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

anatomy

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.

 
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2 thoughts on “Functions of the Patella – Knee Cap

    1. In hyper-mobility the joints go beyond the range that is seen in the majority of the population. While this in itself may not be a bad thing, problems can stem from the joints going into more extreme positions than usual which can lead them to be damaged or prevent them from being stable.

      As an aside, this often leads to a paradox I see a lot in our clinic. The hyper-mobile patient with a very stiff back and neck. A few of the reasons for this finding is mentioned in our post on fascia and I hope to go in to that more at a later date.

      In answer to your specific question about patella dislocation. There is more to keeping the joints congruent than the ligaments alone. In the knee, excessive hyper-extension can prevent the patella from resting correctly. Failure of proper hip, knee, ankle alignment due to poor training, poor development, or poor awareness can increase force laterally with problematic results. Simply strengthening muscles without proper goals can compound these mistakes, especially if exercises fail to promote proper function and balance.

      You need awareness of normal posture and normal joint movement. You also need to make sure the muscles or training does not make the situation worse. Too often people train a muscle rather than a function. In the case of patella stability the function you want is stability. Stability such passive stability (while standing or resting) or dynamic stability (knee stable while moving other parts). Lastly, Stretching. Stretching may seem a bad idea in hyper-mobility, but actually it can also be very important. The difficulty though is what kind of stretches and which area.

      To summarize. Rehabilitation can aid with awareness such as perception of correct posture or neurologically such as proprioceptive training. Learning what you can do to protect your joints as well as use your joints more efficiently and finally make you work with your body rather than feel there is something wrong.

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