IntroductionFirst published in 1969, Dwyer instrumentation was the first anterior system for correction of scoliotic deformities of the spine [2]. Major disadvantages of this system were a marked kyphogenic effect, ineffectiveness of derotation, frequent cable fractures with pseudarthrosis and screw pullouts. Ventral Derotation Spondylodesis (VDS), also known as Zielke instrumentation, was developed to preserve the advantages and to eliminate the disadvantages of Dwyer's technique [21]. VDS is the gold standard of scoliosis surgery from the anterior approach [7]. Whereas frontal plane correction and derotation have been reported to be superior to posterior instrumentation techniques, the influence of VDS on the sagittal plane has been a subject of debate during the last two decades. A few authors pointed out that the sagittal plane can be positively influenced with VDS [3,4,21]. However, others have reported a kyphogenic effect [1,11,[13][14][15][16][17][18]20]. Another major disadvantage of VDS is lack of stability, which makes longterm brace or even cast treatment necessary. Screw pullouts, especially at the most superiorly instrumented level and fractures of the threaded rod were reported by several authors [8,13,16,19]. These were associated with painful pseudarthrosis and loss of correction in quite a number of patients. Halm-Zielke instrumentation (HZI) was developed to eliminate the disadvantages of Zielke VDS.Abstract Halm-Zielke instrumentation (HZI) was developed to eliminate the disadvantages of Zielke instrumentation (VDS) in terms of lack of primary stability and a kyphogenic effect. HZI is an anterior double-rod system. The system is composed of a lid-plate, which is fixed at the lateral aspect of the vertebral body with two screws, a sunk screw anteriorly and a VDS screw posteriorly. The lid-plate design provides the lowest possible implant profile. The longitudinal components consist of a threaded VDS rod and a solid, fluted rod. Correction is performed with the threaded rod and the solid rod. The solid rod allows internal derotation and relordosation, eliminates the Zielke three-point lever system and augments the system. The fluted design of the rod provides rotatory stability. This is a report of the first ten consecutive adolescent idiopathic scoliosis patients in a prospective clinical trial using HZI with a minimum follow-up of 2 years. Curves ranged from 36°to 77°. Correction of the frontal plane averaged 77.5% and 72.2% postoperatively and at follow-up, respectively. Thoracolumbar kyphosis was present in three patients and corrected in all from an average of + 18°to +1.7°at follow-up. Implant-related complications were not observed. All patients were treated without any additional external immobilization. In our opinion, HZI is a major improvement on the original Zielke VDS. It eliminates the kyphogenic effect and provides primary stability.

Severe fracture-dislocation of the thoracic spine without neurological deficit is rare. Both translational and rotational deformity of the midthoracic spine makes transection of the cord almost inevitable due to the confined dimensions of the cord and spinal canal. Even though associated fractures of posterior elements are frequently seen, they seldom result in neural sparing. The case of a 24-year-old man who sustained a severe rotational fracture-dislocation of T9/T10 with considerable anterolateral displacement is reported. Due to a fractured left pedicle and a right-sided vertical fracture through the posterior aspect of the vertebral body, alignment of the posterior elements in the spinal canal was maintained and there was no neurological deficit. The patient was operatively treated with posterior segmental instrumentation, and was completely asymptomatic at follow-up 5 years later.

We report on 30 unstable fractures of the thoracolumbar spine which were operatively treated between 1987 and 1992 with the AO Internal Fixator and transpedicular bone grafting. There were 26 flexion-compression fractures, 2 flexion-distraction injuries and 2 fracture-dislocations. Follow-up ranged from 2 to 5 years. All patients were examined and their histories reviewed. New radiographs were obtained and a standardized questionnaire on pain and on functional and economical status was answered. The radiographical analysis included measurement of the vertebral, segmental and local kyphosis and of the sagittal index. The preoperative vertebral kyphosis averaged +17 degrees and was corrected to +7 degrees at follow-up with the sagittal index improving from 0.59 to 0.86. The segmental respectively local kyphosis was reduced from +15 degrees respectively +8 to +5 degrees respectively -3 degrees. The fractured vertebra remained stable. We registered an average postoperative loss of correction of 4 degrees in the upper disc space due to collapse of the injured disc. The lower disc space was frequently overcorrected which was neutralized postoperatively due to a process of reequilibration of less than 3 degrees. The loss of correction occurred both before and after removal of the implant. There was no significant change of the sagittal plane apart from a successful realignment of the flexion-distraction injuries. Five out of 8 patients with neurological symptoms improved by at least 1 Frankel grade. We had no case of neurological deterioration. The results of the questionnaire were good or very good in 70%. At follow-up, the average back pain score was 3 out of 10, 10 being unbearable pain.

Halo treatment for cervical spine fracture in patients with ankylosing spondylitis is a challenging task for orthopedic surgeons and neurosurgeons.

Selective anterior correction and fusion in idiopathic thoracic scoliosis enables a satisfactory correction of both primary and lumbar secondary curves. The advantage of selective anterior correction and fusion of thoracic scoliosis is the short fusion length, better derotation and satisfactory correction of the secondary lumbar curve. The disadvantages of single threaded rod techniques in terms of lack of primary stability and a kyphogenic effect have been eliminated by the development of a primary stable, small size double rod instrumentation.