Anthropometrical and mechanical considerations in determining normal parameters for the sagittal lumbar spine

To develop a mechanical model incorporating anthropometrical data to determine individual parameters for the sagittal lumbar curve.

Factors commonly used to define a normal sagittal lumbar spine are considered, including, degree of lordosis, Ferguson's base angle and the gravitational weight line. The methods used to obtain these values and to determine their ranges are reviewed. The mechanical factors underlying these measurements and their relevance to the minimization of stresses acting on the spine are outlined.

This information is incorporated in a model of the lumbar spine along with a formula for entering anthropometrical data obtained from radiographs.

The result is a method for defining the normal sagittal lumbopelvic configuration for each individual.

The model and formula predict absolute values for Ferguson's sacral base angle and lumbar curve angle. The clinical application of the formula has yet to be verified. The establishment of a mechanical concept of normal for the spine, as opposed to statistical values, is useful in identifying the forces and stresses acting on the spine as well as the underlying functional characteristics of the spine.