The Patella

The patella is a large sesamoid bone which articulates with the trochlea of the femur. It presents for description two surfaces, two borders, a base, and an apex.

The anterior or free surface (Facies libera) is irregularly quadrilateral, convex, and rough for muscular and ligamentous attachment.

The posterior or articular surface is smaller and is triangular in outline. It presents a vertical rounded ridge, which corresponds to the groove on the trochlea of the femur, and separates two concave areas. Of the latter, the inner cavity is much the larger, and is not very well adapted to the inner lip of the trochlea; in the fresh state, however, it is completed and rendered more congruent by the curved accessory fibro-cartilage.

The lateral borders converge to the apex below, and each forms a prominence or angle at the base. The inner angle and the adjacent part of the border give attachment to the fibro-cartilage of the patella, which increases the articular surface. The external border is rounded and its angle is less prominent.

The base (Basis patellæ) faces upward and backward, and is convex transversely, concave from before backward.

The apex forms a blunt point directed downward.

Development.—The patella develops as a sesamoid bone from a single center in a cartilaginous deposit in the tendon of the quadriceps femoris muscle.