Knee Overview Summary PDF

6.1 Knee Overview Knee Fxn • lower/elevate body weight ex: sitting, squatting, climbing • • joints of knee • tibiofemoral • patellofemoral • rot of body over planted foot walking & running sustaining vertical forces 4x6 bw knee jt motions • hinge jt (2 DOF) • 2 planes (flex/ext, IR, ER)...

6.1 Knee Overview Knee Fxn • lower/elevate body weight ex: sitting, squatting, climbing • • joints of knee • tibiofemoral • patellofemoral • rot of body over planted foot walking & running sustaining vertical forces 4x6 bw knee jt motions • hinge jt (2 DOF) • 2 planes (flex/ext, IR, ER) • combination of motions • driven by geometry of jt, soft tissue, muscle actions (distal femur/prox tibia) • influences jts above and below knee open chain = distal end free ex: kick leg out while sitting - knee closed chain = distal end fixed ex: sit to stand knee angle normal angle of inclination of prox femur: 125 degrees normal angle of lateral knee: 170-175 degree NORMAL GENU VALGUM!! Genu valgum: angle less than 170 Genu varum: angle greater than 180 Line of Force • weight bearing down lower extremity: center of hip to center of ankle jt • lets weight bearing be equally distributed b/w medial & lat condyles of knee mechanical axis goes down head of femur & condyles Intercondylar notch ligaments found here • ACL/PCL size of notch can vary • proximal tibia • med/lat epicondyle • intercondylar area: cruciate ligament attachment • tibial tuberosity: distal attachment for quadriceps femoris muscle via patellar tendon meniscus: shape • • crescent shaped fibrocartilage lateral meniscus - deeper - more circular - more mobile - o shape • medial meniscus - more oval/semi lunar (C shape) - less mobile - gets injured more blood supply/ attachments • greater near outer border • medial meniscus: attachments to MCL & jt capsule • lat meniscus: attachment to jt capsule & popliteal tendon passing b/w lat meniscus and LCL ex: tear on inner 3rd, wont repair bc can’t heal as much meniscus fxn: • accept/disperse compression in tibfemoral jt • assist w/ jt stab • lubricate art cart • assist w/ arthrokinematics of knee Ligaments collateral: medial collateral ligament/lat collateral cruciate: ant/post cruciate medial collateral ligament • cross med aspect of knee • broad & flat fan shaped • blend w/ medial patella reticular fibers • attaches to medial meniscus • resist valgus stress lat collateral ligament • crosses lat aspect • long rope like • distal blend w/ tendon of biceps femoris • resist varus stress collateral ligaments • taut in ext • slack in flexion • allows axial rot of knee in flexion cruciate ligament (ACL & PCL) • cros in intercondylar notch • named according to attachment to tibia • resist forces in all planes of knee for stab • resist ant/post motion of tibiofemoral jt • less taut in 30-50 degrees flexion ex: shear in everyday activities (walking, running, squatting & jumping can do lachman test Anterior Cruciate Ligament 1. extends from med to lat femoral condyle 2. runs oblique/med to attach to anterior intercondylar area of tibial plateau 3. primary fxn resist ant translation of tibia on femur 4. becomes taut near full ext anterior translation on femur Posterior cruciate ligament (PCL) • extends from lat side of med femoral condyle to post intercondylar area of tibia • thicker than ACL • taut w/ greater flexion of knee (90-120) • prevents excessive ant translation of femur on tibia or posterior tib translation on femur summary: knee jt largest jt w/ congruency bc geometry, meniscus provide shock/absorption & increase stab, provide stab through all motions 6.2 Knee Biomechanics Patellofemoral Joint (PFJ) PFJ Joint: Function -protects knee jnt -mechanical advantage for quadriceps Patella -triangular bone embedded in quadriceps Medial facet is larger in size w tendon extra facet on the edge -biggest sesamoid bone in the body -covered w thick layer of cartilage; ideal for compressive forces -vertical ridge & medial/lateral facet Role of the Muscles: Quadriceps 4 muscles 1. Vastus lateralis (VL) 2. Vastus intermedius (VI) 3. Rectus femoris (RF) 4. Vastus medialis (VM) • net force on VL and VM result in compression of the patella Patellofemoral Motion -medial/Lateral slide -medial/Lateral Tilt -superior/Inferior