Methods for determining spine instability and for eliminating the impact of patient effort on stability determinations

Inventors

Hipp, John A. • Wharton, Nicholas

Assignees

Medical Metrics Diagnostics Inc

Abstract

The present disclosure describes a method for determining spinal instability, more particularly, a method for quantifying the type and extent of spinal instability in a standardized way. The disclosure also describes a method comprising measurement of the intervertebral rotation and intervertebral translation between a vertebrae pair using simple images, and from these measurements, determining if one or more vertebrae pair of the spine is unstable. Finally, the disclosure describes software that may be used to quantify the type and extent of spinal instability.

Core Innovation

The invention provides methods for calculating a spinal translation per degree of rotation (TPDR) and for quantifying spinal stability from intervertebral rotation and intervertebral translation measured from paired x-ray images of a first and a second vertebra. The method obtains x-ray film or digital images for the vertebrae in a first position and a second position in which the degree of intervertebral rotation between the two positions is greater than 3 degrees. At least one landmark on the first vertebra is marked on the first image, and the two x-ray films or images are superimposed and aligned on the first vertebra to determine the rotation and translation required to align the second vertebra.

Intervertebral rotation is measured between the first and second positions, and the translation of the landmark on the first vertebra between the two positions is measured while holding the second vertebra fixed. The translation measurement is normalized based upon a vertebral dimension, and TPDR is generated by dividing the normalized intervertebral translation by the intervertebral rotation. The normalized translation per degree of rotation is intended to be independent of vertebrae size.

To convert TPDR into a stability metric, the method multiplies TPDR by a standardizing factor specific to the first and second vertebrae, the vertebrae pair. The disclosed stability metric is reported such that an asymptomatic spine is at zero and instability is displayed as a positive or negative value, or as a number of standard deviations away from the same metric for an asymptomatic and radiographically normal population. The disclosure further describes using a vertebra-pair-specific standard derived from measurements in asymptomatic radiographically normal individuals to define normal limits and interpret TPDR values as outside the normal range.

Claims Coverage

The document includes three independent claims that cover a TPDR calculation method, a spinal stability quantification method using TPDR standardization and a stability metric, and a non-transitory computer readable medium implementing the intervertebral motion analysis and stability metric generation. Across these claims, the inventive features center on paired-position x-ray imaging, landmark-based translation measurement, rotation-based normalization to compute TPDR intended to be independent of vertebrae size, and converting TPDR to a vertebra-pair-specific standardized stability metric relative to an asymptomatic radiographically normal population.

Across the independent claims, the core coverage requires measuring landmark-based intervertebral translation and intervertebral rotation from paired x-ray images taken with greater than 3 degrees of intervertebral rotation, normalizing translation by a vertebral dimension to compute TPDR, and converting TPDR to a vertebra-pair-specific standardized spinal stability metric relative to an asymptomatic radiographically normal population, either as a positive or negative instability value or as standard deviations from the asymptomatic population.

Stated Advantages

Documented Applications