KNEEDr. Michael P. Gillespie

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. 2

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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.10

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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 TendonPatellar retinacular fibers

Quadriceps

Lateral Lateral collateral ligamentLateral patellar retinacular fibersIliotibial band

Biceps femorisTendon of the popliteusLateral head of gastrocnemius

Posterior Oblique popliteal ligamentArcuate popliteal ligament

PopliteusGastrocnemiusHamstrings, especially the tendon of semimembranosus

Posterior-Lateral Arcuate popliteal ligamentLateral collateral ligament

Tendon of popliteus

Medial Medial patellar retinacular fibersMedial collateral ligamentThickened fibers posterior-medially

Expansions from the tendon of the semimembranosusTendons 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 femorisBursa 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. 32

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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 knee’s 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 2:1. 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. 53

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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 ligamentsJoint contact laterallyCompression of the lateral meniscusMedial retinacular fibersPes 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 bandBiceps femoris tendonJoint contact mediallyCompression of the medial meniscusAnterior and posterior cruciate ligamentsGastrocnemius (lateral head) 58

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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)

1. Resists valgus (abduction)2. Resists knee extension3. Resists extremes of axial

rotation (especially knee external rotation)

1. Valgus-producing force with foot planted

2. Severe hyperextension of the knee

Lateral collateral ligament

1. Resists varus (adduction)2. Resists knee extension3. Resists extremes of axial

rotation

1. Varus-producing force with foot planted

2. Severe hyperextension of the knee

Posterior capsule 1. Resists knee extension2. Oblique popliteal ligament

resists knee external rotation

3. 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

1. Most fibers resist extension (either excessive anterior translation of the tibia, posterior translation of the femur, or a combination thereof)

2. Resists extremes of varus, valgus, and axial rotation

1. Large valgus-producing force the foot firmly planted

2. Large axial rotation torque applied to the knee, with the foot firmly planted

3. The above with strong quadriceps contraction with the knee in full or near-full extension

4. Severe hyperextension of the knee

Posterior cruciate ligament

1. Most fibers resist knee flexion (either excessive posterior translation of the tibia or anterior translation of the femur, or a combination thereof)

2. Resists extremes of varus, valgus, and axial rotation

1. Falling on a fully flexed knee (with ankle fully plantar flexed) such that the proximal tibia first strikes the ground

2. Any event that causes a forceful posterior translation of the tibia (i.e. “dashboard” injury) or anterior translation of the femur

3. Large axial rotation or valgus-varus applied torque

4. 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 knee’s 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 PlexusSartorius Hip flexion,

external rotation, and abductionKnee flexion and internal rotation

Femoral nerve Lumbar

Gracilis Hip flexion and abductionKnee flexion and internal rotation

Obturator nerve Lumbar

Quadriceps Rectus Femoris

Vastus Group

Knee extension and hip flexionKnee extension

Femoral nerve Lumbar

Popliteus Knee flexion and internal rotation

Tibial nerve Sacral

Semimembranosus

Hip extensionKnee flexion and internal rotation

Sciatic nerve (tibial portion)

Sacral

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ACTIONS & INNERVATIONS OF MUSCLES THAT CROSS THE KNEE

Muscle Action Innervation PlexusSemitendanosus 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 extensionKnee flexion and external rotation

Sciatic nerve (tibial portion)

Sacral

Gastrocnemius Knee flexionAnkle plantar flexion

Tibial nerve Sacral

Plantaris Knee flexionAnkle 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 body’s 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 body’s 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

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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.

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QUADRICEPS PULL & Q-ANGLE

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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.

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LOCALLY PRODUCED FORCES ACTING ON THE PATELLA

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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. 90

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BOWSTRING FORCE ON THE PATELLA

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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. 92

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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 ligamentLaxity or attrition of medial collateral ligamentLaxity 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 bandIncreased tightness of the internal rotator or adductor muscles of the hip

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CAUSES OF EXCESSIVE LATERAL TRACKING OF THE PATELLA

Structural of Functional Cause Specific Examples

Extremes of bony or joint alignment

Coxa varusExcessive anteversion of the femurExternal tibial torsionLarge Q-angleExcessive 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)

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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 patella’s tracking.

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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

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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.

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KNEE FLEXOR-ROTATOR MUSCLES: GROUP ACTION

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KNEE AS A PIVOT POINT – AXIAL ROTATION

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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.

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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.

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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).

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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.

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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.

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GENU VARUM (BOW-LEG)

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GENU VARUM (BOW-LEG) / HIGH TIBIAL OSTEOTOMY

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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.

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GENU VALGUM

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“WIND-SWEPT” DEFORMITY / GENU VALGUM & GENU VARUM

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“WIND-SWEPT” DEFORMITY BEFORE & AFTER KNEE REPLACEMENT

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SAGITTAL PLANE: GENU RECURVATUM Full extension with slight external rotation is

the knee’s 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.

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GENU RECURVATUM

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