Download unit 2 – biomechanics of the lower limb

UNIT 2 – BIOMECHANICS OF THE LOWER LIMB
Dr M J Dolan
Department of Orthopaedic & Trauma Surgery
University of Dundee
Dr T Drew
Department of Orthopaedic & Trauma Surgery
University of Dundee
SECOND EDITION
Edited by
Dr T Drew
Department of Orthopaedic & Trauma Surgery
University of Dundee
Illustrations by
Mr I Christie
Published by
Distance Learning Section
Department of Orthopaedic & Trauma Surgery
University of Dundee
Second Edition published 2005: ISBN 1-903562-47-3
ISBN 978-1-903562-47-5
First Edition published 1994: ISBN 1-899476-50-4
Copyright © 2005 University of Dundee. All rights reserved. No part of this publication may be
reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic,
mechanical, photocopying, and recording or otherwise, without prior permission from the publisher.
The University of Dundee is a Scottish Registered Charity, No SC01509.
UNIT 2 – BIOMECHANICS OF THE LOWER LIMB
CONTENTS
1. HIP JOINT
1.1 Range of Motion
1.2 Hip Joint Loading During Standing
1.3 Hip Joint Forces During Daily Activities
2. KNEE JOINT
2.1 Motion of the Knee
2.2 Range of Motion
2.3 Function of the Patella
2.4 Function of the Menisci
2.5 Knee Joint Forces During Daily Activities
3. ANKLE AND FOOT
3.1 Ankle Joint
3.2 Ankle Joint Motion
3.3 The Foot
3.4 Subtalar Joint
3.5 The Arched Structure of the Foot
4. MOMENTS ABOUT JOINTS
4.1 Gait Analysis
4.2 Gait Cycle
4.3 Range of Joint Movement
4.4 Ground Reaction Forces
4.5 Joint Forces and Moments
SUMMARY
SAQ ANSWERS
END OF UNIT EXERCISE
UNIT 2 – BIOMECHANICS OF THE LOWER LIMB
OBJECTIVES
On completing your study of this unit you should be able to:
1. Describe the structure of the hip joint.
2. Define the terms: ball-and-socket joint and circumduction.
3. Describe the motion and range of motion of the hip joint.
4. Explain why the force at the hip joint is increased so greatly during unilateral stance
compared with bilateral stance.
5. Describe the structure of the knee joint.
6. Describe the motion and range of motion of the knee joint.
7. Explain the function of the patella.
8. Explain the function of the menisci.
9. Describe the structure of the ankle and foot.
10. Describe the motion and range of motion of the ankle joint.
11. Describe the motion and range of motion of the subtalar joint.
12. Explain the function of the plantar fascia.
13. Discuss the relative stability of the lower limb joints.
14. Define the terms: gait, reciprocal gait and gait analysis.
15. List the equipment used in a gait laboratory.
16. Briefly describe the use of a motion analysis system.
17. Briefly describe the use of a force plate.
18. Describe the gait cycle.
19. List the phases and events of the gait cycle.
20. Draw a typical graph of the motion of the lower limb joints during reciprocal gait.
21. Explain the term: ground reaction force.
22. Draw a typical butterfly diagram and a graph of the vertical ground reaction force
against time.
23. Describe the moments acting at the joints of the lower limb during reciprocal gait.
UNIT 2 - BIOMECHANICS OF THE LOWER LIMB
In this unit we will be looking at the major joints of the lower limb and examining the
roles they play in walking. Walking is one of the most commonly executed human
activities and is also one of the most demanding. Orthopaedic and rehabilitation devices,
such as joint replacements, fracture fixation devices and lower limb prostheses and
orthoses, must be able to withstand the demands placed on them during walking. A
knowledge of these demands is therefore important to orthopaedic surgeons,
prosthetists, orthotists and the designers of orthopaedic and rehabilitation devices. In
particular, they must consider the range of joint motion required, the magnitudes of the
joint forces and moments, and the interface pressures between the device and the
patient, to ensure that the patient regains as much function as possible and that the
device does not break during use.
femoral head
innominate bone
thigh
femoral neck
femoral shaft
femur
patella
fibula
tibia
leg
foot
metatarsals
phalanges
FIGURE 1. THE LOWER LIMB.
The lower limb (Figure 1) consists of three segments: the thigh, the leg and the foot.
The thigh is formed by the femur, the leg by the tibia and fibula and the foot by the
tarsals, metatarsals and phalanges.
Three major joints allow these segments to move relative to one another and the pelvic
girdle. They are the hip, knee and ankle joints. These joints are synovial joints, held
together by muscles and ligaments. When considering the joints of the lower limb it is
important to remember that the joints are designed both for movement and for weight
bearing.
SAQ 1
(a) Name the three segments of the lower limb.
(b) Name the three major joints of the lower limb.
(c) State the two functions of the joints of the lower limb.
Unit 2 - Biomechanics of the Lower Limb
1
1. HIP JOINT
The hip joint is a ball-and-socket shaped synovial joint. A ball-and-socket joint
consists of the ball-shaped end of one bone fitted into a cup-shaped depression of
another bone (Figure 2B). In the hip joint, the ball consists of the head of the femur
which fits into the socket-shaped acetabulum of the pelvic girdle (Figure 2A). This
ball-and-socket shape allows the hip joint to rotate in three directions: flexion and
extension, abduction and adduction, and internal and external rotation. The ball-andsocket shape also allows the hip joint to circumduct, whereby the femur moves in a
circle relative to the pelvis. This movement is called circumduction (Figure 2C).
HIP JOINT
BALL-AND-SOCKET
CIRCUMDUCTION
abduction
acetabulum
head of femur
adduction
(B)
external
rotation
internal
rotation
flexion
extension
circumduction
(C)
(A)
FIGURE 2. (A) THE HIP JOINT (B) BALL-AND-SOCKET JOINT MOTIONS (C) CIRCUMDUCTION.
The hip joint is a synovial joint, as are the other very mobile joints of the body which
allow the major movements of the skeletal system. In synovial joints the surfaces of the
bones that form the joint are covered in articular cartilage; a low friction material.
Synovial joints are enclosed in a sleeve of tough fibrous tissue, the joint capsule, which
forms the synovial cavity (Figure 3). The synovial cavity is filled with synovial fluid
which lubricates the joint and provides nutrients to the articular cartilage. The synovial
fluid resembles egg white; it is this resemblance that gives synovial fluid its name
derived from the Latin for egg, ovum. The synovial fluid is produced by the synovial
membrane which lines the inner surface of the capsule.
bone
joint capsule
synovial fluid in
synovial cavity
articular cartilage
synovial membrane
bone
FIGURE 3. A SYNOVIAL JOINT.
