The quantification of low back disorder using motion measures. Methodology and validation

STUDY DESIGN

Trunk angular motion features were used as a means to quantify the extent of a low back disorder in healthy people and patients with chronic low back disorders.

OBJECTIVE

To refine and validate a previously reported means of quantifying the extent of a low back disorder.

SUMMARY AND BACKGROUND

Many assessment tools of low back disorder are subjective. A quantitative assessment tool would facilitate the tracking of the recovery and help document the appropriateness of treatments.

METHODS

The trunk motion characteristics of 374 healthy people and 335 patients with chronic low back disorders of varying severity were documented as they flexed and extended their trunks in five different planes of motion. The trunk motion features were normalized as a function of age and gender. Four classification techniques were used to assess the ability of the quantitative motion measure to identify those with and without low back disorders. In addition, 31 patients were observed longitudinally to determine whether the motion measures agreed with observed changes in back pain symptoms.

RESULTS

The quantitative trunk motion measure distinguished between people with low back disorders and healthy people between 88% and 94% of the time, depending on which classification system was used. Sensitivity and specificity varied between 83% and 97%. The quantitative measure also showed promise as a means to distinguish between muscle-based and structure-based low back disorders. Prospective findings indicated that the quantification system agreed well with clinical observations of progress.

CONCLUSIONS

The quantification of trunk motion can serve as a measure of the extent of a low back disorder. When considered along with other clinical information, the ability to assess and treat low back disorders is enhanced.

Dynamic low back functional motion capacity evaluation

Most current functional capacity evaluations focus on range of motion and strength as measures of Wellness. The goal of this study was to evaluate the dynamic functional motion capacity of controls (those without low back pain) and low back pain patients in the three cardinal planes of the body. The hypothesis was that injury would not only affect sagittal motion but also lateral and twisting motion that would load the spine in a different manner. Twenty-six age and gender matched controls and low back pain patients were tested. Trunk motion parameters of range of motion (ROM), velocity, and acceleration were measured in all three planes of the body as subjects performed three separate tasks eliciting motion in each of the three cardinal planes of the body. Controls exhibited significantly higher performance than low back pain patients in all three planes of the body for velocity and acceleration but not ROM. Single parameter discriminant function models indicated that the velocity and acceleration motion parameters distinguished between LBP patients and the control group more effectively than ROM in the cardinal planes. Multiple parameter discriminant function demonstrated that coupled motion models further increased the ability to distinguish between the control and patient groups. These results provide insight into new methods of evaluating functional capacity using velocity, acceleration, and coupling which may provide valuable information in determining the recovery of a patient.

The classification of anatomic- and symptom-based low back disorders using motion measure models

STUDY DESIGN

This study observed the trunk angular motion features of healthy subjects and those experiencing chronic low back disorders as they flexed and extended their trunks in five symmetric and asymmetric planes of motion. Trunk angular position, velocity, and acceleration were evaluated during several cycles of motion.

OBJECTIVE

The trunk angular motion features of the low back disorder group were normalized relative to the healthy subjects and used to 1) evaluate the repeatability and reliability of trunk motion as a measure of trunk musculoskeletal status, 2) quantify the extent of the disorder, 3) determine the extent to which trunk motion measures might be used as quantifiable means to help classify low back disorders.

SUMMARY OF BACKGROUND DATA

Given the magnitude of the low back disorder problem, it is problematic that there are few quantitative methods for objectively documenting the extent of a disorder. Impairment ratings of low back disorders can vary by as much as 70% using current systems. Diagnoses and classification schemes are rarely based upon quantitative indicators and we are unable to easily assess and diagnose low back disorders. It is important to quantitatively evaluate low back disorders so that proper treatment can be administered and the risk of exacerbating the problem can be minimized.

METHODS

Three-hundred-thirty-nine men and women between 20 and 70 years old who had not experienced significant back pain were recruited as the healthy subjects in this study. One hundred-seventy-one patients with various chronic low back disorders also were recruited and compared with the healthy group of subjects. All subjects wore a triaxial goniometer on their trunks that documented the angular position, velocity, and acceleration of the trunk as the subjects flexed and extended their trunks in each of five planes of motion. Trunk motion features first were normalized for subject gender and age. Several two-stage eight-variable models that account for trunk motion interactions were developed to classify the 510 healthy and low back injured subjects into one of 10 anatomic and symptom-based low back disorder classification categories.

