In approx. 10-15% of all fracture patients, there is a prolonged healing time or even a complete absence of fracture healing (non-union). As a result, these patients require further surgical interventions, combined with renewed or prolonged hospitalisation/rehabilitation and incapacity to work. To summarise, this therefore represents a serious socio-economic problem. At present, there is no prognostic method for the early prediction of patients at risk of a disturbed healing process. However, if these patients are successfully stratified, there are already a variety of therapeutic strategies available to additionally stimulate fracture healing. Therefore, the aim is to conduct a prospective clinical study to validate CD8+ TEMRA cells as a prognostic marker of impaired fracture healing. The investigators assume that preoperative CD8+ TEMRA cell expression represents a prognostic biomarker with high diagnostic precision for differentiating between a) normal healing patients, b) delayed healing patients and c) pseudarthrosis patients. Furthermore, the sensitivity and specificity should be high enough, health-economically significant and realisable in clinical routine.