Validation of a long bone fracture non-union healing score after treatment with mesenchymal stromal cells combined to biomaterials

•A four stage bone healing evaluation in long bone non-union treatment with MSCs and tricalcium phosphate is proposed.•Three out of four cortical radiographic and CT assessment were compared.•Interrater concordance correlation coefficient about consolidation was higher with time.•Internal consistency confirmed the efficacy of this score to define bone healing in non-unions, particularly after this specific treatment.