Knee

TERMINOLOGY

Abbreviations

• Origin (O), insertion (I), function (F)

GROSS ANATOMY

Overview

• Largest and most complex joint

Hinge joint throughout its main range of motion

Stability is maintained by ligaments, tendons, capsule, and menisci
• Motion of knee and relationship of osseous structures

In full flexion

– Supporting ligaments are not taut and rotation of leg is allowed

During knee extension

– Patella slides upward on femur, engaging with femoral trochlea until near full extension

– Femoral condyles roll forward on tibial condyles and menisci

– Lateral femoral condyle is shorter anteroposteriorly than medial so reaches full extension earlier

– Medial tibial condyle continues to slide after lateral stops rotating slightly laterally on femur (“screw home” mechanism)

– Tightens cruciate ligaments and stabilizes knee in extension

Initiating flexion from fully extended knee

– Requires slight medial rotation of tibia, produced by popliteus muscle

– Unlocks joint, allowing remainder of motion to take place

IMAGING ANATOMY

Osseous Anatomy

• Distal femur

Medial femoral condyle larger than lateral

Anteriorly, V-shaped trochlear groove accommodates patella
• Proximal tibia

Gerdy tubercle anterolateral just distal to joint

Tibial tubercle (apophysis) anterior and slightly lateral, several cm distal to joint
• Proximal fibula

Posterolateral relative to tibia
• Tibiofibular joint

True synovial joint; subject to any arthritic process

Connects to knee joint in 10%
• Patella

Triangular sesamoid bone wider at base superiorly than at apex inferiorly

Nonarticular outer surface may develop prominent enthesopathy where quadriceps tendon I blends into O of inferior patellar tendon

Bipartite (multipartite) patella: Always upper outer quadrant; osseous fragments may not appear to “match,” but cartilage is continuous over defect

Articular Capsule

• Complex, noncontiguous structure

Extensor Mechanism

• Quadriceps

Quadriceps tendon inserts onto anterosuperior surface of patella

Tendon contributions from rectus femoris, vastus lateralis, medialis, and intermedius muscles

3-layered structure but may have 1-5 laminae separated by fibrofatty connective tissue

– Rectus femoris → anterior lamina, which continues over patella as prepatellar quadriceps continuation

– Vastus lateralis and medialis → middle lamina

– Vastus intermedius → posterior lamina

Tendons contribute not only to their own lamina but also to other lamina
• Patellar tendon

Runs from inferior pole of patellar to tibial tuberosity

– Rectus femoris fibers that course over patella strengthen continuity with quadriceps tendon

Fibers of vastus lateralis and medialis contribute to lateral and medial patellar retinacula, respectively
• Medial retinaculum

3-layered fascial sheet between patella and medial femoral condyle

– Superficial layer: Investing fascia of thigh (crural fascia)

– Middle layer: Medial collateral ligament (MCL) and medial patellofemoral ligament (MPFL)

– Deep layer: Knee joint capsule to which synovium is attached

MPFL is strongest component of medial retinaculum

– Contributes 60% of medial patellar stability

– Extends from superomedial aspect patella to adductor tubercle at attachment of MCL

– Femoral attachment of MPFL has transverse band (outer fibers) and oblique band (inner fibers)

Transverse fibers cross superficial to MCL

Oblique fibers attach superficially onto anterior fibers of MCL
• Lateral retinaculum (rarely injured)

3-layered fascial sheet between patella and lateral femoral condyle

– Superficial layer: Investing fascia of thigh (crural fascia)

– Intermediate layer: Longitudinal fibers of iliotibial band and more transverse fibers from iliotibial band (iliotibial band-patella fibers)

– Deep layer: Lateral patellofemoral ligament (indistinct thickening of joint capsule)

Fat Pads

• Suprapatellar: Anterior and posterior (prefemoral) to suprapatellar bursa
• Infrapatellar (Hoffa fat pad): Distal to patella, deep to capsule, and superficial to synovium
• Posterior: Posterior joint margin extending into intercondylar region

Medial Supporting Structures

• Superficial (layer 1)

Pes anserinus: Anteromedial tibial I

– Sartorius embedded in crural fascia

– Gracilis immediately deep to sartorius

– Semitendinosus immediately deep to gracilis

– All insert onto anteromedial aspect tibia

Semimembranosus: Posteromedial I

– Oblique popliteal arm → oblique popliteal ligament (OPL) along posterior capsule knee

– Direct arm → groove at posteromedial aspect tibia

– Anterior arm → medial aspect of tibia deep to superficial component MCL

– Capsular arm → posterior oblique ligament (POL), which is capsular thickening of posteromedial corner of knee
• Middle (layer 2)

Superficial MCL (longitudinal and oblique components)

– Runs slightly anteromedially from medial epicondyle to insert onto tibia 5 cm distal to joint line

– Anteriorly, longitudinal component fascia blends with superficial layer

– Posteriorly, oblique component blends with deep layer as POL
• Deep (layer 3)

Capsular layers (deep fibers of MCL) at midportion of knee

– Meniscofemoral ligament: From outer superior aspect of body of meniscus to either superficial MCL or femur

More posteriorly, superficial MCL blends with capsular layers of MCL

POL arises from oblique fibers of superficial MCL extending posteriorly

– Blends with posteromedial meniscus

– Receives fibers from semimembranosus tendon

– Envelops posteromedial aspect of femoral condyle

– Blends with OPL along posterior capsule of knee

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Apr 9, 2020 | Posted by admin in MUSCULOSKELETAL IMAGING | Comments Off

TERMINOLOGY

Abbreviations

GROSS ANATOMY

Overview

IMAGING ANATOMY

Osseous Anatomy

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Knee

Knee

Articular Capsule

Extensor Mechanism

Fat Pads

Medial Supporting Structures

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