knee biomechanics.pptx

All about biomechanics of knee joint

1. Biomechanics of knee joint Dr. Shweta Mistry MPT(musculoskeletal)

2. INTRODUCTION The knee complex is one of the most often injured joints in the human body. the knee complex is responsible for moving and supporting the body during a variety of both routine and difficult activities.

3. The knee complex is composed of two distinct articulations located within a single joint capsule: the tibiofemoral joint the patellofemoral joint.

4. The tibiofemoral joint is the articulation between the distal femur and the proximal tibia. The patellofemoral joint is the articulation between the posterior patella and the femur.

5. TIBIOFEMORAL JOINT STRUCTURE The tibiofemoral , or knee, joint is a double condyloid joint with three degrees of freedom of angular (rotary) motion. Flexion and extension medial/lateral (internal/external) rotation abduction and adduction

6. The double condyloid knee joint is defined by its medial and lateral articular surfaces, also referred to as the medial and lateral compartments of the knee.

7. Femur The proximal articular surface of the knee joint is composed of the large medial and lateral condyles of the distal femur. The medial condyle is larger, with a greater radius of curvature and projects further than does the lateral condyle . The two condyles are separated inferiorly by the intercondylar notch through most of their length but are joined anteriorly by an asymmetrical, shallow groove called the femoral sulcus , patellar groove, or patellar surface that engages the patella during early flexion.

8. Tibia The large convex femoral condyles sit on the relatively flat tibial condyles . The asymmetrical medial and lateral tibial condyles or plateaus constitute the distal articular surface of the knee joint The medial and lateral tibial condyles are separated by a roughened area and two bony spines called the intercondylar tubercles

9. the combined bony architecture of the somewhat convex tibial plateaus and convex femoral condyles does not bind well for joint stability. Because of this lack of bony stability, accessory joint structures (menisci) are necessary to improve joint congruency.

10. Tibiofemoral Alignment and Weight-Bearing Forces The anatomical (longitudinal) axis of the femur, is oblique, directed inferiorly and medially from its proximal to distal end. The anatomical axis of the tibia is directed almost vertically. the femoral and tibial longitudinal axes normally form an angle medially at the knee joint of 180° to 185°.

11. the femur is angled up to 5° off vertical, creating a slight physiological (normal) valgus angle at the knee.

12. If the medial tibiofemoral angle is greater than 185°, an abnormal condition called genu valgum (“knock knees”) exists. If the medial tibiofemoral angle is 175° or less, the resulting abnormality is called genu varum (“bow legs”).

13. In bilateral stance, the weight-bearing stresses on the knee joint are, therefore, equally distributed between the medial and lateral condyles (or medial and lateral compartments). In the case of unilateral stance the weight-bearing line shifts toward the medial compartment. This shift increases the compressive forces on the medial compartment .

14. Genu valgum , for instance, shifts the weight-bearing line onto the lateral compartment, relatively increasing the lateral compressive force. In the case of genu varum , the weightbearing line is shifted medially, further increasing the compressive force on the medial condyle . The presence of genu valgum or genu varum creates a constant overload of the lateral or medial articular cartilage, respectively, which may result in damage to the cartilage.

15. Menisci The relative tibiofemoral incongruence is improved by the addition of medial and lateral menisci, which act to convert the convex tibial plateau into concavities for the femoral condyles .

16. Role of menisci: Distributing weight-bearing forces reducing friction between the tibia and the femur serving as shock absorbers

17. The menisci are fibrocartilaginous discs with a semicircular shape. The medial meniscus is C-shaped, whereas the lateral meniscus forms four fifths of a circle. Lying within the tibiofemoral joint, the menisci are located on top of the tibial condyles , covering one half to two thirds of the articular surface of the tibial plateau

18. Both menisci are open toward the intercondylar tubercles, thick peripherally and thin centrally. The lateral meniscus covers a greater percentage of the smaller lateral tibial surface than the surface covered by the medial meniscus. As a result of its larger exposed surface, the medial condyle is more susceptible to injury.

