KNEEKNEE

Tibiofemoral JointTibiofemoral Joint

Modified hinge joint.Modified hinge joint.Articulating surfaces:Articulating surfaces:

Femoral condyles:Femoral condyles:Convex and asymmetric.Convex and asymmetric.

Medial condyle is larger than the lateral.Medial condyle is larger than the lateral.Condyles are separated anteriorly by Condyles are separated anteriorly by patellar groove.patellar groove.Condyles are separated posteriorly by Condyles are separated posteriorly by intercondylar fossa.intercondylar fossa.

Tibiofemoral JointTibiofemoral Joint

Articulating surfaces:Articulating surfaces:Tibial plateaus:Tibial plateaus:

Concave and asymmetric.Concave and asymmetric.

Articular surface of medial plateau is Articular surface of medial plateau is 50% larger than that of lateral.50% larger than that of lateral.

Separated by intercondylar tubercles.Separated by intercondylar tubercles.

MenisciMenisci

Wedge-shaped fibrocartilage discs.Wedge-shaped fibrocartilage discs.Ends of menisci = horns:Ends of menisci = horns:

Attached to intercondylar tubercles.Attached to intercondylar tubercles.Coronary ligaments:Coronary ligaments:

Attach menisci to rims of plateaus.Attach menisci to rims of plateaus.Anterior transverse ligament:Anterior transverse ligament:

Joins menisci and allows them to move Joins menisci and allows them to move together.together.

MenisciMenisci

Medial meniscus:Medial meniscus:

Larger of the two.Larger of the two.

More securely attached.More securely attached.

Also attached to medial collateral ligament Also attached to medial collateral ligament and to semimembranosus muscle.and to semimembranosus muscle.

More often injured than lateral.More often injured than lateral.

MenisciMenisci

Lateral meniscus:Lateral meniscus:Attached to posterior cruciate ligament:Attached to posterior cruciate ligament:

Via meniscofemoral ligament.Via meniscofemoral ligament.

Attached to popliteus muscle.Attached to popliteus muscle.

MenisciMenisci

Functions:Functions:

Enhance stability of knee:Enhance stability of knee:Deepen articular surfaces.Deepen articular surfaces.

Distribute weight.Distribute weight.

Reduce friction between articular surfaces.Reduce friction between articular surfaces.

MenisciMenisci

Movement:Movement:Medial meniscus moves posteriorly during Medial meniscus moves posteriorly during flexion:flexion:

Due to tension in semimembranosus Due to tension in semimembranosus muscle.muscle.

Medial meniscus drawn forward during Medial meniscus drawn forward during extension:extension:

Due to tension in anterior capsular fibers.Due to tension in anterior capsular fibers.

MenisciMenisci

Movement:Movement:

Lateral meniscus moves posteriorly during Lateral meniscus moves posteriorly during flexion:flexion:

Drawn by tension in popliteal expansion.Drawn by tension in popliteal expansion.

Distorts more than medial meniscus.Distorts more than medial meniscus.

Joint CapsuleJoint Capsule

Large and lax.Large and lax.Deficient on lateral condyle:Deficient on lateral condyle:

For passage of popliteal tendon.For passage of popliteal tendon.Anterior wall replaced by quadriceps Anterior wall replaced by quadriceps

tendon.tendon.Excludes cruciate ligaments.Excludes cruciate ligaments.Commonly communicates with synovial Commonly communicates with synovial

bursae.bursae.

BursaeBursae

Suprapatellar:Suprapatellar:

Upward expansion of synovial cavity Upward expansion of synovial cavity between femur and quadriceps muscle and between femur and quadriceps muscle and tendon.tendon.

Proximally receives insertion of articularis Proximally receives insertion of articularis genus muscle.genus muscle.

BursaeBursae

Prepatellar:Prepatellar:Lies between superficial surface of patella Lies between superficial surface of patella and skin.and skin.

Deep Infrapatellar:Deep Infrapatellar:Lies between patellar ligament and tibia.Lies between patellar ligament and tibia.

BursaeBursae

Subpopliteal.Subpopliteal.

Gastrocnemius:Gastrocnemius:Under medial head of gastrocnemius.Under medial head of gastrocnemius.

BursaeBursae

Anserine bursa:Anserine bursa:

Between pes anserinus and tibial collateral Between pes anserinus and tibial collateral ligament.ligament.

Note: pes anserinus = combined tendons Note: pes anserinus = combined tendons of of semitendinosus, gracilis, and sartorius.semitendinosus, gracilis, and sartorius.

LigamentsLigaments

Collaterals:Collaterals:Medial (tibial):Medial (tibial):

Attachments:Attachments:

Medial femoral condyle.Medial femoral condyle.Proximal tibia.Proximal tibia.

Partly continuous with adductor magnus Partly continuous with adductor magnus tendon.tendon.Attached to medial meniscus.Attached to medial meniscus.Distally separated from tibia by genicular Distally separated from tibia by genicular vessels and nerves.vessels and nerves.

