https://upload.orthobullets.com/topic/3001/images/acl anterior view knee diagram.jpg
https://upload.orthobullets.com/topic/3001/images/acl tibia bony landmarks diagram.jpg
https://upload.orthobullets.com/topic/3001/images/acl tibia landmarks photo.jpg
https://upload.orthobullets.com/topic/3001/images/acl photo.jpg
https://upload.orthobullets.com/topic/3001/images/ampl bundles2_moved.jpg
https://upload.orthobullets.com/topic/3001/images/acl bundles flexion-extension.jpg
  • A diarthrodial joint that allows simultaneous rotation and translation
Overview of Knee Ligament Function
Primary function
Secondary function
Anterior Cruciate Ligament (ACL) Resists anterolateral displacement of the tibia on the femur Resists varus displacement at 0 degrees of flexion
Posterior Cruciate Ligament (PCL) Resists posterior tibial displacement, especially at 90 degrees of flexion Resists varus displacement at 0 degrees of flexion
Lateral Collateral Ligament (LCL) Resists varus displacement at 30 degrees of flexion Resists posterolateral rotatory displacement with flexion that is less than approximately 50 degrees
Popliteofibular Ligament / Posterior Lateral Corner (PLC) Resists posterolateral rotation of the tibia on the femur Resists varus angulation and posterior displacement of the tibia on the femur
Medial Collateral Ligament (MCL) Resists valgus angulation Works in concert with ACL to provide restraint to axial rotation
Lateral Structures of Knee
Layer I Iliotibial tract, biceps femoris
Common peroneal nerve lies between layer I and II
Layer 2 Patellar retinaculum
Layer 3 Superficial: LCL, fabellofibular ligament, ALL
Lateral geniculate artery runs between deep and superficial layer
DeepArcuate ligament, coronary ligament, popliteus tendonpopliteofibular ligament, capsule
Medial Structures of Knee
Layer I Sartorius and fascia (patellar retinaculum)
gracilis, semitendinosis, and saphenous nerve run between layer 1 and 2
Layer 2 Semimembranosus, superficial MCL, MPFL, posterior oblique ligament 
Layer 3 Deep MCL, capsule, coronary ligament

  • Function
    • prevents anterior translation of the tibia relative to the femur
  • Anatomy 
    • extrasynovial but intracapsular
    • origin
      • lateral femoral condyle
      • PL bundle originates posterior and distal to AM bundle (on femur)
    • insertion
      • broad and irregular 
      • anterior and between the intercondylar eminences of the tibia  
    • structure 
      • 33mm x 11mm in size                                                                       
      • two bundles  
        • anteromedial 
          • fibers are parallel in extension
          • fibers are externally rotated in flexion
          • tight in both flexion and extension
        • posterolateral 
          • PL bundle prevents pivot shift 
          • prevents internal tibial rotation with knee near extension
          • tight in extension, loose in flexion
  • Blood supply
    • middle geniculate artery
  • Innervation
    • contains significant innervation by posterior articular branches of tibial nerve
    • contains mechanoreceptors (Ruffini, Pacini, Golgi tendon organs, free-nerve endings) 
    • function of innervation
      • proprioception 
      • modulation of quadriceps function
  • Composition
    • 90% Type I collagen
    • 10% Type III collagen
  • Biomechanics
    • tensile strength 
      • native ACL 2200 N 
      • BPTB 3000N
      • quadrupled hamstring 4000N
Tight in flexion
Tight in extension
  • Function
    • prevents posterior translation of the tibia relative to the femur
    • PCL and PLC work in concert to resist posterior translation and posterolateral rotatory instability
  • Anatomy
    • extrasynovial but intracapsular
    • origin
      • medial femoral condyle  
    • insertion
      • tibial sulcus 
    • structure
      • 38mm x 13mm in size
      • two bundles  
        • anterolateral
          • shorter, thicker and stronger
          • in double bundle reconstruction, tensioned in mid flexion
        • posteromedial
          • longer, thinner, weaker
          • in double bundle reconstruction, tensioned in extension and high flexion
            • tensioning in extension protects against hyperextension
        • insertions
          • medial intercondylar ridge 
            • marks proximal border of femoral insertion
          • medial bifurcate ridge
            • separate the AL from PM bundle
      • variable meniscofemoral ligaments originate from the posterior horn of the lateral meniscus and insert into the substance of the PCL. These include  
        • Ligament of Humphrey (anterior to PCL) 
        • Ligament of Wrisberg (posterior to PCL)
    • blood supply
      •  middle geniculate artery
  • Biomechanics