19. Meniscal Attachments The open anterior and posterior ends of the menisci are called the anterior and posterior horns, each of which is firmly attached to the tibia below. Anteriorly , the menisci are connected to each other by the transverse ligament. Both menisci are also attached directly or indirectly to the patella via the patellomeniscal ligaments

20. At the periphery, the menisci are connected to the tibial condyle by the coronary ligaments. The anterior and posterior horns of the medial meniscus are attached to the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL), respectively.

21. The anterior horn of the lateral meniscus and the anterior cruciate ligament share a tibial insertion site. Posteriorly , the lateral meniscus attaches to the posterior cruciate ligament and the medial femoral condyle through the meniscofemoral ligaments.

22. Meniscal Nutrition and Innervation the first year of life, blood vessels are contained throughout the meniscal body. Once weight-bearing is initiated, vascularity begins to diminish until only the outer 25% is vascularized by capillaries from the joint capsule and the synovial membrane. After 50 years of age, only the periphery of the meniscal body is vascularized .

23. Joint Capsule The joint capsule that encloses the tibiofemoral and patellofemoral joints is large and lax. It is grossly composed of a superficial fibrous layer and a thinner deep synovial membrane.

24. Role: 1. secretion of synovial fluid 2. Absorption of fluid into joint for lubrication 3. Nutrition to avascular structure like menisci

25. Plicae Plicae - Synovial membrane formation occurs in early embryonic development Synovial membrane separates medial and lateral articular surface into separate cavities By 12th week of gestation synovial septae reabsorbs to form a single joint cavity

26. Failure of complete resorption results in persistent folds called PLICAE Plicae may get inflamed or irritated- Plicae Syndrome

27. Ligaments The knee joint ligaments are variously credited with resisting or controlling the following: 1. Excessive knee extension 2. Varus and valgus stresses at the knee (attempted adduction or abduction of the tibia, respectively) 3. Anterior or posterior displacement of the tibia beneath the femur 4. Medial or lateral rotation of the tibia beneath the femur 5. Combinations of anteroposterior displacements and rotations of the tibia, together known as rotary stabilization of the tibia

28. Medial collateral ligament (MCL) Originates from medial epicondyle of femur Inserted into medial tibial plateau, medial meniscus, medial proximal tibia. Restrains excess abduction and lateral rotation stress at knee 

29. Lateral collateral ligament (LCL) Extracapsular Origin: Lateral femoral condyle Insertion: fibular head Checks Varus stress and excessive lateral rotation of tibia

30. Anterior Cruciate Ligament Inferior attachment: anterior tibial spine Extends superiorly, posteriorly to attach to the postero -medial aspect of the lateral femoral condyle Two bands: Anteromedial band (AMB)- taut in flexion Postero -lateral band (PLB)- taut in extension

31. Functions: Restrains anterior translation of tibia on femur Prevents hyperextension of knee Secondary restraint against varus and valgus motion

32. Posterior Cruciate Ligament Origin: Posterior inter- condylar area of tibia Insertion: Lateral side of Medial femoral condyle Anteromedial and posterolateral bands

33. Functions- PCL Primary restraint to posterior translation of tibia on femur Limits the anterior translation of femur over fixed tibia in activities such as rapid descending into squat and landing from jump with partially flexed knee

34. OTHER LIGAMENTS Oblique popliteal ligament Posterior oblique ligament Arcuate ligament

35. Iliotibial Band The iliotibial (IT) band or tract is formed proximally from the fascia investing the tensor fascia lata , the gluteus maximus , and the gluteus medius muscles. The iliotibial band continues distally to attach to the lateral intermuscular septum and inserts into the anterolateral tibia ( Gerdy’s tubercle), reinforcing the anterolateral aspect of the knee joint

36. Bursae Suprapatellar bursa subpopliteal bursa gastrocnemius bursa Prepatellar bursa Infrapatellar bursa

37. The anteriorly located suprapatellar bursa lies between the quadriceps tendon and the anterior femur, superior to the patella. The posteriorly located subpopliteal bursa lies between the tendon of the popliteus muscle and the lateral femoral condyle . The gastrocnemius bursa lies between the tendon of the medial head of the gastrocnemius muscle and the medial femoral condyle .

