The extensor mechanism consists of the anatomical structures which work together to straighten the knee.


Knee extension

This chain of structures reaches from hip bone to tibia bone and contraction of the muscle/tendon unit straightens (extends) the knee. Chief of these is the quadriceps muscle group.

The patella plays a key role in this process by altering the 'lever arm' and thus the mechanical forces involved.

rectus femoris part of quadriceps muscle extensor mechanism The patella is a sesamoid bone, which means that it is integrated in the tendon of the quadriceps muscle.
The rectus femoris is the central part of the quadriceps muscle. The four heads of the quadriceps all pull through the common quadriceps tendon  

An explanation of factors affecting measurement of the Q-angle.

The patella - important anatomical relationships

The kneecap or patella is part of a chain of structures that help to straighten the knee.



Extensor Mechanism Disruption after Total Knee Arthroplasty: A Case Series and Review of Literature. Vaishya R,Amit Kumar Agarwal AK and Vijay V. Cureus. 2016 Feb; 8(2): e479.

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