Biomechanics of

Knee Joint
 The Knee Joint Complex
• The knee joint is one of the largest and most complex joints in the body. It
is constructed by 4 bones and an extensive network of ligaments
&muscles.
• It is a bi-condylar type of synovial concave convex joint joint, which
mainly allows for flexion and extension (and a small degree of medial and
lateral rotation).

• The knee joint complex includes three articulating surfaces, which form
two distinct joints contained within a single joint capsule:
A.The patellofemoral
• B.The tibiofemoral joint.
• The knee is one of the most commonly injured joints in the body.
ANATOMY

A. Tibiofemoral Joint
• The tibiofemoral joint is a modified hinge joint, which has six degrees
of freedom. The bony configuration of the knee joint complex is
geometrically incongruous and lends little inherent stability to the joint
• B.Patellofemoral Joint
• The patellofemoral joint is composed of the articulation of the patella
with the femoral condyles of the femur. The patella is a passive
component of the knee extensor mechanism, where the static and
dynamic relationships of the underlying tibia and femur determine the
patellar-tracking pattern.
What is the meniscus?
• The menisci of the knee are two
crescentic shaped cartilages found
within the knee, situated between
the ends of the femur and the
tibia.

• There are two menisci in each

knee; the medial meniscus and
the lateral meniscus. They are
wedge-shaped in cross-section .
The horns of the medial
meniscus are further apart and
meniscus appears ‘C’ shaped,
than those of the lateral one
where meniscus appears more
‘O’ shaped
Function of the meniscus
• Act as shock absorbers
• Share load within the knee
• Secondary stabilizers of knee particular importance in the ACL-deficient.
• It contributes to proprioception.
• Have a role lubrication of the joint, and they may play a part in nutrition of
the articular cartilage.
• As the curved end of the femur pushes down on the flat upper surface of the
tibia with weight-bearing, the menisci act as shock absorbers and cushions
between the bones, helping to share the weight and dissipate the forces
Joint Capsule

• The joint capsule has thick and fibrous layer superficially and thinner layers
deeper. This along side the capsule ligaments enhances she stability of the knee.
As with all of the structures that from the knee they are under most tension
therefore more stable in an extended (closed packed) position in comparison to
the laxity present in a flexed position (open packed).

• -Inside this capsule is a specialized membrane known as the synovial membrane

which provides nourishment to all the surrounding structures. The synovial
membrane produces synovial fluid which lubricates the knee joint.

• - Other structures include the infrapatellar fat pad and bursa which function as
cushions to exterior forces on the knee.

• -The synovial fluid which lubricates the knee joint is pushed anteriorly when the
knee is in extension, posteriorly when the knee is flexed and in the semi flexed
knee the fluid is under the least tension therefor being the most comfortable
position if there is a joint effusion.
Ligaments

• -Many ligaments cross the knee, significantly enhancing its stability . The location of each ligament
determines the direction in which it is capable of resisting the dislocation of the knee.
 The major ligaments in a knee joint are:
▪ A.Patellar ligament: The continuation of the quadriceps femoris tendon distal to a patella. This attaches to
a tibial tuberosity.
▪ B.Collateral ligaments: Two strap-like ligaments, which act to stabilize a hinge motion of a knee,
preventing excessive medial or even lateral movement.
▪ Tibial (medial) collateral ligament: Wide as well as flat ligament, found on the medial side of the joint.
Proximally, this attaches to a medial epicondyle of a femur, distally it attaches to a medial condyle of the tibia.
▪ Fibular (lateral) collateral ligament: Thinner & rounder than tibial collateral, it attaches proximally to a lateral
epicondyle of a femur, distally this attaches to the depression on a lateral surface of a fibular head.
▪ C.Cruciate Ligaments: These two ligaments connect a femur & a tibia. In doing so, they cross each
other, thus term ‘cruciate’ (Latin for like a cross)
▪ Anterior cruciate ligament: Attaches at an anterior intercondylar region of a tibia where it blends with a medial
meniscus. This ascends posteriorly to attach to a femur in an intercondylar fossa. This prevents anterior
dislocation of a tibia onto a femur.
▪ Posterior cruciate ligament: Attaches at a posterior intercondylar region of a tibia & ascends anteriorly to attach
to an anteromedial femoral condyle. This prevents posterior dislocation of a tibia onto a femur.
Bursae

• -A bursa is synovial fluid filled sac, found between moving

structures in a joint – with the aim of reducing wear and tear on
those structures.

• -There are four bursae found in the knee joint.:

▪ Suprapatellar bursa: An extension of a synovial cavity of a knee,

located between the quadriceps femoris as well as the femur.
▪ Prepatellar bursa: Found between an apex of a patella & the skin.
▪ Infrapatellar bursa: Split into deep as well as superficial. A deep
bursa lies between a tibia & the patella ligament. A superficial lies
between a patella ligament & the skin.
▪ Semimembranosus bursa: Located posteriorly in a knee joint,
between a semimembranosus muscle & a medial head of the
gastrocnemius.
MOVEMENTS AT THE KNEE

• Muscles Crossing the Knee

• Like the elbow, the knee is crossed by a number of two-joint muscles.
• There are four main movements that a knee joint permits:

▪ Extension: Produced by a quadriceps femoris, which inserts into a tibial tuberosity.

