1. Biomechanics of Knee Joint
-Presented by
Dr. Pranali Chougule
MPT[Neuro] 1st year

2. ANATOMY

5. TIBIOFEMORAL ALIGNMENT
The anatomical (longitudinal) axis of the femur is oblique, directed inferiorly and medially from proximal to distal end
Angle is i.e femur is angled up to 50 creating slight physiological valgus angle
>185= genu valgum
<175= genu varus
Mechanical axis or weight bearing line

6. MENISCI
Relative incongruence of the tibiofemoral joint is improved by medial and lateral menisci by converting convex tibial plateau into concavities for femoral condyles

7. MENISCI CONT.. FUNCTIONS OF MENISCI Enhancing joint congruency
Distributing weight bearing forces
Reducing friction between femur and tibia
Serving as shock absorber

8. MENISCI CONT.. MEDIAL MENICUS- C- shaped
Medial meniscus covers a larger medial condyle thus more susceptible to injury from relatively greater compressive loads passes through medial condyle daily
It has greater ligamentous attachments, limiting translations
Relative lack of mobility of this contributes to greater incidence of injury

9. MENISCI CONT.. LATERAL MENISCUS Nearly complete circle
Covers a greater percentage of smaller lateral condyle
Thus lateral condyle is less susceptible to the injury
Has less ligamentous attachment
Thus lateral meniscus is more mobile as compared to medial meniscus

10. MENISCI CONT..
The blood supply of menisci is greatest near periphery. Blood supply comes from the capillaries of synovial membrane and capsule
Internally it is avascular

11. MENISCAL ATTACHMENTS

12. MENISCAL ATTACHMENTS

13. JOINT CAPSULE

14. LIGAMENTS Medial collateral ligament Lateral collateral ligament
Anterior cruciate ligament
Posterior cruciate ligament
Ligaments of posterior capsule
Oblique popliteal ligament
Posterior oblique ligament
Arcuate ligments

16. Medial collateral ligament
It has both superficial and deep parts
Superficial- From the from medial femoral condyle and attaches to the medial aspect of the proximal tibia distally to the pes anserinus.
Deep- continuous to the joint capsule from inferior aspect of the medial femoral condyle to the proximal aspect of the medial tibial plateau and medial meniscus

17. Medial collateral ligament cont..
Function- With knee flexion MCL is important for resisting excessive valgus stress (more in knee flexion compared to extension) Also important foe resisting lateral tibial rotation

18. 2. Lateral collateral ligament
a cord like ligament that begins on the lateral epicondyle of the femur and joins with the tendon of the biceps femoris
Extracapsular
Function- responsible foe resisting varus stress more successfully in full knee extension

19. 3. Anterior cruciate ligament
runs from anterolateral aspect of the medial intercondylar tibal spine
And extends superiorly, laterally, and posteriorly and attaches to posteromedial aspect of the lateral femoral condyle
Prone to injury
Function- resists anterior translation of tibia on femur also provides rotatory stability

20. AMB- Anteromedial bundle
PLB- Posterolateral bundle

21. 4. Posterior cruciate ligment
This ligament runs from the posterior surface of the tibia between the two posterior horns of the menisci it then runs superiorly and anteriorly and attaches to the lateral aspect of the medial femoral condyle.
Much shorter and less oblique than ACL
Function- resists posterior translation of tibia on femur when it is flexed
Although maximum posterior translation of tibia occurs at 75-b 900 of flexion
The popliteal muscle shares the function of PCL

22. Ligaments of posterior knee joint capsule
Oblique popliteal ligament

23. JOINT KINEMATICS Primary angular motion- Flexion and extension
In some amount Medial/Lateral rotation (internal /external rotation) and varus/valgus (adduction/abduction) motion occurs
FLEXION/EXTENSION –
Plane - sagittal
Axis- horizontal line passing through femoral epicondyles
Normal ROM of flexion is degrees and 5-10 degrees beyond 0 degree position (hyperextension)

26. ARTHROKINEMATICS
Flexion= when femur is flexing on a fixed tibia
during initial knee flexion there is posterior rolling of femoral condyles on tibia with flexion continuation after 250 there is anterior gliding of femoral condyle over tibial plateaus

27. Flexion= when Tibia is flexing on a fixed femur
The tibia both rolls and glides posteriorly on relatively fixed femoral condyles (concave-convex rule)

