As the most conspicuous histologic feature of normal adult articular cartilage, the tidemark begs for our understanding. In their original description, Fawns and Landells likened this landmark to the irregular line of debris that is left on a sandy beach by the high point of a now-receding tide1 (Figure 1A). Such tidemarks comprise a mixture of marine flotsam, and so contain a variety of stuff from the sea. If the tidemark of cartilage is aptly named, as I believe it to be, it too should be a passive deposit of debris, but what are its constituents and where do they come from?
Address correspondence to Dr. P.A. Simkin, Division of Rheumatology, Box 356428, Department of Medicine, University of Washington, Seattle, Washington 98195, USA. E-mail: psimkin{at}uw.edu