A look into the 4 main knee ligaments

Ligaments attach from bone to bone. They provide our joints with stability and support.

There are 4 main ligaments in the knee providing support whilst standing, walking and taking part in sports and other daily activities.

The Collateral Ligaments

You will find these at ‘Hinge joints’ in the body – this means joints that primarily move by bending and straightening.

I often refer to these as the ‘scaffolding’ of the knee.

1) Medial Collateral Ligament (MCL)

This is found on the inside of the knee and is the most common ligament to strain. The MCL originates from the inside of the femur (thigh bone), running along the inside of the knee joint and inserting at two attachments on the tibia (shin bone) in the lower leg. It is around 8cm long.

It’s main function is to prevent a force coming from the outside of the knee, causing it to over-stretch inwards. This is referred to as a ‘valgus force’.

The MCL provides strong support to the knee in standing and the superficial fibres of the ligament are especially important for stability in the first 30 degrees of knee bending.

MCL injuries can frequently involve the meniscus (cartilage) on the inside of the knee.

2) Lateral Collateral Ligament (LCL)

This is found on the outside of the knee and is smaller, being around 5cm long. It originates from the femur and passes down to attach onto the Fibula (the smaller bone in the lower leg). Mechanism of injury will often involve rotating the knee on a fixed foot, hyperextension or a direct force to the inside of the knee (‘varus force’).  

A sprain or injury to the LCL only forms around 2% of all knee ligament injuries. It is more common to see it injured in conjunction with other structures such as; the ACL, meniscus (cartilage) and the posterolateral corner (an area made up of multiple structures providing dynamic and static support to the knee).

The Cruciate Ligaments

These are intra-articular, meaning they sit deep within the knee joint.  

Their role is to stop excessive forwards or backwards movement of the tibia (shin bone) in relation to the femur (thigh bone).

3) Anterior Cruciate Ligament (ACL)

The ACL originates from the tibia and crosses the knee from inside to outside, to attach onto the femur. Mechanism of injury: Rotating knee on a fixed foot, decelerating suddenly and a combination of landing and twisting on the leg. There is usually a lot of swelling immediately if the ACL ruptures.

The main function of the ACL is to stop excessive forward movement of the tibia (shin bone) in relation to the femur.

It contributes the most stability out of all ligaments and if left untreated or not rehabilitated there can be a lot of giving way, clicking, lack of control and balance, muscular weakness, pain and accelerated degeneration of other structures e.g. meniscus.

4) Posterior Cruciate Ligament (PCL)

This sits very close to the ACL and also crosses the knee but in the opposite direction, from outside to inside. The mechanism for injury would normally be a blow to the front of the knee exerting a force backwards or falling onto a bent knee.

The main role of the PCL is to stop excessive backwards movement of the tibia in relation to the femur. If this ruptures or is damaged, it can make controlling downhill movements very difficult e.g. stairs and downhill. This is not as common as an ACL rupture or injury. 

Ligament injuries can respond very well to Physiotherapy intervention and specific exercise prescription can help to prepare you for sport and hobbies again. Call us today if you have sustained a knee injury and get it assessed by an experienced Physiotherapist!

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