chapter 5: Arthroscopy of the patellofemoral joint

CLASSIFICATION OF ARTICULAR LESIONS

Chondromalacia has been a misused term over the years to represent everything from softened cartilage to a wastebasket phrase for "I don't know why your knee hurts." Taken literally, chondromalacia means "softened cartilage," which leaves us with the task of defining new language for the rest of the articular lesions we encounter at arthroscopy.

The Outerbridge classification (9) has been widely used to describe articular lesions. Grade 1 represents softening or swelling of the cartilage; Grade 2 is cartilage fibrillation of one half inch diameter or less; Grade 3 is breakdown of greater than one half inch; and Grade 4 is erosion of cartilage down to bone (9).

It is easy to see why confusion arises in this classification. The surgeon is able to classify each lesion regarding character and depth or its size, but not both with this classification. This makes classification of certain lesions difficult when there are characteristics of more than one grade. A good example of this would be a lesion of 5 to 10 mm across. Whether it consists of mild superficial fibrillation or deep fissures down to subchondral bone, the lesion is classified as Grade 2 purely based on size. Other clas­sification systems have been implemented to correct this inconsistency. Insall's classi­fication is based on depth and character of the lesion (13).

This system's major difference from the Outerbridge system is that it does not take size directly into account. Insall's grading describes character and depth only. Grade 1 is softening or blistering of the cartilage without disruption of the surface; Grade 2 has superficial fibrillation or mild fissuring in the softened area; Grade 3 is deeper fibril­lation and breakdown of the lesion, involving greater than half the thickness of the ar­ticular cartilage ("crab meat"); and Grade 4 represents erosion to bone. Location and size are then described in addition to the grade (13). A grading system reported by Beguin and Locker is very similar to the one that Insall introduced (14).

Noyes and Stabler introduced an ambitious system for grading all articular lesions in the knee. Their system was based on depth, character, size, and location (15). The criticism with this system was that these authors reported the lesions on their diagrams as circles. Because many lesions are not circular, this created problems with classification (16).

The classification system I(DB)use combines elements of Insall's system with location. The patella or trochlea lesion location gives insight into the potential outcome of surgery and must, therefore, be recorded (17). The patella is divided into nine zones. Three vertical areas are subdivided by three horizontal areas. The width of the three vertical areas will vary, depending on location of the central ridge. The medial vertical area corresponds to the medial facet; the central vertical area contains the central ridge; and the lateral vertical area contains the lateral facet. The odd facet is described separately, if involved. The horizontal areas remain constant with a proximal, middle, and distal area, all of equal widths. The trochlea is then divided into nine equal zones similar to those on the patella.

Grading of the lesions is similar to that of Insall's system. Grade 1 is a softening or blister of the cartilage with no frank disruption of the cartilage (Fig. 5.10). Grade 2 is superficial breakdown of the cartilage. Fissuring or scuffing of the cartilage is representative of this type of lesion (Figs. 5.11 and 5.12). Grade 3 is deep fissuring or disruption of cartilage that goes down to subchondral bone, but the bone is not exposed (Figs. 5.13 and 5.14). Grade 4 is exposed bone due to a traumatic event such as a patellar dislocation or crush injury without the associated degenerative changes previously listed(Fig. 5.15). Grade 5 is exposed bone with associated degenerative changes such as osteophytes along the patellar or trochlear edges (Fig. 5.16). It is important to differentiate between the Type 4 and 5 lesions, because their outcomes may be different. Additionally, you should characterize lesions when possible as distal central (Ficat critical zone), lateral facet (excessive lateral pressure), medial patella lesion caused by dislocation (see Fig. 5.5), or a proximal crush injury (18).

 

        

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