KNEE

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KNEE

• Dr. Michael P. Gillespie

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KNEE GENERAL CONSIDERATIONS

• The knee consists of lateral and medial
  compartments at the tibiofemoral joint and the
  patellofemoral joint.
• Motion of the knee occurs in two planes
• Flexion and extension
• Internal and external rotation
• Two-thirds of the muscles that cross the knee
  also cross either the ankle or the hip. This
  creates a strong functional association within
  the joints of the lower limb.
• Stability of the knee is based primarily on its
  soft-tissue constraints rather than on its bony
  configuration.

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KNEE BIOMECHANICAL FUNCTIONS

• During the swing phase of walking, the knee
  flexes to shorten the functional length of the
  lower limb, thereby providing clearance of the
  foot from the ground.
• During the stance phase, the knee remains
  slightly flexed allowing for shock absorption,
  conservation of energy, and transmission of
  forces through the lower limb.

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OSTEOLOGY
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BONES AND ARTICULATIONS OF THE KNEE
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DISTAL FEMUR

• At the distal end of the femur are the large
  lateral and medial condyles (Greek kondylos,
  knuckle).
• Lateral and medial epicondyles project from each
  condyle. These serve as attachment sites for the
  collateral ligaments.
• Intercondylar notch passageway for the cruciate
  ligaments.
• Femoral condyles fuse anteriorly to form the
  intercondylar (trochlear) groove. This groove
  articulates with the patella.
• Lateral and medial facets formed from the
  sloping sides of the intercondylar groove.
• Lateral and Medial grooves are etched into the
  cartilage that covers the femoral condyles and
  the edge of the tibia articulates with these
  grooves.

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OSTEOLOGIC FEATURES OF THE DISTAL FEMUR

• Lateral and medial condyles
• Lateral and medial epicondyles
• Intercondylar notch
• Intercondylar (trochlear) groove
• Lateral and medial facets (for the patella)
• Lateral and medial grooves (etched in the
  cartilage of the femoral condyles)
• Popliteal surface

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PATELLA, ARTICULAR SURFACES OF DISTAL FEMUR
PROXIMAL TIBIA
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FIBULA

• The fibular has no direct function at the knee
  however, it splints the lateral side of the tibia
  and helps to maintain its alignment.
• The head of the fibula is an attachment for
  biceps femoris and the lateral collateral
  ligament.
• Proximal and distal tibiofibular joints attach
  the fibula to the tibia.

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PROXIMAL TIBIA

• The proximal end of the Tibia flares into medial
  and lateral condyles which articulate with the
  femur.
• Tibial plateau the superior surfaces of the
  condyles.
• Intercondylar eminence separates the articular
  surfaces of the proximal tibia.
• Tibial tuberosity anterior surface of the
  proximal shaft of the tibia. Attachment point
  for the quadriceps femoris, via the patellar
  tendon.
• Soleal line posterior aspect of tibia.

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OSTEOLOGIC FEATURES OF THE PROXIMAL TIBIA AND
FIBULA

• Proximal Fibula
• Head
• Proximal Tibia
• Medial and lateral condyles
• Intercondylar eminence (with tubercles)
• Anterior intercondylar area
• Posterior intercondylar area
• Tibial tuberosity
• Soleal line

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RIGHT DISTAL FEMUR, TIBIA, AND FIBULA
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LATERAL VIEW RIGHT KNEE
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PATELLA

• The patella (Latin, small plate) is embedded
  within the quadriceps tendon.
• The largest sesamoid bone in the body.
• Part of the posterior surface articulates with
  the intercondylar groove of the femur.

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OSTEOLOGIC FEATURES OF THE PATELLA

• Base
• Apex
• Anterior surface
• Posterior articular surface
• Vertical ridge
• Lateral, medial, and odd facets

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PATELLA
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ARTHROLOGY
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GENERAL ANATOMIC AND ALIGNMENT CONSIDERATIONS

• The shaft of the femur angles slightly medial due
  to the 125-degree angle of inclination of the
  proximal femur.
• The proximal tibia is nearly horizontal.
• Consequently, the knee forms an angle of about
  170 to 175 degrees on the lateral side. The
  normal alignment is referred to as genu valgum.
• Excessive genu valgum a lateral angle less than
  170 degrees or knock-knee.
• Genu varum a lateral angle that exceeds 180
  degrees or bow-leg.