28. Extension= Tibia on fixed femur
Tibial condyles roll and slide anteriorly on the convex femoral condyles

29. Extension= Femur on fixed tibia
While standing up from a deep squat position, the femoral condyles roll anteriorly and slide posteriorly on the relatively concave tibial condyles (convex- concave rule)

30. 2. MEDIAL/LATERAL ROTATION
Axis- longitudinal runs through medial tibial intercondylar tubercle
Medial condyle acts as pivot point while lateral condyle moves through a greater arc of motion
Medial rotation= when tibia is rotating medially on femur then medial condyle of the tibia rotate only slightly and lateral tibial condyle moves anteriorly through larger arc of motion

31. Medial condyle Lateral condyle

32. 2. MEDIAL/LATERAL ROTATION cont..
Lateral rotation= when tibia is rotating laterally over a femoral condyles then medial tibial condyles again moves only slightly and lateral tibial condyle moves larger distance posteriorly on relatively fixed lateral femoral condyle
During both medial and lateral rotation the menisci will distort in the direction of movement of the corresponding femoral condyle
Thus menisci continue to reduce the friction and distribute forces without resisting the motion

33. 2. MEDIAL/LATERAL ROTATION cont..
Both medial and lateral rotation of tibia is available maximum at the 900 of flexion than full extension or full flexion
At 900 of flexion the total medial and lateral rotation of tibia is approx 350
Lateral rotation> medial rotation

35. 3. Valgus (abduction)/ varus (adduction)
Plane- frontal plane
Minimal motion
It only 80 at full extension and 130 with 200 of knee flexion
Excessive valgus or varus motion in knee can lead to ligamentous insufficiency

36. Coupled motions
Biplanar intraarticular motion because of oblique orientation of knee axis motion
Sagittal+ frontal plane motion
Medial femoral condyle lies slightly distal to the lateral femoral condyle, thus physiological valgus angle in extended knee
With knee flexion there is coupled varus motion i.e tibia moves from lateral to the femur to medial
And with knee extension there is coupled valgus motion i.e tibia moves from medial to lateral to the femur

37. Locking of knee joint/ screw home mechanism
There is lateral rotation of tibia during final stages of knee extension which is not voluntary and not produced by muscular actions
Thus called as automatic or terminal rotation
In closed kinematic chain-
During last 300 of non weight bearing knee extension ( ) the larger medial condyle stops rotating while the smaller lateral condyle continues rolling and gliding
These results in medial rotation of femur on tibia , seen in last 5 degree of extension
Open kinematic chain: lateral rotation of tibia on femur.

39. Unlocking of knee joint
To initiate flexion, knee must be unlocked.
A flexion force will automatically result in medial rotation of tibia over femur.
Because the larger medial condyle will move before the shorter lateral condyle.
[Ha yong et al. Screw-Home Movement of the Tibiofemoral Joint during Normal Gait: Three-Dimensional Analysis, 2015]
Popliteus is the primary muscle to unlock the knee
Its function is dependent on whether the lower extremity is in a weight-bearing or non-weight-bearing state; it is considered the primary internal rotator of the tibia in the non-weight-bearing state.
[Scott et al, Anatomy, Bony Pelvis and Lower Limb, Popliteus Muscle]

40. Kinematics of patellofemoral joint
At 1350 of flexion, the patella contacts the femur primarily near its superior pole, in this position the patella rests below the intercondylar groove
In this position, the lateral edge of the lateral facet and the “odd” facet of the patella share articular contact with the femur
With 900 of flexion the contact region of patella starts to migrate over inferior pole

41. Kinematics of patellofemoral joint cont..
Between 90 and 60 degrees of flexion, the patella is usually engaged within the intercondylar groove of the femur. With this the contact area of patella and femur is maximum
With of flexion patella loses much of its mechanical engagement with the intercondylar groove.
Once in full extension, the patella rests completely proximal to the groove and against the suprapatellar fat pad. In this position, with the quadriceps relaxed, the patella can be moved freely relative to the femur.