    • strength: 2500 N (vs posterior translation)
LCL (lateral collateral ligament or fibular collateral ligament)
  • Function
    • resists varus angulation
    • works in concert with MCL to provide restraint to axial rotation
  • Anatomy 
    • origin
      • on lateral femoral condyle posterior and superior to insertion of popliteus 
    • path
      • runs superficial to popliteus  
    • insertion
      •  on the fibula anterior to the popliteofibular ligament on the fibula
      • capsule's most distal extent is just posterior to the fibula
    • structure
      • cord-like
  • Biomechanics
    • tight in extension and lax in flexion
    • strength: 750 N (vs varus stress)
PLC (posterolateral corner)
  • Function
    • works synergistically with the PCL to control external rotation and posterior translation
  • Anatomy  
    • included structures
      • LCL (295N)
      • popliteus muscle and tendon (680N)
      • popliteofibular ligament (229N)
      • lateral capsule
    • variable
      • arcuate ligament   
      • iliotibial band
      • fabellofibular ligament 
  • Function
    • resists valgus angulation
    • works in concert with ACL to provide restraint to axial rotation
  • Anatomy
    • origin
      • MFC to medial tibia extending down several centimeters  
    • structure
      • two components
        • superficial portion (tibial collateral ligament)  
          • lies just deep to gracilis and semitendinosus
          • originates from medial femoral epicondyle and inserts into periosteum of proximal tibia (deep to pes anserinus) 
          • the superficial portion of the MCL contributes 57% and 78% of medial stability at 5 degrees and 25 degrees of knee flexion, respectively.
          • the superficial MCL is the primary stabilizer to valgus stress at all angles
        • deep portion (medial capsular ligament) 
          • separated from superficial portion by a bursa
          • attaches to medial meniscus (coronary ligament)
          • divided into meniscofemoral and meniscotibial portions  
          • posterior fibers of the deep MCL blend with posteromedial capsule and POL
          • the deep MCL and posteromedial capsule act as secondary restraints to valgus stress at full knee extension.
  • Biomechanics
    • strength: 4000 N (vs valgus stress)
Posteromedial corner
  • Function
    • important for rotatory stability
  • Anatomy
    • lies deep to MCL
    • formed by
      • insertion of semimembranosus
      • posterior oblique ligament
        • resists tibial internal rotation in full extension 
      • oblique popliteal ligament
      • posterior capsule
Medial patellofemoral ligament (MPFL)
  • Function
    • provide restraint against lateral translation of the patella from 0° to 30° of knee flexion
  • Characteristics  
    • low tension throughout flexion-extension (2-10N of force)
    • isometric between 0° and 90°, then becomes slack beyond 90°
    • can withstand 200N before tearing
      • much lower load to failure than ACL (1725N)
  • Anatomy
    • lies in 2nd layer of medial soft tissue complex
    • 2 bundles
      • short oblique bundle, inserts on superior patellar pole
      • inferior straight bundle
    • femoral insertion
      • medial femoral condyle, distal to adductor tubercle and proximal to MCL attachment  
      • Schottle's point   
        • 1.3mm anterior to posterior femoral diaphyseal cortex
        • 2.5mm distal to posterior origin of medial femoral condyle
        • proximal to the level of the posterior point of Blumensaat's line
    • patellar attachment
      • fan-like structure inserting at junction between proximal-middle thirds of superomedial border of patella
  • Pathoanatomy
    • tears off femoral attachment > patellar attachment
      • some studies show otherwise
    • risk of 2nd dislocation is 13%
      • risk of 3rd dislocation (after 2nd dislocation) is 50%
Anterolateral Ligament
  • Function
    • rotational stability
  • Anatomy   
    • lies in Layer 3 with LCL 
    • characteristics
      • width 7mm at midpoint/near joint line
        • femoral attachment width 8mm
        • tibial attachment width 11mm
      • length 59mm
    • attachments
      • femoral
        • lateral femoral epicondyle
      • tibial
        • midway between Gerdy's tubercle and head of fibula
    • attachments to middle third of lateral meniscus body
      • meniscotibial portion (dot)   
      • meniscofemoral portion (asterisk)
    • lateral inferior genicular artery and vein contained between lateral meniscus and ALL at level of joint line 
    • NO connections to ITB
  • Pathoanatomy
    • Segond's fracture (associated with ACL rupture) is avulsion fracture of ALL    

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