Abstract
Introduction: Cadaveric intervertebral discs (IVD) must perform consistently and repeatably with time and cyclic loading if the results from long experimental protocols are to be considered valid. Experiment design should take into account the potential for changes in the biomechanical properties of the intervertebral disc. Changes in the pressure distribution and stress profiles across the IVD along with variation in movement of the anterior annulus during a load cycle give a good indication as to the biomechanic status of the IVD. The purpose of this study was to assess the biomechanic response of the IVD to repeated cyclic loading, in normal, flexed and extended positions over a prolonged period.
Methods: Ten multisegment cadaveric lumbar spine specimens (L3-5 or L1-3) were dissected and compressed to 1kN in 6° flexion, neutral and 4° extension. The anterior annulus was imaged during loading using ultrasound. The stress distribution along the mid-sagittal and antero-postero-lateral (APL) diameters of both discs was measured by withdrawing a miniature pressure transducer from posterior to anterior across the IVD during loading. Stress profilometry and ultrasound imaging was performed over a two day period.
Results: Ultrasound imaging provides an easy method for observing disc movement during compressive loading of a multi-segment specimen through positions of extension and flexion. Anterior disc bulging increased by more than 150% as the specimen is loaded from 4° of extension to 6° flexion. Repeated passes of the pressure transducer across both the mid-sagittal and APL diameter of the discs produced repeatable stress profiles. Similarly, ultrasound imaging of the anterior annulus showed comparable disc movement after cyclic loading.
Conclusions: Preliminary results suggest that the biomechanical behaviour of the IVDs of a multi-segment specimen do not change significantly following prolonged testing and multiple cyclic loading.
The abstracts were prepared by Editorial Secretary, Dr Charles Pither. Correspondence should be addressed to SBPR at the Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London WC2A 3PN
