Empire Beauty School Pittsburgh Biomechanics of Knee Exam BIOMECHANICS exam please solve the 4 question that I attached I will attach also powerpoint Biome

Empire Beauty School Pittsburgh Biomechanics of Knee Exam BIOMECHANICS exam please solve the 4 question that I attached I will attach also powerpoint Biomechanics of the Knee
The human knee is,
a modified hinge joint
the largest and perhaps most
complex joint in the body
principally a two-joint structure
composed of the tibiofemoral joint
and the patellofemoral joint
The knee sustains high forces and moments and is situated
between the body’s two longest lever arms, the femur and the
tibia, making it particularly susceptible to injury.
? Any other reason for injury?
Muscles
Extensors
Quadriceps:
All join with the patellar tendon
Flexors
Hamstrings:
• Semimembranosus
• Semitendinosus
• Biceps femoris
Bone Anatomy
The Q angle is formed by the
long axes of the femur and the
tibia and reflects the natural
valgus attitude of the knee
Males ~13°
Females~18°
Potential problems with
abnormal Q angle?
Genu valgum or knock knees
Genu varum is bowed legs
Tibial Plateau
• curved surfaces corresponding to the medial and lateral femoral condyles
• A raised prominence between the curved surfaces helps prevent rotation in
extension
• The lateral tibial plateau is convex in shape. This allows the lateral femoral
condyle to move further backward than the medial condyle. This causes
internal tibial rotation with flexion
Patella
• A sesamoid bone embedded in the extensor muscle/tendon unit
• Efficiency of the extensor groups is increased by 150% due to the
mechanical advantage provided by the patella
• The articular surface of the patella has two facets divided by a ridge, which
helps with tracking over the condyles
Ligaments
Posterior view
Anterior view
Anterior Cruciate Ligament (ACL)
Functional Anatomy
• The ACL attaches to the lateral intercondylar notch of the femur and to a point
lateral to the medial tibial eminence
• The primary function is to restrain anterior tibial subluxation
• Prevents backward sliding of the femur and hyperextension of the knee
•
•
•
•
Limits medial rotation of the femur when the foot is fixed
The ACL tightens with full extension and loosens in flexion
External rotation loosens the ACL and internal rotation tightens it
In flexion, it draws the femoral condyles anteriorly
• ACL deficient knees create increased pressure on the posterior menisci
Posterior Cruciate Ligament (PCL)
Functional Anatomy
• The PCL attaches to the front of the medial intercondylar notch of the femur and to
a point lateral to the posterior tibial plateau
• Its course is inferior, posterior, and lateral in direction
• The primary function is to restrain posterior tibial subluxation
• The ligament is looser in extension and tighter in flexion
• In extension, the PCL pulls the femur posteriorly
• PCL deficient knees place more force on the patellofemoral joint
Medial Collateral Ligament (MCL)
• The MCL attaches to the medial femoral condyle and to the medial upper end of the
tibia
• It has an attachment to the medial meniscus
• In full extension, the MCL tightens to full tension
• Tension is increased with abduction stress at increasing positions of flexion
Lateral Collateral Ligament (LCL)
• The LCL attaches to the lateral femoral condyle posteriorly and superiorly and
attaches to the upper end of the lateral fibula
• It does not have an attachment to the lateral meniscus
• It restrains varus stresses
• Peak stress is achieved with adduction when the knee is at 70° of flexion
Menisci of the Knee
• The two menisci are fibrocartilage of crescent shape
• They deepen the articular surfaces of the tibia to provide more stability for the
femoral condyles
• The peripheral outer third of the menisci are well vascularized
• The inner two-thirds are not well vascularized and cannot usually be surgically
repaired
Medial Meniscus
• The medial meniscus is longer than the lateral meniscus
• It is “C” shaped
• The peripheral border is adherent to the medial collateral ligament
Lateral Meniscus
• The lateral meniscus is nearly circular in shape
• It covers a larger area than the medial meniscus
Knee has a very complex motions and muscle
forces.
But,
Although knee motion occurs simultaneously in
three planes, the motion in the sagittal plane
dominates so that it accounts for nearly all of
the motion
Although many muscles produce forces on the
knee, at any particular instant the quadriceps
muscle group predominates
VML
15-170
VMO
50- 550
Knee Kinematics
motion of a joint in three planes: frontal (coronal or longitudinal),
sagittal, and transverse (horizontal)
RANGE OF MOTION
In the tibiofemoral joint, motion takes place in all
three planes, but the range of motion is greatest in the
sagittal plane.
