The Wiberg Scale is used to describe the shape and size of the medial and lateral facets of a patella. The shape of any patella's facets can be described in one of three ways:

Concave: Having a surface that curves inward, like the interior of a circle or sphere.
Convex: Having a surface that curves outward, like the exterior of a circle or sphere.
Flat: A level, even surface absent of curvature.

IMPORTANT: When determining where on the Wiberg scale a patella belongs, the facet curvatures must be overserved by viewing the patella from the base (or opposite the apex). This principal also applies when photographing the grafts for dissection sheets, therefore the apex of the patella should be placed down onto the photo block, or base-side up toward the camera.

Type I:

Both the medial and lateral facets are concave, and roughly of equal size and shape.

Type II:

The medial facet is mostly flat, or only slightly convex.
The lateral facet is concave.
The lateral facet is slightly larger than the medial facet.

Type III:

The medial facet is markedly convex.
The lateral facet is definitively larger than the medial facet.
The angle between the medial and lateral facets may approach 90°.

Updated on: 05/01/2024