Knee Kinematics
and Kinetics
Definitions:
• Kinematics is the study of movement
without reference to forces
http://www.cogsci.princeton.edu/cgi-bin/webwn2.0?stage=1&word=kinematics
• Kinetics is the study of movement with
reference to forces
The Knee:
The largest and most complex joint structure
• Transmit Loads
• Participate in motion
• Aids conservation of momentum
• Provides a force couple for body activities
Anatomy of the knee
• 3 Bones
– Tibia, Femur, Patella
• 3 Compartments
– Medial, Lateral, Patellofemoral
• 4 Ligaments
– MCL, LCL, ACL, PCL
• 2 Menisci
• Articular Cartilage
The Knee Joint
Peculiar Anatomy
• Menisci
– Fibro-cartilage support
• Internal ligaments
– Carry loads during motion
Two menisci
• Outer - lateral meniscus
–
–
–
Circular shaped , smaller ,more mobile
Attached to the ACL
Attached to the femur via the ligament of Wrisberg
• Inner - medial meniscus
–
–
–
–
“C” shaped
wider posterior than lateral
attached to the MCL
attached to the joint capsule
Menisci
Menisci Functions
• Deepen the articulation
– Increase area of contact
• Shock absorption
– X10 BW
• a skier lands from a jump
• Increase stability
– Cups the femoral condyle
• Nutrition of cartilage
– Sweeping synovial fluid across joint
Range of Motion
• Need to define planes
•
in which the particular
motion is taking place
The knee moves in six
different directions of
motions (6DOF)
– Sagittal plane (0-1400)
Tibia-femoral motion
in the sagittal plane
Activity
Walking
Climbing stairs
Descending stairs
Sitting down
Tying a shoe
Squatting
Knee Flexion
(degrees)
67
83
90
83-110
106
130
Tibio-femoral motion
in the Transverse plane
• Influenced by knee position in sagittal plane
– Ex. If knee is in full extension rotation is
restricted by interlocking of condyes with tibia
• Rotation increases as the knee is flexed
– maximum 900 flexion
• External 450
• Internal 300
• Beyond 900
– decreases, due to soft tissue restriction
Tibia-femoral motion
in the frontal plane
• Abduction and Adduction is also affected
by the amount of knee flexion
– Ex. Full extension precludes motion
• Increased passive abduction and
adduction occurs with knee flexion < 300
Locating an ICR
• Successive films taken 100 intervals of flexion (A,B)
• Tibia is parallel to the x-ray to prevent rotation
• Marking two identifiable points on femur, and join these
•
points and draw perpendicular bisector (B)
The intersection point of the perpendicular bisectors is
the instant center of rotation.
Joint Contact Points in Flexion
• Two contact points
– @ femur & tibia
¾ Medial
• Translates slightly
anterior on tibia
¾ Lateral
• Translates considerably
posterior on tibia
Surface Joint Motion
Types of motion at knee joint
• Rolling Motion
– Initiates flexion
• Gliding Motion
– Occurs at end of flexion
Rolling Motion
Gliding Motion
Instantaneous Center of Rotation
ICR
• "If one rigid body rotates about another rigid
•
body, its motion at any instant can be described
by a point or axis of rotation called the
instantaneous center of rotation.“
For normal knees
– Pathway of ICR is semicircular
– Located on the femoral condyles
ICR (cont’d)
Joint Contact Forces
• Ideally…
we would have
equal distribution
of forces w/o any
varus or valgus
stresses
Figure from Burstein and Wright,
1994
Joint Contact Forces in the knee
Joint Contact Forces in the knee
(cont’d)
• During varus stress
– To balance the stress
• LCL tension rises
• Knee shifts 5° varus
• Increased stress on medial condyle
– Repeated cycles of varus / valgus loading
• Varus / valgus deformity
• Cartilage wear
Patello-femoral Joint
Patellar Kinematics
• Patella directly contacts femoral condyles
in flexion
• Patella acts as the fulcrum
• It is said to be “lateral side dominant”
– Greater surface area of contact on the lateral
side as opposed to the medial
Patellar Kinematics
--Figure from Fulkerson, Disorders … 1997 3rd ed.
