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 Deep: Arcuate ligament, coronary ligament, popliteus tendon, popliteofibular 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 login to view 8 more bullets 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 login to view 12 more bullets variable meniscofemoral ligaments originate from the posterior horn of the lateral meniscus and insert into the substance of the PCL. These include login to view 2 more bullets 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 login to view 11 more bullets 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 login to view 1 more bullet 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 login to view 3 more bullets 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 login to view 2 more bullets length 59mm attachments femoral login to view 1 more bullet tibial login to view 1 more bullet 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