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FRONTAL PLANE DEVIATIONS
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CAPSULE AND REINFORCING LIGAMENTS

• The fibrous capsule of the knee encloses the
  medial and lateral compartments of the
  tibiofemoral joint and patellofemoral joint.
• Five regions of the capsule
• Anterior capsule
• Lateral capsule
• Posterior capsule
• Posterior-lateral capsule
• Medial capsule

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LIGAMENTS, FASCIA, AND MUSCLES THAT REINFORCE THE
CAPSULE OF THE KNEE
Region of the Capsule Connective Tissue Reinforcement Muscular-Tendinous Reinforcement
Anterior Patellar Tendon Patellar retinacular fibers Quadriceps
Lateral Lateral collateral ligament Lateral patellar retinacular fibers Iliotibial band Biceps femoris Tendon of the popliteus Lateral head of gastrocnemius
Posterior Oblique popliteal ligament Arcuate popliteal ligament Popliteus Gastrocnemius Hamstrings, especially the tendon of semimembranosus
Posterior-Lateral Arcuate popliteal ligament Lateral collateral ligament Tendon of popliteus
Medial Medial patellar retinacular fibers Medial collateral ligament Thickened fibers posterior-medially Expansions from the tendon of the semimembranosus Tendons from sartorius, gracilis, and semitendinosus
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ANTERIOR VIEW RIGHT KNEE MUSCLES CONNECTIVE
TISSUES
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LATERAL VIEW RIGHT KNEE MUSCLES CONNECTIVE
TISSUES
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POSTERIOR VIEW RIGHT KNEE MUSCLES CONNECTIVE
TISSUES
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MEDIAL VIEW RIGHT KNEE MUSCLES CONNECTIVE
TISSUES
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SYNOVIAL MEMBRANE, BURSAE, AND FAT PADS

• The internal surface of the capsule is lined with
  a synovial membrane.
• The knee has as many as 14 bursae.
• These bursae form inter-tissue junctions
  involving tendon, ligament, skin, bone, capsule,
  and muscle.
• Some bursae are extensions of the synovila
  membrane and others are formed external to the
  capsule.
• Fat pads are often associated with the
  suprapatellar and deep infrapatellar bursae.

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EXAMPLES OF BURSAE AT VARIOUS INTER-TISSUE
JUNCTIONS
Inter-tissue Junction Examples
Ligament Tendon Bursa between lateral collateral ligament tendon of biceps femoris Bursa between the medial collateral ligament and tendons of pes anserinus (i.e. gracilis, semitendinosus, sartorius)
Muscle Capsule Unnamed bursa between medial head of gastrocnemius and medial side of the capsule
Bone Skin Subsutaneous prepatellar bursa between the inferior border of the patella and the skin
Tendon Bone Semimembranosus bursa between the tendon of the semimembranosus and the medial condyle of the tibia
Bone Muscle Suprapatellar bursa between the femur and the quadriceps femoris (largest of the knee)
Bone Ligament Deep infrapatellar bursa between the tibia and patellar tendon
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KNEE PLICAE

• Plicae or synovial pleats appear as folds in the
  synovial membrane.
• Plicae may reinforce the synovial membrane of the
  knee.
• Three most common plicae
• Superior or suprapatellar plica
• Inferior plica
• Medial plica (goes by about 20 names including
  alar ligament, synovialis patellaris, and
  intra-articular medial band).
• Plicae that are unusually large or thickened due
  to irritation or trauma can cause knee pain.
• Inflammation of the medial plica may be confused
  with patellar tendonitis, torn medial meniscus,
  or patellofemoral pain.
• Treatment includes rest, anti-inflammatory
  agents, PT, and in severe cases arthroscopic
  resection.

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TIBIOFEMORAL JOINT

• Articulation between the large convex femoral
  condyles and the nearly flat and smaller tibial
  condyles.
• The large articular surface area of the femoral
  condyles permits extensive knee motion in the
  sagittal plane.
• There is NOT a tight bony fit at this joint.
• Joint stability is provided by muscles,
  ligaments, capsule, menisci, and body weight.

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SUPERIOR SURFACE OF TIBIA
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POSTERIOR VIEW DEEP STRUCTURES RIGHT KNEE
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MENISCI ANATOMIC CONSIDERATIONS

• The medial and lateral menisci are
  crescent-shaped, fibrocartilaginous structures
  located within the knee joint.
• They transform the articular surfaces of the
  tibia into shallow seats for the large femoral
  condyles.
• Coronary (meniscotibial) ligaments anchor the
  external edge of each meniscus.
• The transverse ligament connects the menisci
  anteriorly.
• Several muscles have secondary attachments to the
  menisci.
• Blood supply to the menisci is greatest near the
  peripheral border. The internal border is
  essentially avascular.