Compressive Forces of Patella
Figure from Fulkerson
1997
Patellar Kinematics
• There are predictable areas of contact
between patella and femoral condyles that
change with degree of flexion:
--figure from Fulkerson 1997
Patellar Kinematics 2
Forces acting on the Patella:
• Laterally- lateral retinaculum, vastus
lateralis m., iliotibial tract
• Medially- medial retinaculum and vastus
medialis m.
• Superior- Quadriceps via quadriceps
tendon
• Inferior- Patellar tendon
Patellar Kinematics 3
Figure from Fulkerson, 1997
Patellar Kinematics 4
• Sum of forces acting in the four directions
– Determine movement pattern of the knee joint
• Additional forces considered are:
– Friction forces, compressive forces, torques,
translational forces and internal stabilizing
forces from soft tissues
Patellar Kinematics 5
Q-angle :
• Angle formed at the knee joint
– By connecting a line from the anterior superior
iliac crest to the center of the patella
– And a second line from the center of the
patella to the center of the patellar tendon
insertion into the tibial tubercle
Q-Angle
Q-Angle (cont’d)
Q-angle of 12 to 15 degrees is considered normal;
while patients with patellar subluxation may
have a Q-angle as high as 30 degrees
Henry J.H., Goletz T.H., and Williamson B. “Lateral Retinacular
Release in Patellofemoral
Subluxation.” Am J of Sports Med. Vol. 14
No.2 1986 pp121129.
Patellar malalignment
• Generally associated with tightness of
– Lateral retinaculum
– Hamstrings
– Iliotibial band
– Quadriceps
– Hip rotators
– Achilles tendon
Knee Kinematics
The "Screw-Home” mechanism
• Rotation between the tibia and femur
– Occurs automatically between full extension
0o and 20o of knee flexion
• SHM is considered a key element to knee
stability for standing upright
“Screw-Home” mechanism
• Tibia
– Internal rotation during the swing phase
– External rotation during the stance phase
• External rotation
– Occurs during the terminal degrees of knee extension
• Difference in radius of curvature of the medial and smaller
lateral condyle
– Results in tightening of both cruciate ligaments
• Locks the knee
• Tibia is in the position of maximal stability with respect to the
femur
Ligament Attachments in the knee
Joint
“Screw-Home” mechanism 2
• During Knee extension
– Tibia rolls anteriorly,
PCL elongates
– PCL's pull on tibia
causes it to glide
anteriorly on femur
Axial View of the
Knee of Right Leg
“Screw-Home” mechanism 3
• During the last 200 of
knee extension
– Anterior tibial glide
persists on the tibia's
medial condyle
• Because its articular
surface is longer in that
dimension than the lateral
condyle‘s
“Screw-Home” mechanism 4
• Prolonged anterior glide
on the medial side
– Produces external tibia
rotation
– The "screw-home"
mechanism
“Screw-Home” mechanism 5
• When the knee begins to
flex from a position of full
extension
– Tibia rolls posterior,
elongating ACL
– ACL's pull on tibia causes
it to glide posterior
– Glide begins first on the
longer medial condyle
“Screw-Home” mechanism 6
• Between 00 extension
and 200 flexion
– Posterior glide on the
medial side produces
• Relative tibial internal
•
rotation
A reversal of the screwhome mechanism
Internal Tibial
Rotation
New flexion and extension axis theory
• A fixed flexion and extension axis
theory [based on 3-D observation of
knee]
• Replacing the classic concept of the
variable flexion and extension theory
[based on observation in the sagittal
plane]
Flexion-Extension Kinematics
• ”it has recently been shown that the F-E axis of
the knee is FIXED within the femur and that the
articular surfaces of the condyles are circular in
profile”
(Hollister et al. 1994, Hollerbach and Hollister,
1995)
Flexion-Extension Kinematics
Kinematics in Osteoarthrosis
THE END