Anatomy of the Knee 22-23.pptx

Anatomy of the Knee Dr Catherine Hennessy [email protected] Learning Outcomes • Describe the skeletal components of the knee joint; the joint surfaces, ligaments and menisci. • Describe the factors strengthening the knee joint. • Describe some of the common causes of knee injury. Knee Joint...

Anatomy of the Knee Dr Catherine Hennessy [email protected] Learning Outcomes • Describe the skeletal components of the knee joint; the joint surfaces, ligaments and menisci. • Describe the factors strengthening the knee joint. • Describe some of the common causes of knee injury. Knee Joint Articulation between distal femur and proximal tibia (not fibula) - Synovial bicondylar hinge joint Extension/flexion Some rotation when Articulation between femur and patella flexed Medial epicondyle Patella Fibrous joint capsule formed by a network of tendons and ligaments Tibia Medial view Functions of the Knee Weight–bearing Incompatible functions Mobility = Frequently injured Factors Strengthening the Knee Joint Several factors help improve stability and strength: Bony factors - Bony expansions - Locking mechanism - Femoral angle Soft tissue factors - Ligaments - Menisci - Muscles Boney Expansions Provides stable base for bipedalism Posterior Anterior Epicondyles Femoral condyles Intercondylar fossa Tibial condyles (tibial plateau) Locking Mechanism Reduces amount of energy required when extended Three factors contribute to the locking mechanism: 1. Shape of femur Round surface In flexion - femoral surfaces round In extension - femoral surfaces flat Flat surface Locking Mechanism 2. Rotation Medial rotation of femur on tibia in extension - Tightens ligaments of the knee 3. Centre of gravity Centre of gravity in front of knee - Maintains extension Femoral Angle In the clinic: ASIS Position of knee joint is critical for weight bearing Adducted femur brings knee joint under pelvis Q angle (~15°) Anatomical axis Mechanical axis Patella Tibia tuberosity Varus Deformity (Genu Varum) Deformity in the angle between femur and tibia Medial displacement of the tibia Common in children under 2 when learning to walk, rickets Pushes knees apart - ‘Bow-legged’ = Decrease in Q angle Increased stress Eventually results in joint degeneration Valgus Deformity (Genu Valgum) Lateral displacement of the tibia Common in children aged 2-4 Brings knees together - ‘Knock-kneed’ = Increase in Q angle Increased stress Eventually results in joint degeneration Ligaments of the Knee Provide stability Two groups of strong ligaments: Extracapsular – outside capsule Medial collateral Lateral collateral Intracapsular – inside capsule Anterior cruciate Posterior cruciate Lateral/Fibular Collateral Ligament Strong round cord Prevents medial displacement of tibia Lateral epicondyle Anterior view Lateral collateral ligament Note space Fibular head Tear of LCL = Varus deformity (causing opening on the lateral side of the joint) Less common Medial/Tibial Collateral Ligament Broad flat band Reinforces joint capsule Prevents lateral displacement of tibia Medial epicondyle Anterior view Medial collateral ligament Attachment to Medial meniscus Tibia Tear of MCL = Valgus deformity (lateral) Intracapsular Ligaments Intercondylar fossa Posterior cruciate ligament Anterior cruciate ligament Posterior in relation to its origin on the tibia Anterior in relation to its origin on the tibia Intercondylar area of tibia Anterior view Cruciate = cross-shaped Cruciate Ligaments Posterior cruciate ligament passes upward, forward and medially L M Anterior cruciate ligament passes upwards, backwards and laterally With flexed knee: Medial rotation of leg – tightens ligaments (limits rotation) (10deg) Lateral rotation of leg – unwinds ligaments (~60deg) Function of Cruciate Ligaments Anterior cruciate Prevents anterior displacement of tibia on femur Posterior cruciate Prevents posterior displacement of tibia on femur Maintain femur against tibia One ligament is always tense Anterior Cruciate Ligament Weaker Common sports injury Anterior cruciate ligament Caused by sudden twisting of knee Lachman test (variation of ’Anterior Drawer’ test): Patient in supine position with knee bent 20-300 of flexion Move tibia anteriorly and posteriorly while maintaining position of femur Laxity during this manoeuvre indicates anterior cruciate ligament injury Anterior view Posterior Cruciate Ligament Stronger - Rarely injured Principle stabilizer when