KNEE MRI: CHONDRAL FIBRILLATION – WHAT TO LOOK FOR (VIDEO)

What is chondral fibrillation?

Chondral fibrillation is the earliest visible change in damaged articular cartilage, appearing after an initial phase of cartilage softening. On MRI it shows up as an irregular, roughened cartilage surface in place of the normal smooth, sharp margin — and the knee, where cartilage is thick, is the easiest joint in which to see it.

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Knee cartilage can show a number of different types of change, progressing along a spectrum:

• Softening — the earliest change of all, preceding any visible surface irregularity.
• Fibrillation — the earliest chondral change actually seen on imaging, an irregularity of the cartilage surface/margin.
• Fissuring — fibrillation progresses to defined clefts within the cartilage.
• Full-thickness chondral loss — the end stage of this progression.

On the sagittal PD sequence, normal cartilage shows intermediate signal with a nice sharp, crisp margin. Where fibrillation is present, that margin is lost:

• The cartilage surface takes on a characteristic “toothbrush” appearance — multiple small, bristle-like irregularities along the surface, rather than a single smooth line.
• This is a surface-level change: the fibrillation itself has not yet progressed to a discrete fissure or to full-thickness loss.

• Chondral fibrillation is the earliest chondral change seen on imaging, occurring after an initial phase of cartilage softening.
• It appears as irregularity of the cartilage surface/margin — on sagittal PD imaging this produces a “toothbrush” appearance in place of the normal sharp, crisp margin.
• Untreated, fibrillation can progress to fissuring and eventually full-thickness chondral loss.
• It is easiest to identify in the knee, where cartilage is thick, occurring at the patellofemoral joint or the medial/lateral compartment; it is harder to see in other, thinner-cartilage joints.