Introduction The unacceptably low fusion rate with stand-alone ALIF cages led to the practice of combining ALIF with posterior instrumentation. Recently ALIF combined with anterior lumbar plate fixation has been promoted to obviate the need for additional posterior surgery. The purpose of this study is to compare the multidirectional flexibility of ALIF combined with posterior instrumentation (either translaminar facet screws or pedicle screws) to that combined with anterior plate fixation.

Methods Ten human lumbar cadaveric motion segments were tested in the following sequence: (i) intact, (ii) stand alone ALIF cages, (iii) ALIF and anterior lumbar plate, (iv) ALIF with translaminar facet screws, (v) ALIF with pedicle screws. In each condition, the specimens were tested under bending moments of 0–8 Nm flexion, 0–6 Nm extension, 0–6 Nm lateral bending and 0–5 Nm axial rotation. 3D motions were measured using an optoelectronic motion monitoring system.

Results The ALIF cages decreased the ROM in the sagittal and frontal planes (p< 0.05). Their effectiveness improved in the sagittal plane with the combination of either anterior plate or posterior fixation (p< 0.05). There was no statistical difference between the ALIF/ Plate and translaminar screws or pedicle screws in flexion-extension and axial rotation ROM. There was a difference in the lateral bending ROM between the ALIF with anterior plate and ALIF with either translaminar facet screws or ALIF with pedicle screws (p< 0.05) favouring posterior fixation. However there was no statistical difference between the combined ROM for ALIF/Plate and translaminar screws or pedicle screws.

Discussion This study shows that the stability achieved with the combination of ALIF with an anterior plate is comparable to that achieved with posterior instrumentation with translaminar facet screws or pedicle screws. This suggests that sufficient segmental stability may be provided by anterior plating, obviating the need for a concomitant posterior approach.

Purpose: The purpose of this biomechanical study was to assess: (1) the effect of thoracic vertebral compression fracture (VCF) on kyphosis and physiologic compressive load path, and (2) the effect of balloon kyphoplasty and spinal extension on restoration of normal geometric and loading alignment.

Methods: Six fresh human thoracic specimens, each consisting of three adjacent vertebrae were used. In order to create a VCF, IBTs were placed transpedicularly into the middle VB and cancellous bone was disrupted by inflation of IBTs. After cancellous bone disruption the specimens were compressed using bilateral loading cables until a fracture was observed. Fracture reduction by spinal extension, and then by balloon kyphoplasty was performed under a physiologic compressive preload of 250 N. The vertebral body heights, kyphotic deformity, and location of compressive load path were measured on video-fluoroscopy images.

Results: The VCF caused anterior VB height loss of 3715%, middle-height loss of 3416%, segmental kyphosis increase of 147.0 degrees, and vertebral kyphosis increase of 135.5 degrees (p< 0.05). The compressive load path shifted anteriorly by 20% of A-P endplate width in the fractured and adjacent VBs (p=0.01). IBT inflation alone restored anterior VB height to 918.9%, middle-height to 9114%, and segmental kyphosis to within 5.65.9 degrees of pre-fracture values. The compressive load path returned posteriorly in all three VBs (p=0.00): the load path remained anterior to the pre-fracture location by 9–11% of the A-P endplate width. The extension moment fully restored the compressive load path to its pre-fracture location. Under this moment, the anterior and middle VB heights were restored to 858.6% and 749.4% of pre-fracture values, respectively. The segmental kyphosis was fully restored to its pre-fracture value; however, the middle height and kyphotic deformity of the fractured VB remained smaller than the pre-fracture values (p< 0.05).

Conclusions: An anterior shift of the compressive load path in VBs adjacent to VCF can induce additional flexion moments. The eccentric loading may contribute to the increased risk of new VB fractures adjacent to an uncorrected VCF deformity. Extension moment could fully correct the segmental kyphosis but could not restore the middle height of the fractured vertebral body. Balloon kyphoplasty reduced the VCF deformity and partially restored the compressive load path to normal alignment.

Purpose: A retrospective study comparing the fusion rate and, the incidence of junctional spinal stenosis between a rigid (Wiltse) and a semirigid (Varifix) posterior spinal fusion system.

Material & Methods: 92 patients, mean age 52.3 year old, underwent posterior fusion with semirigid Varifix system (rod diameter 5.0 mm), and 89 patients, mean age 49.8 year old, with rigid Wiltse system (6.5 mm). The mean follow-up was 4.8 years (range 2–9) for Varifix group and 11.7 years (range 9–17) for Wiltse group. Preoperative diagnosis was spinal stenosis (n=56), disc degenerative disease (n=43), degenerative spondylolisthesis (n=37), post-laminectomy instability (n=34), and isthmic spondylolisthesis (n=11). In all patients autologous iliac crest bone graft was used. Spinal fusion was confirmed by A-P, lateral, and flexion-extension radiographic studies, or by direct surgical exploration and observation. Pain intensity was recorded using the Visual Analogue Scale (VAS).

Results: Successful fusion was achieved in 92.4% in the semirigid group and in 93.2% for the rigid group. There was no statistical difference in fusion rate between these two groups (p=0.82). Eight patients with pseudoarthrosis were treated by anterior fusion and 5 by repaired posterior fusion, with a fusion rate of 100%. Postoperative infection was diagnosed in 5 patients (5.4%) in the semirigid group and in 4 patients (4.5%) in the rigid group. They were treated by debridement, irrigation, and intravenous antibiotics. Hardware removal because of pain was performed in 9 patients (9.8%) in the semirigid group, and 17 patients (19.1%) in rigid group. Removal of hardware resulted in improvement in pain in all patients. Junctional spinal stenosis was diagnosed in 2 patients (2.2%) in semirigid group and in 7 patients (7.9%) in rigid group. There was a trend for higher incidence of adjacent level stenosis in rigid group (p=0.07).

Conclusion: Biomechanical studies have shown that the stiffness of spinal construct depends on rod diameter and a decrease in rod rigidity can increase the risk of implant failure. In our study we didn’t find any difference in the fusion rate and in complication rate between these two systems. The increased percentage of the junctional spinal stenosis in rigid group may be explained by the longer follow-up in this group. According to our data the semirigid system may be better tolerated than the rigid system.