LigamentsLigaments

Collaterals:Collaterals:Lateral (fibular):Lateral (fibular):

Splits tendon of biceps femoris muscle.Splits tendon of biceps femoris muscle.

Separated from lateral meniscus by Separated from lateral meniscus by popliteal popliteal tendon.tendon.

LigamentsLigaments

Anterior cruciate:Anterior cruciate:

Weakest of cruciates.Weakest of cruciates.

Slack during flexion and taut during Slack during flexion and taut during extension.extension.

Prevents backward sliding of femur on Prevents backward sliding of femur on tibia.tibia.

Prevents hyperextension of knee.Prevents hyperextension of knee.

LigamentsLigaments

Posterior cruciate:Posterior cruciate:

Taut during flexion and slack during Taut during flexion and slack during extension.extension.

Prevents forward sliding of femur on tibia.Prevents forward sliding of femur on tibia.

Prevents hyperflexion of knee.Prevents hyperflexion of knee.

MovementsMovements

Flexion:Flexion:First part (0 to 25 degrees):First part (0 to 25 degrees):

Posterior rolling and spinning.Posterior rolling and spinning.

Anterior sliding of femoral condyles on Anterior sliding of femoral condyles on tibial tibial plateaus.plateaus.

Extension:Extension:First part:First part:

Femoral condyles roll anteriorly and slide Femoral condyles roll anteriorly and slide posteriorly.posteriorly.

Followed by rolling and spinning of Followed by rolling and spinning of condyles.condyles.

MovementsMovements

Lateral-medial rotation of tibia:Lateral-medial rotation of tibia:At 90 degrees of knee flexion:At 90 degrees of knee flexion:

Up to 40 degrees of lateral rotation.Up to 40 degrees of lateral rotation.

Up to 30 degrees of medial rotation.Up to 30 degrees of medial rotation.

Greater than 90 degrees of flexion:Greater than 90 degrees of flexion:Medial and lateral rotation ROM Medial and lateral rotation ROM

decreases.decreases.

Locking at Full ExtensionLocking at Full Extension

During final few degrees of extension:During final few degrees of extension:Femur rotates medially on tibia.Femur rotates medially on tibia.

(Note that tibia would also rotate laterally on (Note that tibia would also rotate laterally on femur.)femur.)

Knee is brought into close-packed position:Knee is brought into close-packed position:Tibial tubercles are lodged in intercondylar notch.Tibial tubercles are lodged in intercondylar notch.Menisci are tightly interposed between tibial and Menisci are tightly interposed between tibial and

femoral condyles.femoral condyles.= Locked or screw-home mechanism.= Locked or screw-home mechanism.

Popliteus laterally rotates femur for unlocking at Popliteus laterally rotates femur for unlocking at beginning of knee flexion.beginning of knee flexion.

AxesAxes

Mechanical axis:Mechanical axis:From head of femur to head of talus.From head of femur to head of talus.

Almost equivalent to anatomic axis of tibia.Almost equivalent to anatomic axis of tibia.Anatomic axis:Anatomic axis:

Extends along femoral shaft.Extends along femoral shaft.

AxesAxes

Physiologic valgus:Physiologic valgus:Normal angle at knee where femoral and Normal angle at knee where femoral and tibial axes meet:tibial axes meet:

170 – 175 degrees.170 – 175 degrees.

AxesAxes

Genu valgum:Genu valgum:Lateral deviation of tibia.Lateral deviation of tibia.

Less than 170 degrees.Less than 170 degrees.

Results in “knock knees.”Results in “knock knees.”

AxesAxes

Genu varum:Genu varum:Medial deviation of tibia.Medial deviation of tibia.

Greater than 170 degrees.Greater than 170 degrees.

Results in “bow legs.”Results in “bow legs.”

Patellofemoral JointPatellofemoral Joint

During knee flexion/extension:During knee flexion/extension:

Central ridge of patella slides along central Central ridge of patella slides along central groove of femur.groove of femur.

Patellofemoral JointPatellofemoral Joint

During flexion:During flexion:Tibia moves posteriorly.Tibia moves posteriorly.

Ligamentum patellae pulls patella distally Ligamentum patellae pulls patella distally and posteriorly:and posteriorly:

Causes patella to remain firmly in Causes patella to remain firmly in apposition apposition to femur.to femur.

Patellofemoral JointPatellofemoral Joint

During extension:During extension:

Patella is pulled proximally by quadriceps.Patella is pulled proximally by quadriceps.

Vastus lateralis tends to pull patella Vastus lateralis tends to pull patella laterally.laterally.

Vastus medialis oblique counteracts Vastus medialis oblique counteracts vastus vastus lateralis.lateralis.

Patellofemoral JointPatellofemoral Joint

Q-angle:Q-angle:

Formed by vector of quadriceps:Formed by vector of quadriceps:From ASIS to middle of patella.From ASIS to middle of patella.

And vector of pull of ligamentum patellae:And vector of pull of ligamentum patellae:From tibial tubercle to middle of patella.From tibial tubercle to middle of patella.

15 degrees.15 degrees.