Introduction: Low back pain is one of the major causes of disability worldwide. Intervertebral disc (IVD) degeneration, characterized by microscopic changes such as cellular senescence as well as macroscopic changes such as height reduction, is known to be a main driver for low back pain. This degeneration can be induced by excessive mechanical loading of the IVD. Using an animal organ culture model, we investigated the link between detrimental mechanical loading, IVD degeneration and release of pain-associated factors that sensitize nerve cells.
Methods: Juvenile bovine tails were dissected and IVD were kept under continuous physiological or degenerative loading in sterile culture medium (CM) for one week. We exchanged the CM and measured the IVD’s heights and diameters daily in order to detect time-dependent changes. The CM was analyzed for degeneration-indicating markers. The CM’s potential to provoke nerve excitation, which may reflect pain transmission, was analyzed using the imaging of calcium influx in a nerve-derived cell line.
Results: Degenerative loading induced a strong disc height loss compared to physiological loading. Imaging of calcium influx revealed a different effect of the CM of physiological and degenerative loading: CM of degenerative IVD induced higher spontaneous nerve cell responses and higher peak responses, which are associated with increased spontaneous pain and hyperalgesia, respectively. It also induced longer outgrowth of nerve cells compared to physiological loading, which is concordant to extended innervation of degenerative IVD in vivo.
Conclusion: Excessive mechanical loading can result in IVD degeneration and nerve excitation, which is associated with pain development. Our results help to better understand the relation between degenerative spinal loading and the development of low back pain.