The document provides an overview of the biomechanics of the knee joint, including its structural components and functional movements. It describes the tibiofemoral and patellofemoral joints, the bones that make up the knee (femur and tibia), supporting ligaments (ACL, PCL, MCL, LCL), menisci, and the range of motions involved in flexion/extension, rotation, and abduction/adduction. It also discusses how the cruciate ligaments and "screw home mechanism" aid in locking the knee during full extension and unlocking it to allow flexion.

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

10.  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.

11. 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°.

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

14.  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”).

15.  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.

16.  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.

18. 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.

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

21.  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

22.  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.

23. 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

24.  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.

25.  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.

27. 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.

28. 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.

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

30. 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

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

33. 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

34. 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

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

36. 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

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

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

41.  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

42. OTHER LIGAMENTS
 Oblique popliteal ligament
 Posterior oblique ligament
 Arcuate ligament

45. 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

47. Bursae
 Suprapatellar bursa
 subpopliteal bursa
 gastrocnemius bursa
 Prepatellar bursa
 Infrapatellar bursa

48.  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.

49.  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

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

52. TIBIOFEMORAL JOINT
FUNCTION

53. 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.

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

57.  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.

59. Role of the Cruciate Ligaments

60. 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°

61.  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.

62. 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.

63.  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.

65.  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.

66.  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°).

67. 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.

68. 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.

69. 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.

70.  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.

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

72.  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.

73.  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.

74.  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.

76. Muscles

77. 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

78.  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.

79.  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.

80. 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.

81.  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.

82. 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.

83.  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.

84.  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.

86. 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.”

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

88. PATELLOFEMORAL JOINT

89.  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.

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

93. 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.

94.  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).

97.  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.

98. 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.

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

101.  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.