Relative movement of bone fragments affects healing processes. In vivo data exist for patients with reduced transverse fractures only. The gap movements that occur under more complex conditions such as in tibial osteotomies, however, are unknown. The goal of this study was to determine the initial gap movements in tibial correction osteotomies, to monitor movements during the early healing period, and to determine the suitability of initial fixation stability in relation to daily activities. The interfragmentary movements were measured in six patients with correction osteotomies stabilized by Ilizarov ring fixator constructs until union or until conversion to internal fixation. Consolidation was determined by clinical evaluation and standard radiographic techniques. Co-contraction led to gap movements comparable with level walking or standing. Shear generally exceeded axial compression. Although ground reactions and fixation stiffness were comparable with those reported for reduced fractures, movement magnitudes generally were larger than 2 mm. The shear movement component reflected the nature of the mechanical conditions at the bone gap. In a direct comparison with data from animal experiments, the local mechanical environment at the bone gap seemed unstable rather than overly stable. The method introduced in this study opens the perspective of adjusting osteosynthesis stability to the specific needs of each patient.