The Knee and Related Structures. Knee Introduction. Knee Anatomy. Bones, Joints, Ligaments, Muscles

Transcription

1 The Knee and Related Structures Bones, Joints, Ligaments, Muscles Knee Introduction Complex joint that endures great amounts of trauma due to extreme amounts of stress that are regularly applied Knee Anatomy Designed to provide stability in weight bearing and mobility in locomotion Stability: Comes from ligaments, joint capsule, and muscles Very unstable laterally & medially 1

2 Knee Anatomy cont. Bones femur fibula tibia patella Bones Patella Largest sesamoid bone Lies within the patellar tendon Articulates between the femoral condyles Improves function of the quadriceps 2

3 Knee Movement & Capsule z Range of Motion y Flexion/ Extension y Internal / External Rotation x Usually considered a hinge joint xnot totally true because rotation of the tibia is an essential component of the knee movement z Joint capsule y surrounds the circumference of the knee y supported by ligaments & muscles Knee Ligaments z Collateral ymedial & Lateral (MCL & LCL) z Cruciates yanterior & Posterior (ACL & PCL) x Outside the synovial capsule x Named for attachment on tibia 3

4 Ligaments: MCL z medial epicondyle of the femur tibia, below the pes anserinus (common attachment of the semitendinosus, sartorius, and gracilis) y Attached to medial meniscus y Some fibers are taut in flexion & extension z Function: y prevents the knee from valgus and external rotatory forces Ligaments: LCL z Round, fibrous cord shaped like a pencil z lateral femoral epicondyle fibular head y Taut during knee extension, relaxed during flexion z Function y Protects varus forces between full and 30 degrees of extension 4

5 Ligaments: ACL z anterio-medial tibia posterio-lateral femur ytravels posteriorly and laterally z Function: yprevents the femur from moving posteriorly during weight bearing ystabilizes the tibia against excessive IR, stabilizes knee in full extension and prevents hyperextension Ligaments: ACL cont. z 2 segments: y Anteromedial bundle & Posterolateral bundle x ACL wind upon itself x full extension - posterior bundle tight x flexion - anterior bundle tight z Most strain on the ACL is internal rotation with 15 degrees of flexion Ligaments: PCL z Shorter & Stronger z posterio-lateral tibia anterio-medial femur y travels superior & anterior path crosses medially to ACL y Some part is tight throughout full ROM z Function: y Prevents hyperextension of the knee & femur y Resists internal rotation of the tibia 5

6 Menisci z Two oval shaped cartilages y Similar to intervertebral disks z Medial y C-shaped y Attached to fibers of Semimembranosus muscle, joint capsule, & MCL z Lateral y O-shaped y Joined to the PCL by the ligament of Wrisberg y Joined to the medial meniscus by the transverse ligament z Generally meniscus have poor blood supply y Outer one-third has the best vascular blood supply 6

7 Menisci: Function z Deepens the articulation of the joint z Provides lubrication z Provides shock absorption z Increases stability of the joint 7

8 Bursae Flattened sac composed of synovial tissue which is separated by a thin film of fluid (like a balloon) Function: reduce friction between anatomical structures Suprapatellar bursa above the patella Prepatellar bursa Anterior to patella Subcutaneous infrapatellar bursa distal portion of the patellar tendon Deep infrapatellar bursa between tendon & tibia 8

9 Fat Pads Infrapatellar fat pad Largest Cushions front of knee Separates patellar tendon from joint capsule Muscles of the Knee: Posterior - Hamstring Bicep Femoris- Lateral tendon Knee flexion & external rotation Semimembranosus - Medial tendon Knee flexion & internal rotation Semitendinosus-Medial tendon & part of Pes Anserine tendon Knee flexion & internal rotation 9

10 Muscles of the Knee Popliteus Posterior Knee flexion & internal rotation Gracilis -Medial & part of Pes Anserine tendon Knee flexion & internal rotation Sartorius -Anterior & part of Pes Anserine tendon Knee Flexion & internal rotation Tensor Fasciae Latae IT band Knee extension; dynamic lateral stabilizer Plantaris Knee flexion Muscles of the Knee: Anterior - Quadriceps All of the following muscle perform knee extension Rectus Femoris Vastus Medialis Vastus Lateralis Vastus Intermedius 10

11 Knee Anatomy Nerves: Tibial, common peroneal, and femoral nerves Blood Supply: Popliteal artery Functional Anatomy Screw home mechanism As the knee extends, the tibia external rotates Occurs because medial femoral condyle is larger than lateral condyle When WB, the tibia must rotate externally to achieve full extension When WB, the popliteus muscle must contract and ER the femur to unlock the knee so flexion can occur Gives a great deal of stability to the knee in full extension During the last 15 degrees of ext., tibia ER and ACL unwinds In full extension, ACL is taut 11