Functions of the Patella – Knee Cap

anatomy, Common conditions, knee, Lifestyle, Pain

knee cap

The only time feeling weak at the knees would be a normal phenomenon is when you are standing at the edge of a cliff or doing a bungee jump.

Experiencing weak knees with joint pain can be quite debilitating. We can sit, stand, walk, run and move about easily because of our knees. What we should know is that our kneecap is a part of the knee joint and it should remain ‘in the groove’  for optimal function.

The kneecap, also called the patella bone, is a sesamoid bone in the front of your knee. It’s called the sesamoid bone as it has the shape of a sesame seed. The sesamoid bone is a bone that grows within a tendon. The patella has many biomechanical functions which are responsible for the protection, support and movements at your knees.

Anatomy of the knee cap


The knee joint (Patellofemoral joint) is comprised of the three bones. The thigh bone (Femur), the shin Bone (Tibia) and the patella (Kneecap). The patella  lies in a groove at the lower end of the femur and acts as an attachment point for the four main muscles of the thigh (quadriceps). The lowest part of the patella continues on as a tendon that attaches to the tibia. The muscles pull on the patella and the patella pulls on the tibia allowing you to straighten your knee from a bent position.

knee extension action

Cartilage of Patella

articular cartilage of patella

The cartilage is a taut protective structure underneath the kneecap. It found to be among the thickest cartilage in the body providing cushioning for the patella bone. The cartilage helps to prevent friction and acts as a shock absorber protecting the bony surfaces.

Why is the patella so important?

  • Patella functions as a natural pulley

The kneecap plays an important role, it increases the leverage of the quadriceps tendon (thigh muscle tendon) and protects the front of the knee from direct trauma.

lever arm quads

The quadriceps muscle is providing the force like the man in the picture, the patella bone acts as a fulcrum to provide more leverage for lifting the stone.

In real life though, the patella is a little more complicated by not only providing increased force, but also by aiding in balancing forces as well as providing a direction for the forces.

  • Prevents excessive weight-bearing compressive stress 

As weight bearing stress falls on our knees, the patella acts as a spacer protecting the quadriceps tendon and bone from coming into compression and creating a frictional force. The patella also allows for smoother movements when bending and straightening the leg.

  • Maintaining the Quadriceps Angle

Q angle

The quadriceps angle or the Q angle is determined by drawing one line from the hip bone (anterior superior iliac spine) through the center of the patella and a second line from the center of the patella through the leg bone (tibial tuberosity).

normal Q angle

As the Q angle increases above 15 degrees, it potentially could cause the patella bone to move out of its groove. This is as if the Q angle is increased, forceful contraction of the quadriceps muscle can cause the patella to move outwards and possibly dislocate. Slight changes in the Q angle would cause imbalances in the muscle forces causing compression stress, symptoms of pain and inflammation at the knee joint.

Knee Pain related to the Patella 

Although patellar dislocation, fracture, and patellar tendon inflammation are the common sports-related injury. Many patella related problems may also occur during daily activities.

  • Runner’s knee/ Patellofemoral pain syndrome 

Patellofemoral joint pain is a condition seen in runners causing pain during running or while at rest. Pain usually occurs in the front of the knee.

  • Condromalacia Patellae (“soft cartilage under the knee cap”)

This often affects young, otherwise healthy athletes. Chondromalacia patella is one of the conditions that cause pain in front of the knee. When pain exists in the absence of cartilage softening, it can be referred to as patellofemoral pain syndrome (Runner’s knee). Although it’s common to sporting individuals, it can also affect individuals with weak quadriceps muscles. It is common among individuals engaging in activities like football, cycling, tennis, weightlifting, runners. In other words, any sport that involves running, jumping, squatting and landing on the knees.

  • Prepatellar bursitis (between patella bone and skin)

Prepatellar bursitis has historically been referred to as “housemaid’s knee”, which is derived from a condition that was commonly associated with individuals whose work necessitated kneeling for extended periods of time. Prepatellar bursitis is common in professions such as carpet layers, gardeners, roofers, and plumbers.

  • Infrapatellar Bursitis (Below the Kneecap)

This is common among individuals who engage in activities that involve kneeling down for long hours causing inflammation of the bursa below the patellar tendon. It can also occur conjunctively with a condition called jumper’s knee.

  • Suprapatellar Bursitis (Above the kneecap)

Injuries such as direct trauma and overuse injury to the bursa beneath the quadriceps tendon cause inflammation of this bursa.Overuse injuries caused due to running on uneven surfaces or doing jobs that require crawling on the knees.

  • Osteoarthritis 

Patellofemoral arthritis occurs when the articular cartilage on the underside of the patella wears down causing friction between the patella and the end of the thigh bones. It gets extremely painful during weight bearing with swelling, inflammation around the knee. It is generally a degeneration condition which requires immediate medical attention to manage the condition.

  • Patellar Dislocation 

This type of injury happens when the kneecap (patella) moves out of its groove due to the sudden change in direction engaging in high impact sports. It most commonly occurs among young girls or hypermobile individuals due to laxity and increased hip angle. Direct trauma to the kneecap could also cause dislocations.

As a precautionary measure, using knee pads during sports and regular exercises of your knee muscles will have great benefits for your patella. Generally, most of the injury conditions can be managed with appropriate treatment and rehabilitation.

However, if you’ve only begun to feel pain while doing activities or just by standing, you might like to seek medical attention to prevent long-term pain or further damage to your patella.


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.