[Multi-segment ventral stabilization of the lumbar spine: a comparative biomechanical study]

[Anterior scoliosis surgery. State of the art and a comparison with posterior techniques]

For more than 2 decades ventral derotation spondylodesis (Zielke VDS) as a major improvement over Dwyer instrumentation (DI) was the gold standard of instrumented curve correction and stabilization from the anterior approach. As the first available system it enables a true three-dimensional curve correction. A disadvantage is the low internal stabilization capability with a need for long-term external stabilization by means of cast and brace treatment postoperatively. Meanwhile with the development of modern single and dual solid rod systems these disadvantages can be avoided completely. Video-assisted (thoracoscopic) anterior scoliosis surgery accounts for less than 2% of anteriorly treated scoliosis cases, mainly due to a long operating time and significant learning curve.From the posterior approach the Cotrel-Dubousset instrumentation (CDI) as a polysegmentally attached posterior hook threaded dual rod system used to be state of the art for a long time, since it eliminated the disadvantages of Harrington instrumentation (HI) in terms of only one-dimensional correction and low stabilization capabilities. However even with CDI effective derotation was impossible. In posterior scoliosis surgery there is a strong trend away from hook systems towards transpedicular segmentally fixed dual rod systems not only in the lumbar spine but also in the thoracic area. Advantages of these newer techniques are shorter fusion, improved correction, and less loss of correction over time.Advantages of modern anterior instrumentation systems in comparison to posterior transpedicular instrumented dual rod systems are less blood loss, better derotation, slightly shorter fusion levels, and a better influence on sagittal plane control or improvement especially for hypokyphotic thoracic scoliosis cases. Our data also document a superior spontaneous correction of the lumbar curve after selective anterior instrumented correction (Lenke 1B+C), although other studies could not find significant differences. In our experience the neurological risk of anterior instrumented correction is also lower than that of posterior scoliosis surgery, although the morbidity and mortality data of the Scoliosis Research Society could not prove that anymore in recent years. A negative effect of anterior transthoracic scoliosis surgery in comparison to posterior surgery is a more negative effect on lung function, which improves slower after surgery and does not quite reach the levels of posterior surgery at follow-up. But new data on posterior segmental transpedicular correction and fusion also prove a lordosating effect with negative effect on lung function.

Operative treatment of spondylodiscitis--what is the most effective approach?

In a study the results recorded in 34 surgically treated patients with specific or unspecific spondylodiscitis after dorsoventral one-stage instrumentation with CDI and anterior grafting (group 1) were compared with those obtained in a group of 38 patients treated with anterior CDH instrumentation in combination with anterior grafting (group 2). The mean observation periods were 48.4 (19-82) months in group 1 and 29.0 (8-54) months in group 2. In both groups the infection healed after fusion without a secondary operation. In group 1 the mean values for blood loss, operating time, length of hospital stay and fusion length (3.5 segments) were significant higher than those in group 2; in particular, the fusion length was shorter (1.3 segments) in group 2. Only 8 patients in group 1 were treated with postoperative external support. The mean preoperative segmental angle of 18.2 degrees (group 1) was corrected by a mean of 11.9 degrees, and the reposition loss during follow-up amounted to an average of 2.7 degrees. Group 2 showed a mean preoperative segmental deformity angle of 13.4 degrees, which was corrected by 11.6 degrees, and the loss of reposition was 2.9 degrees on average. Even in florid spondylodiscitis a short-range anterior fusion of the affected spinal segment can be performed with a primary stable implant, avoiding a second operation without an increased risk of infection-related dislocation. In the authors' own experience a secondary dorsal operation can be avoided except in the case segment L-5/S-1, the fast mobilization without external support allows a up-to-date treatment in this severe spinal disease.

Preoperative estimation of screw fixation strength in vertebral bodies

STUDY DESIGN

Bone mineral density and bone cross-sectional area of human cadaveric vertebral bodies were investigated radiologically and histologically, respectively. After ventral instrumentation with ventral derotation spondylodesis screws, axial pullout force was measured and compared with radiologic and histologic data.

OBJECTIVES

To elucidate how well ventral derotation spondylodesis screw fixation strength can be estimated before surgery by specified applications of dual-energy x-ray absorptiometry, quantitative computed tomography, T2*-relaxation time in magnetic resonance imaging, and histomorphometry.

SUMMARY OF BACKGROUND DATA

It is postulated that bone quality plays a crucial role in initial strength of the instrumented spine. Bone quality is even more important in anterior fixation because of the prevalence of spongy bone in the vertebral body.

METHODS

Bone mineral density of human cadaveric lumbar-vertebral bodies was assessed by dual-energy x-ray absorptiometry and quantitative computed tomography (cancellous and cortical bone separately). Cancellous bone was also characterized by T2*-relaxation time, measured by magnetic resonance imaging and histomorphometric study. Vertebral bodies were instrumented ventrally with VDS screws, and screw axial pullout force was measured and correlated with each of the nonmechanical measures. Patients with manifest osteoporosis, osteomalacia and tumors were excluded. For statistical analysis, the Mann-Whitney rank sum test was used with a significance value of P < 0.05.