RESULTS

Using conservative cross-validation measures, it was found that the stage one eight-variable model could correctly classify more than 94% of the subjects as either healthy or having a low back disorder. One of the stage two eight-variable models was able to reasonably classify the patients with low back disorders into one of 10 low back disorder classification groups.

CONCLUSION

The motion-related parameters may relate to biomechanical or learned sensitivities to spinal loading. This study suggests that higher-order trunk motion characteristics hold great promise as a quantitative indicator of the trunk's musculoskeletal status and may be used as a measure of the extent of a disorder and as a measure of rehabilitative progress. Furthermore, once the interactive nature of these trunk motion characteristics is considered, the model could help diagnose low back disorders. However, independent data sets are needed to validate these findings.

Cervical injuries under flexion and compression loading

Cervical spine segmental tests were performed to determine the specific patterns of initial cervical injury in response to loading just beyond the point of structural failure. Well-defined combinations of flexion rotation and compression translation were applied to segments with varying degrees of disc and facet degeneration. Twelve cervical spine specimens (from human cadavers ages 52-91 years), each consisting of three vertebrae (two motion segments) from the middle (C2-C5) or lower (C5-T1) regions, were subjected to pure flexion rotation (seven specimens) or to combined flexion rotation and axial compression translation (five specimens). Specimens were sectioned and dissected to determine the patterns of structural failure. Pure flexion, and combined flexion and compression produced similar patterns of injuries. The disc was the most commonly injured structure, with annular injuries noted in 8 of the 12 specimens, and with anterior herniation of the nucleus occurring in two specimens. Wedge fractures and posterior ligament injuries were noted in both specimen groups and with both modes of loading. We conclude that similar patterns of initial anterior bony compressive failure and posterior ligamentous failure can occur with both flexion and with combined flexion-compression, without axial or lateral rotation, at low rates of loading. Anterior cervical disc herniations were produced in both middle and lower cervical segments.

Posterolateral lumbar and lumbosacral fusion with and without pedicle screw internal fixation

Forty-seven patients who had lumbar or lumbosacral fusion with or without pedicle screw internal fixation by one surgeon for treatment of degenerative lumbar disease with clinical instability were retrospectively reviewed by an independent observer. Eighteen of the 21 patients whose fusions were internally fixed with the Variable Spinal Plating (VSP) system were available for review. A control group consisted of 27 patients who had fusion without internal fixation. The rate of pseudarthrosis did not significantly differ between the two groups (VSP group, 22%; versus control group, 26%). Twelve (67%) of the 18 patients treated with fusion and VSP instrumentation were considered to have had a good or excellent outcome, whereas 19 (70%) of the 27 patients treated by fusion without internal fixation had good or excellent results. Two VSP-instrumented patients had postoperative leg dysesthesias, whereas this complication was not observed in the control group. Bilateral posterolateral lumbar or lumbosacral fusion without internal fixation is as effective as and safer than fusion with pedicle screw instrumentation.

Three-dimensional load displacement properties of posterior lumbar fixation

Pedicular fixation devices for the posterior treatment of segmental spinal instability are thought to offer enhanced stabilization compared with sublaminar wire systems, while avoiding the immobilization of multiple normal motion segments. We compared the performance of three dissimilar stabilization systems: the Hartshill rectangle, the Acromed/Steffee interpedicular screw and plate, and the Synthes/Dick fixateur interne. Human cadaveric lumbosacral specimens were first tested intact, then after a laminectomy and a facetectomy at the L3/L4 level, and finally after the fixation devices were sequentially attached. Constructs spanning two to four vertebral levels were compared for stabilization of the resected lumbar spine segments. When tested in compression, the Acromed/Steffee system with pedicular screws at L2-L5 allowed significantly less intersegmental distraction than the Synthes/Dick construct with screws at L2 and L5 only, and less than the intact and the destabilized uninstrumented spine. When sagittally rotated, the Acromed/Steffee construct with screws at L2-L5, or at L2 and L5, allowed significantly less distraction than the intact or destabilized segments, and the construct with screws at L2 through L5 allowed less distraction than the Synthes/Dick constructs with screws at L3/L4 or L2/L5. With the exception of the Acromed/Steffee system with screws at four levels, there were no significant differences in distraction allowed between the Synthes/Dick and Acromed/Steffee constructs, or between the multisegment and single segment constructs. There were no significant differences in stiffness across levels L3/L4 with the various implants. Results indicate that the use of posterior spine constructs significantly augment the stability of posterior segmental defects. Pedicular fixation immediately cephalad and caudad to the defect provided stable fixation in this application.