Knee Joint Extensors

Extensors of the Knee Joint

• The quadriceps femoris muscle group is included
• Consists of the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius

Rectus Femoris

• Has straight and reflected heads

Vastus Lateralis

• Positioned lateral to the rectus femoris

Vastus Medialis

• Positioned medial to the rectus femoris

Vastus Intermedius

• Located deep to the rectus femoris and in the middle

Tensor Fascia Lata and Ilio-tibial Band

• These can extend the leg at the knee joint

The quadriceps femoris

• Comprises four muscles

Origin of Rectus Femoris

• Straight head originates from the anterior inferior iliac spine (AIIS)
• Reflected head originates from an area above the acetabulum

Origin of Vastus Medialis

• Originates from the lower part of inter-trochanteric line, spiral line, medial lip of linea aspera, and medial supracondylar ridge

Origin of Vastus Lateralis

• Originates from the root of the greater trochanter, lateral lip of gluteal tuberosity, and lateral lip of linea aspera

Origin of Vastus Intermedius

• Originates from the upper 2/3 of the anterolateral surface of the femur

Insertion of the Quadriceps Femoris

• The four muscles merge to form the quadriceps tendon
• Inserts into the base of the patella
• Continues as the ligamentum patellae, which inserts into the tibial tuberosity
• Two fibrous expansions descend from vastus medialis and vastus lateralis
• They attach to the capsule of the knee joint for support (patellar retinaculae)

Actions of the Quadriceps Femoris

• Main extensor of the knee joint
• Rectus femoris can flex the thigh at the hip joint

Actions of the Quadriceps Femoris (continued)

• Lower deep fibers of vastus intermedius form the articularis genu muscle
• Articularis genu tenses and pulls the knee joint capsule superiorly during knee extension to prevent crushing between the femur and tibia
• The quadriceps muscle is supplied by the femoral nerve and is an anterior compartment muscle
• Each head has its own branch from the femoral nerve

Flexors of the Knee Joint

• Include the hamstrings: biceps femoris, semitendinosus, and semimembranosus
• Also include the popliteus (short muscle behind the knee joint), sartorius, and gracilis muscles, which can flex the leg at the knee joint

Biceps Femoris

• Has both long and short heads

Semitendinosus

• The lower part is like a tendon

Semimembranosus

• The upper part is like a membrane

Biceps Femoris Origin

• Long head originates from the ischial tuberosity and sacrotuberous ligament
• Short head originates from the lower part of the lateral lip of linea aspera and the upper part of the lateral supracondylar ridge

Biceps Femoris Insertion

• Inserts into the head of the fibula

Biceps Femoris Action

• Flexion of the leg at the knee joint
• Lateral rotation of the semi-flexed leg at the knee joint
• Extension of the thigh at the hip joint (long head only), used in walking

Semitendinosus Origin

• Arises from the ischial tuberosity, sharing origin with the long head of biceps femoris

Semitendinosus Insertion

• Attaches into the SGS area, located on the upper part of the medial surface of the tibia

Semitendinosus Action

• Flexion of the leg at the knee joint.
• Medial rotation of the semi flexed leg at the knee joint.
• Extension of the thigh at the hip joint, and is used in walking.

Pes Anserine Tendon (SGS)

• Muscles that form act like guy ropes
• Stabilize the pelvis on the lower limb
• Supports from anterior, medial, and posterior aspects

Semimembranosus Origin

• Ischial tuberosity.

Semimembranosus Insertion

• Inserts into a groove behind the medial tibial condyle.

Semimembranosus Action

• Leg flexion at the knee joint
• Medial rotation of the semi flexed leg at the knee joint.
• Thigh extension at the hip joint, and is used in walking.

Hamstring Muscle Action

• All hamstring muscles act on both the hip and knee joints
• The exception is the short head of the biceps femoris, which only acts on the knee joint

Popliteus Origin

• Lateral aspect of the lateral femoral condyle (popliteal groove).

Popliteus Insertion

• Upper part of the posterior aspect of the tibia (above the soleal line).

Popliteus Action

• Leg flexion at the knee joint.
• Medial rotation of the tibia and lateral rotation of the femur at the knee joint.
• Acts as the "un-locker" of the knee joint.

Nerve Supply to Hamstrings

• All hamstring muscles are supplied by the sciatic nerve
• Except for the short head of the biceps femoris, which is supplied by the common peroneal (common fibular) part.
• The popliteus is supplied by the tibial nerve.

Knee Joint Type

• Is a Modified hinge
• Allows limited rotation

Knee Joint Articular Surfaces

• Medial condyle of the femur with the medial condyle of the tibia
• Lateral condyle of the femur with the lateral condyle of the tibia
• Back of the patella with the patellar surface of the femur

Fibrous Capsule of the Knee

• Attaches posteriorly and on either side to the margins of the articular surfaces
• Anteriorly, incomplete
• Replaced by the tendon of the quadriceps muscle, patella, and patellar ligament

Synovial Membrane of the Knee

• Lines the capsule
• Covers the non-articular areas of the bones forming the joint

Capsular Ligaments of the Knee

• Includes patellar ligament and patellar retinaculae, which support the joint anteriorly
• Includes tibial (medial) collateral ligament, which supports the joint medially
• Includes fibular (lateral) collateral ligament, which supports the joint laterally
• Popliteal ligaments support the joint posteriorly

Intra-capsular Structures of the Knee

• Consists of two menisci and two ligaments

Medial and Lateral Menisci

• A pair of semi-lunar fibrocartilage pads lying between the femoral and tibial articular surfaces

Anterior Cruciate Ligament (ACL)

• Originates from the anterior part of the intercondylar area of the tibia
• Attaches to the lateral femoral condyle
• Passes upwards, backwards, and laterally to prevent anterior displacement of the tibia

Posterior Cruciate Ligament (PCL)

• Originates from the posterior part of intercondylar area of the tibia
• Attaches to the medial femoral condyle
• Passes forwards and medially
• Prevents posterior displacement of the tibia

Locking and Unlocking the Knee Joint - Full Extension

• Ineviatable Lateral rotation of the tibia
• Medial rotation of the femur because of un-equality between the medial and lateral femoral and tibial condyles
• All ligaments are now tense while the extensors are relaxed, and the knee joint is locked

Locking and Unlocking the Knee Joint - Flexing

• To unlock the joint first needs to happen
• Performed by medial rotation of the tibia or lateral rotation of the femur, this is the action of the Popliteus