Unit 2 - Biomechanics of the Lower Limb
2
SYNOVIAL JOINT
The hip joint is surrounded by a very strong articular joint capsule and several
ligaments. These are surrounded by several large, strong muscles. This arrangement is
intrinsically stable and allows for the wide range of movement required for common
daily activities such as walking, sitting and squatting. The stability of the hip joint
derives from its shape, the joint capsule and the surrounding ligaments and muscles.
Because of this stability dislocations of the hip are very rare in adults, and are usually
only seen after serious road traffic accidents when very large impact forces are applied.
SAQ 2
(a) What type of joint is the hip joint?
(b) What are the two functions of synovial fluid?
(c) Why is the hip joint intrinsically stable?
1.1 Range of Motion
The hip joint has a wide range of movement in all three planes (Figure 4). The range of
motion is greatest in the sagittal plane, where flexion and extension occur. Flexion
ranges from 0 to about 140 degrees and extension from 0 to 15 degrees. In the frontal
plane, abduction and adduction occur. Abduction ranges from 0 to 30 degrees and
adduction ranges from 0 to 25 degrees. In the transverse plane, external and internal
rotation occur. External rotation ranges from 0 to 90 degrees and internal rotation ranges
from 0 to 70 degrees when the hip is flexed. Less external and internal rotation is
possible when the hip is extended due to the restrictions of soft tissues. The hip joint can
also be circumducted.
5°
extension
25°
adduction
35°
flexion
30°
abduction
90°
external rotation
70°
internal rotation
FIGURE 4. RANGE OF MOTION OF THE HIP JOINT.
To perform common daily activities, such as walking, standing up and sitting down,
ascending and descending stairs, and stooping to pick up an object from the floor at
least 120º of flexion-extension and 20 degrees of abduction-adduction and rotation are
required. For example, standing up and sitting down in a chair requires about 110º of
flexion-extension, 20º of abduction-adduction and 15 degrees of rotation. In walking,
the most significant motion is in the sagittal plane with about 35 degrees of flexion and
5º of extension. Only about 12º of the motion is required in the other two planes.
Unit 2 - Biomechanics of the Lower Limb
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5°
110°
40°
120°
FIGURE 5. MAXIMUM HIP FLEXION-EXTENSION ANGLES DURING STANDING UP, WALKING AND LIFTING.
SAQ 3
(a) In which plane does the greatest range of motion of the hip joint
occur?
(b) Typically, what range of motion is required at the hip joint to
stand up and sit down?
1.2 Hip Joint Force During Standing
The force acting at the hip joint during standing can be calculated using simple
mechanics. In this section we will calculate the hip joint force during standing on both
feet (bilateral stance) and during standing on one foot (unilateral stance) (Figure 6). The
latter case illustrates the importance of muscle activity in determining the magnitude
and direction of joint forces. In both cases we will consider only the forces acting in the
frontal plane.
(A)
(B)
FIGURE 6. (A) BILATERAL STANCE (B) UNILATERAL STANCE.
1.2.1 Bilateral stance
During bilateral stance (Figure 6A) there are normally no muscles active at the hip joint.
Therefore to calculate the hip joint force we only need to consider the external forces
Unit 2 - Biomechanics of the Lower Limb
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present. There are only three external forces acting on the pelvis: the weight of the
upper body acting downwards and two reaction forces, one at each hip joint, acting
upwards (Figure 7).
WHAT
d = 14 cm d = 14 cm
R1
R2
FIGURE 7. FORCES ACTING ON THE PELVIS IN BILATERAL STANCE.
The weight of the upper body (the Head, Arms and Trunk - HAT). The upper body
makes up approximately 70% of total body weight, W. The remaining body weight is
made up by the two lower limbs at 15% each. Thus, for an individual weighing 800 N
the upper body weight, WHAT, can be calculated as follows:
WHAT = W ×
70%
= 800 × 0.70 = 560 N
100%
The width between the two hip joints can be measured. In this case we will use 28 cm.
The weight distribution is symmetrical thus the moment arm, d, about each hip is 14
cm.
To calculate the force acting at the left hip, RLEFT, we apply the second condition of
static equilibrium - the sum of all the moments is zero (Figure 8).
d
WHAT
RLEFT
right
hip
joint
2d
FIGURE 8. MOMENTS ABOUT THE RIGHT HIP JOINT CENTRE.
Summing the moments about the right hip joint centre (anti-clockwise is defined as
positive):
RLEFT × 2d – WHAT × d = 0
Rearranging the equation for RLEFT:
Unit 2 - Biomechanics of the Lower Limb
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RLEFT =
WHAT d WHAT 560
=
=
= 280 N
2d
2
2
Thus the force acting at the left hip joint is 280 N. We can find the force acting at the
right hip joint using the same method but instead of summing the moments about the
right hip joint the moments are summed about the left hip joint. Alternatively we can
use the first condition of static equilibrium - the sum of all the forces is zero (Figure 9).
WHAT
RRIGHT
RLEFT
FIGURE 9. FORCES ACTING ON THE PELVIS.
Summing all the forces (up is defined as positive):
RRIGHT + RLEFT – WHAT = 0
Rearranging the equation for RRIGHT:
RRIGHT = WHAT – RLEFT = 560 – 280 = 280 N
Thus the force acting at the right hip joint is 280 N. As you would expect this is the
same as the force acting at the left hip joint. From this analysis we can conclude that
during normal bilateral standing the forces acting at the hip joints are vertical and equal
to half the upper body weight.
1.2.2 Unilateral stance
During unilateral stance (Figure 6B) abductor muscle activity is required to stabilise the
position of the body. To calculate the hip joint force we will consider the forces acting
on the lower limb. There are four forces: the weight of the lower limb acting
downwards, the abductor muscle force, the joint force at the hip, and the ground
reaction force acting vertically upwards on the foot. To simplify the problem the
abductor muscles are grouped with a single insertion point on the greater trochanter of
the femur.
Activity: Stand on both feet and palpate the flesh between your greater trochanter
and pelvis. Whilst still palpating this area shift your weight on to that side so that you
are standing on one foot. You should be able to feel the underlying hip abductor
muscles (the glutei) contract to stabilise your position.
All the forces are shown in Figure 10 along with various dimensions of the lower limb.
A two-dimensional rectangular reference frame is used; the x-axis is defined as
horizontal going from the lateral to the medial sides of the lower limb, the y-axis is
defined as going vertically upwards, and for convenience the origin is at ground level
directly below the insertion of the abductor muscle group.
Unit 2 - Biomechanics of the Lower Limb
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y
A
Jy J
Ay
Jx
Ax
14 cm
11 cm
9 cm
mg
x
G
FIGURE 10. FREE BODY DIAGRAM OF LOWER LIMB DURING UNILATERAL STANCE.
