patella
Nicole Wendler holds a PhD in biology in the field of oncology and immunology. As a medical editor, author and proofreader, she works for various publishers, for whom she presents complex and extensive medical issues in a simple, concise and logical manner.
More about the experts All content is checked by medical journalists.Patella is the Latin name for the kneecap. As part of the knee, the small, flat, heart-shaped bone between the upper and lower leg protects the knee joint and facilitates its movements. Numerous discomfort or pain in the knee can result from the kneecap. Read everything you need to know about the patella!
What is the patella?
The name kneecap describes the appearance of the patella very well. The bone, which when viewed from the front resembles a triangle or a heart, sits as a flat disk directly in front of the knee joint. It is about four to five inches long and at its widest point two to three inches wide. The fact that every knee looks a little different is hereditary and owed to different loads.
The kneecap belongs to the sesamoid bones (Os sesamoideum), a group of small bones that ensure that tendons and bones do not rub against each other in several places in the body. The largest of the small sesame bones in our body is the kneecap, the ossification of which begins in the 3rd to 4th year of life.
The front of the patella (facies anterior) is arched (convex) with vertical furrows and a rough surface. The back facing the joint capsule (facies posterior) is covered with a layer of cartilage about six to eight millimeters thick. The hyaline cartilage covers the upper two thirds of the surface and is different depending on the age and stress on the knee. It does not have any blood vessels or nerves of its own, so nutrients only reach it from the surrounding synovial fluid (synovia) and from neighboring blood vessels. Most of the cartilage consists of a connective tissue-like mass and contains only a few cells (less than ten percent), which is why cartilage damage is generally rather difficult to regress.
What is the function of the patella?
The kneecap facilitates any movement that involves bending or straightening the knee. As an attachment point for the tendon of the large thigh muscle (quadriceps, quadriceps femoris muscle), it enables the problem-free transmission of force from the anterior thigh muscles via the patellar tendon (patellar ligament) on the shin (tibia). In addition, as a spacer between the tendon and the underlying bone, the patella improves the leverage and biomechanics of the tendon.
In addition to the smooth cartilage on the back of the patellar, a bursa (bursa subcutanea prepatellaris) between the skin and the kneecap and a fat pad (Hoffa fat body) sitting between the lower edge of the kneecap and the upper edge of the shinbone prevent irritating friction when the knee is bent.
If we didn't have a kneecap, we would have to apply a lot more force in the thigh and the joint would be much more stressed. A support or a fall on the knee would be associated with significantly more pain without the patella. Because of the missing cartilage, any movement would be painful. The patella sits like a protective shield in front of the joint surface and buffers an impact with its cartilage mass.
Where is the patella located?
The patella is part of the knee joint. Together with its cartilage surface, the synovial fluid and the underlying bones, it forms a so-called synovial joint. The kneecap is embedded in the extensor tendon of the thigh muscles (quadriceps tendon) and the patellar tendon that pulls towards the shin. It sits right at the point at which the tendon deflects between the upper and lower leg. If the leg is stretched out and the muscles are relaxed, the kneecap can be easily moved. This is hardly possible in a tense state. The reason for this are ligaments that run on the front (ligamentum patellae) as well as on the left and right of the kneecap (collateral ligaments). They also ensure that the kneecap does not slip when the knee moves. The main stabilizer of the knee joint is the medial patellofemoral ligament (MPFL).
What problems can the patella cause?
The kneecap is responsible for some knee problems. It is not always the bones themselves that cause problems - the complaints are often caused by tendons or the cartilage on the back of the kneecap.
Anterior knee pain is often grouped under the term patellofemoral pain syndrome (FPS). Various factors can be considered as their triggers:
- Overloading or improper loading
- Shortening of muscles or ligaments
- Trauma or sports injury
- Misalignment or an improperly formed kneecap
- benign or malignant neoplasm
As a result, the kneecap can hurt, jump, shift, or become inflamed. The inflammation also affects neighboring areas such as the bursa or Hoffa fat bodies (prepatellar bursitis, infrapatellar bursitis, Hoffa-Kastert syndrome).
Wear and overload
Symptoms in the area of the kneecap that are based on wear and tear or overload are, for example:
- Chondropathy (Chondromalaciapatellae): mostly affects girls and young women, kneecap cartilage becomes soft and wears out
- Kneecap arthrosis (retropatellar arthrosis, cartilage degeneration): abraded, worn cartilage
- Sinding-Larsen-Johansson syndrome in children or patellar tip syndrome (jumper's knee) in adults: altered tendon tissue at the bone-tendon junction
- Osgood-Schlatter disease: parts of the shin bone die at the point of attachment of the patellar tendon
Misalignment or malformation
Possible misalignments or malformations of the kneecap are:
- Congenital patellar dysplasia: malformation of the kneecap
- Patella alta: the kneecap is too high
- Patella bipartita or P. multipartita: kneecap consists of two or more parts; The reason is impaired bone formation (ossification disorder)
- Misalignment of the kneecap due to bow-leg or knock-knees (genu valgus, genu varus) or in the case of flat feet
Accident and trauma
Accidents and trauma can cause various types of damage to the patella:
- Kneecap contusion (knee contusion)
- Kneecap fracture (patellar fracture)
- Cartilage damage
- Patellar tendon rupture: partly with bony avulsion (possibly previous damage to the tendon from other diseases)
- Kneecap dislocation: Patella jumps out of the joint (dislocation) or shifts sideways (subluxation); also possible as a result of a misalignment
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