Knee Cap
or PATELLA, a sesamoid bone, developed in the single tendon of the the rectus, crureus, vastus externus, and internus muscles-the great quadriceps extensor muscle of the leg. It is heart-shaped in form, the broad end being directed upward, and the apex downward.
This bone is liable both to dislocation and fracture. Dislocation may occur either inward or outward; but it is most frequent in the outward direction. The displacement may be caused either by mechanical violence, or by too sudden of the extensor muscles in whose conjoined tendon it lies; and is most liable to occur in knock-kneed, flabby persons. Except in one rare variety, the dislocation is capable of being reduced without any difficulty. Fracture of the patella may, like dislocation, be caused either by muscular action or by mechanical violence.
Fracture by violent muscular action, as when a person in danger of falling forward attempts to recover himself by throwing the body backward, is the more common of the two forms.