Flexion—135°
Extension—0°
Internal Rotation—10°
External Rotation—10°
The knee has some hyperextension 3° (–3° flexion)
Thigh-calf contact is usually the major factor in limiting flexion
Flexion
Normal ROM is 130-1400
Can be as high as 160° in deep kneeling
Extension
5 – 100 hyperextension can be
considered as a normal
The range of motion in the sagittal plane during level walking
Activities
Knee Flexion
normal gait/level
surfaces
60°
stair climbing
80°
sitting/rising from
most chairs
90°
sitting/rising from
toilet seat
115º
advanced function
> 115°
Ascending stairs
The actual degree of knee flexion
required to ascend stairs is
determined not only by the height
of the step, but also by the height of
the patient.
For the standard 7″ step
approximately 65° of flexion will be
required.
In climbing stair , lever arm can be
reduced by leaning forward. Also, in
stair climbing the tibia is maintained
relatively vertical, which diminishes
the anterior subluxation potential of
the femur on the tibia.
Descending stairs
In standard step 85° of flexion is
required.
The tibia is steeply inclined toward
the horizontal, bringing the tibial
plateaus into an oblique orientation.
The force of body weight will now
tend to sublux the femur anteriorly.
This anterior subluxation potential will
be resisted by the patellofemoral joint
reaction force, and the tension which
develops in the posterior cruciate
ligament.
In the compromise of a posterior cruciate ligament, only the
collateral ligaments are available to assist the patellofemoral joint
reaction force in providing anterior-posterior stability.
Many patients with arthritis will report difficulty descending
stairs normally, this will also be true after total knee replacement.
A simple remedy is to have them descend either sideways or
backward, which is biomechanically the equivalent of ascending
the stairs with its decreased mechanical and range of motion
demands.
Motion in the frontal plane, abduction (varus) and adduction
(valgus), is similarly affected by the amount of joint flexion
A maximum of only a few degrees at 30° flexion
Beyond 30°, motion in the frontal plane again decreases because
of the limiting function of the soft tissues
SURFACE JOINT MOTION
• Surface joint motion, which is the motion between the
articulating surfaces of a joint, can be described for any joint
in any plane
• Because these methods are highly technical and complex, a
simpler method, Instantaneous Center technique, is used
• The skeletal portion of a body segment is called a link. As one
link rotates about the other, at any instant there is a point that
does not move, that is, a point that has zero velocity.
Knee Rotation
• As the knee flexes, the instant center of rotation on the femur
moves posteriorly, indicating a combination of rolling and
sliding between the articular surfaces
• Allows for increased knee flexion by avoiding impingement

If there were pure rolling, the femoral
condyle would displace off the posterior
of the tibial plateau
The unique mechanism prevents the
femur from rolling off the posterior
aspect of the tibia plateau as the knee
goes into increased flexion
The mechanism that prevents complete
roll-off is the link formed between
the tibial and femoral attachment sites of
the anterior and posterior cruciate
ligaments and the geometry of the
femoral condyles
Arthrokinematics
1st 250 – mainly roll
>250 roll and ant glide
a. Extension: contact is located centrally.
b. Early flexion: posterior rolling; contact continuously
moves posteriorly.
c. Deep flexion: femoral sliding; contact is located
posteriorly
Screw-Home mechanism
• Happening during 0 ° – 20 ° (last stage of extension)
Tibia
– Internal rotation during the swing phase
– External rotation during the stance phase
• External rotation
– Difference in radius of curvature of the medial and smaller
lateral condyle ? Medial condyle still moving after lateral
condyle has stopped
– Results in tightening of both cruciate ligaments
– Locks the knee
– Tibia is in the position of maximal stability with respect to the
femur
Average contact points of the normal knee
The mean movement (mm) in each meniscus during knee
flexion
Patellofemoral Joint
The surface motion of the patellofemoral joint can be described
by the instant center technique
In early flexion, the contact point
is distal on the patella.
In 75° to 90° flexion, the contact
point is superior on the patella.
This transference distributes the
contact areas over the entire
patella surface during flexion
•At full extension, the distal portion of the patella is in contact with the
superior portion of the trochlea
•As knee flexion, the contact area moves proximately
•Contact area increases from 0.8 cm2 at knee full extension to 4 cm2 at 90º of
flexion
Forces on Patella
Q-angle of 12 to 15 degrees is considered normal;
Patients with patellar subluxation may have a Q angle as high
as 30 degrees Q-angle
The Q-angle is higher with the knee in extension when the
screw-home mechanism causes the tibia to rotate externally
The lateral force component puts the patella at risk for subluxing
Laterally
This is prevented by the slope and height of the patella groove on
the lateral side
Simple example
?
