PurposeThis study investigates the occurrence of (progressive) posttraumatic valgus deformity after proximal metaphyseal greenstick fractures of the tibia in young children, and whether non-surgical or surgical treatment influences the outcome.MethodsA retrospective multi-center study was conducted including surveys and X-rays of patients < 12 years of age with a fracture of the proximal tibia. In patients with greenstick fractures, the medial proximal tibia angle (MPTA; defined as the angle of the tibial axis and the joint-line of the knee) was measured at trauma, short-term follow-up (st-FU), and long-term FU (lt-FU) as defined for the 2 groups of non-surgically and surgically treated patients.ResultsOf a total of 322 fractures, 91 were greenstick fractures. Of these, 74 were treated non-surgically and 17 were treated surgically. The mean MPTA at trauma of non-surgically treated patients was 91.14°, and of surgically treated patients was 95.59° (p= 0.020). The MPTA in non-surgically treated patients significantly increased from the timepoint of trauma to st-FU (92,0°;p= 0.030), and lt-FU (92,66°,p= 0.016). In surgically treated patients, the MTPA improved after trauma to st-FU (94.00°;p= 0.290), and increased again to lt-FU (96.41°;p= 0.618).ConclusionProgressive valgus deformity after greenstick fractures of the proximal tibia occurred in both non-surgically and surgically treated patients. In non-surgically treated patients, this was of statistical, but not clinical significance. In surgically treated patients, progressive valgus was observed after metal removal for an unknown reason. Therefore, surgery for proximal greenstick fractures of the tibia in this age group has only limited effect and may be indicated only in selected cases. Further studies are needed to explain the responsible mechanisms.Level of evidenceIII, retrospective analysis.