Effects of Thrombopoietin (TPO) on Longitudinal Mouse Hind Limb Crush Injury Model

Approximately 645 people suffer from blunt force trauma injury to the femur every day and recovery time can last anywhere from 3‐6 months. Thrombopoietin (TPO) was used as a growth factor to induce bone and muscle healing. In this study, 9 separate mouse model groups were utilized (10 mice per group): Crush PBS and TPO, Surgery PBS and TPO at days 3 and 17, and controls with no surgery/crush/treatment. Crush models were introduced to hind limb crush injury by a mechanical‐gravity driven Einhorn device. Skeletal muscle was harvested from the experimental impact, experimental adjacent, and normal contralateral skeletal muscle sections. The muscles were fixed, processed, sectioned, and stained with H&E, Masson's Trichrome, and F4/80 stains. The slides were reviewed for skeletal muscle injury, inflammation, muscle repair, and regeneration. Microscopic examination at day 3 showed sporadic muscle fiber vacuolation, focal necrosis, muscle contraction bands, and infiltration of macrophages. On day 17, the skeletal muscle injury was generally healed. The main histologic lesions seen were variable sizes of muscle fibers, early fibroplasia, fat infiltration, some macrophages, satellite cells, and neovascularization. A follow‐up immunostain (CD206 double labeled with F4/80) was performed to characterize the macrophages in and around the lesions at day 3. M2 macrophages were seen around the periphery of the lesion. There were minimal differences in M2 numbers between the PBS and TPO treated groups at day 3. In conclusion, comparing the TPO treated mice versus the PBS control group with F4/80 immunostain showed the lesions at both time points were less in the TPO treated mice.