Kinetics of Patellofemoral Joint
Increases angle of pull of quads on tibia, leading increase of
moment arm length,
? improves the torque by 50%
Other Functions of Patella
RF 5-7°
• Centralizes divergent tension of
quads into a single line of action
• Provide some protection of anterior
aspect of knee
VI 15-17°
VL 30-40°
VMO 50-55°
The quadriceps muscle force and the torque around the
patellofemoral joint can be extremely high, particularly when the
knee is flexed, as a result of an eccentric contraction of the
quadriceps
Example of torque on the knee
When lifting a barbell weighing 175 kg, at the instant of tendon
rupture, the knee was flexed 90°,
The torque on the knee joint was 550 Nm, and the quadriceps
muscle force was approximately 10,330 N
Kinetics
Kinetics involves both static and dynamic analysis of the forces and
moments acting on a joint
For a body to be in equilibrium, two conditions must be met: The
sum of the forces in any direction must be zero, and the sum of
the moments about any point or axis must be zero. These
conditions are expressed as ?F = 0 and ?M= 0
Dynamics is the study of the forces and moments acting on a body
when it is accelerating or decelerating.
If the resultant force on the body is not equal to zero, there will be
acceleration in the direction of the force: Newton’s second law
expresses this as F = ma where F is the force, m is the mass, and a
is the acceleration
DYNAMICS OF THE TIBIOFEMORAL JOINT
Two more factors in addition to those in static analysis
• The acceleration of the body part under consideration
• The mass moment of inertia of the body part.
The mass moment of inertia is the unit used to express the
amount of force needed to accelerate a body and depends on the
shape of the body and the mass distribution.
The steps for calculating the minimum magnitudes of the forces acting on a
joint at a particular instant in time during a dynamic activity are as follows:
1.
The anatomic structures are identified: definitions of structures, anatomic
landmarks, point of contact of articular surface, and lever arms involved in
the production of forces for the biomechanical analyses.
2.
The angular acceleration of the moving body part is determined.
3.
The mass moment of inertia of the moving body part is determined.
4.
The torque (moment) acting about the joint is calculated.
5.
The magnitude of the main muscle force accelerating the body part is
calculated.
6.
The magnitude of the joint reaction force at a particular instant in time is
calculated by static analysis.
The torque about the joint can now be calculated using Newton’s
second law of motion, which states that when motion is angular,
the torque is a product of the mass moment of inertia of the
body part and the angular acceleration of that part:
T = Ia
where
T is the torque expressed in newton meters (Nm)
I is the mass moment of inertia expressed in newton
meters seconds squared (Nm sec2)
a is the angular acceleration expressed in radians per
second squared (r/sec2)
The torque is not only a product of the mass moment of inertia
and the angular acceleration of the body part, but also a product
of the main muscle force accelerating the body part and the
perpendicular distance of the force from the center of motion of
the joint (lever arm). Thus,
T = Fd
where
F is the force expressed in newtons (N)
d is the perpendicular distance expressed in meters (m).
Example – kicking
The angular acceleration of the tibia is
determined by photographical
methods: 453 radian/sec^2.
The mass moment of inertia for the
tibia was determined
to be 0.35 Nm sec^2
T= Ia,
0.35 Nm sec2 × 453 r/sec2 = 158.5 Nm
After the torque had been
determined to be 158.5 Nm and the
perpendicular distance from the
subject’s patellar tendon to the
instant center for the tibiofemoral
joint had been found to be 0.05 m,
The muscle force acting on the joint
through the patellar tendon was
calculated using the equation torque
equals force times distance
(T = Fd),
158.5 Nm= F × 0.05 m
F = 158.5 Nm/0.05 m
F = 3,170 N
An increase in angular acceleration of the body part will produce a
proportional increase in the torque about the joint.
Although in the body the mass moment of inertia is anatomically set, it can be
manipulated externally. For example, it is increased when a weight of the boot
is applied to the foot during rehabilitative exercises of the extensor muscles of
the knee.
Normally, a joint reaction force of approximately 50% of body weight results
when the knee is slowly (with no acceleration forces) extended from 90° of
flexion to full extension.
In a person weighing 70 kg, this force is approximately 350 N. If a 10-kg weight
boot is placed on the foot, it will exert a gravitational force of 100 N. This will
increase the joint reaction force by 1,000 N, making the joint force almost four
times greater than it would be without the boot.
FORCES IN THE KNEE
• All of the peak forces occur at heel-strike and toeoff, which is
when all the body weight is carried on one leg.
