Efficacy of dynamic load during walking on the prediction of rebound effects following guiding growth intervention in children with angular deformities

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Rationale: Malalignment of knee joints is predisposed to the development of unicompartmental degenerations because of the excessive load placed on one side of the knee. Therefore, guided growth in skeletally immature patients is recommended. However, a rebound effect (recurrence of the malalignment) after implant removal frequently occurs. Up to now, the reasons for this phenomenon are not well understood and standards for optimal timing for hardware removal do not exist. This timing is crucial for the long term success of the axial corrections. In addition, indication for hardware removal is based on static measures during standing that does not reflect the actual load situation and individual compensatory mechanisms during walking. Objectives: The aim of the study is to investigate the influence of the dynamic load during walking on the rebound effect following a guiding growth intervention using tension band plates. Methods: Gait analysis and standing radiographs will be captured the day before implantation and explantation of tension band plates. To analyse rebound effects, non-invasive gait analysis will be performed 6 and 12 months after explantation. To assess daily cumulative loadings mobile step trackers will be used. In order to predict the knee joint loading regime as a function of acting muscles, multi-body simulations will be applied and additionally compared with knee joint loading measures of gait analyses. Populations: 142 children with idiopathic varus or valgus leg malalignment and 60 typically developed age matched controls. Timeframe: The anticipated duration is 3 years. During the first six quarters patients and controls will be recruited. The expected time of axial correction through guiding growth is on average 12 month, the follow up time after removal is 6 and 12 months. Expected outcome: According to the current algorithm for hardware removal, which is based only on static measurements, a few patients may show a pathologic knee joint loading after explantation. Since the load situation affects bone remodelling, pathological loads may be related to higher rebound effects. The results of this study should give first time insights into the mechanical integrity of bones and muscles during and after guiding growth. This may improve the treatment algorithm.