Intraoperative measurement of lumbar spine motion segment stiffness.

STUDY DESIGN: Prospective trial. OBJECTIVES: To test an intraoperative diagnostic tool to determine if it provided the surgeon with a safe, reproducible, accurate, quantitative measure of lumbar spine motion segment stability. SUMMARY OF BACKGROUND DATA: Several devices have been developed to measure motion segment stiffness, however, few have been tested intraoperatively on humans, and none, to the best of the authors' knowledge have been tested as extensively as the device described in this study. Objective criteria, such as those provided by an intraoperative gauge, can be helpful in determining when and what type of fusion of a degenerated spinal motion segment unit should be performed following decompressive surgery. METHODS: The spinal stiffness gauge, placed between spinous processes of adjacent vertebrae, applies a controlled, constant loading rate along the spine's longitudinal axis, producing a load-displacement curve from which stiffness, range of motion, and hysteresis can be computed. Measurements from this tool were then used to investigate differences in stiffness of the motion segment before and after decompressive surgery, between spine levels, and between male and female subjects. RESULTS: The spinal stiffness gauge stiffness measurements correlated with the surgeon's subjective stiffness measurements on the same motion segments. The stiffness measurements had excellent repeatability. Stiffness was dependent on the spine level, gender, and degree of disc degeneration. CONCLUSIONS: This study demonstrated the efficacy of the spinal stiffness gauge for providing an objective, quantitative, intraoperative stiffness (stability) measurement of the lumbar spine motion segment.

The clinical usefulness of intraoperative spinal stiffness measurements.

STUDY DESIGN: Determination of clinical results at least 2 years after lumbar spine surgery during which spinal stiffness measurements were made. OBJECTIVES: To determine whether spine stiffness is predictive of clinical results after lumbar spine surgery for spinal stenosis, disc herniation, or degenerative spondylolisthesis. SUMMARY OF BACKGROUND DATA: The implied clinical wisdom is that instability of the spine portends a poor prognosis for relief of back pain after surgery in the absence of a fusion. The possibility that an objective measure of lumbar spinal motion segment unit stiffness could aid the surgeon in predicting satisfaction with treatment was considered. METHODS: A total of 298 patients were measured intraoperatively with the spinal stiffness gauge to determine motion segment stiffness. Intraoperative spinal stiffness was analyzed to determine the influence of this measurement on clinical results. RESULTS: Statistical analysis revealed that stiffness measurements did not correlate with clinical results of surgery. Patients with loose motion segment units before decompression did not demonstrate a significantly different level of satisfaction with surgical results a minimum of 2 years after surgery, whether they were fused or not fused. Based on stiffness measurements, a diagnosis of herniated nucleus pulposus or degenerative spondylolisthesis was indicative of a more unstable spine than a diagnosis of spinal stenosis. CONCLUSIONS: Intraoperative spinal stiffness measurements did not predict clinical results after lumbar spine surgery.