1. Anatomy biomechanics & kinematics of the knee

2. Knee Anatomy

3. 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

4. Femoral Anatomy

5. Femoral Anatomy

6. 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

7. The Patella Oval shape wider medial to lateral Diameter 30 – 55mm
Thickness – 26mm
Bi-concave posterior surface with 4 – 5mm thick articular cartilage
Articulates with the trochlear groove

8. Tibial Anatomy

9. Tibial Anatomy

10. Tibial Anatomy
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
Lateral
Medial

11. 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

12. 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
Posterior cruciate ligament
Lateral co-lateral ligament
Medial co-lateral ligament
Lateral meniscus
Synovial membrane
Anterior cruciate ligament
Infrapatellar fat pad
Patellar ligament

13. The Menisci
Coronal cross section
Medial
Lateral

14. Knee Stabilisers
Static: Congruent Articular Geometry Co-lateral ligaments Cruciate ligaments Capsule
Dynamic: Muscles Menisci

15. 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

16. 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

17. 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

18. Lateral co-lateral ligament Medial co-lateral ligament
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

19. The Medial Collateral Ligament
Broad & fan-shaped originates on the medial
femoral epicondyle inserts 4 – 5cm distal to
the tibial plateau
Consists of two bundles
Anterior free of capsular attachment
Posterior blends with the medial meniscus
and the joint capsule

20. 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

21. Limb and Joint Alignments

22. Limb & Joint Alignment
Anatomic Axis A line connecting the centre of a bone proximally to the centre of a bone distally
Mechanical Axis A 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

23. Anatomic Axis Mechanical Axis
Limb & Joint Alignment
Anatomic Axis Mechanical Axis

24. 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

25. 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°

26. Limb & Joint Alignment
Valgus deformity
Varus deformity

27. Femoral Alignment
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

28. Kinematics

29. 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

30. 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

31. Range of Motion Active Flexion Passive Flexion 160° Rotation
When the hip is in extension °
When the hip is in flexion °
Passive Flexion °
Rotation
Is only possible in flexion
40° lateral 30° medial at 90° of flexion

32. Angle of flexion required for daily activities
Walking : ° – 67°
Climbing stairs : ° – 83°
Descending stairs : 0° – 90°
Sitting down : ° – 93°
Tying a shoe : ° – 106°
Lifting an object : 0° – 117°

33. Biomechanics

34. Forces during gait Heel strike Stance phase Toe off
generates 2 – 3 x bodyweight associated with the
contraction of the hamstrings
Stance phase
generates 2 x bodyweight and is associated with
contraction the of the quadriceps
Toe off
generates 2 – 4 x bodyweight
and is associated with contraction of gastrocnemius

35. 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 N
The patella ligament exerts a
force of N
Therefore the tibio-femoral
joint reaction force is N

36. Biomechanics Loads transmitted across the knee
Walking – 4 BW Running – 5 BW Stairs – 7 BW Parachute jump BW

37. 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
Rectus femoris
Vastus intermedius
Vastus lateralis
Vastus medialis

38. 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

39. 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

40. 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

41. 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

42. 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

43. 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

44. Anatomy Biomechanics & Kinematics of the Knee

45. 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

46. Femoral Component 6° of Freedom
4. Varus / Valgus 5. Flexion / Extension: Gross flexion: The prosthesis has to hyper extend in extension Gross Extension: Tends to notch the anterior cortex
6. Internal / External

47. 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