The direction of the abductor muscle force, A, is known but not its magnitude. It is
acting at an angle of 70° to the horizontal. To simplify the calculations we will divide it
into its two components: one acts along the x-axis, Ax, and one along the y-axis, Ay.
The joint force, J, also has two components: one acts horizontally and laterally along the
x-axis, Jx; and one acts vertically downwards along the y-axis, Jy.
The ground reaction force is equal and opposite to the total body weight (Newton’s
third law - to every action there is an equal and opposite reaction). Thus for an
individual weighing 800 N the ground reaction force will also be 800 N.
Each lower limb makes up approximately 15% of total body weight, W. Thus, for an
individual weighing 800 N the weight of one of their lower limbs, WLL, can be
calculated as follows:
WLL = W ×
15%
= 800 × 0.15 = 120 N
100%
One of the unknown forces, the vertical component muscle force, acts through the
insertion point of the abductor muscles. Thus we can calculate the other unknown force
of the vertical component of the joint force, Jy, by summing all the moments about this
point (see Figure 11).
Unit 2 - Biomechanics of the Lower Limb
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dJ = 6 cm
Jy
dW = 11 cm
WLL
G = 800 N
dG = 20 cm
FIGURE 11. MOMENTS ABOUT THE INSERTION POINT OF THE ABDUCTOR MUSCLES.
Summing the moments about the insertion point of the abductor muscles (anticlockwise
is defined as positive):
-JydJ – WLLdW + GdG = 0
Rearranging the equation for Jy:
JydJ = GdG - WLLdW
Jy =
Gd G − WLL d W 800 × 0.2 − 120 × 0.11 160 − 13.2 146.8
=
= 2446.67 N
=
=
dJ
0.06
0.06
0.06
We can find the vertical component of the muscle force by summing all the forces in the
vertical direction (Figure 12).
Ay
Jy = 2446.67
WLL = 120 N
G = 800 N
FIGURE 12. VERTICAL FORCES ACTING ON LOWER LIMB.
Summing all the forces (up is defined as positive):
Ay – Jy – WLL + G = 0
Rearranging the equation for RRIGHT:
Ay = Jy + WLL – G = 2446.67 + 120 – 800 = 1766.67 N
Unit 2 - Biomechanics of the Lower Limb
8
Ay = A sin 70°
A
70°
Ax = A cos 70°
FIGURE 13. ABDUCTOR MUSCLE FORCE.
The magnitude of the abductor muscle force can be calculated using trigonometry
(Figure 13):
Ay = A sin 70°
Rearranging for A:
A=
Ay
sin 70°
=
1766.67
= 1880.05 N
0.939693
Thus the abductor muscle force acting to stabilise unilateral standing is around 1880 N.
This is approximately equal to 3.4 times the subject’s upper body weight (560 N).
SAQ 4 - Express the magnitude of abductor muscle force as a ratio of
the subject’s total body weight.
Using trigonometry we can also calculate the horizontal component of the abductor
muscle force:
Ax = A cos 70° = 1880.05 × 0.342020 = 643 N
We can now find the last remaining unknown force, the horizontal component of the
joint force, by summing the horizontal forces (Figure 14):
Rearranging for Jx:
Jx = Ax = 643 N
Ax
Jx
FIGURE 14. HORIZONTAL FORCES ACTING ON LOWER LIMB.
We now have values for the two components of the joint force. We can therefore
calculate the magnitude and direction of the joint force using trigonometry (Figure 15).
Unit 2 - Biomechanics of the Lower Limb
9
Jx
J
θ
Jy
FIGURE 15. HIP JOINT FORCE.
To calculate the magnitude we can use Pythagoras’ theorem:
J 2 = J 2x + J 2y
J = J 2x + J 2y = 643.015 × 643.015 + 2446.67 × 2446.67 = 2529.76 N
To calculate the direction:
tan θ =
Jy
Jx
Rearranging:
⎛ Jy
θ = tan-1 ⎜⎜
⎝ Jx
⎞
⎟ = tan-1 ⎛⎜ 2446.67 ⎞⎟ = 75°
⎟
⎝ 643.015 ⎠
⎠
The hip joint force during unilateral stance was calculated as having a magnitude of
around 2530 N and as acting at about 75° to the horizontal. Its magnitude is
approximately 3.2 times body weight. This force is considerably larger than the hip joint
force during bilateral stance which was calculated as being around 0.5 times the upper
body weight. This increase in hip joint force is only partially accounted for by the fact
that during unilateral stance only one hip is supporting the whole upper body rather than
the two in bilateral stance. Most of the increase is due to the contraction of the hip
abductor muscles which is required to stabilise the hip. The contraction of the hip
abductor muscles effectively pulls the sides of the hip joint together greatly increasing
the force at the hip joint. This interpretation is supported by the fact that the abductor
muscle force was calculated as having a magnitude of around 3.4 times the upper body
weight and as acting at about 70º to the horizontal.
SAQ 5
(a) How does the abductor muscle activity affect the hip joint force
during unilateral stance compared to bilateral stance?
(b) Express the magnitude of the hip joint forces during bilateral and
unilateral stance as ratios of the subject’s total body weight.
1.3 Hip Joint Forces During Daily Activity
In the previous section we calculated that the hip joint forces during static bilateral and
unilateral stance. Because the weight of the subject is so important in determining the
magnitude of joint forces they are usually expressed as a ratio of the subject’s total body
weight. This makes the results much more easier to understand. Thus from the previous
example we have magnitudes of 0.4 body weight during bilateral stance, and 3.2 body
weight during unilateral stance. We could expect similar results from subjects of very
Unit 2 - Biomechanics of the Lower Limb
10
different body weights, despite the fact that the actual force magnitudes in newtons will
vary greatly.
During most daily activities the hip joint force is usually greater than body weight. For
example during walking you could expect hip joint forces as high as 3 to 7 body weight
depending on the speed of walking - the faster you walk the higher the force.
Note: Many authors use the abbreviation BW for body weight. For example they may
say that the average force was equal to 5.5 BW. This means that the average force
was equal to 5.5 times the subject's total body weight.
2. KNEE JOINT
The knee joint is the largest and perhaps most complex joint in the human body (Figure
16). It is composed of two articulations: the tibiofemoral (between the proximal surface
of the tibia and the distal surface of the femur) and the patellofemoral (between the
patella and the distal surface of femur). The movement of the knee joint is accounted for
mostly by the tibiofemoral articulation with the patellofemoral articulation acting in
concert to assist this movement.
femur
tibiofemoral
articulation
meniscus
KNEE JOINT
patellofemoral
articulation
patella
articular
cartilage
tibia
FIGURE 16. THE KNEE JOINT.
