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Knee, Knee Femur, tibia and patella Tibiofemoral joint is the largest…

- - - - Patellar retinacular fibres are extensions of fibrous connective tissue covering the vastus lateralis, vastus medialis, and iliotibial band, and have attachments to femur, tibia, patella, quadriceps, patellar tendon, collateral ligaments and menisci.
        
        Clinical implication of tight retinaculum and surgical indication
    - - The iliotibial band, lateral head of the gastrocnemius, and biceps femoris are cut to better expose the lateral collateral ligament, popliteofibular ligament, popliteus tendon, and lateral meniscus, all of which reinforcing the lateral capsule.
    - - Posterior capsule is reinforced by the oblique popliteal and arcuate popliteal ligaments.
        
        The lateral and medial heads of the gastrocnemius and plantaris muscles are cut to expose the posterior capsule.
        
        Note the popliteus muscle deep in the popliteal fossa, lying partially covered by the fascial extension of the semimembranosus
    - - The tendons of the sartorius and gracilis are cut to better expose the superficial part of the medial collateral ligament and the medial capsule.
        
        Anterior 1/3: medial patellar retinacular fibres.
        
        Middle 1/3: medial collateral ligaments.
        
        Posterior 1/3: muscles
    - - Medial collateral ligament and lateral collateral ligaments are at the Tibiofemoral Joint
        
        MCL
        
        Protects against a valgus force in the frontal plane.
        
        Proximal: Medial epicondyle of femur
        
        Distal: Posterior section attaches on the medial epicondyle of tibia; anterior section attaches along the middle superior aspect of medial tibia distal to the pes anserine.
        
        Superficial part: 10 cm from femoral medial epicondyle to the medial-proximal tibia; blends with medial patellar retinacular fibres
        
        Deep part: shorter and oblique fibres, distal and posterior to superficial fibres, attached to posterior-medial capsule, medial meniscus and semimembranosus tendon
        
        LCL
        
        Protects against a varus force in the frontal plane.
        
        Proximal: Lateral epicondyle of the femur
        
        Distal: Head of the fibula on its lateral aspect. It also merges with the biceps femoris tendon
        
        Short, cordlike, more vertical, between lateral epicondyle and fibular head; blends distally with the biceps femoris tendon; no attachment to lateral meniscus.
        
        Popliteus tendon runs between lateral meniscus and LCL.
      - Anterior Cruciate Ligament and Posterior Cruciate Ligament are at the Tibiofemoral Joint
        
        ACL
        
        Prevents anterior displacement of tibia on femur and protects against hyperextension.
        
        Proximal: Anterior inter-condylar tibialfossa behind anterior attachment of medial meniscus
        
        Distal: Postero-medial aspect of lateral femoral condyle.
        
        Intracapsular ligaments, covered by synovial membranes
        
        Poor blood supply (medial genicular artery). Slow recovery
        
        Both are thick, strong and capable of withstanding large forces before rupture
        
        E.g. ACL –1,800 N
        
        Together they resist the extremes of all knee movements
        
        But primarily anterior-posterior shear forces between femur and tibia.
        
        Functions:
        
        Provide multiple planar dynamic stability to the knee
        
        Restrains anterior-posterior sliding between tibia and femur
        
        Contribute to proprioception of the knee
        
        PCL
        
        Prevents posterior displacement of the tibia on the femur and protects against hyperflexion.
        
        Proximal: Posterior tibial spine
        
        Distal: Travels medial to the ACL to the anterolateral surface of medial femoral condyle.
      - "Supporting" cast of
        
        Arcuate ligament
        
        Bblique popliteal ligament
        
        Popliteo-fibular ligament
        
        Ligament of Humphrey (anterior menisco-femoral ligament)
        
        Ligament of Wrisberg (posterior femoral ligament)
        
        Arcuate ligament
        
        Protects the postero-lateral capsule against hyper-extension and rotational forces.
        
        Oblique Popliteal Ligament
        
        Protects posterior knee from hyper-extension.
        
        Popliteo-fibular ligament
        
        Resists postero-lateral tibia lrotation and posterior tibial translation.
        
        Ligament of Humphrey
        
        Anchors lateral meniscus. Note: It is common to have either the Ligament of Humphrey or Wrisberg, but not both.
        
        Ligament of Wrisberg
        
        Stabilizes lateral meniscus.
      - Patellar ligament, which is at the patella-femoral joint
        
        Serves as a continuation of the quadriceps tendon and protects the anterior knee.
        
        Proximal: apex of the patella
        
        Distal: Tibial tuberosity
  - - - Features
        
        Two menisci: medial and lateral.
        
        Crescent-shaped and fibrocartilaginous.
        
        Lateral is more mobile than medial menisci.
        
        Attachments
        
        Anchored to intercondylar regions by anterior and posterior horns.
        
        Attached to tibia and adjacent capsule by coronary (or meniscotibial) ligaments, which are loose, allowing movements.
        
        Medial meniscus is attached to MCL and medial capsule; lateral meniscus to lateral capsule.
        
        Transverse ligament links both menisci together.
        
        Muscles
        
        Some muscles have fibres attached to menisci, e.g. quadriceps, semimembranosus; popliteus to lateral meniscus.
        
        Nourishment
        
        Peripheral 1/3 receives blood from branches of popliteal artery.
        
