Knee Anatomy – The Basics

August 2017

Understanding anatomy is essential in helping to work out what may be going wrong or causing pain and instability in knees.
Here is a basic outline of essential knee anatomy with some pictures below too. Hope you find it useful:
The knee is a highly complex joint and is composed of multiple different structures, all of which work in harmony to allow the knee to perform its function; which is a pain free, stable range of movement and stability throughout the gait cycle.
The knee joint is formed where the femur and tibia meet. The distal (far) end of the femur is composed of the medial and lateral femoral condyles (rounded ends of the femur), which articulate with the proximal (near) end of the tibia which is slightly dished on the medial side and slightly domed on the lateral side. The ends of both bones are covered in articular cartilage. Articular cartilage is amazing stuff which is so amazing that it deserves its own blog, and I’ll get onto that next time. Basically, it allows frictionless articulation between the 2 bones whilst bearing weight and transmitting incredible forces.
In front of the femur, within the Trochlea sits the Patella (knee cap), the under-side of which is also covered in articular cartilage. The purpose of the Patella is to help reduce the amount of force required for the Quadriceps to perform its function. It does this by increasing the lever arm from the centre of rotation and thereby reducing the forces (if you can remember your physics!). It really comes into its own when ascending and descending stairs / slopes. The Patella is a sesamoid bone (a bone that exists within a tendon). The Quadriceps muscle turns into the quads tendon which envelops the Patella and then turns into the patellar tendon, which attaches to the Tibial Tuberosity. This bunch of structures is called the extensor mechanism, and allows the leg to extend or straighten during gait. Injury at any point in the extensor mechanism will result in extensor lag and de-function the leg.

In between the femur and tibia sit the medial and lateral menisci. These are C shaped “shock absorber” type structures that are essential in helping to protect the articular cartilage. They absorb and also distribute the forces over the articular surface thereby protecting the cartilage. These are commonly torn and cause pain and mechanical (locking or giving way) symptoms. Repairing the meniscus and trying to maintain it is very important. Knees lacking menisci are predisposed to osteoarthritis.
The key to knee stability are the ligaments that hold the 2 bones together, as well as the muscles that cross the joint and attach around the knee. We’ll focus on the ligaments. There are ligaments within the middle of the knee and also on the outside of the knee. The central ones and the “cruciate” ligaments; so called as the cross over and form a cross (cruciate = cross in Latin). These are the ACL and PCL (anterior and posterior cruciate ligaments). The ACL is most famous due to its predisposition to injury. This has 2 bundles and attaches from the medial tibial spine to the inside of the lateral femoral condyle. This stops the tibia from sliding too far forwards. The PCL is much bigger and also has 2 bundles. This attaches to the inside of the medial femoral condyle and stops the tibia sliding too far backwards. Then there are the collaterals – medial and lateral (MCL and LCL). These stop varus and valgus (side to side) instability. The MCL has a deep and superficial component and runs from the medial tibia to the medial femoral epicondyle. The LCL attaches to the head of the fibula and runs to the lateral epicondyle. These sets of ligaments provide stability throughout the range of movement. Their structure allows them to be taught at all angles of knee movement and therefore provide stability.
The more one thinks about anatomy, the more one appreciates the beauty and perfection of the human body.
We’ll do more on anatomy again. Bit more complex next time! 😊