Ch19: Knee Joint Flashcards
The knee is supported and maintained entirely by…
Muscles and ligaments with no bony stability, and it frequently is exposed to severe stresses and strains. Therefore, it should be no surprise that it is one of the most frequently injured joints in the body.
What is the largest joint in the body?
The knee, and it is classified as a synovial hinge joint
What are the possible motions at the knee?
Flexion and Extension (accessory rotation)
From 0 degrees of extension, there are approximately how many degrees of flexion?
120 to 135
Genu Recurvatum
Beyond 5 degrees of hyperextension (Due to some ligament laxity, the knee may have a few degrees of hyperextension beyond 0)
Unlike the elbow, the knee joint is not a true hinge, because it has…
A rotational component. This rotation is not a free motion but rather an accessory motion that accompanies flexion and extension.
Knee joint (lateral view)
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Knee motions (lateral view)
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Flexion vs. Extension End-Feel
- Knee Flexion= Soft End Feel (soft tissue approximation) due to the contact between the muscle bellies of the thigh and leg.
- Knee Extension= Firm End Feel (soft tissue stretch) due to tension of the joint capsule and ligaments.
All three types of arthrokinematic motion occur during…
Knee Flexion and Extension (glide, roll, spin)
The convex femoral condyles move on the concave tibial condyles or vice versa depending on whether its…
An open- or closed-chain activity.
The articular surface is greater on which condyles and longer on which?
- The femoral condyles articular surface is much greater than that of the tibial condyles
- The articular surface of the medial femoral condyle is longer than that of the lateral femoral condyle
How do the femur and tibia move about each other during closed chain extension?
The femur must glide posteriorly on the tibia as it rolls into extension. As extension occurs, the articular surface of the lateral femoral condyle is used up while some articular surface remains on the medial femoral condyle Therefore, the medial condyle of the femur must also glide posteriorly to use its entire articular surface. It is this posterior gliding of the medial femoral condyle during the last few degrees of weight-bearing extension (closed-chain action) that causes the femur to spin (rotate medially) on the tibia.
How do the femur and tibia move about each other during open-chain extension?
With same spin, or rotational, movement during non–weight-bearing extension (open-chain action), the tibia rotates laterally on the femur. These last few degrees of motion lock the knee in extension; aka the screw-home mechanism of the knee. With the knee fully extended, an individual can stand for a long time without using muscles.
How do the femur and tibia move about each other in flexion?
For knee flexion to occur, the knee must be “unlocked” by laterally rotating the femur on the tibia. This small amount of rotation of the femur on the tibia, or vice versa, 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.
Arthrokinematic movements of the knee joint surfaces in a closed-chain activity of knee extension in which the femur moves on the tibia (medial view).
(A) Pure rolling of the femur would cause it to roll off the tibia as the knee extends. (B) Normal motion of the knee demonstrates a combination of rolling, gliding (posteriorly), and spinning (medially) in the last 20 degrees of extension.
The knee has a convex-on-concave relationship in what chain?
Closed Chain
The knee has a concave-on-convex relationship in what chain?
Open Chain where the concave tibial condyles glide posteriorly with flexion, and anteriorly with extension, while the distal end of the tibia moves in the same direction
Open Packed Position of the Knee
25 degrees, that is the position where most joint play is available.
A mobilizing force applied to the proximal tibia in an anterior direction will facilitate…
Knee extension, whereas a posterior glide will promote flexion.
Patellofemoral Joint
The articulation between the femur and patella; The smooth, posterior surface of the patella glides over the patellar surface of the femur.
The Main Functions of the Patella
Involve increasing the mechanical advantage of the quadriceps muscle and protecting the knee joint. An increased mechanical advantage is achieved by lengthening the quadriceps moment arm.
Moment Arm (patella)
The perpendicular distance between the muscle’s line of action and the center of the joint (axis). By placing the patella between the quadriceps, or patellar tendon, and the femur, the action line of the quadriceps muscles is farther away. Hence, the moment arm lengthens, allowing the muscle to have greater angular force. Without the patella, the moment arm would be shorter and much of the muscle’s force would be a stabilizing force directed back into the joint.
Screw-home motion of the left knee.
In the weight-bearing position (closed-chain activity), the femur rotates medially on the tibia as the knee moves into the last few degrees of extension. xxx