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MENISCI FUNCTIONAL CONSIDERATIONS

• The menisci reduce compressive stress across the
  tibiofemoral joint.
• They stabilize the joint during motion, lubricate
  the articular cartilage, provide proprioception,
  and help guide the knees arthrokinematics.
• Compression forces at the knee reach 2.5 to 3
  times the body weight when one is walking and
  over 4 times the body weight when one ascends
  stairs.
• The menisci nearly triple the area of joint
  contact, thereby significantly reducing the
  pressure.
• With every step, the menisci deform peripherally.
• The compression force is absorbed as
  circumferential tension (hoop stress).

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MENISCI COMMON MECHANISMS OF INJURY

• Tears of the meniscus are the most common injury
  of the knee.
• Meniscal tears are often associated with a
  forceful, axial rotation of the femoral condyles
  over a partially flexed and weight-bearing knee.
• The axial torsion within the compressed knee can
  pinch and dislodge the meniscus.
• A dislodged or folded flap of meniscus (often
  referred to as a bucket-handle tear) can
  mechanically block knee movement.
• The medial meniscus is injured twice as
  frequently as the lateral meniscus. Axial
  rotation with a valgus stress to the knee can
  cause this.

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OSTEOKINEMATICS AT THE TIBIOFEMORAL JOINT

• Two degrees of freedom
• Flexion extension in the sagittal plane
• Provided the knee is slightly flexed, internal
  and external rotation.

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TIBIOFEMORAL JOINT FLEXION AND EXTENSION

• The healthy knee moves from 130 to 150 degrees of
  flexion to about 5 to 10 degrees beyond the
  0-degree (straight) position.
• The axis of rotation for flexion and extension is
  not fixed, but migrates within the femoral
  condyles.
• The curved path of the axis is known as an
  evolute.
• With maximal effort, internal torque varies
  across the range of motion.
• External devices attached to the knee rotate
  about a fixed axis of rotation. A hinged
  orthosis can cause rubbing or abrasion against
  the skin. Goniometric measurements are more
  difficult. Place the device as close as possible
  to the average axis of rotation.

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SAGITTAL PLANE MOTION AT THE KNEE
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THE EVOLUTE
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TIBIOFEMORAL JOINT INTERNAL AND EXTERNAL (AXIAL)
ROTATION

• Internal and external rotation of the knee occurs
  about a vertical or longitudinal axis of
  rotation.
• This motion is called axial rotation.
• The freedom of axial rotation increases with
  greater knee flexion.
• A knee flexed to 90 degrees can perform about 40
  to 45 degrees of axial rotation.
• External rotation generally exceeds internal
  rotation by a ratio of nearly 21.
• Once the knee is in full extension, axial
  rotation is maximally restricted.
• The naming of axial rotation is based on the
  position of the tibial tuberosity relative to the
  anterior distal femur.
• External rotation of the knee is when the tibial
  tuberosity is located lateral to the anterior
  distal femur.
• This does not stipulate whether the tibia or
  femur is the moving bone.

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INTERNAL AND EXTERNAL (AXIAL) ROTATION OF THE
RIGHT KNEE
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ARTHROKINEMATICS AT THE TIBIOFEMORAL JOINT
EXTENSION OF THE KNEE

• Tibial-on-femoral extension
• The articular surface of the tibia rolls and
  slides anteriorly on the femoral condyles.
• Femoral-on-tibial extension
• Standing up from a deep squat position.
• The femoral condyles simultaneously roll anterior
  and slide posterior on the articular surface of
  the tibia.

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ARTHROKINEMATICS OF KNEE EXTENSION
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ARTHROKINEMATICS AT THE TIBIOFEMORAL JOINT
SCREW-HOME ROTATION KNEE

• Locking the knee in full extension requires about
  10 degrees of external rotation.
• It is referred to as screw-home rotation.
• It is a conjunct rotation. It is mechanically
  linked to the flexion and extension kinematics
  and cannot be performed independently.
• The combined external rotation and extension
  maximizes the overall contact area. This
  increases congruence and favors stability.

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SCREW-HOME LOCKING MECHANISM
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ARTHROKINEMATICS AT THE TIBIOFEMORAL JOINT
FLEXION OF THE KNEE

• For a knee that is fully extended to be unlocked,
  it must first internally rotate slightly.
• This internal rotation is achieved by the
  popliteus muscle.

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ARTHROKINEMATICS AT THE TIBIOFEMORAL JOINT
INTERNAL AND EXTERNAL (AXIAL) ROTATION OF THE KNEE

• The knee must be flexed to maximize independent
  axial rotation between the tibia and femur.
• The arthrokinematics involve a spin between the
  menisci and the articular surfaces of the tibia
  and femur.

