Biomechnics unit 3 Biomech of the lower limb - deck 4

Question 1

State one of the principle functions of the lower limb

Answer 1

Locomotion (walking and running)

Question 2

Define what is meant be the term gait

Answer 2

The manner or style of locomotion (walking and running)

Question 3

What is the name used to describe the gait used for walking ?

Answer 3

Reciprocal gait (fig. A)

Question 4

Describe what happens during a reciprocal gait

Answer 4

The lower limbs are used alternatively to provide support and propulsion.

Question 5

When are other gait patterns used ?

Answer 5

When reciprocal gait is not possible

Question 6

Give an example of a gait pattern someone may use when a reciprocal gait pattern is not possible and describe the gait pattern

Answer 6

Swing-through gait (Fig. B)

1. In swing-through gait, crutches are used for support and both legs swing through the crutches landing ahead of the crutches
2. The crutches are then moved forward and the process is repeated

e.g. used when someone has a broken femur

Question 7

Define what gait analysis is

Answer 7

This is the clinical examination of a patients gait

Question 8

A wide variety of parameters of gait can be studied, what will the chosen parameters to be studied depend on ?

Answer 8

The pathology of the patient and the aims of the examination.

Question 9

Give some examples of the purpose of using gait analysis

Answer 9

1. To determine the surgical intervention required e.g. to improve the gait of a child with cerebral palsy.
2. To quantify the severity of a disorder
3. To determine the outcome of an operation e.g. after a joint replacement.
4. To ensure the best alignment of a prosthesis e.g. an artificial leg to ensure that the gait of an amputee is as comfortable, as energy efficient and as cosmetically acceptable as possible.

Question 10

What are the different ways in which someones gait can be analysed?

Answer 10

1. An experienced examiner may simply watch the patient walking back and forth +/ - Video taping of the patient walking back and forth
2. Nowadays - gait laboratories equipped with motion analysis systems, force plates and electromyography equipment

Question 11

What is one of the problems with performing gait analysis with experienced examiner simply watching the patient walk back and forth and state how this problem can be avoided?

Answer 11

• If the patient is elderly or suffering from some disorder they may become tired very quickly
• To avoid this a video recording may be used so that the examiner may replay the tape and even slow down the tape to make the observation easier.

Question 12

What does the technique of an experienced examiner and video taping of someones gait rely on and what cannot be done using these gait analysis tehcniques ?

Answer 12

Both these techniques rely on the experience of the examiner and neither gives any quantitative data which may be compared to data collected from able-bodied persons

Question 13

What does the equipment in gait laboratories allow to be studied along with studying a patients gait ?

Answer 13

Other common activities of daily living such as standing up and sitting down as well as movements performed in a variety of sporting activities.

Question 14

Describe how motion analysis systems work

Answer 14

• These systems use cameras that only see special markers which are placed over prominent parts of the patient’s body (shown in fig.)
• The motion analysis system is able to calculate the position of each marker in three dimensions and using all the markers the movement of the patient can be reconstructed by computer.

Question 15

How many cameras does each marker placed on the patient in a motion analysis system need to be seen by to allow the system to calculate the position of each marker in three dimensions?

Answer 15

Two or more

Question 16

What does the motion analysis system enable the examiner to do?

Answer 16

• To view the patient from any angle they wish, say from the side and the front at the same time
• To obtain quantitative data (such as the joint angles) which they can compare to a database of data collected from able-bodied persons.

Question 17

What 2 other pieces of equipement are motion analysis systems often integrated with ?

Answer 17

1. Force plates
2. Electromyogrpahy

Question 18

What do force plates measure ?

Answer 18

Ground reaction forces

Question 19

What does electomyogrpahy measure ?

Answer 19

Muscle activity

Question 20

To understand and analyse reciprocal gait what is the walking pattern divided into?

Answer 20

The gait cycle

Question 21

Define what the gait cycle is

Answer 21

It is one stride which is equal to two steps; one taken by each lower limb

Question 22

State what is the start and end of one gait cycle

Answer 22

It starts with the initial contact of one foot on the ground, termed heel contact, and ends with the next heel contact of the same foot.

Question 23

Define what the stance phase is during the gait cycle

Answer 23

This is when one of the feet is in contact with the ground for part of the gait cycle (during walking there is always one foot in contact with the ground)

Question 24

Define what the swing phase is during the gait cycle

Answer 24

This is the part of the gait cycle when the foot has lost contact with the ground

Question 25

Define what the double support part of the gait cycle is

Answer 25

This is a period of time when both feet are in touch with the ground during walking

Question 26

As the speed of locomotion is increased what happens to the duration of the double support part of the gait cycle ?

Answer 26

Its duration decreases until eventually there is no period of double support.

Question 27

What marks the transition from running to walking ?

Answer 27

When there is no period of double support ==> During running there is a period when neither foot is in contact with the ground.

