Fibrocartilage at the entheses of the suprascapular (superior transverse scapular) ligament of man - a ligament spanning two regions of a single bone

The suprascapular ligament converts the suprascapular notch into a foramen separating the vessels and nerve of the same name. It connects 2 regions of the same bone and does not cross any joint, and no mechanical function has yet been attributed to it. Nevertheless, variations in its thickness and l ength, and its tendency to ossify, suggest that the ligament responds to ch anges in mechanical load. This should be reflected in the composition of th e extracellular matrix. The primary purpose of the present study is to demo nstrate that the suprascapular ligament has fibrocartilaginous entheses (i. e. insertion sites), even though there is no obvious change in insertional angle that directly results from joint movement. Such a change is more typi cal of tendons or ligaments that cross highly mobile joints. The complete l igament (including both entheses) was removed from 7 cadavers shortly after death and fixed in 90% methanol. Cryosections were immunolabelled with a p anel of monoclonal antibodies against collagens (types I II, III, VI), glyc osaminoglycans (chondroitin 4 sulphate, chondroitin 6 sulphate, dermatan su lphate and keratan sulphates), proteoglycans (aggrecan and versican) and li nk protein. Both entheses were strongly fibrocartilaginous, and a moderatel y fibrocartilaginous matrix was also detected throughout the remainder of t he ligament. The extracellular matrix of both entheses labelled strongly fo r type II collagen, aggrecan and link protein. The fibrocartilaginous chara cter of the entheses suggests that the insertion sites of the ligament are subject to both compressive and tensile loading and are regions of stress c oncentration. This in turn probably reflects the complex shape of the scapu la and the presence of a conspicuous indentation (the suprascapular notch) near the ligament. The loading patterns may reflect either the attachment o f muscles and/or the forces transmitted to the suprascapular ligament from the neighbouring coracoclavicular ligament.