Knee Complex – Exam Quick Notes

Anatomy & Functions

  • Bones: femur, tibia, patella (largest sesamoid)
  • Patella functions: ↑ extensor torque, centralizes quad force, smooths tendon glide, augments stability, protects anterior knee

Key Joints

  • Tibiofemoral: modified hinge, 2∘2^{\circ} freedom; femoral condyles (convex) on tibial plateaus (concave)
  • Patellofemoral: modified plane; patella tracks in trochlear groove
  • Superior tibiofibular: plane synovial; assists ankle motion

Alignment

  • Anatomical axes: femur oblique ↓/medial, tibia vertical
  • Tibiofemoral angle normal 180−185∘180{-}185^{\circ}
    • >185∘>185^{\circ} → genu valgum
    • <175∘<175^{\circ} → genu varum
  • Mechanical axis: hip-to-ankle line; equal WB in neutral

Patellar Position (Insall-Salvati)

  • Tendon length : patellar length ≈ 1:11:1
    • Alta = long tendon, high ride
    • Baja = low ride

Menisci

  • Medial & lateral fibrocartilage; carry 50−70%50{-}70\% load in gait/stairs
  • Vascular: full at birth → outer 13\frac13 adult (poor healing)

Capsule & Plicae

  • Largest in body; synovial (nutrition) + fibrous (support)
  • Plica types: infra-, supra-, medio-, lateral; inflamed ⇒ plica syndrome

Primary Ligaments

• Collaterals

  • MCL: resists valgus/lateral rotation; taut ext
  • LCL: resists varus; no meniscal attachment
    • Cruciate (intracapsular-extrasynovial)
  • ACL (PLS): checks anterior tibial shear; AMB taut flex, PMB near ext
  • PCL (SAL): checks posterior shear; ALB taut 80−90∘80{-}90^{\circ} flex

Muscle–Ligament Interplay

  • Quads & gastrocs ↑ anterior shear ⇒ stress ACL
  • Hamstrings & soleus ↑ posterior shear ⇒ assist ACL / stress PCL absent

Kinematics

• Flex-Ext

  • OKC: tibial plateau slides same direction; terminal ext → tibial ER
  • CKC: femoral condyles slide opposite; squat
    • Axial Rotation @ 90∘90^{\circ} flex: lateral ≈ 22 × medial
    • Screw-Home (last 20−30∘20{-}30^{\circ} ext)
  • Lock: tibial ER (OKC) / femoral IR (CKC) ≈ 10∘10^{\circ}
  • Unlock: opposite + flex

Patellofemoral Tracking

  • 0∘0^{\circ} ext: free; only apex contacts fat pad
  • 25∘25^{\circ} flex: enters groove
  • 90∘90^{\circ}: max contact (~13\frac13 surface)
  • 135∘135^{\circ}: odd + lateral facets only
  • Patellar motion: flex ↓ glide, ext ↑; slight medial rotation to unlock

Kinetics

  • Walking stance (≈20∘20^{\circ} flex): PFJ force 0.25−0.50.25{-}0.5 BW
  • Joint reaction ↑ sharply 30−60∘30{-}60^{\circ} flex; peaks squat ≈90∘\approx90^{\circ} then levels
  • Open-chain free weight: peak PFJ force ≈30∘30^{\circ}; variable resistance peak stress 60∘60^{\circ}, compression 75∘75^{\circ}

Stability Systems

  • Longitudinal: Quad tendon ↑ / patellar tendon ↓ ; patellotibial ligs (passive)
  • Transverse: VMO & VL (dyn); M/L patellofemoral ligs & ITB (passive)

Q-Angle

  • Landmarks: ASIS → mid-patella → tibial tubercle
  • Norms: males 13∘13^{\circ}, females 18∘18^{\circ}
    • ↑ ⇒ valgum; ↓ ⇒ varum

Deformity

  • Genu recurvatum: hyper-ext >10∘>10^{\circ}; due to laxity, quad spasticity, or hamstring paralysis