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MEDIAL AND LATERAL COLLATERAL LIGAMENTS ANATOMIC
CONSIDERATIONS

• The medial (tibial) collateral ligament (MCL)
• A flat, broad structure that crosses the medial
  aspect of the joint.
• Superficial part
• Deep part
• Attaches to the medial meniscus
• The lateral (fibular) collateral ligament
• A round, strong cord that runs nearly verticle
  between the lateral epicondyle of the femur and
  the head of the fibula
• Does NOT attach to the lateral meniscus
• The popliteus tendon crosses between these two
  structures

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MEDIAL AND LATERAL COLLATERAL LIGAMENTS
FUNCTIONAL CONSIDERATIONS

• The function of the collateral ligaments is to
  limit excessive knee motion within the frontal
  plane.
• The MCL provides resistance against valgus
  (abduction) force.
• The lateral collateral ligament provides
  resistance against varus (adduction) force.
• Produce a general stabilizing tension for the
  knee throughout the sagittal plane range of
  motion.

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ANTERIOR POSTERIOR CRUCIATE LIGAMENTS GENERAL
CONSIDERATIONS

• Cruciate, meaning cross-shaped, describes the
  spatial relation of the anterior and posterior
  cruciate ligaments as they cross within the
  intercondylar notch of the femur.
• The cruciate ligaments are intracapsular and
  covered by extensive synovial lining.
• Together, they resist the extremes of all knee
  movements.
• The provide most of the resistance to anterior
  and posterior shear forces.
• They contain mechanoreceptors and contribute to
  proprioceptive feedback.

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ANTERIOR CRUCIATE LIGAMENT ANATOMY AND FUNCTION

• The anterior cruciate ligament (ACL) attaches
  along an impression on the anterior intercondylar
  area of the tibial plateau.
• It runs obliquely in a posterior, superior, and
  lateral direction.
• The fibers become increasingly taut as the knee
  approaches and reaches full extension.
• The quadriceps is referred to as an ACL
  antagonist because contraction of the quadriceps
  stretches (or antagonizes) most fibers of the
  ACL.

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ANTERIOR CRUCIATE LIGAMENT COMMON MECHANISMS OF
INJURY

• The ACL is the most frequently totally ruptured
  ligament of the knee.
• Approximately half of all ACL injuries occur in
  persons between the ages of 15 and 25.
• Landing from a jump
• Quickly and forcefully decelerating, cutting, or
  pivoting over a single planted limb
• Hyperextension of the knee while the foot is
  planted firmly on the ground

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POSTERIOR CRUCIATE LIGAMENT ANATOMY AND FUNCTION

• The posterior cruciate ligament (PCL) attaches
  from the posterior intercondylar area of the
  tibia to the lateral side of the medial femoral
  condyle.
• The PCL is slightly thicker than the ACL.
• The posterior drawer test evaluates the
  integrity of the PCL.
• The PCL limits the extent of anterior translation
  of the femur relative to the fixed lower leg.

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POSTERIOR CRUCIATE LIGAMENT COMMON MECHANISMS OF
INJURY

• Most PCL injuries are associated with high energy
  trauma such as an automobile accident or contact
  sports.
• Falling over a fully flexed knee with the ankle
  plantar flexed
• Dashboard injury the knee of a passenger in
  an automobile strikes the dashboard subsequent to
  a front-end collision, driving the tibia
  posterior relative to the femur.
• Often after a PCL injury the proximal tibia sags
  posterior relative to the femur when the lower
  leg is subjected to the pull of gravity.

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GENERAL FUNCTIONS OF ANTERIOR POSTERIOR
CRUCIATE LIGAMENTS

• Provide multiple plane stability to the knee,
  most notably in the sagittal plane
• Guide the natural arthrokinematics, especially
  those related to the restraint of sliding motions
  between the tibia and femur
• Contribute to the proprioception of the knee

