Knee Extensor Mechanism

Description

Basic illustration of the extensor mechanism of the knee

The cortical reflection of the patella is to the left and is the proximal hyperechoic arc with shadowing deep to it. The hyperechoic, fibrous echotexture of the patellar tendon demonstrates a sharp “beak-like” origin from the patella, and the tendon thickens to display a uniform band of fibers. Deep to the tendon are mixed/marbled echoes of Hoffa’s Fat Pad.

Extended field of view in long axis of the extensor mechanism

Extensor Mechanism

• Quadriceps tendon inserts into superior Patella
• Patella Tendon in turn attaches to Tibial Tubercle

Quadriceps Femoris

• Formed by the confluence of 4 muscles into the quadriceps tendon
• Rectus Femoris, Vastus Lateralis, Vastus Intermedius, Vastus Medialis

Quadriceps Tendon

• Insertion on the proximal pole of the patella as well as on the dorsal, lateral, and medial surfaces
• Composed of 3 planes: superficial (rectus femoris), middle (vastus medialis and lateralis), deep (vastus intermedius)

Patella

• Largest sesamoid bone in the body is embedded in the quadriceps tendon
• Quadriceps tendon is proximal/superior pole
• Patellar tendon originates on the distal/inferior pole

Patellar Tendon

• Distal continuation of quadriceps tendon when it extends past the inferior patellar pole
• Inserts onto tibial tubercle

Dimensions

• Thickness 4-7 mm (proximal), 5-6 mm (distal)
• Length 4-6 cm
• Width 25-40 mm

Additional Considerations

• Does not have a well-developed paratenon
• Hoffa fat pad deep to tendon has close relationship to tendon

Actions

• Action is to transmit forces from the quadriceps to the proximal tibia
• Efficiency is increased 1.5x because of the presence of the patella

Vascular Supply

• Descending branches of the Lateral Femoral Circumflex Artery
• Descending geniculate
• Medial and lateral superior geniculate artery

Innervation

• Femoral Nerve

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Clinical Significance

• Patellar Fracture
• Quadriceps Tendon Rupture
• Quadriceps Tendonitis
• Patellar Tendon Rupture
• Patellar Tendonitis
• Quadriceps Contusion

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See Also

• Knee Pain Main
• Knee Anatomy Main

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