knee flexed (Especially when walking down hill) Posterior cruciate ligament Menisci of the Knee Joint Crescent-shaped plates of fibrocartilage Deepen the articulating surfaces/stability Shock absorbers Provides smooth viscous film for joint Lateral meniscus - Smaller + more circular Medial meniscus - Larger Attachments of the Menisci Horns of menisci attached to intercondylar area ofPosterior horns of the menisci tibia Mobile (Accommodates rolling of femoral condyles) Medial meniscus less mobile than lateral meniscus (attached to medial collateral ligament) Anterior view Posterior view Anterior horns of the menisci Medial Meniscus Lateral Meniscus Medial collateral ligament Unhappy Triad Twisting on a flexed knee and blow to lateral side TWIST Contact sports (e.g. rugby tackle) Rupture: BLOW 1. Anterior cruciate ligament 2. Medial collateral ligament 3. Medial meniscus (attached to MCL) Poor blood supply to intracapsular structures Don’t repair easily Muscles Acting on the Knee Joint Knee reinforced by tendons from surrounding muscles and iliotibial tract Iliotibial tract - Reinforces joint capsule - Stabilizes extended knee (gluteus maximus, tensor fascia lata) Extensors of the Knee Joint Quadriceps extend the knee joint Also a major stabilizing muscle of the knee 4 heads 1. Rectus femoris 2. Vastus lateralis 3. Vastus intermedius 4. Vastus medialis Quadriceps Femoris Anterior inferior iliac spine Vastus medialis Vastus intermedius Lateral pull (due to adducted femur) Vastus lateralis Rectus femoris (cut) Quadriceps tendon Oblique fibres of vastus medialis prevents lateral tracking of patella Extensor Mechanism Lateral patellar retinaculum Quadriceps tendon Extensor mechanism Medial patellar retinaculum - Aponeurotic expansions of vastus lateralis and medialis Patella - Help stabilise the patella Patellar ligament Tibial tuberosity L M Patella Triangular-shaped sesamoid shaped Protects quadriceps tendon from stresses during locomotion Smooth oval facet on posterior surface for articulation with femur Extensor Mechanism Injury Damage/rupture of quadriceps tendon or patellar ligament Fracture of the patella - Due to fall or blow to knee - Results in loss of active extension Dislocation of patella common - Due to sudden twisting/jumping or ligamentous laxity Flexors of the Knee Joint Hamstrings and gastrocnemius flex the knee joint Hamstrings also medially and laterally rotate the leg at the knee joint when knee flexed Hamstrings muscles are: 1. Biceps femoris 2. Semimembranosus 3. Semitendinosus Hamstrings M Semitendinosus L Ischial tuberosity Biceps femoris Semimembranosus - Reinforces joint capsule Unlocking of the Extended Knee Joint Popliteus unlocks knee joint - laterally rotates femur on tibia when foot is on ground Popliteus - Passes through joint capsule - Passes through space under lateral collateral ligament Lateral condyle Popliteus Posterior tibia Synovial Membrane From the margins of the articular surfaces of femur to tibia Attached to patella Extends superiorly behind quadriceps tendon Cuffs anterior surface of cruciate ligaments Synovial membrane L M Patellar ligament Infrapatellar fat pad – separates synovial membrane from patellar ligament Bursae Synovial fluid filled sac lined by synovial membrane Suprapatellar bursa - Continuous with synovial membrane Prepatellar bursa Infrapatellar bursa - Protection - Reduce friction Other Bursae Many bursae associated with the knee Lateral Iliotibial tract Medial Semimembranosus Biceps femoris Occur at tendon insertions Semitendinosus Gracilis Sartorius Bursitis Inflammation of bursae Due to repetitive movements or direct pressure Prepatellar bursitis (‘housemaid’s knee’) Seen in carpet fitters Leaning forward on the knees brings the prepatellar bursa in contact with floor Bursitis Infrapatellar bursitis (‘clergyman’s knee’) Seen in roofers After prolonged periods of prayer clergymen sat back on their heels bringing infrapatellar bursa in contact with floor Baker’s (Popliteal) Cyst Abnormal fluid filled sacs in popliteal fossa - Due to herniation of bursa Popliteal fossa Common in patients with chronic inflammatory joint disease (e.g. arthritis) - Presents as swelling in the popliteal fossa - Can affect joint movement Treat by aspiration and cortisone injection L Vascular Supply Anastomosis around knee - Femoral artery Genicular branches - Popliteal artery Limited blood supply to intracapsular structures - poor repair following injury