RESULTS

The highest correlation with pullout force was for density of cancellous bone determined by quantitative computed tomography (r = 0.72; P < 0.001), immediately followed that determined by dual-energy x-ray absorptiometry (r = 0.70; P < 0.001). Results of measurement of T2*-relaxation time and those of histomorphometric study correlated moderately (r = 0.55; r = 0.50), whereas cortical bone density determined by quantitative computed tomography showed negligible correlation (r = 0.2).

CONCLUSIONS

The absorptiometric techniques, quantitative computed tomographic scan of cancellous bone and dual-energy x-ray absorptiometric study, provide more accurate readings for preoperative estimation of initial VDS screw fixation strength than do the other methods studied.

Operative treatment of scoliosis with Cotrel-Dubousset-Hopf instrumentation. New anterior spinal device

STUDY DESIGN

This study analyzes the effects of a new anterior spinal instrumentation system and the results of use in 50 patients with scoliosis.

OBJECTIVES

Anterior spine systems are reviewed. The principles of a new anterior spinal instrumentation system allowing for postoperative care without external support are discussed.

SUMMARY OF BACKGROUND DATA

Numerous different implants have been presented in the literature for anterior spinal surgery. Nevertheless a primary stable anterior instrumentation was not available for multisegmental procedures until now, and the restoration of lordosis in the lumbar spine was very difficult with the common devices. The development of more stable devices that also allow a restoration of lordosis in combination with derotation and compression is discussed.

METHODS

Fifty patients with scoliosis of different etiologies (neuromuscular: n = 33; idiopathic: n = 16; congenital: n = 1) underwent anterior spinal surgery at the thoracic, thoracolumbar, and lumbar spine. During follow-up, no revision operation was necessary after the monosegmental and multisegmental application of this method, and there were no vessel complications. The results were controlled with a mean follow-up of 26.6 (range 12-41) months.

RESULTS

Clinical and radiologic follow-up and complications are reported. Statistical data obtained show a different average blood loss and operation time depending on the different etiology of the scoliotic deformity. The mean corrections for the scolioses by etiology are as follows: myelomeningocele (MMC) (mean preoperative angle 89 degrees, mean correction 54%); neuromuscular (81 degrees, 46%); and idiopathic (55 degrees, 69%). The mean lordosis of the lumbar spine was 29.2 degrees (measured between T12-S1) and could be corrected to 45.2 degrees depending on the etiology of the curvature, whereas the angle of the thoracic kyphosis did not show an essential change. The segmental measurement in idiopathic scoliosis did not show a kyphosization in the lumbar spine. Derotation of the apical vertebra in 15 patients in relation to the sagittal plane was 37%.

CONCLUSIONS

The study shows the effect of a new anterior device allowing the application of three-dimensional correction forces to the spine. Particularly in scoliosis derotation, compression and restoration of lordosis are possible. Primary stability is obtained by anchoring the implants with a new wedge-locking technique, which makes postoperative external support unnecessary.

Primary stable anterior instrumentation or dorsoventral spondylodesis in spondylodiscitis? Results of a comparative study

The operative results of 23 patients with a specific or unspecific spondylodiscitis were documented over 2 years after the focus of the inflammation had been eradicated, bone chip had been interposed and a CDH instrumentation had been performed by an anterior approach only. These outcomes were compared with the results of 32 patients in whom the focus had been removed and the defect had been filled with bone graft from an anterior approach, followed by stabilisation with CD instrumentation through an additional dorsal approach. In the cases where CDH instrumentation was applied, the range of fusion averaged 1.3 segments. This was clearly less extensive than in dorsoventral stabilisation, in which on average 3.5 segments were fused. In 47 of 55 cases mobilisation was achieved without orthesis. Eight months after the operations bony fusion could be observed radiologically in all patients. The mean preoperative kyphotic angle of the affected segments was 14.4 degrees, compared to 4 degrees after the operation. The mean loss of reposition was measured to be about 2.7 degrees in both groups. Average operation time and blood loss were about 50% higher in the patients treated dorsoventrally. We conclude that even in the case of florid spondylodiscitis, a short-range anterior fusion of the affected spinal segment may be performed by use of a stable-angle implant without an increased risk of infection-related loosening.

CDH: preliminary report on a new anterior spinal instrumentation

CDH (Cotrel-Dubousset-Hopf) instrumentation was developed with the aim of improving stability in ventral operation procedure and facilitating treatment of all anterior spinal diseases. The implantation of anterior plates and drawers, the use of a double-rod fixation within the implant in nonparallel directions, which provide an automatic locking mechanism against displacement, the prevention of dislocation of the cancellous bone srews, and the crosslink principle are its main characteristics. The device can be applied to the spine in accordance with its three-dimensional anatomy by any kind of force (distraction, compression, and rotation). Additional posterior instrumentation and postoperative external support are unnecessary in most cases because of improved stability. No reoperation was necessary following the mono- and multisegmental application of this method in 60 patients (28 with scoliosis, 12 with spondylodiscitis, 8 with primary tumors or isolated metastasis, 6 with fractures, 3 with failed back syndrome, 1 with kyphotic deformity, 1 with spondylolisthesis on two levels, and 1 with loss of correction after the dislocation of another posterior spinal instrumentation). Average blood loss was 950 ml; the average operating time was 3 h. In all, 16 monosegmental and 44 multisegmental procedures were carried out. In 25 patients, in particular those with paralytic scoliosis, a double-stage anterior and posterior spondylodesis was done.