Knee Muscles

Quadriceps

• Vastus Lateralis
• O - Intertrochanteric line, Inferior border of greater trochanter; lateral lip of linea aspera
• I - lateral border of patella and patellar tendon to tibal tiberosity
• A - Extend knee
• Vastus Intermedius
• O - Upper 2/3 anterior surface of femur; linea aspera
• I - Upper border of patella and patellar tendon to tibial tuberosity
• A - Extend knee
• 

Quadriceps

• Vastus Medialis
• O - Intertrochanteric line; medial lip of linea aspera
• I - Medial border of patella and patellar tendon to tibial tuberosity
• A - Extend knee
• Rectus Femoris
• O - Anterior inferior iliac spine
• I - Superior aspect of patella and patellar tendon to tibial tuberosity
• A - Extend knee and flex hip
• 

Other Muscles in the Knee

• Popliteus
• Required for initation of flexion - 'unlocks' knee by slight medial rotation of tibia
• O - Posterior surface of lateral
• I - Upper posterior medial surface of tibia
• A - Flex knee; medial rotation of knee as it flexes
• 

Calf Muscles

• Gastrocnemius
• O - Lateral head: Lateral condyle and posterior surface of femur. Medial head; popliteal surface of femur, above medial condyle
• I - Posterior surface of the calcaneous
• A - Flexes knee, plantar flexes ankle
• 

Calf Muscles

• 
• Plantaris
• O - lateral supracondyle ridge of femur, oblique popliteal ligament
• I - Posterior surface of the calcaneus
• A - Flexes knee, plantar flexes ankle