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ANTERIOR POSTERIOR CRUCIATE LIGAMENTS
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MUSCLE CONTRACTION AND TENSION CHANGES IN
ANTERIOR CRUCIATE LIGAMENTS / ANTERIOR DRAWER TEST
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KNEE FLEXION POSTERIOR CRUCIATE LIGAMENTS /
POSTERIOR DRAWER TEST
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TISSUES THAT PROVIDE PRIMARY SECONDARY
RESTRAINT IN FRONTAL PLANE
Valgus Force Varus Force
Primary Restraint Medial collateral ligament, especially superficial fibers Lateral collateral ligament
Secondary Restraint Posterior-medial capsule (includes semimembranosus tendon) Anterior and posterior cruciate ligaments Joint contact laterally Compression of the lateral meniscus Medial retinacular fibers Pes anserinus (i.e. tendons of the sartorius, gracilis, and semitendinosus) Gastrocnemius (medial head) Arcuate complex (includes lateral collateral ligament, posterior-lateral capsule, popliteus tendon, and arcuate popliteal ligament) Iliotibial band Biceps femoris tendon Joint contact medially Compression of the medial meniscus Anterior and posterior cruciate ligaments Gastrocnemius (lateral head)
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FUNCTIONS OF KNEE LIGAMENTS COMMON MECHANISMS
OF INJURY
Structure Function Common Mechanism of Injury
Medial collateral ligament (and posterior-medial capsule) Resists valgus (abduction) Resists knee extension Resists extremes of axial rotation (especially knee external rotation) Valgus-producing force with foot planted Severe hyperextension of the knee
Lateral collateral ligament Resists varus (adduction) Resists knee extension Resists extremes of axial rotation Varus-producing force with foot planted Severe hyperextension of the knee
Posterior capsule Resists knee extension Oblique popliteal ligament resists knee external rotation Posterior-lateral capsule resists varus 1. Hyperextension or combined hyperextension with external rotation of the knee
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FUNCTIONS OF KNEE LIGAMENTS COMMON MECHANISMS
OF INJURY
Structure Function Common Mechanism of Injury
Anterior cruciate ligament Most fibers resist extension (either excessive anterior translation of the tibia, posterior translation of the femur, or a combination thereof) Resists extremes of varus, valgus, and axial rotation Large valgus-producing force the foot firmly planted Large axial rotation torque applied to the knee, with the foot firmly planted The above with strong quadriceps contraction with the knee in full or near-full extension Severe hyperextension of the knee
Posterior cruciate ligament Most fibers resist knee flexion (either excessive posterior translation of the tibia or anterior translation of the femur, or a combination thereof) Resists extremes of varus, valgus, and axial rotation Falling on a fully flexed knee (with ankle fully plantar flexed) such that the proximal tibia first strikes the ground Any event that causes a forceful posterior translation of the tibia (i.e. dashboard injury) or anterior translation of the femur Large axial rotation or valgus-varus applied torque Severe hyperextension of the knee causing a large gapping of posterior aspect of joint
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FEMORAL-ON_TIBIAL EXTENSION WITH ELONGATION OF
FIBERS
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PATELLOFEMORAL JOINT

• The patellofemoral joint is the interface between
  the articular side of the patella and the
  intercondylar (trochlear) groove of the femur.
• The quadriceps muscle, the fit of the joint
  surfaces, and passive restraint from retinacular
  fibers and capsule all help to stabilize this
  joint.
• Abnormal kinematics of this joint can lead to
  anterior knee pain and degeneration of the joint.
• As the knee flexes and extends, a sliding motion
  occurs between the articular surfaces of the
  patella and intercondylar groove.

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PATELLOFEMORAL JOINT KINEMATICS

• The patella typically dislocates laterally.
• There is an overall lateral line of force of the
  quadriceps muscle.

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POINT OF MAXIMAL CONTACT OF PATELLA ON FEMUR
DURING EXTENSION
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POINT OF MAXIMAL CONTACT OF PATELLA ON FEMUR
DURING EXTENSION
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PATH OF CONTACT OF PATELLA ON INTERCONDYLAR GROOVE
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MUSCLE AND JOINT INTERACTION
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INNERVATION OF THE MUSCLES

• The quadriceps femoris is innervated by the
  femoral nerve (one nerve for the knees sole
  extensor group).
• The flexors and rotators are innervated by
  several nerves from both the lumbar and sacral
  plexus, but primarily the tibial portion of the
  sciatic nerve.

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SENSORY INNERVATION OF THE KNEE

• Sensory innervation of the knee and associated
  ligaments is supplied primarily by spinal nerve
  roots from L3 to L5.
• The posterior tibial nerve is the largest
  afferent supply of the knee.
• The obturator and femoral nerve also supply some
  afferent innervation to the knee.

