Mechanical instability of the lumbar spine following intervertebral disc injury: a comparison of two injury methods.

Intervertebral disc (IVD) degeneration is a potential contributor to low-back pain. While experimental IVD injury models have demonstrated IVD structural changes, the early mechanical consequences remain unclear. This study aims to assess and compare the effects of two IVD injury models on lumbar spine instability and assess back musculature adaptations to IVD injury. Thirty-one adult male Wistar rats were assigned to three groups: IVD knife stab lesion (knife), IVD needle puncture (needle), and sham surgery control (control). In the knife and needle groups, L4/L5 IVDs were injured at 14 weeks of age. One to two weeks post-intervention, lumbar multifidus (MF) and medial longissimus (ML) muscles were excised, L4-L5 spinal segments were harvested for mechanical testing, and IVDs were collected for histology. The needle group exhibited lower peak stiffness, peak moment and hysteresis than controls in flexion, with no difference in lateral bending. IVD height and area did not differ between groups, but the needle group had a smaller nucleus relative to the annulus area compared to controls. Morphological changes were observed in both injury groups. The needle group showed a higher normalized ML mass, while the normalized MF mass was unchanged. In conclusion, lumbar spine instability was successfully established via IVD needle injury in the rat.