This paper is about putting knee anatomy into context. Although it is very easy nowadays to find information online, it can be quite difficult for the non-medical reader to put this material and these illustrations into context. In this article, I hope to offer a contextual explanation of knee anatomy to enable a beginner to dig deeper because of a clearer understanding.
The various components of the knee perform different roles. Although some side-to-side movement is possible, the knee is fundamentally a hinge, where the two long bones are in contact with one another at the knee joint, allowing the knee to bend and straighten. To hold them in this hinge arrangement there are a number of fibrous structures that help to stabilise the joint, while the muscles around the knee create the movement. The inside of the joint is lubricated with joint fluid and cushioning shock absorbers absorb any impact. All of these structures together allow fluid movement, but with stability and control.
The two long bones forming the 'hinge' are the femur (thighbone) and the tibia (shinbone). The hinge is fundamentally imperfect, because the femur ends in two rounded surfaces, while the corresponding surfaces of the tibia are flat. This is why it is really an unstable hinge and other parts of the anatomy are needed in order to offer stablity.
Right inside the joint cavity, in the middle of the knee, are two ligaments that cross over one another, preventing the two long bones from too much movement forwards or backwards in relation to one another. These are called the 'cruciate ligaments'.
Injury to these ligaments is dreaded by most competitive sportspeople, because they cannot heal themselves and surgery is technically challenging and rehabilitation is demanding.
Stabilising the joint in a side-to-side direction are another set of ligaments called the 'collateral ligaments'. The collateral ligaments are important, but healing occurs more readily and surgery is less often necessary.
The muscles of the knee are several with the main muscle groups being the quads (or quadriceps) in the front of the knee and the hams (or hamstrings) at the back. Because these muscles span the joint and are attached to the bone beyond it via their tendons, any contraction of the muscle creates movement at the hinge. Opposite muscles act as a team - with the one muscle group contracting, while the opposite muscle group plays out the tension and controls the overall movement.
One bony structure I have not yet mentioned is the patella (or kneecap) which is actually embedded in the quads muscle and serves as a kind of pivot for the hinge. It is really important because it acts as a fulcrum, facilitating the quads movement and making the muscle contraction more efficient. It is also contained in a bony groove in the femur which serves to keep the quads pulling in the right direction.
Finally we come to the shock absorber between the femur and the tibia. Because the end of the femur is rounded and the end of the tibia is flat, a cushion-like structure called a meniscus fills the gap between the points of contact, to make the shapes more congruent and to absorb much of the impact.
All of these elements are important for normal knee movement, and injury to any one structure can disrupt stability and affect function. Because all the forces of the body are transmitted through the knee during normal sitting, walking and running even subtle changes in the anatomy can leave a person feeling pretty unhappy.
Well that covers the basic anatomy, and I hope that this helps to clarify things a bit better for you. There’s just one last thing that I want to mention. When I was talking about the meniscus (or the shock absorber), a lot of the people who are researching online don’t know this term, because lay people tend to talk of the term ‘cartilage’ when they actually mean ‘meniscus’. The meniscus is the shock absorber - it used to be called a ‘semi-lunar’ (or half-moon-shaped) cartilage - the semi-lunar cartilage - but this term has fallen into disuse in medicine, and it is now called the meniscus. What is called ‘cartilage’ is the white shiny gristle at the end of the long bones. Doctors talk down to patients sometimes and refer to the meniscus as the cartilage because they think that the patient understands that term better, but for the sake of researching online it is best to call the meniscus the meniscus, and to call the gristle at the end of the long bones the cartilage and then there is no confusion.