This document discusses the biomechanics of the normal and replaced knee. It covers the axes of motion of the lower limb, tibiofemoral motion including flexion, extension, rotation, and stability mechanisms like muscles, ligaments, and menisci. It then discusses the goals and designs of total knee replacements, including whether to retain or sacrifice the cruciate ligaments, the use of cam and spine mechanisms to substitute for the PCL, and considerations for femoral and tibial implant design. Recent research topics discussed include the adductor moment, rotatory knee arthritis, and the shape of the tibial plateau.

2. BIOMECHANICS
OF
NORMAL
&
REPLACED KNEE

4. BIOMECHANICS
KNEE :Force closed mechanism
HIP :Self closed mechanism

5. The Axis Of Lower Limb
•Vertical Axis
•Mechanical Axis
•Anatomical Axis of Femur
•Anatomical Axis of Tibia

8. Tibio-Femoral Motion
•Flexion –
Extension
•Abduction –
Adduction
•Internal –
External Rotation

9. Instantaneous centre of motion
FLEXION - EXTENSION

10. Instantaneous center pathway
FLEXION - EXTENSION

11. Sliding/Rocking

12. FLEXION - EXTENSION
Sliding/Rocking of femur

13. Gliding/Rolling

14. FLEXION - EXTENSION
Gliding/Rolling of femur

15. FLEXION - EXTENSION
Knee glides & Slides
Rocks & Rolls!

17. ROTATION OF KNEE
•Screw home
movement
•Rotation increases as
knee is flexed
•Arc ranges 30 – 60

18. Abduction - Adduction
•Normal angulation of
7 Degrees with knee
extended
•Motion permitted by
cruciate and
collaterals
•No movement in
flexion

19. Flexion
40
0
40Extension
HS
FF
HO
TO

22. Flexion - Extension
•Sit & Rise from a
chair
90 -110 degrees

23. Flexion - Extension
•Descending stairs 90 degrees

24. Flexion - Extension
•Ascending stairs 82 degrees

25. Int – Ext Rotation
•Normal 30-60 Degrees
•13 degrees in normal
walking
•More in stair walking
•More on rough ground
walking

26. Loads Applied to Knee
•3X - in Level Walking
•4X – in Stair Climbing
•Area of Contact is less in Flexion
•Medial side bears more weight

27. STABILITY
•Surface geometry
•Muscles crossing
the joint
•Ligaments and
capsule
•Menisci

28. SURFACE GEOMETRY
Femur is convex
Tibia is concave medially
Tibia is convex laterally
Tibial eminence aids in stability

29. •Resists deforming force
•Resists slow forces
•Increase joint compression
•Increase stability
MUSCLES

30. •Resists motion
•Resists translatory movement
•Resists excessive rotation
LIGAMENTS

31. •Joint conformity
•Varus valgus stability
•Resists translation
MENISCUS

32. IDEAL KNEE
• Extends fully & achieves excellent stability
• Flexes beyond 110 & still retains stability
• Gliding and sliding occurs simultaneously
• Allows more rotation as knee flexes
• Articular contact maximum throughout range

33. • Reduplicate the function of menisci
• Reduplicate the function of cruciates
• Achieve excellent ligament balance
• Have anatomic femur & tibial surface
IDEAL KNEE

34. RESTORATION OF
MECHANICAL AXIS

43. RESTORATION OF MECHANICAL
AXIS
Perpendicular to the
Mechanical &
Anatomical axis of
the Tibia

47. BIOMECHANICS OF TKR
Should none, one
or both cruciate
ligaments be
sacrificed

48. ACL & PCL SACRIFICED
• Conforming
concave surface of
tibia producing
inherent stability
• Long term results
from HSS still
remains the gold
standard

49. • Limited knee motion
• Tibial component
subluxated posteriorly
• Stair climbing was difficult
TOTAL CONDYLAR DESIGNS

50. TOTAL CONDYLAR DESIGNS

51. RETAIN THE PCL
• PCL roll back in flexion
• Roll back needs flat tibial surface

52. ROLL BACK WITH PCL

53.  More arc of motion
 Intact PCL prevents post
subluxation of tibia
 Stability is increased
 Decreased interface
stresses
 Shear forces are well
tolerated
RETAIN THE PCL

54. • Proprioception is better
• Retention of PCL helps in
maintaining the joint line
RETAIN THE PCL

55. Why surgeon sacrifices
PCL?
• Minimum tibial resection
• Easier surgical technique
• Easier correction of deformity

56. PCL
SUBSTITUTING
KNEE
• Spine & Cam mechanism
• Produces roll back
• Prevents posterior subluxation

57. • Anterior tibial subluxation
not prevented
• Does not substitute
collaterals
• Posterior slope in tibia
necessary
PCL SUBSTITUTING
KNEE

58. PCL SUBSTITUTING
KNEE

59. PCL SUBSTITUTING
KNEE
• Bad for valgus knee
• Wear of spine
• Bone loss

60. Can we substitute the PCL by
ultra congruent insert ?
PCL SUBSTITUTING KNEE

61. PCL SUBSTITUTING KNEE
• Patellectomy
• Old PCL injury
• Over release of PCL
• Inflammatory conditions ?

62. MENISCAL BEARING KNEE
• ACL, PCL retaining
• PCL retaining

63. ROTATING PLATFORM KNEE
• Cruciate sacrificing
• Spin off
• Undersurface wear

64. FEMUR
• Anatomic
• Decrease
radius of
curvature
posteriorly

65. EXTERNAL ROTATION OF FEMUR

66. EXTERNAL ROTATION OF FEMUR

67. EXTERNAL ROTATION OF FEMUR

68. TIBIAL
TRAY
• Concave conforming
• No rotation in extension
• Intercondylar eminence to prevent
translocation
• Anterior Posterior margin equal height

69. •Anatomic
TIBIAL
TRAY

70. PATELLA

71. PATELLA

72. Recent thoughts…
• Adductor moment
• Rotatory arthritis of
knee (RAK)
• Does tibia really
slope posteriorly?

73. Adductor Moment

74. Rotatory Arthritis of Knee
• Deformities in Knee are
triplanar – frontal, saggital &
coronal
• ACL ‘s role
• Soft tissue involvement

75. Posterior slope of tibia