Intra-bone marrow transplantation (IBMT) is a method for introducing material directly into the bone marrow cavity. It has been extensively used in studies ranging from stem cell therapy to cancer research as it might improve the seeding efficiency of transplanted cells compared to the routinely used intravenous injection.
As far as I know, this is the first study about the impact of IBMT on mice in terms of pain and suffering. Current IBMT protocols are optimized for ease of use and to improve experimental results irrespective in considerations about the consequences of IBMT on animal welfare. Here I report the results of pain assessment after IBMT and the effects of my established refinement compared to the current standard procedure. IBMT was performed under general anaesthesia either into the tibia or the femur of a recipient mouse. Impact was determined using clinical scoring of different parameters (lameness, grip capacity, body weight loss, footprint analysis), behavioural tests (burrowing, open field), monitoring of stress hormones and post mortem histology. The results reveal that IBMT definitely induces severe postoperative distress. It leads to profound lameness scores and limping up to 3 weeks post-operation. Although IBMT into the tibia is technically easier, the degree of impairment and the distress observed was consistently higher compared to the transplantation into the femur. A refinement for IBMT into the tibia was achieved by using 30- instead of 26-gauge needles and sparing the patellar tendon. The refined procedure reduced the pain score of the tibia transplanted mice by one level (from highly to moderately painful). In the femur the refinement failed to improve animal welfare. Because of anatomical conditions the injection into the femur is challenging and therefore more likely to fail (e.g. fracturing the femoral condyles due to introducing the needle from an incorrect angle in trying to avoid the patellar tendon). Nevertheless for IBMT I recommend using the femur as the post-operative burden is consistently lower compared to the tibia. If the tibia is required due to its better feasibility it is strongly advisable to use my refined protocol. In addition a certain injection leads to a reduction of the number of animals needed for an experiment. Above all IBMT should definitely be limited to one leg per animal.