slide flex ex -medial/Lateral Rotation Biomechanics of the Patella Important because of the moment arm from the axis of the femur it creates a longer movement arm Someone without a patella would require greater force of the quads to extend the knee PFJ: Squats PF compression is a resultant vector between the patella and femur • little compression • compression increases • significant compression with squats to 90° PFJ: Compression -bw 90-60° flexion the patella is in contact w femoral intracondylar groove • considered area or degrees of greatest compression or contact area • bw 30-20° flexion the patella begins to lose contact w the intracondylar groove Knee Joint: Axis -since femur slides as it moves into flex & ex the axis of motion changes during the range of motion. -instantaneous center of rotation or ‘evolute’ Makes it difficult to develop total knee replacements that replicate the knee in a mechanical situation or even braces that can say they can control the rotation or the axis of the knee Axial Rotation of the Knee • rotation increases w increased flex • greatest rotation at 90° • ER exceeds IR w a ratio of 2:1 • rotation restricted at full ex Axial Rotation of the Knee -occurs in open chain & in close chain -consider tibia moving on femur or femur moving on fixed tibia Arthrokinematics: OKC knee ex Tibia on Femur leg ex • Tibia slides anteriorly on the femoral condyles -anterior roll and slide Menisci are pulled ant by the quadriceps Open chain- concave tibia on a convex femur Arthrokinematics: CKC knee extension Femur on Tibia leg ex - femoral condyles roll anteriorly and slide posteriorly -Quadriceps stabilize menisci against shear Screw Home’ Mechanism: OKC • ‘Conjunct rotation’ meaning is cannot occur exclusively by itself. • • • Combo of rotation & flex-extension Optimizes congruency and increases stability Locking the knee requires about 10 degrees ER Arthrokinematics: OKC Knee Joint Flexion • tibia moving on femur femur will internally rotate on a • Menisci relative external rotated tibia to • Pulled posterior by hamstrings/ post roll and glide Screw Home Mechanism: CKC • popliteus contraction cause screw home locking mechanism Role of the Popliteus -Laterally rotates the femur on the tibia (to ‘unlock’ the knee in order to....ie squat) Role of the Hamstrings • Assists in medial rotation of the tibia & flex at Flex of the knee in OKC: assists w post tibial glide the knee -Assists in pulling the lateral meniscus posterior -Assists in unlocking an extended knee -Provides some lateral knee stability Arthrokinematics: CKC Knee Joint Flexion Femur moving on tibia -post roll/anterior glide Menisci -move posterior (lateral >medial) Summary • convex femur & concave tibia create arthrokinematics of the knee joint • patella glides along the femur and is compressed by tension in the quadriceps • conjunct rotation occurs at the tibial-femoral joint to create a screw home mechanism for locking in ex 6.3 Ankle & Foot Overview 1. Primarily shock absorption & conforming to forces that occur when striking the ground (also protects & sends feedback to muscles of LE) 2. walking, running 3. changing dir/pivot 4. propulsion forces to jump & leap 5. proprioceptive to maintain balance Ankle joint: talocrural jt • talus, tibia, and fibula • aka mortise joint Weight bearing • mortise = 90% of load transferred through limb • lateral structures/talus/fibula = 10% Foot joints • subtalar jt - INV/EV, predicts pronation/supination!! • transverse tarsal jt • tarsometatarsal jt • metatarsophalangeal jt • interphalangeal jt 3 foot sections 1. rearfoot: talus & calcaneus 2. mid-foot: tarsal bones 3. Forefoot: metatarsals, phalanges transverse tarsal jt Talonavicular & Calcaneocuboid • connects rear foot to midfoot • tells us what happens at subtalar jt (stability depends on position of this) • allows foot to adapt to all types of surfaces via pro/sup midfoot to forefoot • distal intertarsal jts assist w/ pro/sup • tarsometatarsal jts: 2nd & 3rd provide stab while rest provide mob • metatarsalphalangeal jts: ext (DF) flex (PF), abd, add (CONCAVE/ CONVEX) ex: first/first toe want to reach ground so want it mobile to propel forward deltoid/medial collateral ligaments lateral collateral ligaments inner