The proximal surface of the tibia is flat and covered with the menisci (Figure 17). The
menisci are two crescent shaped pieces of fibrocartilage that are attached to the tibia by
short tough ligaments. The menisci make the flat top of the tibia slightly concave which
aids stability. They also act as load distributors and shock absorbers.
anterior
cruciate
ligament
lateral
meniscus
medial
meniscus
posterior
cruciate
ligament
FIGURE 17. VIEW OF TIBIAL PLATEAU FROM ABOVE SHOWING THE POSITION OF THE MENISCI.
Unit 2 - Biomechanics of the Lower Limb
11
MENISCI
The distal end of the femur is formed by two circular-shaped condyles - the femoral
condyles. The femoral condyles are covered by articular cartilage. The smooth anterior
depression between the femoral condyles is called the trochlea. This develops into the
deep posterior depression between the femoral condyles called the intercondylar
notch. The cruciate ligaments, that help to bind the femur to the tibia, are lodged in the
intercondylar notch.
FEMORAL CONDYLES
The patella (knee cap) is the largest sesamoid bone (that is a bone found in a tendon) in
the body. It is located in the tendon of the quadriceps femoris muscle. 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.
PATELLA
Note the fibula does not form part of the knee joint, however, it does act as an anchor
for the biceps femoris muscle and lateral collateral ligament.
SAQ 6
(a) Name the two articulations that comprise the knee joint.
(b) What type of bone is the patella?
Unlike the hip joint, the shape of the bones that form the knee joint are such that they
contribute very little to its stability. Instead, the stability of the knee joint is derived
mainly from its ligaments (Figure 18). Within the joint the anterior and posterior
cruciate ligaments cross each other in the centre of the joint. They limit forward and
backward sliding of the femur on the tibia and limit hyperextension. The joint is
surrounded by a tough fibrous joint capsule which is thickened around the posterior on
the medial and lateral sides. Outside the capsule on either side lie the medial and lateral
collateral ligaments which prevent abduction and adduction respectively. The
quadriceps muscle also aids stability as do the menisci, especially during rotation.
CRUCIATE LIGAMENTS
COLLATERAL
LIGAMENTS
anterior
cruciate
ligament
lateral
collateral
ligament
medial
collateral
ligament
lateral
meniscus
medial
meniscus
posterior
cruciate
ligament
lateral
collateral
ligament
(A)
(B)
FIGURE 18. THE LIGAMENTS OF THE KNEE JOINT (A) ANTERIOR VIEW (B) POSTERIOR VIEW.
SAQ 7 - What gives the knee joint its stability?
2.1 Motion of the Knee
The knee joint is generally considered to behave like a hinge joint. However, although
the knee joint can be adequately described as a hinge joint it does demonstrate subtle
variations.
Unit 2 - Biomechanics of the Lower Limb
12
HINGE JOINT
A hinge always rotates about the same axis (Figure 19A). 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 Figure 19B. This semicircular pattern arises because the femoral
condyles are not perfectly circular and because of the restrictions imposed by the knee
ligaments. Deformities of the knee joint surfaces cause the centre of rotation to follow
more complex patterns.
centre
of
rotation
axis of
rotation
(A)
(B)
FIGURE 19. (A) HINGE JOINT (B) ROTATION OF KNEE JOINT.
When the rotation of the knee joint is studied in all three dimensions and not just in the
sagittal plane it 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 the
knee flexes the tibia rotates internally and as the knee extends the tibia rotates externally
(Figure 20). This spiral motion 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).
extension
flexion
and
internal
rotation
flexion
external
rotation
extension
and
external
rotation
internal
rotation
FIGURE 20. SCREW-HOME MECHANISM OF THE KNEE JOINT.
In addition to rotation, the knee joint also allows a limited amount of abduction and
adduction, and internal and external rotation.
Unit 2 - Biomechanics of the Lower Limb
13
SCREW-HOME
MECHANISM
SAQ 8
(a) Describe how the knee joint’s centre of rotation changes in the
sagittal plane as it flexes and extends.
(b) What does the screw-home mechanism describe?
2.2 Range of Motion
The range of joint motion in the knee joint can be attributed to the tibiofemoral
articulation. This essentially hinged synovial joint allows the greatest motion to occur in
the sagittal plane, although motion in the other two planes does occur.
rotation 0° at
full extension
extension <5°
(B)
(A)
internal rotation 30°
flexion 140°
external rotation 45°
at 90° flexion
FIGURE 21. RANGE OF MOTION OF THE KNEE JOINT (A) SAGITTAL PLANE (B) TRANSVERSE PLANE.
In the sagittal plane, flexion and extension occur. The range of motion is from a few
degrees of extension to about 140 degrees of flexion (Figure 21A).
In the frontal plane, abduction and adduction occur; the range of motion in this plane is
dependent upon how much the knee is flexed. It is at its maximum at about 30 degrees
flexion but is still only a few degrees.
In the transverse plane, internal and external rotation occur (Figure 21B). This motion is
also dependent on how much the knee is flexed. At full extension, rotation is almost
completely restricted by the interlocking femoral and tibial condyles. The range of
motion increases with flexion, reaching a maximum at about 90 degrees flexion where
external rotation ranges from 0 to about 45 degrees and internal rotation ranges from 0
to 30 degrees. Beyond 90 degrees of flexion the range of rotation decreases.
Activity: Whilst sitting down, extend your knee joint and holding your thigh firmly try
to abduct and adduct your knee, and then to internally and externally rotate your
knee. Flex your knee joint to about 90 degrees and do the same. Is there any
difference in the range of motion?
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,
requires a range of knee joint motion in the sagittal plane from full extension to about
115 degrees of flexion and about 10 degrees of rotation in the transverse plane.
Unit 2 - Biomechanics of the Lower Limb
14
SAQ 9
(a) In which plane does the majority of knee motion occur?
(b) How is the range of motion in the transverse plane dependent on
the amount of flexion and extension?
(c) During standing up how will the amount of motion in the sagittal
plane be affected when the height of the chair is lowered?
2.3 Function of the Patella
The most important function of the patella is to increase the lever arm of the quadriceps
femoris muscle. It assists knee extension by increasing the lever arm of the quadriceps
muscle force by displacing the quadriceps tendon. This function is illustrated in Figure
22 below, it shows a close-up of the knee joint whilst standing with the knee flexed. The
quadriceps femoris provides the effort force required to maintain the knee joint’s
position, overcoming the resistive force, the ground reaction force, produced by the
weight of the body acting behind the knee.
F
R
FIGURE 22. LEVER ARM PRODUCED BY THE PATELLA.
