Cartilage fibrillation at the ankle joint in Liverpool necropsies.

The articular surfaces have been examined in 45 left ankle joints from a random series of adult necropsies in the city of Liverpool. Foci of overt fibrillation, with frank splitting of the articular cartilage surface, were extremely common in the ankle joint and were often already apparent in young adults. With increasing age overt fibrillation tended on the whole to become extensive, but this tendency was partly obscured by considerable variation between individuals. It initially and especially affected the periphery of the cartilage sheets and the boundaries between the central and malleolar articulation territories. Possible explanations for this peripheral susceptibility are discussed. One or more sites on the non-peripheral parts of the lateral and medial malleolar surfaces were next in order of susceptibility. The central territory of the articulation was the least susceptible to overt fibrillation. Minimal fibrillation, with a very superficial splitting of the cartilage surface, could occur at any site on the ankle joint surfaces. With increasing age, extensive involvement of the central territory by this minimal change was much more common than extensive overt fibrillation here. The surface markings of minimal fibrillation sometimes showed a macroscopially apparent orientation en face. In one sort these were parallel to flexion-extension movement and consistent with track markings from abrasive-adhesive wear. In a second sort they were parallel to the dominant en face orientation of the superficial cartilage collagen. The topography and natural history of cartilage fibrillation at the ankle joint is discussed with reference to Liverpool data from other joints. Some of the older ankles showed peripheral segments of fibrous tissue-covered cartilage loss. This feature was attributed to "ageing" rather than osteoarthrosis. Only 1 of 20 left ankles from subjects more than 70 years old showed any region of full-thickness uncalcified cartilage loss with abrasive wear of 'osteoarthritic' type. Thus it would seem that in the majority of the Lverpool population the articular cartilage of the normal ankle joint has a high resistance to the type of vertical wear found in clinically demonstrable osteoarthrosis. The practical implications of this conclusion are discussed.