Question 28

Reciprocal gait is characterised by a number of events which occur sequentially during the gait cycle, state these events in order

Answer 28

For this I start with the left foot as the pic shows that:

1. Left heel contact
2. Left foot flat
3. Left mid stance
4. Left heel off
5. Left toe off
6. Left mid swing

Note heel contact until toe off is the stance phase

Toe off to heel contact again is the swing phase

Question 29

What may cause one or two events may be missing, or the order that they occur may be changed in the gait cycle of someone and give an example

Answer 29

• A person with a disorder e.g. someone who has suffered a mild stroke or has weak dorsiflexor muscles may suffer from foot drop.
• In foot drop, the foot hangs down during the swing phase, so that the toes will make contact with the ground before the heel

(Fig shows foot during swing phase with toes making contact).

Question 30

Describe the typical variation of joint angles in the hip, knee and ankle during a normal reciprocal gait cycle in the sagittal plane (as this is the plane most motion in these joints occurs)

Answer 30

• The range of motion at the hip joint varies from around 15 degrees extension to 30 degrees flexion
• The range of motion is greatest at the knee joint, where it varies from a few degrees of extension to around 70 degrees of flexion.
• The range of motion at the ankle joint is less than at the hip and knee joints. It varies from around 15 degrees of plantarflexion (extension) to 10 degrees of dorsiflexion (flexion)

Question 31

List some of the factors which causes variation in the joint angles during a normal reciprocal gait cycle

Answer 31

1. Varies from person to person
2. Also varies with speed
3. The ground surface (compare walking on sand and on concrete)
4. Type of footwear

Question 32

During the reciprocal gait cycle during what part of the gait cycle does the peak amount of flexion and extension of the hip occur ?

Answer 32

• Peak hip extension occurs shortly before toe off as the leg is left trailing behind
• Peak hip flexion occurs shortly after midswing to ensure a long step

Question 33

During the reciprocal gait cycle during what part of the gait cycle does the peak amount of flexion of the knee occur ?

Answer 33

Peak flexion occurs during the swing phase as the knee is flexed to allow the foot to clear the ground as it swings past the other limb

Question 34

During the reciprocal gait cycle during what part of the gait cycle does the peak amount of dorsiflexion and plantarflexion of the ankle occur ?

Answer 34

• There are two main peaks of plantarflexion; the first occurs at foot flat and the second shortly after toe off.
• The peak amount of dorsiflexion occurs at around heel off as the foot is left trailing behind the rest of the body

Question 35

Describe what causes a ground reaction force

Answer 35

When the foot is in contact with the ground it exerts a force against the ground. The ground does not give way but exerts an equal and opposite force (Newton’s third law) which is called the ground reaction force

Question 36

In gait analysis what is the ground reaction force measured by ?

Answer 36

A force plate (also called a force platform)

Question 37

Is both feet placed on the force plate?

Answer 37

• No only one is
• The force plate is also level with the surrounding ground

Question 38

Does the ground reaction force during the stance phase (when foot is in contact with the ground) vary?

Answer 38

Yes both its magnitude and direction vary

Fig. shows this variation of the ground reaction force in the sagittal plane at different points of the gait cycle (all part of the stance phase), in what has appropriately become known as a butterfly diagram

Question 39

What is the appearance of a typical vertical ground reaction force against time graph and explain why it is this appearance

Note (this is vertical whereas the butterfly one this is in all different directions)

Answer 39

• It characteristically has a double hump appearance
• The first peak is due to the deceleration of body mass as the weight is transferred on to the foot and the second due foot pushing off the ground.

Question 40

How can the forces and moments acting at the joints during walking be calculated using a gait lab?

Answer 40

1. The position of the body is measured using a motion analysis system.
2. The external forces and moments acting on the foot are measured using a force plate.
3. The weight of each body segment may be determined from the patient’s own weight and standard anthropometric data.
4. The forces exerted by the muscles and the tension in the ligaments can be estimated using electromyography data and mathematical models.

Question 41

This pic shows a graph which can be calculated using the gait lab which shows the internal moments generated by the muscles on the joints

Why at the hip, after heel contact, is there a positive extension moment produced?

Answer 41

It is produced by the hip extensors to prevent the upper body falling forward.

Question 42

This pic shows a graph which can be calculated using the gait lab which shows the internal moments generated by the muscles on the joints

Why at the knee, just after heel contact, is there a small flexion moment?

Answer 42

As the hamstrings contract to prevent hyperextension of the knee. This changes to an extension moment as the quadriceps contract to prevent the knee from buckling.

Question 43

This pic shows a graph which can be calculated using the gait lab which shows the internal moments generated by the muscles on the joints

Why at the ankle joint does the plantarflexion moment increases to a peak just before toe off?

Answer 43

As the triceps surae contracts to push the foot up and off the ground.