The Patella

Anatomy > Gray's Anatomy of the Human Body > II. [Osteology]] > 6c. 4. The Patella

Henry Gray (1821–1865). Anatomy of the Human Body. 1918.

The Patella

(Knee Cap)

The patella (Figs. 255, 256) is a flat, triangular bone, situated on the front of the knee-joint. It is usually regarded as a sesamoid bone, developed in the tendon of the Quadriceps femoris, and resembles these bones (1) in being developed in a tendon; (2) in its center of ossification presenting a knotty or tuberculated outline; (3) in being composed mainly of dense cancellous tissue. It serves to protect the front of the joint, and increases the leverage of the Quadriceps femoris by making it act at a greater angle. It has an anterior and a posterior surface three borders, and an apex.

FIG. 255– Right patella. Anterior surface. (Picture From the Classic Gray's Anatomy)

FIG. 256– Right patella. Posterior surface. (Picture From the Classic Gray's Anatomy)

Surfaces

The anterior surface is convex, perforated by small apertures for the passage of nutrient vessels, and marked by numerous rough, longitudinal striae. This surface is covered, in the recent state, by an expansion from the tendon of the Quadriceps femoris, which is continuous below with the superficial fibers of the ligamentum patellae. It is separated from the integument by a bursa.

The posterior surface presents above a smooth, oval, articular area, divided into two facets by a vertical ridge; the ridge corresponds to the groove on the patellar surface of the femur, and the facets to the medial and lateral parts of the same surface; the lateral facet is the broader and deeper. Below the articular surface is a rough, convex, non-articular area, the lower half of which gives attachment to the ligamentum patellae; the upper half is separated from the head of the tibia by adipose tissue.

Borders

The base or superior border is thick, and sloped from behind, downward, and forward: it gives attachment to that portion of the Quadriceps femoris which is derived from the Rectus femoris and Vastus intermedius.

The medial and lateral borders are thinner and converge below: they give attachment to those portions of the Quadriceps femoris which are derived from the Vasti lateralis and medialis.

Apex

The apex is pointed, and gives attachment to the ligamentum patellae.

Structure

The patella consists of a nearly uniform dense cancellous tissue, covered by a thin compact lamina. The cancelli immediately beneath the anterior surface are arranged parallel with it. In the rest of the bone they radiate from the articular surface toward the other parts of the bone.

Ossification

The patella is ossified from a single center, which usually makes its appearance in the second or third year, but may be delayed until the sixth year. More rarely, the bone is developed by two centers, placed side by side. Ossification is completed about the age of puberty.

Articulation

The patella articulates with the femur.

Function

The primary functional role of the patella is knee extension. The patella increases the leverage that the quadriceps tendon can exert on the femur by increasing the angle at which it acts.

The patella is attached to the tendon of the quadriceps femoris muscle, which contracts to extend/straighten the knee. The patella is stabilized by the insertion of the horizontal fibres of vastus medialis and by the prominence of the lateral femoral condyle, which discourages lateral dislocation during flexion. The retinacular fibres of the patella also stabilize it during exercise.

Additional images

• 

  Human left patella from the front

• 

  Human left patella from behind

• 

  Flexion and extension of knee

Gray's Anatomy

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