Common Knee Ligament Injuries

Common conditions, Injury, Lifestyle, Pain


A ligament is a band of connective tissue composed mainly of collagen fibres. The knee joint ligaments connect the femur (thighbone) to the tibia (leg bone) at the knee joint to improve its stability and to limit the amount of mobility in the joint.

The four main ligaments of the knee joint are,

  • ACL: Anterior Cruciate Ligament
  • PCL: Posterior Cruciate Ligament
  • MCL: Medial Collateral Ligament
  • LCL: Lateral Collateral Ligament
knee ligaments

Fig 1: Ligaments of the knee joint

Functions of the knee ligaments

  • Stability to the knee joint

The ligaments of the knee are responsible for preventing the tibia (shin bone) from sliding out of the femur (thigh bone). During rotational movements, knee ligaments work together to prevent both valgus (knee moved inwards) or varus (knee moved outwards) stresses to the knee.

According to their attachments in the knee, the ligaments prevent tibial displacements. For example, ACL prevents forward displacement of the tibia while PCL prevents backward displacement of the tibia. Similarily, the MCL provides support on the inner side of the knee while the LCL provides support on the outer side of the knee.

  • Locking the knee during walking

Apart from supporting the bones, the knee ligaments contribute to the “screw-home” mechanism, a process that locks the knees during walking. For example, just before you strike the heel to the ground your knee is slightly flexed (about 20 degrees bent) then the screw home mechanism works to straighten the knee as your body moves over the planted heel as shown in Fig 2.

swing to stance

Fig 2: Screw-home mechanism

What does a ligament Injury mean?

A ligament injury is the over-stretching or tearing of the ligaments of the knee. A tear may be partial or complete.

mcl injury BY GRADES

Fig 3 Grades of  Ligament injury

What can cause a Knee Ligament Injury?

Extreme movements at the knee joint forcing the knee to move beyond its normal motion can injure a ligament. Most of the injuries occur during weight-bearing activities, as the ligaments resist against perturbations at the knee.

Types of people who usually get them

  • Sports people like football players, basketball players, skiers etc.
  • Hyper-mobile individuals who engage in high-impact sports may have an injury due to excessive laxity in the knee ligaments.
  • Accidental fall on the knees or hit on the knees during contact sports like rugby, football etc or automobile accidents (in which the knees can hit the dashboard)

Mechanism of an injury


Fig 4: Causes of knee injury

  • Hyper extension injury

Extending the knee too far by over straightening of the knee. This can happen when you stop suddenly while running.

  • Flexion and Hyperflexion injury

Jumping and landing on a flexed (bent) knee or falling on your knees with over overbent knees.

  • Rotational injuries

Valgum (inner) or varum (outer) stress on the knees due to twisting of your knee inwards and outwards. Sudden shifting of weight from one leg to the other.

  • Contact Sports

Accidental hit on the knee during sports as shown in Fig 5


Fig 5: Direct hit on the leg

Other Reasons that contribute to a Ligament Injury

  • Lack of force distribution

During movement, the body exerts a force on the ground and at the same time, an equal and opposite ground reaction force (GRF) is exerted by the ground on the body. This GRF is directed towards the center of mass (COM) of the body, a point in the body where the entire body weight is concentrated; in front of the tailbone.

If there is an imbalance, which means the athlete’s knee does not bend on landing and remains straight, the GRF creates a forward shear force that pushes the tibial forwards, stressing the ligaments. Hamstring muscles on the back of the thigh play a vital role in stabilizing the knee joint especially when the athlete lands. Normally, the knees normally bend slightly to absorb GRF as shown in Fig 6.


Fig 6: Hamstring action advantage for absorbing GRF

  • Lack of trunk control

Without trunk control, there will be greater movements in the trunk following a perturbation (disturbance) which could affect the distribution of the GRF.

Lack of control in the trunk motion happens because of diminished proprioception. In such a situation, if the trunk moves more on the side of the knee joint laterally, the GRF tracks the COG and follows the movement of the trunk. As the GRF tracks the COM, and if it progresses beyond the center of the knee joint, it results in a movement of the knee joint into a valgus alignment stressing the knee ligaments as shown in Fig 6.