        Inner 1/3 is nourished by synovial fluid.
- - - - Valgus Force
        
        Primary Restraints
        
        MCL
        
        Superficial fibres (20-30°knee flex)
        
        Deep fibres (full extension)
        
        Secondary Restraint
        
        Posterior-medial capsule (incl. semimembranosus tendon)
        
        ACL and PCL
        
        Joint contact laterally
        
        Compression of lateral meniscus
        
        Medial retinacular fibres
        
        Pes anserinus
        
        Gastrocnemius –medial head
      - Varus Force
        
        Primary Restraint
        
        LCL
        
        Secondary Restraint
        
        Posterior-lateral corner of the knee (posterior-lateral capsule, arcuate popliteal ligament, and popliteus tendon)
        
        ITB
        
        Biceps femoris tendon
        
        Joint contact medially
        
        Compression of medial meniscus
        
        ACL and PCL
        
        Gastrocnemius - lateral head
    - - Kinematics at the patellofemoral joint during active tibial-on-femoral extension.
        
        As the knee extends, the contact point on the patella migrates from its superior pole to its inferior pole.
        
        Between about 90 and 60 degrees of flexion, the patella is usually well engaged within the trochlear groove of the femur. Within this arc of motion, the contact area between the patella and femur is therefore greatest
        
        Even at this maximum, only about one-third of the total surface area of the posterior patella is in contact with femur.
        
        Joint pressure (i.e. compression force per unit area) can therefore be very high. This contributes to stability during functional activities and prevents dislocation of the knee
        
        In full extension
        
        The patella rests completely proximal to the trochlear groove and against the suprapatellar fat pad.
        
        Only 45% of the contact area occurring at 60 degrees knee flexion is present between patella and trochlear groove in full extension.
        
        This reduced fit between patella and femur predisposes subluxation of patella laterally (in line of force of quadriceps).
        
        If quadriceps are relaxed, patella can be moved freely.
  - - - Contraction of the quadriceps muscle extends the knee and slides the tibia anterior relative to the femur.
        
        Knee extension also elongates
        
        Most of the anterior cruciate ligament (ACL)
        
        Posterior capsule
        
        Hamstring muscles
        
        Collateral ligaments
        
        Adjacent capsule
        
        The quadriceps and ACL have an antagonistic relationship throughout most of the terminal range of extension.
        
        Quads pull knee into extension
        
        ACL prevents excessive extension
        
        The anterior drawer test evaluates the integrity of the ACL (tibia to be moved forward). Spasm in the hamstring muscles places a posterior force on the tibia, which can limit the tension on the ACL
      - Three factors associated with ACL injury
        
        Strong quadriceps contraction in near/full extension
        
        Marked valgus force with foot firmly planted
        
        Excessive external rotation of tibia (or internal rotation of femur on fixed tibia)
    - - Contraction of the hamstring muscles flexes the knee and slides the tibia posterior relative to the femur.
        
        Knee flexion elongates the quadriceps muscle and most of the fibers within the posterior cruciate ligament(PCL).
        
        The posterior drawer test evaluates the integrity of the PCL.
  - - - “Screw-home” or Terminal Rotation
        
        In Extension
        
        Full extension requires about 10 degrees of conjunct rotation (external rotation of tibia).
        
        Different from the ‘axial rotation’ of a flexed knee, coupled to full extension and cannot be independently performed.
        
        Driven by shape of medial femoral condyle, tension in ACL and lateral pull of quadriceps.
        
        Outcome is maximum joint contact. • Function to increase joint congruence and thus stability.
        
        Flexion
        
        Reverse occurs.
        
        Driven by popliteus muscles externally rotating femur to initiate femoral-on-tibial flexion or internally rotating tibia to initiate tibial-on-femoral flexion
- - - - Summary
        
        Tibial-on-femoral extension (e.g. open chain leg extension). Max Torque/moment arm overlaps approximately 45-60°.
        
        External (flexion) torque greatest 45°to 0°
        
        At full extension, weaker quadricep muscles may not hold the position
        
        Internal (muscle) torque greatest 45°to 70° flexion
        
        Internal moment arm (leverage) greatest 20°to 60°flexion
        
        Femoral-on-tibial extension (e.g. squat to stand)
        
        External (flexion) torque greatest from 90°to 45°
        
        As the knee moves near extension, the quadriceps's ability to produce force is significantly diminished. A patient who is unable to achieve full active knee extension but has full passive motion into extension has an extensor lag.
        
        The patella functions to increase the internal moment arm of the knee extensor mechanism, thereby increasing the potential force produced by quadriceps muscles.
- - - - Global Factors
        
        Excessive genu valgum (e.g. MCL laxity or weak hip abductor resulting in ipsilateral trunk leaning or excessive pronation (subtalar eversion)
        
        Increase Q-angle and hence bowstringing effect
        
        Excessive internal rotation of femur or external rotation of the tibia
        
        Increase Q-angle and hence bowstringing
      - Local Factors
        
        Tight ITB
        
        Pulls patella laterally
        
        Tight lateral patellar retinacular fibres
        
        Pulls patella laterally
        
        Weak Vastus Medialis Oblique muscles
        
        Unable to balance the pull from the lateral side
      - Summary of causes on slide 47
  - - - Control of Tibial-on-Femoral Osteokinematics
        
        Flexor-rotator muscles accelerate or decelerate lower leg during swing phase of walking or running.
        
        These muscles produce low-to-moderate forces but at high shortening or lengthening velocities.
        
        These muscles rapidly contract to accelerate knee flexion to shorten functional length of lower limb during swing phase but also quickly eccentrically to decelerate knee extension during late swing phase.
      - Maximal Torque Production of Flexor-Rotator Muscles
        
        Maximal-effort knee flexion torque is generally greatest in the last 20 degrees of knee extension, and then declines steadily as the knee is flexed.
        
        The internal moment arm (leverage) used by the knee flexors (hamstrings) is greatest between about 50 and 90 degrees of knee flexion
      - Line of force of the ACL is the same direction of the hamstrings while knee is flexed