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MUSCULAR FUNCTION AT THE KNEE

• Muscles of the knee are described as two groups
• Knee extensors (quadriceps femoris)
• Knee flexor-rotators

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ACTIONS INNERVATIONS OF MUSCLES THAT CROSS THE
KNEE
Muscle Action Innervation Plexus
Sartorius Hip flexion, external rotation, and abduction Knee flexion and internal rotation Femoral nerve Lumbar
Gracilis Hip flexion and abduction Knee flexion and internal rotation Obturator nerve Lumbar
Quadriceps Rectus Femoris Vastus Group Knee extension and hip flexion Knee extension Femoral nerve Lumbar
Popliteus Knee flexion and internal rotation Tibial nerve Sacral
Semimembranosus Hip extension Knee flexion and internal rotation Sciatic nerve (tibial portion) Sacral
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ACTIONS INNERVATIONS OF MUSCLES THAT CROSS THE
KNEE
Muscle Action Innervation Plexus
Semitendanosus Hip extension Knee flexion and internal rotation Sciatic nerve (tibial portion) Sacral
Biceps femoris (short head) Knee flexion and external rotation Sciatic nerve (common fibular portion) Sacral
Biceps femoris (long head) Hip extension Knee flexion and external rotation Sciatic nerve (tibial portion) Sacral
Gastrocnemius Knee flexion Ankle plantar flexion Tibial nerve Sacral
Plantaris Knee flexion Ankle plantar flexion Tibial nerve Sacral
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EXTENSORS OF THE KNEE

• Quadriceps femoris

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QUADRICEPS FEMORIS ANATOMIC CONSIDERATIONS

• Quadriceps femoris
• Rectus femoris
• Vastus lateralis
• Vastus medialis
• Vastus intermedius
• Contraction of the vastus group produces about
  80 of the extension torque at the knee. They
  only extend the knee.
• Contraction of the rectus femoris produces about
  20 of the extension torque at the knee. The
  rectus femoris muscle extends the knee and flexes
  the hip.
• The inferior fibers of the vastus medialis exert
  an oblique pull on the patella that help to
  stabilize it as it tracks through the
  intercondylar groove.

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QUADRICEPS CROSS-SECTION
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QUADRICEPS FEMORIS FUNCTIONAL CONSIDERATIONS

• The knee extensor muscles produce a torque that
  is about two thirds greater than that produced by
  the knee flexor muscles.
• Isometric activation stabilizes and protects
  the knee
• Eccentric activation controls the rate of
  descent of the bodys center of mass during
  sitting and squatting. Provides shock
  absorption at the knee.
• Concentric activation accelerates the tibia or
  femur toward knee extension. Used in raising the
  bodys center of mass during uphill running,
  jumping, or standing from a seated position.

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EXTERNAL TORQUE DEMANDS AGAINST QUADRICEPS

• During tibial-on-femoral knee extension, the
  external moment arm of the weight of the lower
  leg increases from 90 to 0 degrees of knee
  flexion.
• During femoral-on-tibial knee extension (as in
  rising from a squat position), the external
  moment arm of the upper body weight decreases
  from 90 to o degrees of knee flexion.

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EXTERNAL (FLEXION) TORQUES
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QUADRICEPS WEAKNESS PATHOMECHANICS OF EXTENSOR
LAG

• People with significant weakness of the
  quadriceps often have difficulty completing the
  full range of tibial-on-femoral extension of the
  knee.
• They fail to produce the last 15 to 20 degrees of
  extension.
• This is referred to as extensor lag.
• Swelling or effusion of the knee increases the
  likelihood of an extensor lag.
• Swelling increases intra-articular pressure.
• Passive resistance from hamstring muscles can
  also limit full knee extension.

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FUNCTIONAL ROLE OF THE PATELLA

• The patella acts as a spacer between the femur
  and the quadriceps muscle, which increases the
  internal moment arm of the knee extensor
  mechanism.
• Torque is the product of force and its moment
  arm.
• The patella augments the extension torque at the
  knee.

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USE OF PATELLA TO INCREASE THE INTERNAL MOMENT ARM
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PATELLOFEMORAL JOINT KINETICS

• The patellofemoral joint is exposed to high
  magnitudes of compression force.
• 1.3 times body weight during walking on level
  surfaces
• 2.6 times body weight during performance of a
  straight leg raise
• 3.3 times body weight during climbing of stairs
• 7.8 times body weight during deep knee bends
• The knee flexion angle influences the amount of
  force experienced at the joint.
• Both the compression force and the area of
  articular contact on the patellofemoral joint
  increase with knee flexion, reaching a maximum
  between 60 and 90 degrees.

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TWO INTERRELATED FACTORS ASSOCIATED WITH JOINT
COMPRESSION FORCE ON THE PATELLOFEMORAL JOINT

• 1. Force within the quadriceps muscle
• 2. Knee flexion angle

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COMPRESSION FORCE WITHIN THE PATELLOFEMORAL JOINT
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FACTORS AFFECTING THE TRACKING OF THE PATELLA
ACROSS THE PATELLOFEMORAL JOINT

• If the patellofemoral joint has less than optimal
  congruity, it can lead to abnormal tracking of
  the patella.
• The patellofemoral joint is then subjected to
  higher joint contact stress, increasing the risk
  of degenerative lesions and pain.
• This can lead to patellofemoral pain syndrome and
  osteoarthritis.
• Excessive tension in the iliotibial band or
  lateral patellar retinacular fibers can add to
  the natural lateral pull of the patella.

