Adjacent long bone fractures associated with different trauma severity affect the expression of microRNA of the infrapatellar fat pad in a porcine polytrauma model

Introduction Long bone fractures are common in severely injured patients and can be associated with future osteoarthritis and immobility. Previous studies have shown that the infrapatellar fat pad (IPFP) can signal early pro-arthritic changes in the affected joint. Recent porcine models have indicated that both local and systemic inflammatory responses are influenced by the severity of trauma. MicroRNAs (miRNAs) are significant mediators for such responses. This study aimed to investigate the effect of an adjacent femur fracture and trauma severity on miRNA expression in the IPFP.

Material & Methods German Landrace pigs were randomised into three study groups: sham (n=4), minor-multiple trauma (MiMT, n=4, blunt chest trauma, unilateral femoral fracture) and major-multiple trauma (MaMT, n=4; blunt chest trauma, unilateral femoral fracture, haemorrhagic shock). 90 minutes after trauma induction, pigs were stabilised by medication and surgical treatment (Fixateur externe). Pigs were sacrificed after 72 hours of observation in an intensive care unit. IPFP was extracted from fractured and non-fractured legs, miRNAs were isolated, qPCR array analysis followed by in silico mRNA target prediction was performed.

Results The fractured leg of the MiMT group showed increased anti-inflammatory miRNAs (e.g., miR-16, miR-23b) and decreased pro-inflammatory miRNAs (e.g., miR-21, miR-223). In contrast, the fractured leg of the MaMT group exhibited higher expression of cells essential for bone tissue development and regeneration. Sequence analyses identified target structures related to immune responses and tissue regeneration.

Conclusions This study indicates a correlation between miRNA expression in the IPFP and adjacent femoral fractures, as well as trauma severity. The different miRNA expression patterns suggest that the IPFP plays a crucial role in maintaining joint homeostasis after trauma. Further research is needed to investigate such associations.

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