Biomechnics unit 3 Biomech of the lower limb - deck 2

Question 1

What is the largest and perhaps most complex joint in the human body?

Answer 1

The knee joint

Question 2

What 2 articulations is the knee joint comprised of ?

Answer 2

1. The tibiofemoral (between the proximal surface of the tibia and the distal surface of the femur)
2. The patellofemoral (between the patella and the distal surface of femur).

Question 3

Which of the two articulations of the knee joint allows most of the movement in the knee joint ?

Answer 3

• The tibiofemoral articulation
• The patellofemoral articulation acts in concert to assist this movement.

Question 4

What is the shape of the proximal surface of the tibia and what is this surface covered by ?

Answer 4

The proximal surface of the tibia is flat and covered with the menisci

Question 5

Describe the shape of the menisci of the knee and state what they are

Answer 5

They are two crescent shaped pieces of fibrocartilage

Question 6

What are the menisci attached to the proximal surface of the tibia by ?

Answer 6

Short tough ligaments

Question 7

What is the functions of the menisci of the knee ?

Answer 7

• 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

Question 8

What is the distal end of the femur formed by ?

Answer 8

It is formed by two circular-shaped condyles called the femoral condyles.

Question 9

What are the femoral condyles covered in ?

Answer 9

Articular cartilage

Question 10

What is the smooth anterior depression between the femoral condyles is called?

Answer 10

The trochlea

Question 11

As you move posteriorly around the femoral bone what does the trochlea develop into?

Answer 11

The trochlea develops into the deep posterior depression between the femoral condyles called the intercondylar notch.

Question 12

What is lodged in the intercondylar notch ?

Answer 12

The cruciate ligaments that help to bind the femur to the tibia,

Question 13

Define what a sesamoid bone is

Answer 13

This is a bone found in a tendon

Question 14

What is the largest sesamoid bone in the body ?

Answer 14

The patella (knee cap)

Question 15

Where is the patella bone located ?

Answer 15

It is located in the tendon of the quadriceps femoris muscle.

Question 16

Describe the posterior structure of the patella bone and state the functional relevance of this structure

Answer 16

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.

Question 17

Does the fibula form part of the knee joint ?

Answer 17

No

Question 18

What does the fibula act as an anchor for ?

Answer 18

The biceps femoris muscle and lateral collateral ligament.

Question 19

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 ?

Answer 19

No - they contribute very little stability

Question 20

What structures mainly provide stability of the knee joint ?

Answer 20

The ligaments - mainly the cruciate and collateral ligaments

Question 21

Within the knee joint what 2 ligaments are present ?

Answer 21

The anterior and posterior cruciate ligaments, they cross each other in the centre of the joint

Question 22

What is the function of the anterior and posterior cruciate ligaments ?

Answer 22

They limit forward and backward sliding of the femur on the tibia and limit hyperextension

Question 23

What is the knee joint surrounded by ?

Answer 23

A tough fibrous joint capsule which is thickened around the posterior on the medial and lateral sides.

Question 24

Where do the collateral ligaments of the knee lie ?

Answer 24

Outside the joint capsule on the medial and lateral sides

Question 25

What is the function of the medial and lateral collateral ligaments ?

Answer 25

• The medial collateral ligament prevents abduction
• The lateral collateral ligament prevents adduction

Question 26

What 2 other things contribute to the stability of the knee joint and especially during what movement?

Answer 26

The quadriceps muscle also aids stability as do the menisci, especially during rotation.

Question 27

Specifically what type of joint is the knee joint ?

Answer 27

A synovial type hinge joint

Question 28

Although the knee joint can be described as a hinge joint what subtle variations from normal hinge joints does it display ?

Answer 28

• 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)

Question 29

Why does the semicircular pattern of the knee joints centre of rotation moving arise ?

Answer 29

Because the femoral condyles are not perfectly circular and because of the restrictions imposed by the knee ligaments

Question 30

What do deformities of the knee joint surfaces cause the centre of rotation to do ?

Answer 30

To follow more complex patterns of movement (rather than the semicircle)

Question 31

When the rotation of the knee joint is studied in all three dimensions and not just in the sagittal plane what becomes apparent ?

Answer 31

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

Question 32

Describe the screw-home mechanism of motion as the knee flexes and extends

Answer 32

• As the knee flexes the tibia rotates internally
• As the knee extends the tibia rotates externally

Question 33

Why does the spiral motion of the screw-home mechanism of the knee joint occur ?

Answer 33

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)

Question 34

In addition to rotation, the knee joint also allows a limited amount of what type of movements ?

Answer 34

• Abduction and adduction
• Internal and external rotation.

Question 35

What articulation of the knee joint allows for its range of motion?

Answer 35

The tibiofemoral articulation

Question 36

In what planes does motion of the knee joint occur in ?

Answer 36

The greatest motion occurs in the sagittal plane, although motion in the other two planes does occur.

Question 37

State the range of motion of the knee joint in the sagittal plane and the type of movement which occurs

Answer 37

In sagittal plane flexion and extension occur

< 5 degrees of extension to about 140 degrees of flexion

Question 38

State the type of movement which occurs in the knee joint in the coronal plane and state the range of this motion

Answer 38

• In the frontal plane, abduction and adduction occur
• The maximum range is only a few degrees

Question 39

In the frontal/ coronal plane what is the range of motion dependent on ?

Answer 39

Dependent on how much the knee is flexed - knee flexion of 30 degrees allows for maximum range of abduction and adduction

Question 40

State the type of movement which occurs in the knee joint in the transverse plane and state the range of this motion

Answer 40

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.

Question 41

What is the range of motion of internal and external rotation of the knee dependent on?

Answer 41

On how much the knee is flexed - the range of motion increases with flexion

Question 42

At full extension what is the range of motion of rotation of the knee joint and why?

Answer 42

Rotation is almost completely restricted by the interlocking femoral and tibial condyles.

Question 43

At what degree of flexion is the range of motion of rotation of the knee joint at its max?

Answer 43

90 degrees of flexion

Question 44

At 90 degrees of flexion what is the range of motion of rotation of the knee joint ?

Answer 44

• External rotation ranges from 0 to about 45 degrees
• Internal rotation ranges from 0 to 30 degrees.

Question 45

Beyond 90 degrees of flexion what happens to the range of motion of the knee joint ?

Answer 45

The range of motion decreases

Question 46

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)

Answer 46

From full extension to about 115 degrees of flexion and about 10 degrees of rotation in the transverse plane