Residual kyphotic deformity is considered the main factor for the increased risk of new fractures after an osteoporotic vertebral fracture. We hypothesized that even in the absence of kyphotic deformity, the altered pressure profile of the disc after a fracture will increase the risk for subsequent fractures.

Materials and Methods: Six fresh-frozen, human thoracolumbar specimens, consisting of 5 adjacent vertebrae, were used. A void was randomly created under the upper (n=3) or the lower (n=3) endplate of the middle vertebra. The specimen was then compressed in flexion until a selective fracture of the weakened endplate was observed. Vertebral kyphosis was reduced with extension. After cementation of the fracture, the rest of the trabecular content was evacuated and was filled with cement. Specimens were tested in flexion-extension (±6Nm) under 400N preload before and after the index fracture. Pressure was recorded at the discs above and below the fractured VB and strain at the anterior wall of the adjacent VBs. Finally, the specimen was loaded in flexion until a subsequent fracture was observed on fluoroscopy.

Results: In the intact specimens, nucleus pressure increased by 26.4±13.9% in full flexion compared to neutral posture. After the index fracture, the pressure in full flexion increased by 15.2±11 % in the discs with unfractured endplates, but decreased by 19±26.7% in the discs with the fractured endplate (p< 0.05). Anterior wall strain at the VB adjacent to the fractured endplate increased by 94.2%±22.8% (p=0.02), compared to an 18.2%±7.1% (p=0.98) increase at the VB adjacent to the unfractured endplate. Subsequent loading of the specimens after cementation of the index fracture resulted in a fracture of the adjacent VB close to the fractured endplate of the middle vertebra in 4 specimens and at the upper potted VB in one specimen. Maximum load applied with the actuators failed to create a fracture in one specimen.

Discussion: The effects of the fractured endplate were isolated by eliminating other known parameters. Vertebral kyphosis was reduced and cement was similarly distributed under both endplates.

In the intact specimens, nucleus pressure gradually increased during flexion. This can more evenly distribute the load during flexion to the entire surface of the endplate and avoid excessive load concentration to the anterior portion. After an endplate fracture, the nucleus pressure gradually decreased during flexion, meaning that the anterior annulus was forced to bear more load. This uneven load transfer to the anterior part of the VB resulted in doubling the strain at the VB adjacent to the fractured end plate. All adjacent factures were observed at the vertebra next to the damaged endplate. The altered mechanical behavior of the nucleus can be ascribed to the increased available space after the endplate depression.

The circulatory effects of multilevel balloon kyphoplasty (BK) are not adequately addressed, neither the effectiveness of egg shell cementoplasty in preventing anticipated cement leakage in difficult cases. The purpose of this study was to evaluate

the effect of multilevel BK to blood pressure and arterial blood gasses;

Materials and methods: This is a prospective study of 89 patients (215 vertebral bodies-VBs) with osteoporotic compressive fractures (OCF), and 27 with osteolytic tumors (OT) (88 VBs). The mean age was 67.6 years. 27 patients with OCF were treated at one level, 26 at two, 21 at three, 7 at four, 6 at five, and 2 at six levels at the same sitting. Three patients with OT were treated at one level, 6 at two, 9 at three, 3 at four, 4 at five, and 2 at seven. Egg shell balloon cementoplasty to prevent cement leakage was performed in 10 patients with severe endplate fracture or vertebral wall lytic destruction. Arterial blood pressure and oxygen saturation were monitored during surgery. Arterial blood gases were measured before and 3 min after cement injection. Cement leakage was assessed by the postoperative x rays and computer tomography scans.

Results: A drop in blood pressure of more than 25mmHg during cement injection was observed in 6 patients, and was not associated with the number of VB treated. Blood pressure was dropped more than 40mm in 2 patients and the procedure was aborted after completing 1 level in the first and 2 levels in the second. Drop in arterial O2 saturation was noted in 4 patients. One patient treated for 5 levels developed fever and tachepnoea for 24 hours after surgery. Arterial O2 and chest x-rays were normal. Cement leakage was found in 9.7% (21/215) of VBs treated for OCF. Its incidence per location was: epidural, 0.9% (2 VBs); intraforaminal, 0.5% (1 VB); intradiscal, 3.2% (7 VBs); and through anterior or lateral walls, 5.1% (11 VBs). In the OT group cement leakage was found in 10.2% (9/88) of the treated VBs. Its location included 8 (9%) through the anterior or lateral walls and one (1.1%) intradiscal. Cement leakage had no clinical consequences. No cement leakage was observed in cases treated with egg shell balloon cementoplasty.

Conclusions: BK is a safe procedure when applied for multiple levels in the same sitting, and its rare circulatory effects are not related to the number of levels treated. The incidence of cement leakage in this study was 10%, which is far less than that reported with vertebroplasty using routine postoperative CT scan. Egg shell balloon cementoplasty can effectively minimize cement leakage in cases with fractured endplate or lytic destruction of VB walls.

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.