The lever arm of the quadriceps femoris muscle (the effort lever) is dependent on the
position of the patella which is in turn dependent on the amount of knee flexionextension. At full extension the quadriceps tendon is displaced anteriorly, lengthening
the effort lever arm considerably. As the knee flexes the contribution of the patella to
the length of the lever arm decreases as the patella sinks into the intercondylar notch. At
full flexion, the patella is located in the intercondylar notch where it contributes little to
the effort arm (Figure 23).
FIGURE 23. THE CHANGE IN THE POSITION OF THE PATELLA AS THE KNEE FLEXES REDUCES THE PATELLA'S
CONTRIBUTION TO THE EFFORT ARM.
Unit 2 - Biomechanics of the Lower Limb
15
Activity: If you flex your knee beyond 90 degrees you should be able to feel the
smooth anterior depression between the femoral condyles (the trochlea) just above
the patella. If you slowly extend your knee you should be able to feel the patella rise
up the trochlea.
If the patella is removed (patellectomy), the lever arm is reduced (Figure 24). To
compensate for this the force produced by the quadriceps muscle must increase
considerably (by up to 30% at full extension) in order to provide the required turning
moment.
FIGURE 24. REDUCTION IN LEVER ARM AFTER A PATELLECTOMY.
Clinical note: Severe fractures of the patella are treated by patellectomy (removal of
the patella) when the fragments can not be accurately reassembled. If an irregular
surface is left it will cause osteoarthritis in later life.
SAQ 10
(a) Classify the lever system shown in Figure 22.
(b) Is the quadriceps femoris muscle working at a mechanical
advantage or a mechanical disadvantage?
2.4 Function of the Menisci
The menisci act as force distributors and shock absorbers between the femur and the
tibia. The menisci distribute the force over nearly the entire surface of the tibial plateau
(Figure 25A). Since the force is distributed over a large area the stress in the articular
cartilage and underlying bone tissue is small (remember stress is equal to the force
divided by area). If the menisci are removed the force is no longer distributed but is
concentrated in the area of contact between the tibia and femur (Figure 25B). This
increases the stress in the joint tissues and will increase the likelihood of wear and joint
damage. In fact there is approximately a three fold increase in stress when the menisci
are removed.
Unit 2 - Biomechanics of the Lower Limb
16
(A)
(B)
FIGURE 25. (A) WITH THE MENISCI INTACT THE FORCE IS WELL DISTRIBUTED MINIMISING THE STRESS (B) WITH THE
MENISCI REMOVED THE STRESS IS INCREASED DRAMATICALLY.
Clinical note: If the menisci are damaged they have no capacity to heal because
there is only a blood supply to their outer edges. Tears in the menisci can obstruct
the motion of the knee and cause it to jam. Injured knees with part or all of the
menisci removed (a meniscectomy) may still function adequately but the articulating
surfaces are more likely to be damaged and there is a significantly increased
likelihood of the development of degenerative osteoarthritis. For this reason, if
possible the menisci are preserved after injury.
SAQ 11
(a) What are the two main functions of the menisci?
(b) When the menisci are removed how does this affect the stress in
the joint tissues?
2.5 Knee Joint Forces During Daily Activities
As with the hip the knee joint forces are dependent on the weight of the subject and the
amount of muscle activity. Generally, when there is little or no muscle activity the
tibiofemoral joint force will be higher than the hip joint force since the knee must also
support the weight of the thigh. However, when there is muscle activity the contribution
of the weight of the thigh to the joint force becomes small in comparison to the large
forces generated by the muscles. Typical peak joint forces are given in the table below
for the tibiofemoral joint and the patellofemoral joint during various daily activities.
Note that the joint forces presented are the peak joint forces during an activity. These
peak joint forces are generally not sustained for very long. Also note that the
patellofemoral joint forces are generally lower than the tibiofemoral joint forces.
Tibiofemoral joint force
(body weight)
Patellofemoral joint force
(body weight)
Walking
3 to 5
0.5 to 1
Stair ascent
4 to 5
3 to 4
Stair descent
3 to 4
3 to 4
Standing up
3 to 7
3 to 4
SAQ 12 - What is the range of peak hip and knee joint forces during
walking? Give a brief explanation for the difference between them.
Unit 2 - Biomechanics of the Lower Limb
17
3. ANKLE AND FOOT
3.1 Ankle Joint
The ankle joint is essential a hinge synovial joint formed by the distal ends of the tibia
and fibula and the talus (Figure 26). It consists of three articulations: tibiotalar
(between the tibia and the talus), the fibulotalar (between the fibula and the talus) and
the distal tibiofibular (between the distal ends of the tibia and fibula).
tibia
fibula
distal
tibiofibular
articulation
tibiotalar
articulation
fibulotalar
articulation
talus
FIGURE 26. THE ANKLE JOINT.
The two distinctive bony prominences on the lateral and medial sides of the ankle joint
are called the lateral malleolus and the medial malleolus respectively. The lateral
malleolus is the distal end of the fibula and the medial malleolus is the distal end of the
tibia.
As with the hip joint the arrangement of the bones that form the ankle joint is
intrinsically stable. However, because of the high loads that the ankle must withstand,
additional stability is necessary. This is provided by the ligaments that surround the
joint and to a smaller extent by the surrounding muscles. The three most important
ligaments are the anterior inferior talofibular ligament, the medial ligament and the
lateral ligament (Figure 27).
anterior inferior
talofibular ligament
lateral
ligament
medial
ligament
FIGURE 27. THE LIGAMENTS OF THE ANKLE JOINT.
Unit 2 - Biomechanics of the Lower Limb
18
ANKLE JOINT
SAQ 13
(a) Name the bones that form the ankle joint.
(b) How many articulations are there in the ankle joint?
(c) Name the three main ligaments that stabilise the ankle joint?
3.2 Ankle Joint Motion
The ankle joint is essentially a hinge joint with motion occurring primarily in the
sagittal plane (Figure 28). The axis of rotation corresponds approximately to the line
joining the lateral malleolus and the medial malleolus. Flexion of the ankle joint is
termed dorsiflexion (toes move upwards) and extension is termed plantarflexion (toes
move downwards - planting themselves into the ground).
DORSIFLEXION
PLANTARFLEXION
axis of
rotation
15° dorsiflexion
30° plantarflexion
FIGURE 28. ANKLE JOINT MOTION.
The range of motion varies widely among individuals but is usually around 45 degrees.
This is made up of 10 to 20 degrees of dorsiflexion and 25 to 35 degrees of plantarflexion. During walking the ankle joint motion is around 10 to 15 degrees of dorsiflexion and around 15 to 20 degrees plantarflexion.
