Patella

The kneecap ( patella lat ) is a flat, disc-shaped, viewed from the front triangular bone that lies in front of the knee, at the joint surfaces he is involved. The patella acts as a sesamoid bone in the tendon of the quadriceps femoris ( four -headed thigh muscle). It protects the knee joint and multiplies the force of the quadriceps development by extending the lever arm. The ossification of the patella occurs in humans over several ossification centers from the age of three.

Anatomy

The patella has two surfaces:

• The facies anterior ( " front face " ) is ( curved outward ) is convex and has small openings through which draw the supplying vessels in the interior of the bone. Superficial portions of the quadriceps tendon covers the patella and thus consist of quadriceps distally ( away from the body ) in the patellar ligament ( patellar ligament ) away. The majority of the quadriceps tendon radiates from proximal ( close to the body ) in the kneecap and exits distally out again to form the patellar ligament Patellar Ligament. Next the front allows a bursa, the bursa subcutanea prepatellaris for padding and movability against the skin.
• The posterior surface ( " rear surface " ) is covered in the upper two thirds of hyaline cartilage, which is about 6 mm of the thickest articular cartilage in the human body. The posterior surface has a vertical ridge that fits into the gap ( intercondylar sulcus ) between the condyles ( condyles ) of the femur. He divides the posterior surface into two facets, which are in turn connected to the condyles in conjunction ( articulate ). Normally, the angle between the two facets is 120 ° -140 °. The lateral (side ) facet is much wider.

Corresponding to the two areas, the patella has two edges:

• The upper, strong edge ( Margo superior) serves as an approach ( Insertionsfläche ) for the quadriceps, specifically for two of its muscle heads, rectus femoris and vastus intermedius.
• The inner edge ( medial border ) tapers away from the body and serves as the mating surface for the medial portion of the quadriceps (vastus medialis).
• The lateral edge ( lateral margin ) is also tapered away from the body and provides a guide surface for the lateral part of the quadriceps (vastus lateralis).

The downward expiring tip (apex patellae ) serves as the origin of the patellar ligament, which runs to the shin.

Special features in birds

The knee cap of the birds behaves substantially as that of mammals. It is relatively large for the water fowl. Due to the peculiarities in the anatomy of the quadriceps muscles in birds are nomenclaturally called Musculi femorotibiales. The kneecap of the birds on the front has an additional muscle groove ( sulcus musculi ambientis ).

Function

The patella increases the distance of the force vector of the quadriceps from the center of rotation of the knee joint, thereby extending the lever arm of the extensor muscles of the thigh. The result is a lever extension of the results in a power savings of up to 44%. The patella centralized measurement of the forces of the four heads of the quadriceps femoris and transmits friction distal to the patellar ligament and the tibial tuberosity. The forces acting on the patellar tendon of the quadriceps muscle and ligament, are different. The patella plays a protective function for the femur and increases the contact area therewith. It thus ensures a better distribution of force on the femur and has the advantage of two coated with articular cartilage articular surfaces. During the stretching motion (extension) the kneecap covers a distance of about eight to ten centimeters above the thigh bone.

Due to the high forces in the patella joint, which can occur during stress, is the joint at which the patella is one which is most commonly affected by osteoarthritis joint of the people in Germany.

Diseases of the patella

Malformations of the kneecap may take the form of inadequate training ( Patelladysplasie ), by a lack of fusion of the ossification centers ("shared kneecap ", bipartite patella ) occur or insufficient training of the sliding bearing with dislocation of the kneecap ( patellar luxation ).

An external force can lead to fracture of the kneecap ( patella ).

Inflammatory changes in the approach of the patellar ligament can lead to the detachment of the patellar tip ( patellar tendinitis, Larsen - Johansson disease). In disorders of the contact pressure of the patella in its plain bearings, there is an insufficient supply of the cartilage coating on the back of the kneecap and thus cartilage damage ( Chondromalacia patellae ). Chronic changes of the patellar joint ( osteoarthritis ) manifest themselves mostly behind the kneecap ( Retropatellar ).