Centrode characteristics of the lumbar spine as a function of segmental instability.

A cadaveric study provides a quantitative measurement of early degenerative disc disease before significant radiographic changes are present. Accurate assessment of spinal motion is hampered by the inaccessibility of the lumbar joints and because of the small range of motion at each motion segment. Using Moiré fringes and, more recently, computerized digitization of spinal motion, the authors have developed a technique of measuring centers of rotation for small ranges of motion. The centers of rotation when joined form a locus that has characteristics that allow one to identify spines with degenerative disc disease. These loci, or centrodes, are longest in the earliest stages of degeneration, but maintain their length through moderate degenerative disc disease. Furthermore, radiographic changes consistent with moderate disc disease are associated with inferior migration of the centrode.