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ROLE OF QUADRICEPS MUSCLE IN PATELLAR TRACKING

• As the knee is extending, the quadriceps muscle
  pulls the patella superior, slightly lateral, and
  slightly posterior in the intercondylar groove.
• Vastus lateralis has a larger cross sectional
  area and force potential.
• The quadriceps angle (Q-angle) is a measure of
  the lateral pull of the quadriceps.
• Q-angles average about 13 to 15 degrees.

87
QUADRICEPS PULL Q-ANGLE
88
LOCAL FACTORS THAT NATURALLY OPPOSE THE LATERAL
PULL OF THE QUADRICEPS ON THE PATELLA

• Local factors
• The lateral facet of the intercondylar groove is
  normally steeper than the medial facet which
  blocks or resists the approaching patella.
• The oblique fibers of the vastus medialis balance
  the lateral pull.
• Medial patellar retinacular fibers are oriented
  in medial-distal and medial directions (referred
  to as the medial patellofemoral ligament). Often
  ruptured after a complete lateral dislocation of
  the patella.

89
LOCALLY PRODUCED FORCES ACTING ON THE PATELLA
90
GLOBAL FACTORS

• Factors that resist excessive valgus or the
  extremes of axial rotation of the tibiofemoral
  joint favor optimal tracking of the
  patellofemoral joint.
• Excessive genu valgum can increase the Q-angle
  and thereby increase the lateral bowstring force
  on the patella. Increased valgus can occur from
  laxity or injury to the MCL.
• Weakness of the hip abductors (coxa vara) can
  allow the hip the slant excessively medial, which
  in turn places excessive stress on the medial
  structures of the knee.
• Excessive internal rotation of the knee, which is
  related to excessive pronation of the subtalar
  joint during walking.

91
BOWSTRING FORCE ON THE PATELLA
92
PATELLOFEMORAL PAIN SYNDROME

• Patellofemoral pain syndrome (PFPS) is one of the
  most common orthopedic conditions encountered in
  sports medicine outpatient settings.
• It accounts for about 30 of all knee disorders
  in women and 20 in men.
• Diffuse peripatellar or retropatellar pain with
  an insidious onset.
• Aggravated by squatting, climbing stairs, or
  sitting with knees flexed for a prolonged period
  of time.
• Pain or fear of repeated dislocations may be
  severe enough to significantly limit activities.
• Abnormal movement (tracking) and alignment of the
  patella within the intercondylar groove.

93
CAUSES OF EXCESSIVE LATERAL TRACKING OF THE
PATELLA
Structural of Functional Cause Specific Examples
Bony Dysplasia Dysplastic lateral facet of the intercondylar groove of the femur (shallow groove) Dysplastic or high patella (patella alta)
Excessive laxity in periarticular connective tissue Laxity of medial patellofemoral ligament Laxity or attrition of medial collateral ligament Laxity or reduced height of the medial longitudinal arch of the foot (overpronation of the subtalar joint)
Excessive stiffness or tightness in periarticular connective tissue and muscle Increased tightness in the lateral patellar retinacular fibers or iliotibial band Increased tightness of the internal rotator or adductor muscles of the hip
94
CAUSES OF EXCESSIVE LATERAL TRACKING OF THE
PATELLA
Structural of Functional Cause Specific Examples
Extremes of bony or joint alignment Coxa varus Excessive anteversion of the femur External tibial torsion Large Q-angle Excessive genu vlagum
Muscle weakness Weakness or poor control of Hip external rotator and abductor muscles The vastus medialis (oblique fibers) The tibialis posterior muscle (related to overpronation of the foot)
95
TREATMENT PRINCIPLES FOR ABNORMAL TRACKING AND
CHRONIC DISLOCATION OF THE PATELLOFEMORAL JOINT

• Reduce the magnitude of the lateral bowstring
  force on the patella.
• Strengthen hip abductor and external rotator
  muscles.
• Strengthen the oblique fibers of the vastus
  medialis.
• Strengthen the medial longitudinal arch of the
  foot.
• Stretch tight periarticular connective tissues of
  the hip and knee.
• Mobilize the patella.
• Use a patellar brace or using a foot orthosis to
  reduce excessive pronation of the foot.
• Patellar taping to guide the patellas tracking.

