Anatomy biomechanics & kinematics of the knee. Knee Anatomy.
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Transcript of Anatomy biomechanics & kinematics of the knee. Knee Anatomy.
Anatomy biomechanics & kinematics of the knee
Knee Anatomy
Femoral Anatomy
The largest and most complicated
joint in the body
Consists of three joints
( compartment)
medial & lateral tibio-femoral joints
patello-femoral joint
Sustains large forces between the
body’s two longest lever arms
Femoral Anatomy
Femoral Anatomy
Femoral Anatomy
The medial & lateral femoral condyles
have different Sagittal radii
The distal medial condyle is shorter, narrower
and more oblique than the lateral condyle
Medial Lateral Lateral Medial
The Patella
Oval shape wider medial to lateral
Diameter 30 – 55mm
Thickness 19 – 26mm
Bi-concave posterior surface with 4 – 5mm thick articular cartilage
Articulates with the trochlear groove
Tibial Anatomy
Tibial Anatomy
Tibial Anatomy
Lateral
The medial condyle is concave making the medial compartment more stable than the convex lateral side
The metaphysis is angled posteriorly and the plateau slops posteriorly from 3° – 15°
Lateral
Medial
Tibial Anatomy
The intercondylar eminence divides the tibial plateau
contributes to M/L stability and provides attachment for
the menisci and the ACL
The lateral side is more circular than the longer medial side
The patella ligament inserts into the tibial tuberosity
The Menisci
Maintain contact between the femur and the
tibia and bear 60% of the loads in the knee
Lateral: moves 10 – 12mm A/P
Medial: moves 4 – 5mm A/P
Lateral co-lateral ligament
Lateral meniscus
Posterior cruciate ligament
Synovial membrane
Infrapatellar fat padAnterior cruciate ligament
Patellar ligament
Medial co-lateral ligament
The Menisci
Coronal cross section
Lateral Medial
Knee Stabilisers
Static:Congruent Articular Geometry Co-
lateral ligaments Cruciate ligaments Capsule
Dynamic:MusclesMenisci
Cruciate Ligaments
So called because they cross in the coronal and sagittal planes
Provide antero-posterior and some medio-lateral stability
Interact with the MCL LCL and the menisci to control motion
In flexion the ACL is almost horizontal and the PCL vertical this reverses in extension
The Anterior Cruciate Ligament
Originates in the intercondylar notch on internal aspect of the lateral femoral condyle
The tibial insertion is anterior and medial and consists of three distinct groups of fibres
Prevents anterior displacement of the tibia
The Posterior Cruciate Ligament
Originates in the intercondylar notch on the postero-medial aspect of the femoral condyle
The tibial insertion is long extending from the intercondylar eminence on the posterior tibial plateau inferiorly for 1 – 2cms
Consists of four distinct groups of fibres
Prevents posterior displacement of the tibia
Collateral Ligaments
Taut in extension to provide medio-lateral stability and looser in flexion to allow rotation of the tibia
Lateral co-lateral ligament
Medial co-lateral ligament
The Medial Collateral Ligament
Broad & fan-shaped originates on the medialfemoral epicondyle inserts 4 – 5cm distal tothe tibial plateau
Consists of two bundles
Anterior free of capsular attachment
Posterior blends with the medial meniscusand the joint capsule
The Lateral Collateral Ligament
Narrow and cord like
originates on lateral femoral epicondyle
Inserts on the head of the fibula
free of any meniscal or capsular attachments
Limb and Joint Alignments
Limb & Joint Alignment
Anatomic AxisA line connecting the centre of a bone proximally to the centre of a bone distally
Mechanical AxisA line connecting the point of input of a load on a bone to its output to an associated structure
e,g. The centre of the femoral head to the centre of the knee
Limb & Joint Alignment
Anatomic Axis Mechanical Axis
The HKA Axis
A line connecting the centre of the femoral head the centre of the knee and the centre of ankle
This line runs inferiorly medial forming an angle of approx. 3° to the midline in normal stance
The joint line is perpendicular to the midline and therefore lies approx. 3° medially oblique to the HKA axis
Limb & Joint Alignment
Varus = Towards the Midline
Valgus = Away from the Midline
The tibia & femur do not form a
straight line but form an obtuse
angle of 170° – 175° the average
being 173° which is the physiological
Valgus of the knee 173°
Limb & Joint Alignment
Valgus deformity Varus deformity
Neutral Alignment of the femoral A/P cut will usually produce a trapezoidal Flexion Gap
3° external rotation of the femoral A/P cut will usually produce a parallel flexion gap
Femoral Alignment
Kinematics
Kinematics The Study of Joint Motion
