A model of unloaded human intervertebral disk based on NMR relaxation

NMR relaxation rates were related to the composition of the nucleus pulposu s from 11 and anulus fibrosus from six human intervertebral disks. Tissue w ater was proportional to glycosaminoglycan (GAG) and residue, the noncollag en, non-GAG portion of the dry weight (R-2 = 0.74), The solid signal fracti on depended on collagen and residue protons (R-2 = 0.89), 1/T-1 was proport ional to collagen and residue (R-2 = 0.97), T-2 showed 2-4 components label ed A, B, C, and D, with means +/- standard deviations of 3.1 +/- 1.6, 17.5 +/- 9.5, 64 +/- 22, and 347 +/- 162 msec. Signal fractions of A and B depen ded on the collagen-associated water protons (R-2 = 0.94 and 0.85), C on re sidue-associated water protons (R-2 = 0.82), and D on GAG-associated water protons (R-2 = 0.74). The data led to a model of disk architecture in which the collagen and residue were largely solid, forming distinct water compar tments; the remaining water was present in a proteoglycan gel, Magn Reson M ed 43:34-44, 2000, (C) 2000 Wiley-Liss, Inc.