SAQ 14
(a) What is dorsiflexion?
(b) What is plantarflexion?
Clinical Note: The most common ankle injury is a sprained ankle. It is partial tear of
the anterior inferior talofibular ligament resulting from a sudden adduction of the foot
whilst the ankle is plantarflexed.
3.3 The Foot
The foot is a very complex structure made up of 26 bones, 57 synovial joints, and
numerous ligaments and tendons. This complexity is required to fulfil its diverse
functional requirements. It needs to adapt to a variety of ground surfaces and still
Unit 2 - Biomechanics of the Lower Limb
19
FOOT
maintain a stable and secure contact, it is required to distribute and absorb loads to
avoid injury, and it must transmit loads between the ground and the rest of the body.
The foot can be usefully considered to consist of three parts: the hindfoot, the midfoot
and the forefoot (Figure 29). The hindfoot consists of the talus and the calcaneus (os
calcis). The midfoot consists of the cuboid, medial, intermediate and lateral cuneiforms
and the navicular. The forefoot consists of the metatarsals and phalanges.
forefoot
midfoot
HINDFOOT
MIDFOOT
FOREFOOT
hindfoot
os calcis
(calcaneus)
phalanges
metatarsals
cuneiforms
navicular
cuboid
talus
FIGURE 29. THE BONES OF THE FOOT.
SAQ 15 - What are the three parts of the foot called and which bones
make up each part?
3.4 Subtalar Joint
The subtalar joint is the articulation between the talus and the calcaneus. The joint has
an oblique axis positioned at about 42 degrees to the plantar surface and 16 degrees
medial to the mid-line of the foot (Figure 30).
SUBTALAR JOINT
talus
os calcis
(calcaneus)
42°
mid-line
of foot
16°
(A)
(B)
FIGURE 30. THE AXIS OF ROTATION OF THE SUBTALAR JOINT.
The subtalar joint allows the inversion and eversion of the foot (Figure 31). Inversion is
the inward rotation of the foot so that the plantar surface (the underneath surface) faces
medially (inwards). Eversion is the outward rotation of the foot so that the plantar
surface faces laterally (externally). The subtalar joint can on average be inverted by
about 20 degrees and everted by about 5 degrees. During walking the range of motion is
around 6 degrees.
Unit 2 - Biomechanics of the Lower Limb
20
INVERSION
EVERSION
(A)
(B)
20° inversion
5° eversion
FIGURE 31. (A) INVERSION OF THE FOOT (B) EVERSION OF THE FOOT.
SAQ 16
(a) Name the bones that form the subtalar joint.
(b) What movements occur at the subtalar joint?
3.6 The Arched Structure of the Foot
The foot has a two-way arched structure formed from the bones of the foot and kept in
place by strong ligaments (Figure 32). There are five longitudinal arches that extend
from the calcaneus along the five sets of tarsals and metatarsals. The transverse arch
runs across the foot.
LONGITUDINAL ARCH
TRANSVERSE ARCH
medial longitudinal arch
lateral longitudinal arch
transverse arch
FIGURE 32. ARCHES OF THE FOOT.
The longitudinal arch is supported by the plantar fascia. The plantar fascia extends
from the calcaneus to attach to the plantar aspect of the proximal phalanges. It is a
heavy ligamentous structure that may only be elongated slightly when loaded. It
functions as a cable between the heel and toes and as a shock absorber.
During standing, the bones of the longitudinal arch and the plantar fascia function like a
truss (Figure 33). The plantar fascia prevents the vertical force acting downwards at the
ankle joint from collapsing the longitudinal arches.
Unit 2 - Biomechanics of the Lower Limb
21
PLANTAR FASCIA
plantar fascia
FIGURE 33. TRUSS-LIKE ACTION OF THE PLANTAR FASCIA.
When the toes are dorsiflexed the plantar fascia is put under tension and the two ends of
the foot are drawn together raising the longitudinal arches (Figure 34). The bones of the
foot are thus held together tightly and function as a single unit rather than as separate
bones.
FIGURE 34. ACTION OF THE PLANTAR FASCIA AS THE FOREFOOT DORSIFLEXES CAUSING THE LONGITUDINAL ARCH TO
RISE.
Activity: Place your foot flat on the ground and place your fingers under the medial
arch of the foot. When you dorsiflex your toes you should be able to feel the plantar
fascia tighten.
SAQ 17 - Name the ligamentous structure which supports the
longitudinal arches of the foot.
Unit 2 - Biomechanics of the Lower Limb
22
4. THE BIOMECHANICS OF RECIPROCAL GAIT
One of the principal functions of the lower limb is locomotion (walking and running).
Here we will be examining the biomechanics of the gait (the manner or style of
locomotion) commonly used for walking, termed reciprocal gait (Figure 35A). In
reciprocal gait, the lower limbs are used alternatively to provide support and propulsion.
Other gaits are usually only used when reciprocal gait is not possible. For example,
someone who has broken their femur may use swing-through gait (Figure 35B). In
swing-through gait, crutches are used for support and both legs swing through the
crutches landing ahead of the crutches, the crutches are then advanced forward and the
process is begun again. A well practised user of swing-through gait can get about twice
as fast using it compared to reciprocal gait!
RECIPROCAL GAIT
(A)
(B)
FIGURE 35. (A) RECIPROCAL GAIT (B) SWING-THROUGH GAIT.
4.1 Gait Analysis
A wide variety of parameters of gait can be studied. The ones chosen by the clinician,
physiotherapist, prosthetist, orthotist or bioengineer will be dependent on the pathology
of the patient and the aims of the examination. The clinical examination of the gait of a
patient is called gait analysis. Gait analysis may be used for a wide variety of purposes.
It may be used to determine the surgical intervention required to improve the gait of a
child with cerebral palsy. It may be used to quantify the severity of a disorder or to
determine the outcome of an operation such as in osteoarthritis and joint replacement. It
may also be used to ensure the best alignment of an artificial leg to ensure that the gait
of an amputee is as comfortable, as energy efficient and as cosmetically acceptable as
possible.
Gait analysis can be performed using a variety of techniques. An experienced examiner
may simply watch the patient walking back and forth. However, 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. Both these techniques rely on the
Unit 2 - Biomechanics of the Lower Limb
23
GAIT ANALYSIS
experience of the examiner and neither gives any quantitative data which may be
compared to data collected from able-bodied persons. Nowadays, gait laboratories
equipped with motion analysis systems, force plates and electromyography
equipment are commonly used. This equipment enables not only gait to be studied but
also other common activities of daily living such as standing up and sitting down as
well as movements performed in a variety of sporting activities.
