Knee Kinematics and Kinetics

Transcription

1 Knee Kinematics and Kinetics

2 Definitions: Kinematics is the study of movement without reference to forces Kinetics is the study of movement with reference to forces

3 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

4 Anatomy of the knee 3 Bones Tibia, Femur, Patella 3 Compartments Medial, Lateral, Patellofemoral 4 Ligaments MCL, LCL, ACL, PCL 2 Menisci Articular Cartilage

5 The Knee Joint

6 Peculiar Anatomy Menisci Fibro-cartilage support Internal ligaments Carry loads during motion

7 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

8 Menisci

9 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

10 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 ( )

11 Tibia-femoral motion in the sagittal plane Activity Walking Climbing stairs Descending stairs Sitting down Tying a shoe Squatting Knee Flexion (degrees)

12 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 90 0 flexion External 45 0 Internal 30 0 Beyond 90 0 decreases, due to soft tissue restriction

13 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 < 30 0

14 Locating an ICR Successive films taken 10 0 intervals of flexion (A,B) Tibia is parallel to the x-ray x 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.

15 Joint Contact Points in Flexion Two contact femur & tibia Medial Lateral Translates slightly anterior on tibia Translates considerably posterior on tibia

16 Surface Joint Motion

17 Types of motion at knee joint Rolling Motion Initiates flexion Gliding Motion Occurs at end of flexion

18 Rolling Motion

19 Gliding Motion

20 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

21 ICR (cont d)

22 Joint Contact Forces Ideally we would have equal distribution of forces w/o any varus or valgus stresses Figure from Burstein and Wright, 1994

23 Joint Contact Forces in the knee

24 Joint Contact Forces in the knee (cont d) During varus stress To balance the stress LCL tension rises Knee shifts 5 5 varus Increased stress on medial condyle Repeated cycles of varus / valgus loading Varus / valgus deformity Cartilage wear

25 Patello-femoral Joint

26 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

27 Patellar Kinematics --Figure from Fulkerson, Disorders rd ed.

28 Compressive Forces of Patella Figure from Fulkerson 1997

29 Patellar Kinematics There are predictable areas of contact between patella and femoral condyles that change with degree of flexion: --figure from Fulkerson 1997

30 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

31 Patellar Kinematics 3 Figure from Fulkerson, 1997

32 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

33 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

34 Q-Angle

35 Q-Angle (cont d) Q-angle of 12 to 15 degrees is considered normal; while patients with patellar subluxation may have a Q-angle Q 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 pp

36 Patellar malalignment Generally associated with tightness of Lateral retinaculum Hamstrings Iliotibial band Quadriceps Hip rotators Achilles tendon

37 Knee Kinematics

38 The "Screw-Home Home mechanism Rotation between the tibia and femur Occurs automatically between full extension 0 o and 20 o of knee flexion SHM is considered a key element to knee stability for standing upright

39 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

40 Ligament Attachments in the knee Joint

41 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

42 Screw-Home mechanism 3 During the last 20 0 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

43 Screw-Home mechanism 4 Prolonged anterior glide on the medial side Produces external tibia rotation The "screw-home" mechanism

44 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

45 Screw-Home mechanism 6 Between 0 0 extension and 20 0 flexion Posterior glide on the medial side produces Relative tibial internal rotation A reversal of the screw- home mechanism Internal Tibial Rotation

46 New flexion and extension axis theory A fixed flexion and extension axis theory [based on 3-D 3 D observation of knee] Replacing the classic concept of the variable flexion and extension theory [based on observation in the sagittal plane]

47 Flexion-Extension Kinematics it has recently been shown that the F-E 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)

48 Flexion-Extension Kinematics

49 Kinematics in Osteoarthrosis

50 THE END