Fibrocartilage in the transverse ligament of the human atlas

Study Design. Immunohistochemical investigation. Objective. To determine whether molecules typical of articular cartilage ar e present in the transverse ligament and whether the ligament may be a targ et for an autoimmune response in rheumatoid arthritis. Summary of Background Data. In chronic rheumatoid arthritis there is often a marked instability of the atlantoaxial complex, and the transverse ligame nt can show degenerative changes that compromise its mechanical function. I n some rheumatoid patients there can be an autoimmune response to cartilage link protein, aggrecan, and Type It collagen. Methods. Transverse ligaments were removed from 13 cadavers and fixed in 90 % methanol. Cryosections were immunclabeled with antibodies against proteog lycans (aggrecan, link protein, and versican), glycosaminoglycans (chondroi tin-4-sulfate, chondroitin-6-sulfate, dermatan sulfate, and keratan sulfate ), and collagens (Types I, II, III, and VI). Results. Labeling for aggrecan and link protein was characteristic of the f ibrocartilages, but versican was only detected in the fibrous regions. Equa lly, Types I, II, and VI collagens and keratan, dermatan, and chondroitin-4 -sulfates were found throughout the ligament, but labeling for Type II coll agen and chondroitin-6-sulfate was restricted to the fibrocartilages. Conclusion. The presence of molecules typical of articular cartilage (aggre can, link protein, and Type II collagen) in the transverse ligament explain s why it can be a target for destruction in rheumatoid arthritis and also s uggests that it is subject to constant compression against the dens rather than only at the extremes of movement.