The knee does not flex around a fixed centre it is capable of axial rotation and transverse movements
During the first 20° of flexion the femur moves posteriorly on the tibia femoral " roll-back "
Roll-back is initiated and controlled by the cruciate ligaments
As flexion increases roll-back stops and the femoral condyles slide on the the tibial plateau allowing the knee to flex
Femoral Roll-Back
Rolling only would cause the knee to dislocate as the distance around the femoral condyles is approximately twice the A/P width of the tibial plateau
Sliding only would cause impingement of the posterior femoral shaft on the posterior tibial plateau and block flexion
Rolling and sliding together allow the knee to remain stable and flex fully
Range of Motion
Active FlexionWhen the hip is in extension 120°
When the hip is in flexion 140°
Passive Flexion 160°
Rotation Is only possible in flexion
40° lateral 30° medial at 90° of flexion
Angle of flexion required for daily activities
Walking : 0° – 67° Climbing stairs : 0° – 83°Descending stairs : 0° – 90°
Sitting down : 0° – 93° Tying a shoe : 0° – 106°
Lifting an object : 0° – 117°
Biomechanics
Forces during gait
Heel strikegenerates 2 – 3 x bodyweight associated with the
contraction of the hamstrings
Stance phasegenerates 2 x bodyweight and is associated with
contraction the of the quadriceps
Toe offgenerates 2 – 4 x bodyweight
and is associated with contraction of gastrocnemius
Forces during gait
Ground reaction force (GRF) occurs
during gait from heel strike to toe off
GRF is counterbalanced the joint reaction force and the patella tendon force
For 1 bodyweight the GRF is 700N The patella ligament exerts a force of 2100N Therefore the tibio-femoraljoint reaction force is 2800N
Biomechanics
Loads transmitted across the knee
Walking 2 – 4 BW
Running 3 – 5 BW
Stairs 5 – 7 BW
Parachute jump 20 BW
The Extensor Mechanism
Made up of the 4 quadriceps muscles and the patella
The quadriceps muscles are responsible for knee extension
Help to prevent posterior displacement of the tibia
Vastus medialis
Vastus lateralis
Rectus femoris
Vastus intermedius
The Extensor Mechanism
The patella increases the
efficiency and guides the pull
of the quadriceps
The patella stays with the femur
when the tibia rotates it is
stabilised by it’s congruent fit
in the trochlear groove and the
medial and lateral retinaculae
Lateral retiaculum
Medial retinaculum
Joint Reaction Force
Patello-femoral joint reaction force
is a vector force ranging from
0.5 BW at 9° of flexion to
7 – 8 BW at 130° of flexion
Joint Reaction Force
The patellar moment arm r can be changed during patellar reconstruction
Excessive bone resection will reduce r and the quadriceps will have to pull harder
Insufficient bone resection will
increase r producing high patello-femoral contact forces
Both increase the PFJRF and may lead to patellar instability, pain, patella fracture, loosening, and excessive polyethylene wear
The ‘Q’ Angle
The angle between a line drawn from the centre of the patella to the anterior superior iliac crest and a line drawn from the centre of the tibial tuberosity through the centre of patella normally 15°
Any increase in the Q angle will predispose the patella to instability
Tibial rotation has the greatest effect on the Q angle
Summary
The knee is capable of complex motion and sustains high
dynamic loads during daily activities
Both tibio-femoral and patello-femoral articulations play a part
in the function of the knee
The knee is able to dissipate high loads through the muscles
and ligaments as well as the more compliant tissues of the
menisci and cartilage
Summary
If the knee is damaged the biomechanics change
the natural knee can compromise to an extent
Prosthetic replacements must restore function and be
capable of sustaining high dynamic loads in both the
aligned and mal-aligned condition
Prosthetic designs focus around load dissipation and
lowering wear in the tibio-femoral and patello-femoral
articulations
Anatomy Biomechanics & Kinematics of the Knee
Femoral Component 6° of Freedom
Anterior / Posterior
Anterior: Not enough posterior condyles,
Patella Kinematics
Posterior: Anterior Notch, elongation of
Posterior Condyles = Tight in Flexion
Medial / Lateral
Proximal / Distal
Femoral Component 6° of Freedom
4. Varus / Valgus5. Flexion / Extension:
Gross flexion: The prosthesis has to hyper extend in extensionGross Extension: Tends to notch the anterior cortex
6. Internal / External
Tibial 6° of Freedom
1. Anterior / Posterior
2. Medial / Lateral
3. Proximal / Distal (Resection Level)
4. Varus / Valgus Rotation
5. Flexion / Extension (Posterior Slope)
6. Internal / External Rotation
The Varus / Valgus position is the most important