Introduction
Intervertebral disc (IVD) herniation is a major cause of low back pain and sciatica. It often involves disruption of the outer region of the IVD, known as the annulus fibrosus (AF). Although mechanical overload is considered an important contributor to disc damage, the role of repeated axial rotation remains insufficiently understood. This is clinically relevant because abnormal rotation of a spinal segment, also described as rotational instability, may contribute to a vicious cycle: mechanical overload damages the disc, and the damaged disc becomes less able to resist further loading. This pilot study investigated whether controlled dynamic axial rotation induces early biological and structural responses in intact IVDs by spatially characterizing cell and matrix responses in an ex vivo bovine IVD whole organ culture model.
Methods
Three bovine IVDs were prepared from the tail of a freshly slaughtered animal (n = 1, female; age: 446 days; body weight: 260 kg). After overnight culture in IVD medium containing glucose, amino acids, serum and other nutrients to maintain the metabolic activity of the disc cells, one disc was harvested at baseline as a T0 control (T0 Ctrl). The remaining two discs were placed in sealed chambers and cultured for three days in a multiaxial loading device for controlled mechanical stimulation. The loaded control (Loaded Ctrl) received static compression at physiological level, while the experimental disc (Exp) received static compression combined with dynamic axial rotation of ±6° at 0.2 Hz. Loading was applied 4h/day. After the final loading, both discs were returned to free swelling overnight and harvested on day 4. To assess early responses, culture medium was collected for release of nitric oxide (NO; indicating inflammation) and sulfated glycosaminoglycan (sGAG; indicating matrix breakdown). Tissue was analysed using Safranin O/Fast Green staining for histology, lactate dehydrogenase/ethidium homodimer staining for spatial cell viability, and RT-qPCR for selected inflammatory, matrix-related, and cell-death-associated genes in different regions of the IVD.
Results
Preliminary data showed high overall cell viability across groups and disc regions. A slight reduction in viability was observed in the outer part of the AF, suggesting that this region may be more sensitive to the applied loading regime. This observation was consistent with increased NO release in the experimental condition compared with the loaded control. sGAG release was also higher after combined compression and rotation. Gene expression showed region-specific responses, including increased IL6 and COL1 expression in the outer AF relative to the loaded control. Safranin O/Fast Green histology showed preserved gross disc architecture, supporting the interpretation that the model captures early biological and matrix-related responses rather than advanced structural failure (Figure 1).
Conclusion
Although these data are preliminary and limited to one donor, they support the feasibility of using a controlled multiaxial organ culture model to study early disc responses to rotational loading. The pilot supports future experiments testing rotational thresholds and AF damage patterns. Regionally and ethically, the study transforms waste bovine tail into a valuable research model without additional animal harm. By combining biomechanics, biology, and engineering, this work contributes to understanding how rotation may initiate early disc stress and potentially inform future strategies for preventing disc degeneration and herniation.