Most motion analysis systems use cameras that only see special markers which are
placed over prominent parts of the patients body (Figure 36). Provided each marker is
seen by two or more cameras 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. This enables the examiner to view the patient
from any angle they wish, say from the side and the front at the same time, and to obtain
quantitative data (such as the joint angles) which they can compare to a database of data
collected from able-bodied persons.
GAIT LABORATORIES
MOTION ANALYSIS
SYSTEMS
FIGURE 36. MARKERS PLACED ON A PATIENT.
Motion analysis systems are often integrated with force plates, which measure the
ground reaction forces (see Section 4.4) and electromyography equipment which
measure muscle activity.
ELECTROMYOGRAPHY
SAQ 18
(a) What is reciprocal gait?
(b) What is gait analysis?
(c) What type of equipment is contained in a gait laboratory?
(d) What is a motion analysis system?
4.2 Gait Cycle
To understand and analyse reciprocal gait the walking pattern is usually divided into a
gait cycle (Figure 37). The gait cycle is equivalent to one stride which is equal to two
Unit 2 - Biomechanics of the Lower Limb
24
GAIT CYCLE
steps; one taken by each lower limb. 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.
left toe off
left
left heel contact
Time
left swing phase
double
support
right
HEEL CONTACT
left toe off
left stance phase
right single
support
double
support
right stance phase
left single
support
right swing phase
right heel
contact
right toe
contact
right heel
contact
FIGURE 37. THE GAIT CYCLE.
During reciprocal gait each foot is in contact with the ground for part of the gait cycle,
termed the stance phase, and for the rest of the cycle it loses contact with the ground,
the swing phase. In walking there is a period of time when both feet are in touch with
the ground, this is termed double support. As the speed of locomotion is increased the
duration of double support decreases until eventually there is no period of double
support. This is the transition from walking to running. During running there is a period
when neither foot is in contact with the ground. (In a walking race, a competitor must
always have at least one foot in contact with the ground, therefore, to achieve a faster
speed they adopt a gait pattern which is slightly different from normal walking.)
STANCE PHASE
SWING PHASE
DOUBLE SUPPORT
Reciprocal gait is characterised by a number of events which occur sequentially during
the gait cycle (Figure 38). These events are useful as landmarks when examining the
gait of a person with a disorder which affects their gait. These events are: heel contact,
foot flat, mid stance, heel off, toe off, and mid swing. The stance phase lasts from heel
contact to toe off, and the swing phase lasts from toe off to the next heel strike.
heel
contact
foot
flat
mid
stance
heel
off
stance phase
toe
off
mid
swing
heel
contact
swing phase
FIGURE 38. RECIPROCAL GAIT EVENTS (SHADED FOOT).
All the events are present in the gait of an able-bodied person. However, one or two
events may be missing, or the order that they occur may be changed, in the gait of a
person with a disorder. For example, 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 (Figure 39).
Unit 2 - Biomechanics of the Lower Limb
25
FOOT DROP
FIGURE 39. FOOT DROP.
SAQ 19
(a) During reciprocal gait what defines the stance phase and the
swing phase?
(b) What is double support?
(c) List the events that occur in reciprocal gait.
4.3 Range of Joint Motion
The typical variation of lower limb joint angles during a complete gait cycle are shown
in Figure 40. The angles shown are those in the sagittal plane where the majority of the
motion occurs during reciprocal gait. The actual variation of the joint angles varies from
person to person and also varies with speed, the ground surface (compare walking on
sand and on concrete) and type of footwear (compare walking in slippers and in high
heeled shoes).
flexion
30
20
10
0
-10
-20
Hip
10
20
30
40
50
60
70
80
90
100
external
flexion
70
60
50
40
30
20
10
0
0
dorsiflexion
plantarflexion
Knee
10
20
30
40
50
60
70
80
90
10
0
-10
-20
100
Ankle
0
10
20
30
40
50
60
70
80
90
100
percent of cycle
heel contact
toe off
heel contact
FIGURE 40. HIP, KNEE AND ANKLE ANGLES DURING ONE RECIPROCAL GAIT CYCLE.
Unit 2 - Biomechanics of the Lower Limb
26
The range of motion at the hip joint varies from around 5 - 10 degrees extension to 30 40 degrees flexion. The peak amount of hip extension occurs shortly before toe off as
the leg is left trailing behind. The peak amount of hip flexion occurs shortly after midswing to ensure a long step.
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 peak amount of knee flexion occurs
during the swing phase as the knee is flexed to allow the foot to clear the ground as it
swings pass the other limb.
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). 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.
SAQ 20
(a) Which lower limb joint has the greatest range of motion during
reciprocal gait?
(b) When does the peak amount of dorsiflexion occur during the gait
cycle?
4.4 Ground Reaction Forces
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. In gait analysis, the ground reaction force is
measured using a force plate (also called a force platform) as the patient steps on the
plate as they walk along (Figure 41). Note that the top surface of the plate is level with
the surrounding floor and that only one foot is placed on the plate.
FIGURE 41. A FORCE PLATE.
The magnitude and direction of the ground reaction force varies during the stance phase
of gait. Figure 42 shows this variation of the ground reaction force in the sagittal plane
at different points of the gait cycle, in what has appropriately become known as a
butterfly diagram.
Unit 2 - Biomechanics of the Lower Limb
27
GROUND REACTION
FORCE
FORCE PLATE
FIGURE 42. GROUND REACTION VECTOR IN THE SAGITTAL PLANE.
A typical example of the vertical force measured using two force platforms (one for
each foot) is shown in Figure 43. The vertical force is characterised by a double hump,
with both peaks being greater than body weight. The first peak is due the deceleration of
body mass as the weight is transferred on to the foot and the second due foot pushing
off the ground.
body weight
time
heel contact
toe off
FIGURE 43. VERTICAL GROUND REACTION FORCE AGAINST TIME.
SAQ 21 - What is a force plate used to measure?
4.5 Joint Forces and Moments
The forces and moments acting at the joints during walking can be calculated using
biomechanics and data collected from the standard equipment found in a gait laboratory.
The position of the body is measured using a motion analysis system. The external
forces and moments acting on the foot are measured using a force plate. The weight of
each body segment may be determined from the patient’s own weight and standard
anthropometric data. The forces exerted by the muscles and the tension in the ligaments
can be estimated using electromyography data and mathematical models.
Unit 2 - Biomechanics of the Lower Limb
28
Typical internal joint moments calculated in this manner are shown in Figure 44. The
graph shows the internal moments generated by the muscles. There are a number of
points of particular interest. At the hip, after heel contact, there is a positive extension
moment produced by the hip extensors to prevent the upper body falling forward. At the
knee, just after heel contact, there is a small flexion moment 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. At the ankle joint the plantarflexion moment increases to a peak just before toe off as the triceps surae contracts to
push the foot up and off the ground.
extension
flexion
extension
flexion
plantarflexion
10
20
30
40
50
60
70
80
90
100
percent of cycle
heel contact
toe off
heel contact
FIGURE 44. INTERNAL JOINT MOMENTS OVER THE GAIT CYCLE.
