What is the patella?
The name kneecap describes the appearance of the patella very well. The bone, which resembles a triangle or a heart when viewed from the front, sits as a flat disc directly in front of the knee joint. It is about four to five centimeters long and two to three centimeters wide at its widest point. The fact that every knee looks a little bit different is hereditary and due to different stresses.
The kneecap belongs to the sesamoid bones (Os sesamoideum), a group of small bones that ensure that tendon and bone do not rub against each other at several points in the body. The largest of the small sesamoid bones in our body is the kneecap, whose ossification begins in the 3rd to 4th year of life.
What is the function of the patella?
The patella facilitates every movement in which the knee is bent or extended. As the attachment point for the tendon of the large thigh muscle (quadriceps, Musculus quadriceps femoris), it enables the smooth transmission of force from the anterior thigh muscles via the patellar tendon (Ligamentum patellae) to the tibia. In addition, the patella, as a spacer between the tendon and the underlying bone, improves the leverage and biomechanics of the tendon.
In addition to the smooth cartilage on the back of the patella, a bursa (bursa subcutanea prepatellaris) between the skin and the patella and a fat pad (Hoffa fat body) located between the lower edge of the patella and the upper edge of the tibia prevent irritating friction when the knee is bent.
Where is the patella located?
The patella is a part of the knee joint. Together with its cartilaginous surface, the synovial fluid and the underlying bones, it forms a so-called synovial joint. The patella is embedded in the extensor tendon of the thigh muscles (quadriceps tendon) and the patellar tendon, which pulls toward the tibia. Thus, it sits directly at the point of deflection of the tendon between the upper and lower leg. When the leg is extended and the muscles are relaxed, the patella can be moved easily. In a tense state, this is hardly possible. This is due to ligaments that run along the front (ligamentum patellae) and to the left and right of the kneecap (collateral ligaments). They also ensure that the kneecap does not slip during knee movements. The main stabilizer of the knee joint is the medial patellofemoral ligament (MPFL).
What problems can the patella cause?
Anterior knee pain is often grouped under the term patellofemoral pain syndrome (FPS). Several factors may be considered as its trigger:
- Overloading or incorrect loading
- Muscle or ligament shortening
- Trauma or sports injury
- Malposition or an incorrectly formed patella
- Benign or malignant neoplasm
As a result, the patella may hurt, bounce, shift or become inflamed. The inflammation then also affects neighboring areas such as the bursa or Hoffa fat body (bursitis praepatellaris, bursitis infrapatellaris, Hoffa-Kastert syndrome).
Wear and overload
Disease patterns in the area of the kneecap that are based on wear and tear or overloading include:
- Chondropathy (chondromalaciapatellae): usually affects girls and young women, patellar cartilage becomes soft and wears away
- Patellar osteoarthritis (retropatellar osteoarthritis, cartilage degeneration): abraded, worn cartilage
- – Osgood-Schlatter disease: death of parts of the tibial bone at the attachment site of the patellar tendon
Malposition or maldevelopment
Possible malpositions or maldevelopments of the patella are:
- Congenital patellar dysplasia: malformation of the patella
- Patella alta: patella lying too high
- Patella bipartita or P. multipartita: patella consists of two or more parts; the reason is a disturbed bone formation (ossification disorder)
- Malposition of the patella due to bow or knock-knees (genu valgus, genu varus) or a flat foot
Accident and trauma
Accidents and trauma can cause various damages in the area of the patella:
- Patellar contusion (knee contusion)
- Patellar fracture (patella fracture)
- Cartilage damage
- Patellar tendon rupture: partially with bony avulsion (possibly pre-damage of the tendon due to other disease)
