Development and Evaluation of a System for Intraoperative Measurement of Spinal Rotational Mobility

Abstract

Quantitative measurement of spinal rotational mobility is critical in assessing spinal instability. We have developed a system for intraoperative measurement of spinal mobility. The system consists of a motor-driven mechanical apparatus with a computerized controller, load cell, optical displacement transducer, and spinous process holders that allow handling of the spinal process without damaging the ligaments. In this study, we examined the ability of this measurement system to detect mobility and corresponding clinical instability of a destabilized model spine comprised of porcine lumbar segments. From the load-displacement curve, we determined three motion parameters: stiffness, neutral zone (NZ), and absorption energy (AE). To demonstrate the potential of the measurement system for clinical application, we applied five cycles of axial rotation to the segment ten times. The measurements were highly reproducible. To verify the utility of the measurement system, we tested destabilized functional spinal units in vitro. In this setting, stiffness and AE decreased and NZ increased with progressive destabilization of the model spine. Significant relationships were observed between the destabilized model and the biomechanical data.

Keywords

• spine
• biomechanics
• instability
• intraoperative measurement
• stiffness
• neutral zone
• absorption energy