Injury Induces More Severe Biomechanical Changes in Middle-Aged and Geriatric Lumbar Spines in a Mouse Ex Vivo Model

Intervertebral disc degeneration (IVDD) is a major cause of global disability that increases with age. IVD age may affect its injury susceptibility, yet few studies examine spine biomechanical changes with age, fewer address multiple injury types, and none investigate the interplay between age and injury.

An ex vivo mouse lumbar spine biomechanical study to determine the effects of age, injury, and their interaction. IVDs of 4, 12, and 24 months' mice were subjected to two injury types: Full disc puncture (DP) mimicking advanced IVDD and annulus fibrosus and endplate (AF + EP) injury simulating herniation with endplate junction failure. Spines were tested biomechanically, analyzed radiologically for IVD dimensions, and with FTIR and histology for biochemical content.

Both age and injury significantly altered biomechanical properties of IVDs. Injury had a greater effect than age, and DP caused larger changes than AF + EP injury. Injury and age exhibited an interactive effect, resulting in more pronounced biomechanical dysfunction in middle-aged (12 months) and geriatric IVDs (24 months), likely due to age-related loss of proteoglycans and collagen denaturation shown with FTIR and histology.

We conclude that both age and injury independently and synergistically affect ex vivo biomechanical properties of mouse lumbar spine. The more severe biomechanical change in middle-aged and geriatric mouse lumbar spines suggests similar injuries may cause greater spinal dysfunction in individuals of comparable ages. These findings provide context for future in vivo studies investigating long-term effects of acute spine injuries.