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
Patellofemoral joint (lateral view)
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Q Angle
Aka Patellofemoral angle; Angle between the quadriceps muscle (primarily the rectus femoris muscle) and the patellar tendon. Determined by drawing a line from the ASIS to the midpoint of the patella, and from the tibial tuberosity to the midpoint of the patella. Angle formed by the intersection of these lines represents the Q angle.
What is the normal range of the Q angle in knee extension?
Ranges from 13 to 19 degrees in normal individuals.
-The angle tends to be greater in females because the pelvis is generally wider in women.
What happens when Q angle is greater or smaller than normal range?
Many different knee and patellar problems, such as patellofemoral pain syndrome, are associated with Q angles greater or smaller than this range
What is the knee composed of?
The distal end of the femur articulating with the proximal end of the tibia.
Moment arm of the quadriceps muscles is greater with a patella…
(A), than without a patella (B) (lateral view).
Patellofemoral Compressive Forces During Flexion and Extension
- Open Packed Position for Patellofemoral Joint: When knee is fully extended, patella lies in its uppermost position, in shallowest portion of patellar surface of femur. With knee extended and leg muscles relaxed, it should be easy to manually glide the patella side-to side
- As knee flexes, patella is pulled downward by patellar tendon through its attachment to tibial tuberosity. In this lower position, the patella becomes quite stable as the depth of the patellar surface and amount of bony contact both increase.
- As knee flexion increases, manual glide of patella side-to side is no longer possible.
- In activities like a deep knee bend, the knee is flexing and quadriceps are eccentrically contracting. This compresses patella tightly against femur due to tension in the quadriceps and patellar tendons. Chronic compression can lead to patellofemoral pain.
Patella mobility during knee flexion/extension.
(A) with knee extended, patella can be moved side-to-side. (B) With knee flexed, side-to-side motion of patella is not possible
Q angle of the knee (anterior view)
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Head of the Femur
The rounded portion articulating with the acetabulum.
Neck of the Femur
The narrower portion located between the head and the trochanters.
Greater Trochanter of the Femur
Large projection located laterally between the neck and the body of the femur, providing attachment for the gluteus medius and minimus and for most deep rotator muscles.
Lesser Trochanter of the Femur
A smaller projection located medially and posteriorly, just distal to the greater trochanter; it provides attachment for the iliopsoas muscle.
Parts of the Femur
(right)
Body of the Femur
The long, cylindrical portion between the bone ends; also called the shaft. It is bowed slightly anteriorly.
Medial Femoral Condyle
Distal Medial End
Lateral Femoral Condyle
Distal Lateral End
Lateral Epicondyle of the Femur
Projection proximal to the lateral condyle
Medial Epicondyle of the Femur
Projection proximal to the medial condyle
Adductor Tubercle of the Femur
Small projection proximal to the medial epicondyle to which a portion of the adductor magnus muscle attaches
Linea Aspera of the Femur
Prominent longitudinal ridge or crest running most of the posterior length
Pectineal Line of the Femur
Runs from below the lesser trochanter diagonally toward the linea aspera. It provides attachment for the adductor brevis.
Patellar Surface of the Femur
Located between the medial and lateral condyle anteriorly. It articulates with the posterior surface of the patella.
Intercondylar Eminence of the Tibia
A double-pointed prominence on the proximal surface at about the midpoint, which extends up into the intercondylar fossa of the femur
Medial Tibial Condyle
Proximal medial end
Lateral Tibial Condyle
Proximal lateral end
Parts of the Tibia
(right)
Tibial Plateau
Enlarged proximal end, including the medial and lateral condyles and the intercondylar eminence
Tibial Tuberosity
Large projection at the proximal end on the anterior surface in the midline
Fibula
Lateral to, and smaller than, the tibia. It is set back from the anterior surface of the tibia, allowing a large space for muscle attachment. This feature gives the lower leg its rounded circumference.
-Not part of the knee joint because it does not articulate with the femur. Although it provides a point of attachment for some of the knee structures, it has a larger role at the ankle.
Patella
A triangular sesamoid bone within the quadriceps muscle tendon. It has a broad, superior border and a somewhat pointed distal portion.
Calcaneus
The most posterior of the tarsal bones and is commonly known as the heel. It is identified here because it provides attachment for the gastrocnemius muscle.
Parts of the Leg
Right Leg (lateral view)
What are the 2 main sets of ligaments that hold the knee together?