intertarsal ligaments: soft tissue restraint medial longitudinal arch of foot • primary load bearing & shock absorbing structure • helps foot adapt to surfaces • rigid lever for propulsion Windlass Mechanism plantar aponeurosis assists in arch support as well as • intrinsic muscles • when the MTP hyperextends tension occurs on aponeurosis • causes longitudinal arch to rise • rigid lever for propulsion ex: ant/post strut (is idk what) tie rod = intrinsic muscles & plantar fascia Distal tibiofibular jt interosseuos membrane b/w tibia and fibula • • distal TF jt is syndesmosis jt • stabilized mortis and hold distal tibia and fibula together lower extremity kinematics • pronation @ foot leads to med rot @ tibia/fibula/femur • supination @ foot leads to rot of adjacent structures why sup important? • closed pack position • helps with arch during push off in windlass • allows to propel Summary • ankle jt accepts majority of forces in closed chain activities • motion at foot determined by position of hind foot • foot adapts to surfaces and helps w/ propulsion 6.4 Ankle & Foot Biomechanics Foot Motions -dorsi & plantaflexion occur in sag plane around a medial-lateral axis -inversion & eversion occur in a frontal plane around a anterior-posterior axis -ABD & ADD occur in a transverse plane around a vertical axis Pronation & Supination • motions occur in all 3 planes so they are triaxial motions • this is due to the oblique angles at both talocrural jnt & subtalar jnt • these motions can be described in both open & close chain Supination & Pronation: Components Supination -combo of inversion, plantarflexion & ADD Pronation -combo of eversion, dorsiflexion & ABD Close/Loose Packed Position Close-packed position of foot is supination - Provides a rigid foot structure Loose-packed position is pronation - foot is supple & flexible Talocrural Joint: axis -talocrural jnt- 1 degree of freedom -axis passes through talus through tips of malleoli Arthrokinematics: Dorsiflexion Convex talus rolls forward relative to the leg while gliding posteriorly on a concave tibia • convex on concave Arthrokinematics : Gait • Main jnts active: talo-Crural & transverse tarsal • Heel Strike: rapid DF->PF - ant tib works to prevent foot slap • Early foot flat: foot must pronate to absorb shock • Late foot flat: foot must supinate (rigid lever) for push off -Knee comes into ext, with relative ext tib rotation... • Heel rise: moving into PF on supinated foot Closed Kinetic Chain: Gait 1. Ankle rapidly plantar flexes to reach the ground 2. During flat foot phase of gait, leg starts to rotate forward over foot (dorsiflexion) pro 3. Dorsiflexion continues until just after heel off tibia moves over ankle pro 4. The ankle becomes very stable at push off as the talus wedges into the mortise with weight bearing Subtalar Joint Small changes occur to allow arch to adapt to absorb forces during wt acceptance Arthrokinematics: Plantarflexion Convex talus rolls posteriorly while gliding anteriorly on a concave tibia • convex on concave Subtalar Joint: Axis Multiplanar motion comes from an oblique axis Subtalar Joint Surfaces • 3 articulations between talus & calcaneus • concave posterior facet of talus on convex calcaneus responsible for majority of the articulation • 2 ant flat articulations Arthrokinematics: Subtalar -Roll & slide are in opposite directions in an open chain Pathomechanics of Gait Convex calcaneus on a concave - When foot fails to supinate talus in late stance, the foot is too -subtalar eversion supple to provide a rigid lever -subtalar inversion for push off -Wt is transmitted medially & carried through toe off - medial side of the great toe is the last point of contact. Transverse Tarsal Joint • Hallux valgus develops. roll and slide are in the same direction for plantarflexion and dorsiflexion Practical Application In CKC Pronation -calcaneal eversion -talar adduction & plantarflexion -tibiofibular medial rotation Summary • ankle & foot have oblique axes allowing foot to move in 3 planes • subtalar joint dictates motion at the midfoot in a close chain position • alteration of the mechanics of the ankle & foot can lead to pathology & altered gait in the review can u explain why moment arm plays a part in putting bag on ipsi side