96
KNEE FLEXOR-ROTATOR MUSCLES

• With the exception of the gastrocnemius, all
  muscles that cross posterior to the knee have the
  ability to flex and to internally or externally
  rotate the knee.
• Flexor-rotator group
• Hamstrings
• Sartorius
• Gracilis
• Popliteus
• The flexor-rotator group has three sources of
  innervation
• Femoral
• Obturator
• Sciatic

97
KNEE FLEXOR-ROTATOR MUSCLES FUNCTIONAL ANATOMY

• The hamstring muscles have their proximal
  attachment on the ischial tuberosity.
• The hamstrings extend the hip and flex the knee.
• In addition to flexing the knee, the medial
  hamstrings (semimembranosus and semitendanosus)
  internally rotate the knee.
• The biceps femoris flexes and externally rotates
  the knee.
• The sartorius, gracilis, and semitendinosus
  attach to the tibia using a common, broad sheet
  of connective tissue known as the pes anserinus.
  The pes muscles are internal rotators of the
  knee.

98
KNEE FLEXOR-ROTATOR MUSCLES GROUP ACTION
99
KNEE AS A PIVOT POINT AXIAL ROTATION
100
POPLITEUS MUSCLE KEY TO THE KNEE

• The popliteus muscle is an important internal
  rotator and flexor of the knee joint.
• As the extended and locked knee prepares to flex,
  the popliteus provides an important internal
  rotation torque that helps to mechanically unlock
  the knee.
• The popliteus has an oblique line of pull.
• This muscle has the most favorable leverage of
  all of the knee flexor muscles to produce a
  horizontal plane rotation torque on an extended
  knee.

101
CONTROL OF TIBIAL-ON-FEMORAL OSTEOKINEMATICS

• An important action of the flexor-rotator muscles
  is to accelerate or decelerate the lower leg
  during the swing phase of walking or running.
• Through eccentric action, the muscles help to
  dampen the impact of full knee extension.
• They shorten the functional length of the lower
  limb during the swing phase.

102
CONTROL OF FEMORAL-ON-TIBIAL OSTEOKINEMATICS

• The muscular demand needed to control
  femoral-on-tibial motions is generally larger and
  more complex than that needed for most
  tibial-on-femoral knee motions.
• The sartorius may have to simultaneously control
  up to five degrees of freedom (i.e. two at the
  knee and three at the hip).

103
ABNORMAL ALIGNMENT OF THE KNEE FRONTAL PLANE

• In the frontal plane the knee is normally aligned
  in about 5 to 10 degrees of valgus.
• Deviation from this alignment is referred to as
  excessive genu valgum or genu varum.

104
GENU VARUM WITH UNICOMPARTMENTAL OSTEOARTHRITIS
OF THE KNEE

• During walking across level terrain, the joint
  reaction force at the knee is about 2.5 to 3
  times body weight.
• The ground reaction force passes just lateral to
  the heel, then upward to the medial knee.
• In some individuals this asymmetric dynamic
  loading can lead to excessive wear of the
  articular cartilage and ultimately to medial
  unicompartmental osteoarthritis.
• Thinning of the articular cartilage and meniscus
  on the medial side can lead to genu varum, or a
  bow-legged deformity, which will further increase
  medial compartment loading.

105
GENU VARUM (BOW-LEG)
106
GENU VARUM (BOW-LEG) / HIGH TIBIAL OSTEOTOMY
107
EXCESSIVE GENU VALGUM

• Several factors can lead to excessive genu valgum
  or knock-knee.
• Previous injury, genetic predisposition, high
  body mass index, and laxity of ligaments.
• Coxa vara or weak hip abductors can lead to genu
  valgum.
• Excessive foot pronation
• Standing with a valgus deformity of approximately
  10 degrees greater than normal directs most of
  the joint compression force to the lateral joint
  compartment.
• This increased regional stress may lead to
  lateral unicompartmental osteoarthritis.

108
GENU VALGUM
109
WIND-SWEPT DEFORMITY / GENU VALGUM GENU VARUM
110
WIND-SWEPT DEFORMITY BEFORE AFTER KNEE
REPLACEMENT
111
SAGITTAL PLANE GENU RECURVATUM

• Full extension with slight external rotation is
  the knees close-packed, most stable position.
• The knee may be extended beyond neutral an
  additional 5 to 10 degrees.
• Hyperextension beyond 10 degrees of neutral is
  called genu recurvatum (Latin genu, knee,
  recurvare, to bend backward).
• Chronic, overpowering (net) knee extensor torque
  eventually overstretches the posterior structures
  of the knee.
• Due to poor postural control or neuromuscular
  disease (i.e. polio). That causes spasticity and
  / or paralysis of the knee flexors.

112
GENU RECURVATUM