43. Kinematics of patellofemoral joint cont..
Patellar Shifting
Along with patellar flexion and extension the patella shifts medially and laterally in frontal plane
This medial and lateral shift is named on the direction in which patella moving in reference to femoral condyles

44. Kinematics of patellofemoral joint cont..
Medial and Lateral Patellar Rotation
With knee flexion there is medial rotation of tibia on femur along with this there is medial rotation of patella approx 50 with of flexion

45. Muscles KNEE FLEXOR GROUP
There are seven muscles that cross the knee joint posteriorly
Semimenbranosus
Semitendinosus
Biceps femoris (short and long head)
Sartorius
Gracialis
Popliteus
gastrocnemius

46. Knee flexors
Five of the flexors (the popliteus, gracilis, sartorius, semimembranosus, and semitendinosus muscles) rotates tibia medially over a fixed femur
And biceps femoris rotates tibia laterally over a fixed femur

47. Knee flexors cont..
The lateral muscles (biceps femoris, lateral head of the gastrocnemius, and the popliteus) produce a valgus torque
whereas those on the medial side of the joint (semimembranosus, semitendinosus, medial head of the gastrocnemius, sartorius, and gracilis) can generate varus moments

48. Knee flexors cont.. Hamstrings- flexors
Greater hamstring force is produced with the hip flexed because the hamstrings are lengthened across the hip
In non-weight bearing knee flexion, the hamstrings generate a posterior shearing force of the tibia on the femur that increases as knee flexion increases more in of flexion
This posterior shear or posterior translational force can reduce strain on the ACL, although conceivably it increases the strain on the PCL

49. Knee flexors cont..
Gastrocnemius muscle is also important in maintaining the dynamic stability of the knee joint
the knee joint has to be positioned close to, or beyond, 165° to take advantage of the gastrocnemius greater contribution to the knee flexion moment.
[Li Li et al, The function of gastrocnemius as a knee flexor at selected knee and ankle angles, 2002]

50. Knee flexors cont..
Sartorius function as flexor and medial rotator of tibia
Pes anserinus provide dynamic stability to the anteromedial aspect of the joint
The popliteal muscle is medial rotator of tibia on femur to unlock the knee

51. Knee flexors cont..
In weight bearing position the soleus assists in knee extension by pulling tibia posteriorly
Also the gluteus max assists in knee extension by pulling femur posteriorly on tibia

52. KNEE EXTENSOR GROUP
4 extensors of knee
Rectus femoris
Vastus lateralis Quadriceps
Vastus medialis
Vastus intermedius
The resultant pull of vastus
lateralis muscle is 350 laterally
and that of vastus medialis is 400
medially

53. Knee extensors
Vastus medialis- the upper fibers are angled medially to the femoral shaft whereas the distal fibers are angled medially
thus the upper fibers are called as Vastus medialis longus(VML) and lower fibers as Vastus medialis oblique(VMO)
The VMO maximize its medial pull on patella

55. Patellar influence on quadriceps
Patella acts as a anatomic pulley for quadriceps as it lengthens the moment arm of the quadriceps .
The patella deflects the action line quadriceps muscle increasing the angle of pull on tibia, enhancing the ability of quadriceps extension torque
With knee extension the moment arm will diminished

57. Patellofemoral stabilization
As the knee flexes the quads tendon pull patella superiorly and this pull is resisted by patellar tendon
These forces generate posterior compressive force of patella on femur
The resultant pull of quads and patellar tendon provides the information about net force on patella in frontal plane

58. Patellofemoral stabilization cont..
Because of physiological valgus at the knee joint there is resultant lateral pull on patella in extension
Longitudinal stabilizer of patella- patellar tendon inferiorly and quads superiorly
Transverse stabilizers- vastus lateralis and vastus medialis

59. Patellar stability in frontal plane
Q angle- angle formed between a line connecting the ASIS to the midpoint of the patella (representing the direction of pull of the quadriceps) and a line connecting the tibial tuberosity and the midpoint of the patella

60. Normal =
Increased Q angle= Increased lateral force on patella

61. References Cynthia Norkin, Joint structure and function, 5th edition
Newman, kinesiology of musculoskeletal system, 2nd edition
Carol Otis, Kinesiology, mechanics and pathomechanics of human movement, 2nd edition
Ha yong et al. Screw-Home Movement of the Tibiofemoral Joint during Normal Gait: Three-Dimensional Analysis, 2015
Scott et al, Anatomy, Bony Pelvis and Lower Limb, Popliteus Muscle
Li Li et al, The function of gastrocnemius as a knee flexor at selected knee and ankle angles, 2002