▪ Flexion: Produced by the hamstrings, gracilis, sartorius as well as popliteus.
▪ Lateral rotation: Produced by a biceps femoris.
▪ Medial rotation: Produced by five muscles; semimembranosus, semitendinosus, gracilis, sartorius as well
as popliteus.
The “screw home mechanism”

▪ The “screw-home” mechanism, considered to be a key element to

knee stability, is the rotation between a tibia & the femur.
▪ It occurs at the end of a knee extension, between full extension (0
degrees) & 20 degrees of the knee flexion.
▪ A tibia rotates internally while an open-chain motions (swing phase)
& externally while a closed-chain movement (stance phase). The
external rotation occurs during a terminal degree of a knee extension
and results in a tightening of both cruciate ligaments, which locks a
knee.
▪ The tibia is then in the position of maximal stability with respect to
the femur.
Locking of the knee joint

▪ Closed kinematic chain extension from 30-degree knee flexion.

▪ A larger medial femoral condyle continue rolling & gliding
posteriorly when the smaller lateral side stopped.
▪ This results in medial rotation of a femur on the tibia, in the last 5
degrees of an extension. The medial rotation of the femur at the final
stage of extension is not voluntary or even produced by muscular
force, which is referred to as “Automatic” or “Terminal Rotation”.
▪ The rotation within a knee joint brings the joint into a closed packed
or locked position. The consequences of automatic rotation are also
known as “locking mechanism” or “screw home mechanism.”
▪ Open kinematic chain: Lateral rotation of a tibia on a femur.
Pseudo Knee Locking

▪ Pseudo-knee locking is much more common

than true locking, & knee motion is limited by
temporary muscle spasming as the body tries to
protect itself in response to pain.
•
Unlocking the knee

▪ To initiate flexion, a knee should be unlocked.

▪ A flexion force will automatically result in a lateral
rotation of the femur.
▪ Owing to the larger medial condyle will move before
the shorter lateral condyle.
▪ Popliteus is the primary muscle to unlock a knee.
 Osteokinematics and Range of motion
• -Theligaments and menisci provide static stability and the muscles and tendons
dynamic stability

• -The main movement of the knee is flexion - extension.

• knee act as a hinge joint, whereby the articular surfaces of the femur roll and glide over
the tibial surface. During flexion and extension,tibia and patella act as one structure in
relation to the femur

• -The quadriceps muscle group is made up of 4 different individual muscles. They join
together forming one single tendon that inserts into the anterior tibial tuberosity.
Embedded in the tendon is the patella, a triangular sesamoid bone, as well as its
function, is to improve the efficiency of the quadriceps contractions. Contraction of the
quadriceps pulls the patella upwards & extends a knee.
Range of motion of Knee joint

• -Knee extension 0 degrees.

• The hamstring muscle group consists of the biceps femoris,
semitendinosus as well as semimembranosus. They are situated at the
back of a thigh as well as their function is flexing or even bending a
knee & providing stability on either side of a joint line.

• -Range of motion: Knee flexion 135 degrees.

• -Secondary movement is internal & external rotation of the tibia in

relation to the femur, but it is possible only when the knee is flexed.
 Extended position
▪ Both lateral & medial collateral ligaments, as well as an anterior part of the anterior
cruciate ligament, is taut.
▪ During extension, the femoral condyles glide as well as roll into a position that
causes the complete unfolding of the tibial collateral ligament.
▪ While the last 10 degrees of extension, an obligatory terminal rotation is triggered in
which the knee is rotated medially 5 degrees.
▪ A final rotation is produced by a lateral rotation of the tibia in a non-weight-bearing
leg, and by a medial rotation of the femur in a weight-bearing leg. A terminal
rotation is made possible by the shape of a medial femoral condyle, assisted by the
contraction of a popliteus muscle as well as the iliotibial tract & is caused by a
stretching of the anterior cruciate ligament.
▪ Both cruciate ligaments are slightly unwinded as well as both lateral ligaments
become taut.
Flexed position

▪ Both collateral ligaments are relaxed while the cruciate ligaments are
taut.
▪ Rotation is controlled by twisted cruciate ligaments; the two
ligaments get twisted around each other whilst a medial rotation of
the tibia which reducing the amount of rotation possible while they
become unwound during lateral rotation of the tibia.
▪

▪ Moreover, the dorsal fibers of the tibial collateral ligament become

tensed while extreme medial rotation, as well as a ligament, also
reduces a lateral rotation to 45–60 degrees.
•
Arthrokinematics:

• -Viewed in the sagittal plane, an articulating surface of

a femur is convex whereas an articulating surface of a
tibia is concave.

• -The knee arthrokinematics is based on the rules of

concavity & convexity
Knee Angles :The Q angle of the knee :

• -is a measurement of the angle between the

quadriceps muscles and the patella tendon. It
provides useful information about the alignment of
the knee joint.
•
• -The Knee Q angle (also known as Quadriceps
Angle) is defined as the angle between the
quadriceps muscle (primarily the rectus femoris)
and the patellar tendon. It sometimes called
quadriceps pull angle.
• -It represents the dynamic “instability” of patella,
the greater it is the more unstable patella will be.
This is the angle subtended by a line
drawn from the anterior superior
iliac spine to the centre of the
patella and another from the centre
of the patella to the tibial tubercle.

*It normally averages about 13

degrees in men and 18 degrees in
women.
• Any angle less than 13° may be
associated with patellofemoral
dysfunction or patella alta.

• -An angle greater than 18° is often

associated with subluxing patella,
increased femoral anteversion, genu
valgum , or increased lateral tibial
torsion or mal-tracking of the patella .
Pathomechanics of Knee Joint:
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