38. The prepatellar bursa, located between the skin and the anterior surface of the patella The infrapatellar bursa lies inferior to the patella, between the patellar tendon and the overlying skin

39. bursae  Reduce friction between intertissue junction during movement. Activities that involve excess and repetitive force at inter tissue junctions frequently leads to Bursitis. 

40. TIBIOFEMORAL JOINT FUNCTION

41. Joint Kinematics The primary angular (or rotary) motion of the tibiofemoral joint is flexion/extension although both medial/lateral (internal/external) rotation and varus / valgus (adduction/ abduction) motions occur to a lesser extent.

42. Flexion/Extension The axis for tibiofemoral flexion and extension can be simplified as a horizontal line passing through the femoral epicondyles .

43. These interdependent osteokinematic and arthrokinematic motions describe how the femur moves on a fixed tibia (e.g., during a squat). The tibia is also capable of moving on a fixed femur (e.g., during a seated knee extension) In this case, the movements would be somewhat different.

44. Role of the Cruciate Ligaments

45. Flexion/Extension Range of Motion Passive range of knee flexion is generally considered to be 130° to 140° Normal gait on level ground requires approximately 60° to 70° of knee flexion, whereas ascending stairs requires about 80°

46. Knee joint extension (or hyperextension) up to 5° is considered within normal limits. Excessive knee hyperextension (e.g., beyond 5° of hyperextension) is termed genu recurvatum .

47. Medial/Lateral Rotation Medial and lateral (axial) rotation of the knee joint are angular motions that describe the motion of the tibia on the femur. These rotations of the knee joint occur about a longitudinal axis that runs through or close to the medial tibial intercondylar tubercle.

48. the medial condyle acts as the pivot point while the lateral condyles move through a greater arc of motion, regardless of the direction of rotation. During both medial and lateral rotation, the knee joint’s menisci will distort in the direction of movement of the corresponding femoral condyle .

49. the range of knee joint rotation depends on the flexion/extension position of the knee. When the knee is in full extension, very little axial rotation is possible. The maximum range of axial rotation is available at 90° of knee Flexion.

50. the total medial/lateral rotation available is approximately 35°, with the range for lateral rotation being slightly greater (0° to 20°) than the range for medial rotation (0° to 15°).

51. Valgus (Abduction)/ Varus (Adduction) Frontal plane motion at the knee, although minimal, does exist and can contribute to normal functioning of the tibiofemoral joint. Frontal plane ROM is typically only 8°at full extension, and 13° with 20° of knee flexion. Excessive frontal plane motion could indicate ligamentous insufficiency.

52. Coupled Motions Flexion and extension of tibiofemoral joint do not occur as pure sagittal plane motions but include frontal plane components termed “coupled motions”. Flexion is considered to be coupled to a varus motion, while extension is coupled with valgus motion.

53. Locking-Unlocking Mechanism of the Knee There is a lateral rotation of the tibia that accompanies the final stages of knee extension that is not voluntary or produced by muscular forces. This coupled motion (lateral rotation with extension) is referred to as automatic or terminal rotation.

54. During the last 30° of non- weightbearing knee extension (30° to 0°), the shorter lateral tibial plateau/femoral condyle pair completes its rolling-gliding motion before the longer medial articular surfaces do. As extension continues, the longer medial plateau continues to roll and to glide anteriorly . This continued anterior motion of the medial tibial condyle results in lateral rotation of the tibia on the femur, with the motion most evident in the final 5° of extension.

55. Consequently, automatic rotation is also known as the locking or screw home mechanism of the knee.

56. To initiate knee flexion from full extension, the knee must first be “unlocked”; that is, the laterally rotated tibia cannot simply flex but must medially rotate concomitantly as flexion is initiated.

57. A flexion force will automatically result in medial rotation of the tibia because the longer medial side will move before the shorter lateral compartment. This automatic rotation or locking of the knee occurs in both weight-bearing and nonweightbearing knee joint function.

58. In weight-bearing, the freely moving femur medially rotates on the relatively fixed tibia during the last 30° of extension. Unlocking, consequently, is brought about by lateral rotation of the femur on the tibia before flexion can proceed.