Trunk dominance

Fig 6: Valgus alignment of the left knee

Signs and Symptoms of Ligament Injury

  • Popping sound at the time of injury can indicate a ligament rupture.
  • The knee swelling within the first 24 to 48 hours
  • Tenderness and possibly redness around your knee on touching. 
  • Knee feels unstable or may buckle during weight bearing. This may cause you to limp or feel wobbly at the knee during walking.
  • Bruising around the knee can develop. 

What to do if you think you have an injury?

If you are having any of the above signs or symptoms, seek immediate medical attention. What can appear to be a simple ligament or soft tissue strain may become something more if left untreated. Diagnostic tests such as an X-ray or MRI scan will be able to show any tears or rupture of the ligaments. According to the severity of the ligament injury, appropriate treatment care will be advised.

Anatomy of the Knee – A simple understanding

anatomy, knee, Lifestyle

Anatomy knee pic

Have you ever imagined your bodies to be like a robot’s? Detaching a part and replacing it as and when we want to? Probably it would be the best idea for those who wish to get rid of their knee aches and pains. But the complexity of being human is that we know our body parts aren’t detachable and that the more we learn about our body, the more there is left to learn.

The way we all understand our body, is that everything is connected. By having basic anatomy knowledge, we can actually help ourselves find the source of our injury and problems.

The Knee Joint

The knee Joint is the largest weight-bearing joint in our body that forms an important part of our lower limbs. It is responsible for the movements of our leg and is basically the foundation on which our body performs complex moves.

The Knee model:

The Knee joint is made of three components; the lower part of the thigh bone (Femur), the upper part of the leg bone or shin bone (Tibia) and the kneecap (Patella).

knee bone anatomy

What’s in between the two bones?

Between the thigh and the shinbone are structures that provide easy joint movements and prevent the two bones to rub against each other. These structures are the articular cartilage and the meniscus.

  • Articular Cartilage

cartillages of knee

Articular cartilage is a slippery structure on the bone surfaces that help the two bones glide against each other without causing any damage to the bones during movement.

  •  Meniscus

Knee meniscus

There are two thick C-shaped rubber-like menisci that are present between the articulating ends of the thigh and shin bone. The one on the inner side of the knee is called the medial meniscus and the one on the outer side of the knee is called the lateral meniscus. Both the menisci act like cushion pads and are great shock absorbers preventing weight bearing stresses to affect the knee.

What’s supporting the knee?

The knee joint has strong supporting structures like the ligaments and tendons that help keep the femur, tibia and the patella bones in place. These structures not only support the joint during movements but also prevent any dislocations at the knee joint.

  • Ligaments

These are fibrous band-like structures that connect one bone to another. There are two types of very important ligaments of your knee namely, the cruciate and the collateral ligaments.

ligaments of the knee

1. Cruciate ligaments (the “X” Structure in between) 

These are called cruciate because they cross each other in between the thigh and shin bone inside the knee joint. The anterior cruciate ligament (ACL) is the one that is seen in the front and the posterior cruciate ligament (PCL) is present at the back. They hold the two bones, the femur and tibia together when the leg is bending and straightening.

2. Collateral ligaments

The medial collateral ligament (MCL) is present on the inner side of the knee and the lateral collateral ligament (LCL) is present on the outer side of the knee. Both the MCL and LCL support the knee joint during side and rotation movements of the leg.

  • Tendons

Muscles end as tendons and attach to bones. Two such important tendons of the knee are the tendon of the quadriceps muscle (the main muscle on the front of the thigh) and the patellar tendon.

Quadriceps tendon attaches itself to the upper part of the patella bone. While the patellar tendon starts from the lower part of the kneecap to the front of the shin bone.


Both the quadriceps and the patellar tendons help to straighten the leg.

Damage to the knee structures

Knee injuries can happen suddenly or gradually over time. Maybe you’re into sporting activities that require plenty of sharp rotation/pivoting actions of your knee. Maybe you’re lifting weights incorrectly or just lifting too much with poor form. Any such strenuous activities could actually cause damage to the supporting structures of your knee which could lead to painful knee conditions.

But sometimes you may not have participated in any strenuous activities at all and yet have knee pains. A simple understanding of this would be that our body acts as a unit and everything is connected, weak muscles and improper mobility around the hip, knee and/or ankle could also create great amount of stress on the knee joint.

So always listen to your body and stop overworking your muscles at any given point in time. Of course, if you start having any knee pain, the best thing for you to do is meet the experts who will help you recover and save your knee from further damage.