to the head of the fibula, independent of any attachment to the lateral meniscus. It protects the joint from stresses to the medial side of the knee. It is quite strong and not commonly injured Collateral ligamnets Located on the sides of the knee are the collateral ligaments. The medial collateral (tibial collateral) ligament is a flat, broad ligament attaching to the medial condyles of the femur and tibia. Fibres of the medial meniscus are attached to this ligament, which contributes to frequent tearing of the medial meniscus when there is excessive stress to the medial collateral ligament.

Medial collateral ligament Tibial collateral ligament The medial collateral ligament, providing medial stability, prevents excessive motion from a blow to the lateral side of the knee.

Lateral collateral ligament Because their attachments are offset posteriorly and superiorly to the axis of flexion, the collateral ligaments become tight during extension, contributing to the stability of the knee, and slack during flexion. On the lateral side is the lateral collateral. It is a round, cordlike ligament that attaches to the lateral condyle of the femur and runs down to the head of the fibula, independent of any attachment to the lateral meniscus. It protects the joint from stresses to the medial side of the knee. It is quite strong and not commonly injured Fibular collateral ligament. It provides stability to the medial side.

Knee Menisci Medial and lateral meniscus a meniscus (from Greek μηνίσκος meniskos, "crescent"[1]) is a crescent- shaped  fibrocartilaginous structure that, in contrast toarticular disks, only partly divides a joint cavity. It usually refers to either of two specific parts of cartilage of the knee: The lateral and medial menisci. Both are cartilaginous tissues that provide structural integrity to the knee when it undergoes tension and torsion. The menisci are also known as 'semi-lunar' cartilages — referring to their half-moon "C" shape — a term which has been largely dropped by the medical profession, but which led to the menisci being called knee 'cartilages' by the lay public. The meniscus (plural: menisci, from the Greek for "crescent") is the curve in the upper surface of a liquid close to the surface of the container or another object, caused by surface tension. It can be either convex or concave. A convex meniscus occurs when the molecules have a stronger attraction to each other (cohesion) than to the material of the container (adhesion)  Medial and lateral meniscus They are two half moon, wedge-shaped fibrocartilage disks located on the superior surface of the tibia and are designed to absorb shock. Because they are thicker laterally than medially and the proximal surfaces are concave, the menisci deepen the relatively flat joint surface. The medial meniscus, perhaps because of its attachment to the medial collateral ligament, is more frequently torn.

Knee Menisci

Knee Bursa The purpose of a bursa is to reduce friction, and approximately 13 are located at the knee joint. They are needed because the many tendons located around the knee have a relatively vertical line of pull against bony areas or other tendons.

Knee Bursa

Knee Bursa

The Popliteal space The popliteal space is the area behind the knee, and it contains important nerves (tibial and common peroneal) and blood vessels (popliteal artery). This diamond-shaped fossa is bound superiorly on the medial side by the semitendinosus and semimembranosus muscles and by the biceps femoris muscle on the lateral side. The inferior boundaries are the medial and lateral heads of the gastrocnemius muscle.

The Popliteal space

The pes anserine It is a muscle group is made up of the (SGS)!!! The pes anserine (Latin, meaning “goose foot”) It is a muscle group is made up of the (SGS)!!!   They all cross the knee posteriorly and medially, then join together to have a common distal attachment on the anterior medial surface of the proximal tibia. Orthopedic surgeons sometimes alter this common attachment to provide for medial stability to the knee.

Muscles of the knee:

The quadriceps muscles!!!!

The popliteus muscle The gracilis and sartorius muscles span the knee medially, contributing greatly to medial stability. The gastrocnemius and hamstring muscles provide posterior stability both medially and laterally, and the quadriceps muscles provide anterior stability.   is a one-joint muscle located posteriorly at the knee in the popliteal space deep to the two heads of the gastrocnemius muscles. It originates on the lateral side of the lateral condyle of the femur and crosses the knee posteriorly at an oblique angle to insert medially on the posterior proximal tibia. Because it spans the knee posteriorly, it flexes the knee. It is credited with “unlocking” the knee, or initiating knee flexion.  

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