Analyse des Reboundphänomens und seiner Einflussfaktoren nach temporärer Hemi-Epiphysiodese mittels Eight-Plate im Kindesalter

The purpose of this study was to quantify the magnitude and identify risk factors for the so-called rebound phenomenon after growth modulation by hemi-epiphysiodesis with the Eight-Plate. Therefore we analysed the records of 60 patients between ten and sixteen years of age who had been treated with the Eight-Plate because of Malalignments in the frontal plane of the lower extremities in the years between 2007 and 2016. The indication for treatment with temporary growth arrest by implanting Eight-Plates was the pathological axis of the lower limbs such as a genu varum or valgum as defined by the norms of Paley. A pathological genu valgum was the most common reason for surgical correction as it covered 50 out of 60 Patients. A total number of 145 plates had been implanted into 116 knees of 40 male and 20 female patients. Full-length standing anteroposterior radiographs of both lower limbs were taken before the initial surgery, at every follow-up visit and once after the removal of the plates to record the mechanical lateral distal femoral angle, the medial proximal tibial angle and the mechanical axis deviation of the lower limbs. The Greulich and Pyle atlas was used to determine the skeletal age and to predict the remaining growth of the lower limbs setting the date for intervention. Removal of the plates was considered when the mechanical axis passed through the centre of the knee. The following clinical variables were recorded: gender, age, body weight, height and body mass index (BMI) at the time of surgery; and change of height and body weight between the initial surgery and the removal of the plates. The mechanical axis deviation was defined as the most important parameter of a Malalignment and was statistically compared with the radiographic and clinical variables using linear regression models. The degree of rebound was measured in millimetres of deviation from the mechanical axis. In this study 96.5% of all patients showed a rebound after removal of the plates, this being most commonly in the direction of the former deformity. In 20% of all patients the axis went back to a pathological Malalignment in comparison to the norms of Paley and Galla et al. In our multivariate regression analysis an independent predictive value for the degree of rebound was shown for low body weight and the extent of correction in the genu varum group. In the genu valgum group the multivariate regression analysis pointed out three significant predictive values for the magnitude of rebound: the age at the time of correction, the total duration of correction as well as the extent of correction. The younger the patients, the faster the correction was achieved by the plates and the bigger the correction of the mechanical axis in the first place, the more likely and greater the rebound after the removal of the plates appeared. Limitations of this study include its retrospective design and small sample size especially the sample size of the cases which originally had genua vara is limited. Therefore no adequate comparison between the two groups was possible. In conclusion, independent predictive variables for the magnitude of the rebound phenomenon measured by the mechanical axis deviation could be determined within this study. We believe that the rate of correction is the strongest independent contributing factor to the rebound phenomenon as it is shown in both groups. Since almost all patients in our study have shown some degree of rebound, a certain amount of overcorrection might possibly be beneficial in terms of maintaining a physiological axis after growth modulation of the lower limbs by hemi-epiphysiodesis with the Eight-Plate. Further examination with larger cohort sizes within prospective studies is needed to show possible effects of over- and undercorrection on the rebound phenomenon regarding the results of this study.