Cruciate and Collateral Ligaments
Cruciate Ligaments
Located within the joint capsule and are therefore called intracapsular ligaments. Situated between the medial and lateral condyles, the cruciates cross each other obliquely (cruciate means “resembling a cross” in Latin). They are named for their attachment on the tibia
Anterior Cruciate Ligament (ACL)
Attaches to the anterior surface of the tibia in the intercondylar area just medial to the medial meniscus. It spans the knee lateral to the posterior cruciate ligament, and it runs in a superior and posterior direction to attach posteriorly on the lateral condyle of the femur.
Posterior Cruciate Ligament (PCL)
Attaches to the posterior tibia in the intercondylar area, and it 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.
-Runs from the anterior tibia to the posterior femur, and the posterior cruciate runs from the posterior tibia to the anterior femur.
Parts of the Knee
(right knee in flexion)
Cruciate ligaments are named for their attachment on the tibia
(lateral view)
What plane do cruciate ligaments provide stability in?
Sagittal Plane
What does the ACL do?
The ACL keeps the femur from being displaced posteriorly on the tibia. Conversely, it keeps 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 ACL keeps the tibia from moving anteriorly.
What does the PCL do?
The PCL keeps the femur from displacing anteriorly on the tibia or the tibia from displacing posteriorly on the femur. It tightens during flexion and is injured much less frequently than the anterior cruciate ligament
What ligaments are located on the sides of the knees?
Medial Collateral Ligament and Lateral Collateral Ligament
Medial Collateral Ligament (MCL)
(aka tibial collateral ligament) Flat, broad ligament attaching to the medial condyles of the femur and tibia. Fibers of the medial meniscus are attached to this ligament, which contributes to frequent tearing of the medial meniscus during excessive stress to the medial collateral ligament.
Lateral COllateral Ligamet (LCL)
(AKA fibular collateral ligament) On the lateral side, this round, cordlike ligament 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 provides stability to the lateral side of the knee against medial-to-lateral forces (varus force).
What plane do the collateral ligaments supply stability in?
Frontal Plane
Parts of the Knee (superior view)
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Forces on the Knee Joint with Varus and Valgus Angles
- When the lower limb is aligned neutrally (Fig. B), the weight-bearing force passes through the midline of the knee joints.
- With genu varus (Fig. A), the weight-bearing line shifts medial to the knee, which compresses the articular surfaces on the medial side of the knee joint.
- With genu valgus (Fig. C), the compressive force moves to the lateral knee joint.
- Once the weight-bearing force shifts medially or laterally, the constant sideward force causes the varus or valgus angle to worsen over time. Greater angles lead to greater compressive forces, which can damage the articular cartilage. Abnormal stresses to the knees will also alter the stresses placed upon the ankle and hip joints.
Muscles that cross the Knee
Bursae around the knee joint (medial view).
Muscular boundaries of the right popliteal space (posterior view).
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Three muscle attachments of pes anserine (medial view).
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Quadriceps muscle group (anterior view).
The three vasti muscles lie deep to the rectus femoris. The vastus medialis and lateralis attach proximally on the posterior femur but join the other two muscles to cross the knee anteriorly.
Hamstring muscle group (posterior view).
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Popliteus muscle (posterior view).
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Gastrocnemius muscle (posterior view)
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Lateral view of Muscle Action
(A) With a paralyzed quadriceps unable to pull the knee into extension, the body weight line falls behind the knee, causing flexion. However, a combined reverse muscle action of the gluteus maximus and gastrocnemius muscles makes knee extension possible during stance. (B) In the closed-chain position, they pull the knee into extension. The soleus assists by plantar flexing the dorsiflexed ankle into a neutral ankle position. This puts the body weight line in front of the knee and ankle axes and allows the knee to remain extended.
Biomechanical Analysis of Wall Slide Exercise
From a starting position (Fig. A) sliding down a wall moves the knee axis further away from the line of gravity for the body (Fig. B). This increases the resistance arm created by the weight of the body, requiring the quadriceps to produce more force to prevent excessive knee flexion. To meet this demand, the rectus femoris maintains a constant length-tension relationship by shortening at the hip and lengthening at the knee while the one-joint vasti muscles are lengthened over the knee. This brings the entire quadriceps group to optimal length where they can create a large amount of force.
Anterior knee muscles (superficial view).
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Anterior knee muscles (deep view).
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