Kinesiology of the Knee: Structure and Function

Medial Tibia-Femoral Compartment

- Medial Femoral Condyle

- Medial Aspect of Tibial Condyle

Lateral Tibia-Femoral Compartment

- Lateral Femoral Condyle

- Lateral Aspect of Tibial Condyle

Patello-Femoral Compartment

- Posterior Aspect of Patella

- Anterior Aspect of Femur

Knee Stability

- less osseous stability

- Primary = soft tissue (ligamentous/tendinous)

Knee Movement

- mostly sagittal (flexion/extension)

- some transverse (can move Tibia in IR/ER)

- frontal (passive)

Knee Function

- flexion/extension for running/walking/etc.

Distal Femur

large lateral & medial condyles for joint articulation

Femoral Epicondyles

projections from each condyle providing elevated sites for collateral ligaments

Intercondylar Notch

- passage for cruciate ligaments

- narrowing = increased risk of ACL injuries

Trochlear Groove

- anterior fusing of the condyles

- pathway for patellar movement

- concave M-L, slightly convex A-P

Lateral & Medial Facets

- sides of Trochlear Groove

- Lateral = much larger

- provides congruency & stability to prevent excessive lateral excursion of Patella

Medial Facet of Trochlear Groove

- more oval shaped

- much longer A-P than M-L

- matches with articular surfaces of Tibia

Patella's Natural Pull

Supero-lateral direction during movement.

Tibial Plateau

Flat surface for weight acceptance from femur.

Intercondylar Eminence

Attachment site for cruciate ligaments & meniscal attachments

Tibial Tuberosity

- Common palpable landmark

- site for quadriceps tendon insertion.

Fibula's Role

Aids in weight dispersion, indirect transfer via Interosseous Ligament

Patella

- Largest sesamoid bone

- embedded in quadriceps tendon

Posterior Surface of Patella

- covered with 4-5mm. of articular cartilage (absorb forces from knee flexion & WB)

- articulates with femur forming Patellofemoral Joint

Apex of Patella

- inferior end

- where patellar tendon inserts

- extends down to Tibial Tuberosity

Osgood-Schlatter Disease

- Inflammation at growth plate in adolescents

- more in males than females

- running/jumping increase quads demand & tendon pulls on bone at insertion

Q Angle

- angle between ASIS & patellar tendon

- average for men = 11.2

- average for women = 15.8

- greater genu valgum = larger Q angle

Genu Varum (knock-knee)

- feet are more lateral than the knees

- angles less than 165

Genu Valgum (bow-leg)

- feet more medial than knees

- angles greater than 180

Genu Recurvatum

- sagittal plane deformity - Hyperextension at knee.

Excessive Plantar-Flexion leads to...

Excessive extension at the knee

Joint Capsule

- Encloses tibiofemoral and patellofemoral joints

- ligaments blend in with capsule to provide support

Arcuate Complex

- Arcuate Popliteal L.

- LCL

- Popliteus M.

- reinforcement of the Postero-Lateral capsule of the knee

CT Reinforcement of Anterior Capsule

- Patellar Tendon

- Patellar Retinaculum

Muscular-Tendinous Reinforcement of Anterior Capsule

Quadriceps

CT Reinforcement of Lateral Capsule

- LCL

- Lateral Patellar Retinaculum

- IT Band

Muscular-Tendinous Reinforcement of Lateral Capsule

- Biceps Femoris

- Popliteus Tendon

- Lateral Gastrocnemius

CT Reinforcement of Posterior Capsule

- Oblique Popliteal L.

- Arcuate Popliteal L.

Muscular-Tendinous Reinforcement of Posterior Capsule

- Popliteus

- Gastrocnemius

- Hamstrings (SemiMem)

CT Reinforcement of Postero-Lateral Capsule

- Arcuate Popliteal L.

- LCL

- Popliteofibular L.

Muscular-Tendinous Reinforcement of Postero-Lateral Capsule

Tendon of Popliteus

CT Reinforcement of Medial Capsule

- Medial Patellar Retinaculum

- MCL

- Thickened Fibers Postero-Medially

Muscular-Tendinous Reinforcement of Medial Capsule

- Expansions from SemiMem Tendon

- Sartorius, Gracilis, SemiTen tendons

Postero-Lateral Knee Compartment

accounts for about 16% of all knee injuries

Synovial Membrane

- Lines internal capsule of the knee

- secretes synovial fluid

- can be a pain generating structure

Plicae

- Folds in synovial membrane

- incomplete resorption of this mesenchymal tissue during development

Fat Pads

- Reduce friction between friction & contractile structures

- can be source of knee pain

Bursae

Fluid-filled sacs reducing friction in joints.

Most prominent Bursa

- Suprapatella

- Deep Infrapatella

Menisci

- Crescent-shaped fibrocartilage in knee joint

- create "seats" for femoral condyles

Functions of Menisci

- improve congruency between tibia & femur

- reduce compressive stress acros Tibiofemoral Joint (70% of load)

- increase stabilty

- provide proprioception

- guide knee arthrokinematics

Characteristics of Menisci

- thick centers & thin inner edges

- anchored to intercondylar region of tibia via Ant. & Post. Horns

Medial Meniscus

C-shaped cartilage on inner knee.

Lateral Meniscus

O-shaped cartilage on outer knee.

Passive Support for Menisci

- Coronary/Meniscotibial Ligaments

- Transverse L. (anterior)

- Mesnicofemoral L. (posterior)

Coronary/Meniscotibial Ligaments

Attach menisci to tibial plateau.

