Oral Presentation 50th International Society for the Study of the Lumbar Spine Annual Meeting 2024

Introduction. Often after animal experiments in spinal research, the question arises – histology or biomechanics? For biomechanical testing, e.g., flexibility measurements, the specimens must be shipped to institutions with special testing equipment, as these spine testers are complex and immobile. The specimens must usually be shipped frozen on dry ice and therefore biological and histological investigations are not possible any more. To allow both biomechanical and biological investigations with the same specimens and, thus, to reduce the number of required animals we developed a spine tester that can be shipped around the world to test on-site.

Methods. The portable spine tester (weight: 82kg, dimensions: 79.5x79.5x115cm) can perform flexibility tests on polysegmental spines by applying pure moments in three motion planes (flexion-extension, lateral bending, and axial rotation) (Fig1A). Based on a combination of two known spine tester principles [1,2], one of three DC motors flex the specimen in one motion plane at a time while an air-bearing XY stage with weight compensation enables all other degrees of freedom. Together with a load cell underneath the specimen and an optical motion tracking system, the new device can simultaneously measure the range of motion (ROM) and the neutral zone (NZ) of each individual segment (even with polysegmental specimens) with respect to simple or complex loading conditions. First experiments abroad involved eight sheep, whose intervertebral discs from L1 to L6 were operated with a nucleotomy to provoke disc degeneration. In a second operation five weeks later, four different hydrogel-based treatments (NPgel or dNCM-PEG with and without MEP cells) were injected into discs of level L1-L2, L3-L4, and L5-L6 (4 groups, n=2 sheep). Three months later, the spines were collected, prepared, and embedded in PMMA and then tested with 2.5Nm and a speed of 1°/s in the new machine immediately in the operating room. The four different treatments were analyzed individually with n=6 discs from two sheep per group normalized to the degenerated discs (n=16). Statistics: Mann-Whitney-U (α<0.05).

Results. The new portable spine tester was able to determine ROM and NZ from hysteresis curves of all eight spines for each disc in each motion plane (Fig1B). Except for NPgel in axial rotation, treatment with one of the two hydrogels without MEPCs increased the ROM up to 25% whereas the hydrogels with MEPCs showed only minor effects or even a decrease of the ROM (Fig1C). No statistical differences were found (p≥0.065).

Discussion. The results have demonstrated that the new portable spine tester can be easily shipped to any location and be used on-site to determine the biomechanical properties of sheep spines, but potentially also of smaller species. The hysteresis curves are consistent with other sheep experiments in the literature [3]. This animal study is limited by the sample size because only two sheep were included per group. However, the overall results show that small difference between treatment groups can be determined. This spine tester “TO GO” is ready to travel to your place.

Acknowledgements. iPSpine (825925)