SAQ 22 - Why do the hamstrings contract at heel contact?
Unit 2 - Biomechanics of the Lower Limb
29
SUMMARY
In this unit you have been introduced to the biomechanics of the lower limb.
Mechanically the lower limb is well adapted to its functions of weight bearing and
locomotion. This is particularly evident at the hip where the joint combines a large
range of motion with considerable stability.
The knee joint is more complex and less stable than the hip joint, having two
articulations and relying on the menisci and ligaments for stability. The knee joint
motion is quite complex but is essentially like a hinge with the patella increasing the
lever arm of the knee extensor muscles.
The ankle joint is also complex, having three articulations, but it is intrinsically stable.
Its motion can also be likened to a hinge producing dorsiflexion and plantarflexion.
The foot is a very complex structure with quite diverse functional requirements. Within
the foot, the subtalar joint allows inversion and eversion and the plantar fascia helps to
maintain the five longitudinal arches.
Reciprocal gait is the most commonly employed manner of walking. Using gait analysis
it is possible to quantify the many features of gait with the aim to improve the treatment
of patients with locomotor disorders.
Unit 2 - Biomechanics of the Lower Limb
30
SAQ ANSWERS
SAQ 1
(a)
The three segments of the lower limb are the thigh, leg and foot.
(b)
The three major joints of the lower limb are the hip, knee and ankle.
(c)
The two main functions of the joints of the lower limb are movement and
weight bearing.
SAQ 2
(a)
The hip joint is a ball-and-socket type synovial joint.
(b)
Synovial fluid lubricates the joint and provides nutrients to the articular
cartilage.
(c)
The hip joint is intrinsically stable due to its shape, its strong joint capsule
and the surrounding ligaments and muscles.
SAQ 3
(a)
The greatest range of hip joint motion occurs in the sagittal plane.
(b)
Typically around 110° of flexion-extension, 20° of abduction-adduction and
15° of rotation is required to stand up and sit down.
SAQ 4
The abductor muscle force is 1880 N and the subject's total body weight is 800
N thus the magnitude of the abductor muscle force is equal to 2.4 times the
subject's total body weight.
SAQ 5
(a)
Muscle activity generally increases the magnitude of the joint forces by
pulling the two sides of the joint together. During unilateral stance the
contraction of the hip joint abductors acts in this way, causing a large
increase in the joint force as compared to bilateral stance when there is
usually no muscle activity.
(b)
The magnitude of the hip joint force is equal to 0.4 total body weight
during bilateral stance, and 3.2 total body weight during unilateral stance.
SAQ 6
(a)
The two articulations which comprise the knee joint are the tibiofemoral
and the patellofemoral.
(b)
The patella is a sesamoid bone.
SAQ 7
The stability of the knee joint is derived from its ligaments, in particular the
cruciate and collateral.
Unit 2 - Biomechanics of the Lower Limb
31
SAQ 8
The knee joint's centre of rotation in the sagittal plane follows a semicircular
path as it flexed and extended.
SAQ 9
(a)
The majority of knee joint motion occurs in the sagittal plane.
(b)
The range of motion in the transverse plane is almost zero at full
extension, increases with flexion to a maximum at around 90° of flexion
and reduces with further flexion.
(c)
If the height of the chair is lowered then the range of knee joint motion
required in the sagittal plane will be increased since the knee will start at a
position of greater flexion.
SAQ 10
(a)
The lever system shown in Figure 22 it has its fulcrum located between
the effort force and resistance force, it is therefore a first class lever.
(b)
The lever arm for the quadriceps femoris muscle is less than that for the
resistance force, it is therefore acting at a mechanical disadvantage.
SAQ 11
(a)
The two main functions of the menisci are to distribute the force more
evenly and to absorb large force peaks.
(b)
When the menisci are removed the stress in the joint tissues is increased
by approximately three times.
SAQ 12
During walking, the peak joint forces at the hip range from 3 to 7 body weight
and at the knee from 3 to 5 body weight. The peak joint force is generally lower
at the knee than at the hip, as the knee must also support the mass of the thigh
this phenomenon must be due to higher muscle forces at the hip.
SAQ 13
(a)
The bones that form the ankle joint are the tibia, fibula and talus.
(b)
The are three articulations in the ankle joint.
(c)
The three main ligaments that stabilise the ankle joint are the anterior
inferior talofibular, the medial and lateral ligaments.
SAQ 14
(a)
Dorsiflexion is flexion of the ankle joint - toes move upwards.
(b)
Plantarflexion is extension of the ankle joint - toes move downwards.
SAQ 15
The three parts of the foot are the forefoot, the midfoot and the hindfoot. The
forefoot is made up of the metatarsals and phalanges. The midfoot is made up
Unit 2 - Biomechanics of the Lower Limb
32
of the cuneiforms, the cuboid and the navicular. The hindfoot is made up of the
talus and calcaneus.
SAQ 16
(a)
The bones that form the subtalar joint are the talus and the calcaneus.
(b)
Inversion and eversion occur at the subtalar joint.
SAQ 17
The ligamentous structure which supports the longitudinal arches of the foot is
called the plantar fascia.
SAQ 18
(a)
Reciprocal gait is the gait most commonly used for walking. During
reciprocal gait the lower limbs are used alternatively to provide support
and propulsion.
(b)
Gait analysis is the examination of gait.
(c)
There are three main pieces of equipment found in a gait laboratory. They
are a motion analysis system, force plates and electromyography
equipment.
(d)
A motion analysis system is a device which records the motion of markers
placed on a patient, thus allowing the patient's movements to be
reconstructed and observed on a computer.
SAQ 19
(a)
During reciprocal gait the stance phase and the swing phase are both
defined by the two events: heel contact and toe off.
(b)
Double support is the period during the gait cycle when both feet are in
contact with the ground.
(c)
The events that occur in reciprocal gait are: heel contact, foot flat, mid
stance, heel off, toe off and mid swing.
SAQ 20
(a)
The knee joint is the lower limb joint with the greatest range of motion
during reciprocal gait.
(b)
The peak amount of dorsiflexion occurs at around heel off.
SAQ 21
A force plate is used to measure the ground reaction force exerted on the foot
during the stance phase of gait.
SAQ 22
The hamstrings contract slightly at heel contact to prevent the hyperextension of
the knee.
Unit 2 - Biomechanics of the Lower Limb
33