Meniscofemoral Ligaments

- attaches posterior horn of lateral meniscus to the lateral aspect of the medial femoral condyle

Functions of Meniscofemoral Ligaments

- Keeps posterior root of lateral meniscus in place

- prevent excessive posterior translation of tibia

- limits meniscus movement to keep contact

Transverse Ligament

connects the anterior portions of the medial and lateral menisci

Dynamic Support for Menisci

- Quadriceps (anteriorly) - SemiMem (medial- posterior)

- Popliteus (postero-lateral)

Screw Home Mechanism

Knee locking mechanism during extension.

Hoop Stress

- menisci deform peripherally as they are compressed

- allows part of the compression force at the knee to be absorbed as circumferential tension

- tear of the meniscus especially the posterior horn, loses its ability to resist

Compression Forces

- 2.5-3x BW while climbing stairs

- menisci 3x area of joint contact & reduce pressure on cartilage

- complete lateral meniscectomy increases peak contact pressure by 230%

Meniscectomy

Surgical removal of meniscus, increases pressure.

Red Zone

- outer edge of meniscus

- tears heal quicker due to better blood supply

White Zone

- innermost edge of menisci

- bad blood supply, injured portion must be removed

White-Red/Pink Zone

- middle area between white & red zones

- intermediate blood supply

ACL Injury Association

50% of acute ACL injuries involve meniscal damage.

Mechanism of Injury (MOI) for ACL

Forceful axial rotation with partially flexed knee while WB

Medial Meniscus Injury

- 2x as likely to be injured compared to lateral

- attachment to MCL

Peak Contact Pressure

Increases to 230% with complete meniscus removal.

Meniscal Repair Criteria

Repair considered with good blood supply.

Meniscal Debridement

Used when blood supply is poor.

Articular Cartilage Type

Hyaline cartilage covering diarthrodial joint surfaces.

Cells composing Articular Cartilage

- Chonrdrocytes

- Extracellular Matrix (water & type 2 collagen/chondroitin sulfate)

Articular Cartilage Layers

- superficial (10-20%)

- middle (40-60%)

- deep (30%)

Superficial Layer of Articular Cartilage

- cells are parallel to articulating surface

- provides resistance to shear forces

Middle Layer of Articular Cartilage

- haphazard arrangement of cells & fibers

- provides resistance in any direction

Deep Layer of Articular Cartilage

- cells/fibers are perpendicular to surface

- resists compressive forces

Osteoarthritis Cause

Biochemical breakdown of articular cartilage.

Chondroitin Sulfate

- important structural component of cartilage

- provides a majority of resistance to compression

- dietary supplement used to treat OA

MCL Characteristics

- Flat, broad ligament with superficial and deep parts

- resists Valgus forces

- Superficial Fibers = stressed in 20-30 of knee flexion

- Deep Fibers = in full extension

LCL Characteristics

- Short, cord-like ligament from femur to fibula

- blends with biceps femoris tendon

Secondary Restraint to Valgus Forces

- Postero-Medial Capsule

- ACL & PCL

- Lateral Joint Contact

- Lateral Meniscus Compression

- Medial Patellar Retinaculum

- Pes Anserinus

- Medial Gastrocnemius

Secondary Restraint to Varus Forces

- Postero-Lateral Corner of Knee

- IT Band

- Bicep Femoris Tendon

- Medial Joint Contact

- Medial Meniscus Compression

- ACL & PCL

- Lateral Gastrocnemius

Cruciate Ligaments

- Cross-shaped ligaments providing knee stability

- poor blood supply, Medial Genicular Artery

- together, resist extremes of all knee motion

ACL Function

Resists anterior translation of the tibia.

Posterolateral Bundle

- taut in extension

- greatest restraint to Ant. translation until about 20 degrees of flexion

Anteromedial Bundle

- tight throughout flexion (more in higher degrees of flexion)

- anteromedial bundle increases tension from 20-90 degrees

Anterior Drawer Test

- Tests anteromedial bundle at 90 degrees flexion

Positive Anterior Drawer Test

Excursion > 6mm with empty end feel.

Lachman's Test

Tests posterolateral bundle near extension.

Antagonist for ACL

Quadriceps

Pivot Shift Test

Assesses overall knee stability.

PCL (posterior cruciate ligament)

- most taut in 90-120 degrees of flexion

- prevents posterior translation of Tibia on Femur

2 sets of PCL

- larger, antero-lateral

- smaller, postero-medial

PCL MOI

- knee flexion

- dashboard injuries

Osteokinematics of Knee

- 2 DOF

- Flexion/Extension (0-150 degrees)

- frontal plane motion, only passive

Evolute

- Migrating axis of rotation in knee movement

- Instantaneous Axis of Rotation moves due to large femur surface

Effects of Evolute movement

- alters length of internal moment arm of flexors/extensors

- causes increased Shear

Tibia on Femur (OKC) Extension

- Concave on Convex

- Roll & Slide = Anterior

Femoral on Tibia (CKC) Extension

- Convex on Concave

- Roll = Anterior

- Slide = Posterior

Factors guiding "Screw-Home" Mechanism

1. shape of medial femoral condyle

2. tension in ACL

3. lateral pull of quads

Ligaments relatively slack in Flexion

- ACL

- MCL

- PMC (Posterior-Medial Capsule)

- OPL (Oblique Popliteal Ligament)

Open Pack Position

25 degrees of knee flexion