BASIC SCIENCE & PATHOLOGY

THE ROLE OF SUBCHONDRAL CIRCULATION FOR ARTICULAR CARTILAGE NUTRITION

S Sadiq, S Kaye, CG Phillips, CP Winlove, ID McCarthy
Departments of Orthopaedic Surgery and Biological and Medical Systems, Imperial College, Charing Cross Campus, Fulham Palace Road, London W6 8RF, UK

Cartilage is avascular. It is generally accepted that the synovial route is the major supply of nutrients to articular cartilage. The contribution of subchondral circulation to articular cartilage nutrition has been doubted in mature animals. This study was undertaken to test the hypothesis that subchondral bone is an important route for cartilage nutrition. Adult rats were divided into two groups. Two groups comprised rats weighing 300-350 grams, and the two other groups comprised mature animals weighing 600-650 grams. All animals were injected with the fluorescent dye rhodamine conjugated with albumin. Two groups of animals (one for each age group) were sacrificed 1-2 minutes after injection of the dye, and the two other groups sacrificed 30 minutes after injection. Undecalcified sections were cut through the distal femorae. Sections were viewed under UV light, and the images captured by viewing with an iCCD camera connected to a frame grabber.

The intensity of rhodamine fluorescence was quantified from the digitized images. Profiles of rhodamine intensity were obtained across cartilage and subchondral bone. Regions of high rhodamine intensity were seen in close proximity to the tise mark. The intensity within calcified cartilage appeared greater adjacent to those regions along the tidemark and deep part of uncalcified cartilage compared to other regions of cartilage.

This study establishes the penetration of albumin labeled with rhodamine from subchondral bone into the calcified zone of articular cartilage and up to the tidemark with a possible contribution in the deep zone of uncalcified cartilage. There is increasing interest in the role of bone in osteoarthritis, and this study suggests possible routes of communication between cartilage and subchondral bone.