Biomechnics unit 3 Biomech of the lower limb - deck 2 Flashcards
What is the largest and perhaps most complex joint in the human body?
The knee joint
What 2 articulations is the knee joint comprised of ?
- The tibiofemoral (between the proximal surface of the tibia and the distal surface of the femur)
- The patellofemoral (between the patella and the distal surface of femur).
Which of the two articulations of the knee joint allows most of the movement in the knee joint ?
- The tibiofemoral articulation
- The patellofemoral articulation acts in concert to assist this movement.
What is the shape of the proximal surface of the tibia and what is this surface covered by ?
The proximal surface of the tibia is flat and covered with the menisci
Describe the shape of the menisci of the knee and state what they are
They are two crescent shaped pieces of fibrocartilage
What are the menisci attached to the proximal surface of the tibia by ?
Short tough ligaments
What is the functions of the menisci of the knee ?
- They act as load distributors and shock absorbers. - primary functions
- The menisci also make the flat top of the tibia slightly concave which aids stability. - secondary function
What is the distal end of the femur formed by ?
It is formed by two circular-shaped condyles called the femoral condyles.
What are the femoral condyles covered in ?
Articular cartilage
What is the smooth anterior depression between the femoral condyles is called?
The trochlea
As you move posteriorly around the femoral bone what does the trochlea develop into?
The trochlea develops into the deep posterior depression between the femoral condyles called the intercondylar notch.
What is lodged in the intercondylar notch ?
The cruciate ligaments that help to bind the femur to the tibia,
Define what a sesamoid bone is
This is a bone found in a tendon
What is the largest sesamoid bone in the body ?
The patella (knee cap)
Where is the patella bone located ?
It is located in the tendon of the quadriceps femoris muscle.
Describe the posterior structure of the patella bone and state the functional relevance of this structure
The posterior surface of the patella has two smooth articular surfaces either side of a slight central ridge.
The two articular surfaces articulate with the respective femoral condyle. The ridge guides the patella along the groove between the femoral condyles as the knee joint flexes and extends.
Does the fibula form part of the knee joint ?
No
What does the fibula act as an anchor for ?
The biceps femoris muscle and lateral collateral ligament.
Like in the hip joint (ball and socket shape) does the shape of the boens of the knee contribute to the stability of the knee joint ?
No - they contribute very little stability
What structures mainly provide stability of the knee joint ?
The ligaments - mainly the cruciate and collateral ligaments
Within the knee joint what 2 ligaments are present ?
The anterior and posterior cruciate ligaments, they cross each other in the centre of the joint
What is the function of the anterior and posterior cruciate ligaments ?
They limit forward and backward sliding of the femur on the tibia and limit hyperextension
What is the knee joint surrounded by ?
A tough fibrous joint capsule which is thickened around the posterior on the medial and lateral sides.
Where do the collateral ligaments of the knee lie ?
Outside the joint capsule on the medial and lateral sides
What is the function of the medial and lateral collateral ligaments ?
- The medial collateral ligament prevents abduction
- The lateral collateral ligament prevents adduction
What 2 other things contribute to the stability of the knee joint and especially during what movement?
The quadriceps muscle also aids stability as do the menisci, especially during rotation.
Specifically what type of joint is the knee joint ?
A synovial type hinge joint
Although the knee joint can be described as a hinge joint what subtle variations from normal hinge joints does it display ?
- A hinge always rotates about the same axis (Fig A). This is not true for the knee joint - its axis of rotation changes as it flexes and extends.
- If the sagittal plane is considered then the centre of rotation of the knee joint moves in an approximate semicircle as shown in (Fig. B)
Why does the semicircular pattern of the knee joints centre of rotation moving arise ?
Because the femoral condyles are not perfectly circular and because of the restrictions imposed by the knee ligaments
What do deformities of the knee joint surfaces cause the centre of rotation to do ?
To follow more complex patterns of movement (rather than the semicircle)
When the rotation of the knee joint is studied in all three dimensions and not just in the sagittal plane what becomes apparent ?
That it is not a hinge joint with a moving axis of rotation. It has a screw-home mechanism, whereby it follows a spiral motion as it flexes and extends
Describe the screw-home mechanism of motion as the knee flexes and extends
- As the knee flexes the tibia rotates internally
- As the knee extends the tibia rotates externally
Why does the spiral motion of the screw-home mechanism of the knee joint occur ?
It is a consequence of the different sizes of the lateral and medial femoral condyles (in a normal knee the medial condyle is about 1.7 cm longer than the lateral condyle)
In addition to rotation, the knee joint also allows a limited amount of what type of movements ?
- Abduction and adduction
- Internal and external rotation.
What articulation of the knee joint allows for its range of motion?
The tibiofemoral articulation
In what planes does motion of the knee joint occur in ?
The greatest motion occurs in the sagittal plane, although motion in the other two planes does occur.
State the range of motion of the knee joint in the sagittal plane and the type of movement which occurs
In sagittal plane flexion and extension occur
< 5 degrees of extension to about 140 degrees of flexion
State the type of movement which occurs in the knee joint in the coronal plane and state the range of this motion
- In the frontal plane, abduction and adduction occur
- The maximum range is only a few degrees
In the frontal/ coronal plane what is the range of motion dependent on ?
Dependent on how much the knee is flexed - knee flexion of 30 degrees allows for maximum range of abduction and adduction
State the type of movement which occurs in the knee joint in the transverse plane and state the range of this motion
In the transverse plane, internal and external rotation occur
- At full extension, rotation is almost 0 due to the interlocking femoral and tibial condyles.
- The range of motion increases with flexion, reaching a maximum at about 90 degrees flexion where external rotation 45 degrees and internal rotation 30 degrees.
- Beyond 90 degrees of flexion the range of rotation decreases.
What is the range of motion of internal and external rotation of the knee dependent on?
On how much the knee is flexed - the range of motion increases with flexion
At full extension what is the range of motion of rotation of the knee joint and why?
Rotation is almost completely restricted by the interlocking femoral and tibial condyles.
At what degree of flexion is the range of motion of rotation of the knee joint at its max?
90 degrees of flexion
At 90 degrees of flexion what is the range of motion of rotation of the knee joint ?
- External rotation ranges from 0 to about 45 degrees
- Internal rotation ranges from 0 to 30 degrees.
Beyond 90 degrees of flexion what happens to the range of motion of the knee joint ?
The range of motion decreases
To perform common daily activities, such as walking, standing up and sitting down, ascending and descending stairs, and squatting down to lift an object from the floor - what range of motion in the sagittal and transverse planes is required?
(frontal/ coronal slightly irrelevant due to barley any movement in this plane)
From full extension to about 115 degrees of flexion and about 10 degrees of rotation in the transverse plane
