Exam 2: Knee joint

Knee Joint Overview

(bicondylar) 2 Joints in 1 capsule

• Tibiofemoral

• Patellofemoral

Contradictory mobility and stability demands

Tibiofemoral Joint

• Bicondylar (or double condyloid) synovial joint

• Degrees of freedom

  • 2 rotatory available

  • 1 obvious DoF in function

• Convex femoral condyles/concave tibial plateau

Femur

Medial and lateral condyles form articulating surfaces

• Larger medial condyle (larger articulating surface)

• Separated by intercondylar notch

• Contains articulating surface for PFJ

Tibia

Flat tibial condyles/plateaus

• Longer medially (A/P direction)

• Slopes posteriorly

• Separated by bony spines

Tibiofemoral Articulation

Closed pack = full extension

• good bony congruency + stability

We have convex femoral condyles with a flat tibial
plateau - WHAT DOES THIS JOINT NEED TO BE FUNCTIONALLY
STABLE?!!!!!

• joint capsule, ligaments → static (No control of it)

• tendon, muscle → dynamic (motor control of knee)

Deviations from Ideal posture

LoG is anterior → wanting extension

Tension forces give internal moment of flexion to stop excessive extension

Tibiofemoral Alignment

Knee (Sagittal)

• knee surgery, injury —> No full extension

• Quads = Internal moment for extension

• Soleus = Internal moment for plantarfexion

Tibiofemoral angulation

Normal angulation:

• some vara

• femur is more oblique for femoral condyles to be in the same plane

Genu valgum:

• > 180 dg

• lateral tensile stress

Genu vara:

• < 180 dg

• medial compressive stress (hyaline cartilage + meniscus)

Role of Meniscus

Roles:

• Increase the concavity of the
  tibial articulating surfaces

  • good for femoral condyles

• Distribution of WB’ing forces

  • Stress → gives wider surface area → low WBing stress to hyaline cartilage

• Reducing friction between articulating surfaces (tibia + femur)

• Shock absorbers to decrease load on articular cartilage (can
  assume over 50% of load)

Meniscus structure

▪ Semicurcular fibrocartilagenous discs
▪ Wedge shaped (thick peripherally, thin centrally). —> inside

Menisci (Nutrition + Innervation)

Nutrition

• Synovial fluid primarily

• Only the outer 1/3 is vascular

• Capacity to heal/regenerate?

  • outside can be healed

Innervation

• Nociceptors

• Mechanoreceptors

  • Proprioceptive function: communicate w/ CNS via sensory messages → dynamic stability

Meniscal Attachments

Medial
▪ Tibia
▪ Patella
▪ Medial capsule
▪ MCL
▪ ACL
▪ PCL
▪ Semimembranosus

Lateral
▪ Tibia
▪ Patella
▪ ACL
▪ PCL
▪ Femur (meniscofemoral ligament)
▪ Popliteus

Joint Capsule

• Close packed position= full extension

• Loose packed position= 25-30 degrees flexion

• Contains both the PFJ and tibiofemoral joints

• Innervated w/ nociceptors and mechanoreceptors

  • Proprioceptive function

• 2 Layers

  • Superficial fibrous layer

  • Deep synovial layer

Joint Capsule fibrous layer

Anterior Portion

• Spans length of the patella

• Extensor Retinaculum

  • Medial retinaculum (MPFL)

  • Lateral retinaculum (LPFL)
    

Posterior Portion

• femoral condyles to tibial condyles

• reinforced by arcuate ligament (lateral) and oblique popliteal ligament (medial)

Joint capsule

Intracapsular

• Everything inside of the fibrous capsule

• ex: hyaline cartilage and deeper parts of lateral meniscus are intrasynovial getting nutrition from synovial fluid

Extrasynovial

• Inside the fibrous capsule but outside of the synovial layer
  ▪ ACL/PCL
  ▪ Fat pads

• they get nutrition from blood supply

MCL

• Superficial (origin)

  • Medial epicondyle of femur to pes anserinus

• Deep (insertion)

  • Continuous w/ joint capsule

  • Firmly attached to medial meniscus

▪ Direct blood supply

MCL Role

Primary:

• resists genu valgus stress via joint rxn force

• resists ER of tibia

Secondary:

• resists anterior shear (implicates ACL inury)

• works best in full extension and important in slight flexion

Injury of MCL: valgus stress

LCL

• Lateral femoral condyle to fibular head

• Joins biceps femoris at attachment

• Separate from the joint capsule

• Blood supply

Role of LCL

• resists genu varum stress

• resists ER of tibia (b/c insertion is further from origin and is @ more of angle)

• Best work in full extension and important in slight flexion

ACL (Anterior Cruciate ligament)

Proximal attachment= posterior medial aspect of lateral femoral condyle

Distal attachment= lateral edge of medial tibial spine

2 Bands

• Anterior/medial

• Posterior/lateral

Direct blood supply

ACL in multiple motions

Extension:

• PLB is more taut

Flexion 90 dg:

• both PLB and AMB are NOT taut and in loose pack

Flexion > 90 dg:

• AMB is more taut

Role of ACL

Primary:

• resist anterior shear on tibia (b/c insertion is further from origin)

• resist transverse and frontal combination

What leads to ACL tear

• loose pack (slightly flex) w/ valgus, IR of tibia

PCL’s role

Primary:

• resist posterior shear of tibia (b/c Insertion is further from origin)

Secondary:

• resist ER of tibia

Impact of Hamstring contraction

What tears PCL?

direct force anterior

Tibiofemoral Joint Function

2 Rotational DoF
▪ Flex/Ext
▪ ER/IR
▪ Ab/Add (valgus/varus - rot in frontal plane)

• ABD → distal end of tibia (knee valgus) and NO muscle control of it, so not really DoF

• ABD → distal end of tibia (knee varus) and NO muscle control of it, so not really DoF

Associated rolling and glide

Flex/Ext of Tibiofemoral Joint

Role of the meniscus
▪ Wedge shaped
▪ Assists in gliding
▪ Deformable
- Post during flexion
- Ant fduring ext.

rxn force from meniscus helps glide of femur

Role of cruciate ligaments

• ACL helps w/ ant glide of femur during flexion

• PCL helps w/ post glide of the femur during ext

Internal/External and Rotation (Med/Lat) of Tibiofemoral Joint

• Transverse plane

• Max rotation available at 90 deg of flex

• Tibial ER needed for full knee extension (open chain)

  • medial part needs to go more anteriorly b/c it is longer

  • for closed chain

    • tibial IR needed for full extension

ER → posterior glide of lateral parts + anterior glide of medial parts

Knee flexors

• hamstrings

• medial knee flexors → internal rotation (brings medial side back)

• lateral knee flexors → internal rotation

Active / Passive Insufficiency

Active insufficiency of hamstrings or passive insufficiency of RF

Flexor group

Fy = rotate tibia and posterior shear

Fx = compression

Extensor group of knee

Quadriceps

patella goes up and lateral and compress patellofemoral joint

Quads (patella)

Patella

• Anatomical pulley to increase MA of Quads

• Peak MA and peak force (length/tension) occur between 45 and 60 deg of flexion

  • Impact on torque production: 45-60 dg have a lot of force from quads

• No patella → smaller MA needing more force from quads

Quad in flexion

Fy (anterior shear + flexion)

Fx (parallel → compress tibia into femur)

@ 60 flexion → quads do NOT make anterior shear → No strain to ACL

Patellofemoral Joint

The Patella

• Triangular shaped bone articulating with the femoral condyles/sulcus

  • Vertical ridge separating into medial and lateral facets

    • helps w/ bony congruency

  • Odd facet

• Subject to high compressive
  forces (hyaline cartilage @ back of patella

• Anatomical pulley for the
  quadriceps

• Very incongruent joint

Congruence and Contact Pressures

Little to no contact in extension

• Variations in starting position

• Implications for stability: increased patella + femur contact press w/ flex
  

Variable contact pressures in flexion

• More stable in flexion (60-90 dg)

Motions of Patella

Knee Flexion
▪ Inferior glide
▪ Medial rotation
▪ Medial glide

Knee Extension
▪ Superior glide
▪ Lateral rotation
▪ Lateral glide

**Apex of the patella follows the tibial tubercle**

Frontal Plane Stability

At rest in extension…
▪ Normal valgus angle
▪ Shallow superior sulcus
▪ Lateral line of pull from quads

During flexion…
▪ Increased stability as patella glides inferior into deeper sulcus

More about frontal plane stability (longitudinal + transverse stabilizers)

Longitudinal stabilizers
▪ Patella tendon
▪ Quad tendon
▪ Patellotibial ligaments

Transverse stabilizers
▪ Extensor retinaculum
▪ MPFL
▪ Lateral lip of sulcus
▪ Muscle balance

PFJ Stresses

Stress= increased Force/unit area

• influenced by quadriceps activity (force) primarily!!!

  • to find joint rxn force of patella

Knee flexion angle for PF

Knee flexion angle matters somewhat in that it adds passive quadriceps tension

Open chain (do EMA, IMA, Quad force, ACL strain)

Close to ___ knee flexion, has high ACL strain

0 dg

Closed chain (do EMA, IMA, Quad force, ACL strain)

Closed chain pt 2 (do EMA, IMA, Quad force, PF stress)

Implications for Exercise

(Where should our patients with PFPS be exercising in closed chain?)

< 45 flexion → less PF stress in squat

> 45 flexion → more PF stress in squat

Why is the slope getting small going from 30 -60

b/c MA of Quad is greatest → not needing a lot of force → less of PFJ force

For these open chain, which would require more quad force at this position

• pulley b/c it’s @ 90 dg flexion meaning more PFJ stress

  • rope makes 90 dg angle to tibia, external moment is most

• NOT ankle weight

  • NONE of force is perpendicular to tibia → NO external moment

  • its external moment increases when going up

For these open chain, which would require more quad force at this position

• ankle weight b/c

  • gravity vector is perpendicular to tibia

  • more quad force → more PFJ stress

• NOT pulley b/c it’s NOT @ 90 dg to tibia

  • less from quad force → less PFJ stress

Cuff weight

cuff weight always going straight down being @ mercy of gravity

• NO pulley changing force vector

pulley

• resistance always making 90 dg to leg (tibia) regardless of ROM

• good challenge to quad throughout range

• quad force is pretty much the same

More of Frontal Plane stability (Q angle)

• line of ASIS → patella

• line of patella → tibial tuberosity

Anteversion → lateral tibial torsion → increase Q angle

Increase Q angle is NOT indication of PFJ pain