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Updated: Oct 2 2023

Ligaments of the Knee

Images
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
  • Introduction
    • A diarthrodial joint that allows simultaneous rotation and translation
      • Overview of Knee Ligament Function
      • Ligament
      • 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 toaxial rotation
      • Lateral Structures of Knee
      • Layer 1
      • 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 1
      • 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
  • ACL
    • 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 flexion and loose in 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
          • ACL/PCL bundles
          • ACL
          • PCL
          • Tight in flexion
          • AM
          • AL
          • Tight in extension
          • PL
          • PM
  • PCL
    • 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 origin 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
  • MCL
    • 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 valgus load and 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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