2. Definition
Biomechanics is the science of the action of forces, internal or
external on the living body.
Statics is the study of forces on bodies at rest
Dynamics is the study of the motion of bodies and the forces that
produce the motion
3. JOINT BIOMECHANICS
Degree of freedom
Joint reaction force
Coupled forces
Joint congruence
Instant center of rotation
Friction and lubrication
4. KINEMATICS
Kinematics is the study of motion in terms of displacement, velocity,
and acceleration with reference to the cause of the motion
Kinesiology is the the study of human movement and motion
5. KINEMATICS - Knee Joint
Hinge type
ROM
• Ext 10-15 degrees
• Flex 130-150
13. MENISCI
Fibrocartilagenous crescent; triangular in cross-section
Lateral meniscus is more circular; medial meniscus more c-shaped
Lateral meniscus has twice the excursion of the medial meniscus
during knee motion.
Anterior horn of LM & post horns of both menisci attach to the
intercondylar eminence
15. MENISCI Contd…
Anterior horns attached to each other by the intermeniscal ligament
Popliteus muscle is attached to lateral meniscus (not the tendon)
Semimembranosis is attached to medial meniscus
17. MENISCI Contd…
Provision of stability
Shock absorption
Provision of increased congruity
Aids lubrication
Prevents synovial impingement
Limits extremes of flexion & extension
Transmits loads across the joint – 50- 100% of load is transmitted
through menisci
Reduces contact stresses
18. MENISCI Contd…
The compression of the menisci by the tibia and
the femur generates outward forces that push
the meniscus out from between the bones.
The circumferential tension in the menisci
counteracts this radial force.
19. HOOP STRESS
Hoop stress is the stress in a direction perpendicular to the axis of an
item
As the thickness of the item decreases the hoop stress increases
20. MENISCI Contd…
These hoop forces are transmitted to the tibia through the strong
anterior and posterior attachments of the menisci.
This hoop tension is lost when a single radial cut or tear extends to
the capsular margin and that in terms of load-bearing, a single radial
cut through the meniscus is equivalent to meniscectomy.
21. MENISCECTOMY
Decrease in TF contact area and increase in contact stress.
Partial Meniscetomy 65% increase in contact stress.
Total Meniscetomy 235%
22. SCREW HOME MECHANISM
• Locking
• Femur internally rotates( external tibial torsion) during last 10-20
degrees of extension
23.
24. FEMORAL ROLL BACK
Posterior roll back of femur on tibia increases during knee flexion
PCL
0.5cm of excursion of the medial meniscus and 1.1cm of excursion of
lateral meniscus during a 0- 120 degree arc of knee motion
31. PCL
2 bundles: posteromedial and anterolateral
Function:
• Limits hyperextension
• Prevents post translation of tibia on femur especially during flexion
39. Tibial articular surface is normally 3 degree varus with respect to
mechanical axis
Femoral articular surface is normally 9 degree valgus
40. The mechanical axis of the lower extremity is in 3 degree of valgus
from the vertical axis
The anatomic axis of the femur is in 6 degrees of valgus, the
mechanical axis(9 degree valgus with the vertical axis)
The anatomic axis of the tibia is in 2-3 degrees of varus from the
mechanical axis
41. Arthrodesis
• The position for knee arthrodesis should be 0-7 degrees of valgus and
10-15 degreees of flexion
43. PATELLOFEMORAL
JOINT
Patella
• Pulley / changes the
direction of pull
• Enhances the moment arm of
quadriceps
• Varies from 6cm at full
extension to about 4cm at
120 degree flexion
Forces at the patellofemoral
jt. tend to increase with
quadriceps muscle force
except during the last 15-20
degrees of ext.
44.
45.
46. Q - ANGLE
Brattstrom
• Q angle formed by the line of pull of the quadriceps mechanism and
that of the patellar tendon as they intersect at the centre of the patella
Males: 8-10 degrees
Females: 15 degrees ± 5 degrees
47. Q - Angle
Q-Angle Line 1
ASIS to midpoint
Of patella
Line 2
Tibial tubercle to
midpoint of patella
Midpoint
of patella
Tibial tubercle
Anterior Superior
Iliac Spine (ASIS)
Line 1
Line 2