Introduction and aim of the study: Halm-Zielke Instrumentation (HZI), in german speaking countries also named the Münster Anterior Doublerod System, was developed to eliminate the disadvantage of VDS-Zielke in terms of lack of primary stability. Additionally sagittal plane control should be improved. Within a prospective clinical trial it was examined, if HZI fulfilled these demands.
Methods: HZI is an anterior doublerod system with a two screw per vertebral body fixation. The longitudinal components consist of a threaded VDS-rod and a solid rod. 12 consecutive patients with idiopathic scoliosis and curves ranging from 36 degrees to 77 degrees were treated with HZI.
Results: Correction of the frontal plane averaged 75% and 73.8% postoperatively and at follow-up, respectively. Derotation averaged 49.3%. Thoracolumbar kyphosis was present in four patients and always completely corrected. Implant related complications were not noted. All patients were treated without any additional external immobilisation.
Conclusion: The aim of improvement of VDS in terms of primary stability and control or improvement of the sagittal plane was completely achieved.