59. Muscles

60. Knee Flexor Group There are seven muscles that cross the knee joint posteriorly , and thus have the ability to flex the knee. These are the semimembranosus , semitendinosus , biceps femoris (long and short heads), sartorius , gracilis , popliteus , gastrocnemius

61. Five of the flexors (the popliteus , gracilis , sartorius , semimembranosus , and semitendinosus muscles) have the potential to medially rotate the tibia on a fixed femur, whereas the biceps femoris has a moment arm capable of laterally rotating the tibia.

62. The lateral muscles (biceps femoris , lateral head of the gastrocnemius , and the popliteus ) are capable of producing valgus moments at the knee, whereas those on the medial side of the joint ( semimembranosus , semitendinosus , medial head of the gastrocnemius , sartorius , and gracilis ) can generate varus moments.

63. Knee Extensor Group The four extensors of the knee (rectus femoris , vastus lateralis , vastus medialis , vastus intermedius ) are known collectively as the quadriceps femoris muscle. The only portion of the quadriceps that crosses two joints is the rectus femoris muscle, which crosses the hip and knee from its attachment on the anterior inferior iliac spine.

64. The quadriceps tendon inserts into the proximal aspect of the patella and then continues distally past the patella, where it is known as the patellar tendon.

65. Patellar Influence on Quadriceps Muscle Function the patella lengthens the moment arm of the quadriceps by increasing the distance of the quadriceps tendon and patellar tendon from the axis of the knee joint. The patella, as an anatomical pulley, deflects the action line of the quadriceps femoris muscle away from the joint center, increasing the angle of pull on the tibia to enhance the ability of the quadriceps to generate extension torque.

66. During initial flexion position, the patella plays a primary role in increasing the quadriceps angle of pull. In full knee flexion, however, the patella is fixed firmly inside the intercondylar notch of the femur, which significantly reduces the patella’s function as a pulley.

67. During knee extension from full flexion, the moment arm of the quadriceps muscle lengthens as the patella leaves the intercondylar notch and begins to travel up and over the rounded femoral condyles . At about 50° of knee flexion, the femoral condyles have pushed the patella as far as it will go from the axis of rotation.

68. Quadriceps Lag If there is substantial quadriceps weakness or if the patella has been removed because of trauma (a procedure known as a patellectomy ), the quadriceps may not be able to produce adequate torque to complete the last 15° of nonweightbearing knee extension. This can be seen clinically in a patient who demonstrates a “quad lag” or “extension lag.”

69. For example, the patient may have difficulty maintaining full knee extension while performing a straight leg raise

70. PATELLOFEMORAL JOINT

71. In the fully extended knee, the patella lies on the femoral sulcus . Given the incongruence of the patella, the contact between the patella and the femur changes throughout the knee ROM.

72. A markedly long tendon produces an abnormally high position of the patella on the femoral sulcus known as patella alta .

73. Motions of the Patella sagittal plane rotation of the patella as the patella travels (or “tracks”) down the intercondylar groove of the femur is termed patellar flexion. Knee extension brings the patella back to its original position in the femoral sulcus , with the apex of the patella pointing inferiorly at the end of the normal ROM. This patellar motion of gliding superiorly while rotating up and around the femoral condyles is referred to as patellar extension.

74. the patella tilts around a longitudinal axis (proximal to distal through the patella), shifts medially and laterally in the frontal plane, spins or rotates around an anteroposterior axis (perpendicular to the patella).

75. As knee flexion is initiated, the patella is pushed medially by the large lateral femoral condyle . As knee flexion proceeds past 30°, the patella may shift slightly laterally or remain fairly stable. Failure of the patella to glide, tilt, rotate, or shift appropriately can lead to restrictions in knee joint ROM, maltracking of the patellofemoral joint, or pain caused by compression of the patellofemoral articular surfaces.

76. Q-Angle The net effect of the pull of the quadriceps and the patellar ligament can be assessed clinically using a measurement called the Q-angle (quadriceps angle). The Q-angle is the angle formed between a line connecting the anterior superior iliac spine 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.

77. A Q-angle of 10° to 15° measured with the knee either in full extension or slightly flexed is considered normal.

78. women have a slightly greater Q-angle than do men because of the presence of a wider pelvis, increased femoral anteversion , and a relative knee valgus angle.

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