chapter 11: Articular Cartilage Lesions in Patellofemoral Pain Patients
This is a particular lesion both in terms of localization and appearance. It is nearly always localized to the medial facet. In its well‑developed form it has the appearance of a sea anemone, and consists of multiple deep fronds of cartilage separated from one another by deep clefts that extend to subchondral bone. The base of attachment of these fronds is usually well limited, but the surgeon is struck by the quantity of cartilage that hangs over the facet, which suggests that the lesion may be proliferative as well as destructive. It is possible that this particular pathologic appearance is due to the special conditions affecting the medial patella, namely, incongruence, intermittent excessive pressure, shearing forces, and the possibility of reduced compression.
Elevation or tearing of the lamina splendens may be considered superficial. Other superficial lesions include surface fibrillation that may be overt or detectable only by India ink (51). Longitudinal striations may be present in the axis of movement of the joint, which, in more severe form, may give the appearance of scoring of the articular cartilage. Some areas of the surface may take on a dull appearance without any other significant abnormalities. These surface changes are frequent findings both at arthrotomy and at autopsy.
In addition to the previously described lesions localized to either facet, there are other, more diffuse forms of patellar articular cartilage degeneration. Fracture of the patella may cause malacic changes on both facets. Also, when there has been significant periarticular fibrosis, the surgeon may observe extensive malacic changes involving the entire patella. Sometimes, if cartilage destruction is diffuse on the patella, it is difficult to be certain as to the site of the original lesion.
There are patients with a typical malacic lesion, with or without fissures, centered perfectly on the median ridge. This may then extend in both directions, but appears to have a tendency toward medial extension. Some of these cases, at least, have the typical findings of excessive pressure on the lateral facet, and release of a tight lateral retinaculum may give some symptomatic relief.
Minor alterations of patellar alignment (particularly lateral tilt) may cause accentuation of lateral facet loads and diminished medial facet loads such that minor insults, or even obesity, can result in diffuse patellar cartilage destruction in some unfortunate patients.
It is important that surgeons accurately describe their findings on open or arthroscopic examination of the patellar or trochlear articular surfaces. Overall, in the arthroscopic or macroscopic assessment of patellar articular cartilage lesions, we have found the Outerbridge classification most helpful.
In essence, the Outerbridge classification is as follows:
Grade 1—Articular cartilage softening (closed chondromalacia) only (Fig. 11.2).
This classification system has been useful because it allows the clinician to quantitate operative or arthroscopic findings in a simple and accurate yet reproducible manner.
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