According to the Outerbridge classification, advanced bone-on-bone arthritis would be classified as?

The Outerbridge classification system is a widely utilized method for categorizing the severity of chondromalacia, which is the softening and damage of the cartilage on the underside of the kneecap (patella). This classification ranges from Grade 1 to Grade 4.

In this system, Grade 4 represents the most severe form of cartilage damage, which is characterized by advanced bone-on-bone arthritis. At this stage, the cartilage has significantly deteriorated, exposing the underlying bone, leading to increased pain and decreased joint function. Patients often experience severe symptoms and may require interventions, such as surgical options, because the cartilage has essentially worn away entirely in the affected area.

Grades 1 through 3 denote progressively worsening conditions but do not reflect the complete loss of cartilage seen in Grade 4. Therefore, advanced bone-on-bone arthritis, which signifies extensive degenerate changes and the absence of protective cartilage coverage, is accurately classified as Grade 4 in the Outerbridge system.