• Forces in all direction exist
• But the vertical force component clearly predominates
For level walking,
• The maximum compressive force was 2.65 BW
In ascending stairs,
• The peak value was 3.55 BW, 34% higher than for level
walking.
In descending stairs,
• The forces was 3.65 BW.
The force distribution between the lateral and medial sides
The medial force/lateral force ratio is 2.7
medial side >> lateral side
Because of that,
Medical tibia plateau and femoral condyle
is larger than lateral side.
Meniscus
Increase contact area between
femur and tibia
Stress = F/A
Without meniscus,
stress is 2- 3x
Common Knee Injuries
• One of the most commonly injured joints, because
– lack of bony and muscular support
– positioned between the 2 longest bones
– weight bearing and locomotion functions
• Often tear or stretching of soft tissue
Ligament Injuries
• ACL
– more prevalent than PCL injuries
– forces directed from posterior side of leg
• PCL
– forces directed from anterior side of leg
– forced flexion of knee w/external
rotation
• wrestling and football
Mechanisms of ACL injury
1) attempting a rapid cutting
maneuver with foot in contact
with the ground and knee flexed
(problem exacerbated if an
external force applied to knee
during this movement)
2) knee hyperextension with
internal tibial rotation
When the knee is extended, the
ACL is at it’s maximal length
putting it at an increased risk of
tearing
Gender issues related to ACL injury
• Women and ACL Tears
NCAA
• Four times more ACL tears in women than men basketball
players.
• Three times more in gymnasts
• 2.4 times more in soccer
• Higher rates are also found among women in team handball,
volleyball and alpine skiing
• Smaller size of ACL
• Smaller intercondylar notch
• Weaker hamstrings
– Ratio of 10 (quadriceps) to 7
(hamstrings)
• Estrogen – reduces collagen strength
• Larger Q-angle
– normal = 17 degrees in women
– Normal = 14 degress in men
PCL Injuries
• The posterior cruciate ligament, or PCL, is not injured as frequently as the
ACL because other ligaments are usually injured or torn, before PCL
• PCL sprains usually occur because the ligament was pulled or stretched too
far, anterior force to the knee
• PCL injuries disrupt knee joint stability because the tibia can sag posteriorly.
• The ends of the femur and tibia rub directly against each other, causing wear
and tear to the thin, smooth articular cartilage. This abrasion may lead to
arthritis in the knee.
MCL & LCL Injuries
• Injuries to MCL more prevalent than LCL
• MCL
– foot planted and force applied to the
lateral side of knee
L
M
Knee Arthroplasty
Degeneration of Knee
Degeneration of Knee (cont’d)
• Osteoarthritis is the most
common cause
• Abnormalities of knee joint
function resulting from
– Fractures
– Torn cartilages
– Torn ligaments can lead to
degeneration many years after
the injury
Total Knee Arthroplasty
• Indications for surgery
– Pain and disability at the point
• When ADL (standing, walking, and climbing stairs)
cannot be done
• It is an artificial joint
– Resurfacing of cartilage and underlying bone
– A metal and plastic implant
– Corrects deformity
Developments in TKA Design
• Early designs failed
– Loosening, wear, osteolysis, stiffness, dislocation,
instability, and extensor mechanism dysfunction
• In 1970’s
– ~ 300 TKA designs
• To provide rotation
– Mobile-bearing implants in the 80’s
• To reduce wear
– Poly concave design
Objectives of TKA
• Function
– Stability
– Motion
• Long-term fixation of implants
• Correction of deformity
– reduce wear
Poly design
• Congruent
femorotibial
articulation
– A larger area of
contact
– Reduces contact
stresses
High contact
Stresses for
“Curved-on-Flat”
design
LCS low contact
stress distributed
over a large area
of polyethylene
Poly design (cont’d)
• Sphericity leads to
congruency in coronal and
sagittal plane
– Reducing this mode of
wear
– Mobility of tibial bearing
reduces
• Rotational torque
• Subsequent loosening of
tibial component
Design criteria
•
•
•
•
•
•
•
•
•
•
Material compatibility and wear
Adequate mechanical strength
Minimization of joint reaction forces
Minimization of fixation interface shear
Avoidance of fixation interface tension
Uniformity of interface compression
Duplication of anatomical function
Adequate fit for patient population
Manufacturability
Reasonable inventory costs
Implant Wear
• Level and type of stresses
– On articulating surfaces
• Material properties
– Imperfections of UHMWPE
• Coefficient of friction
UHMWPE – ultra-high molecular weight polyethylene
Stresses on Implants
• Load
– Peak tibiofemoral force during sport activities
• Around 7 times the body weig…
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