Paul F. Heini

Percutaneous transpedicular vertebroplasty with PMMA: operative technique and early results

Abstract Vertebroplasty-percutaneous cement augmentation of osteoporotic vertebrae is an efficient procedure for the treatment of painful vertebral fractures. From a prospectively monitored series of 70 patients with 193 augmented vertebrae for osteoporotic and metastatic lesions, we analysed a group of 17 patients suffering from back pain due to osteoporotic fractures. The reinforcement of 45 vertebral bodies in these patients led to a significant and lasting pain reduction (P < 0.01). The presented technique is useful, as, in one session, at least four injections can be performed when required, allowing the prophylactic reinforcement of adjacent vertebrae as well. The use of a low-viscosity polymethyl methacrylate (PMMA) in combination with a non-ionic liquid contrast dye provides a reliable and safe procedure. Extraosseous cement leakage was seen in 20% of the interventions; however, none of them had clinical sequelae.

Adjacent vertebral failure after vertebroplasty: A BIOMECHANICAL INVESTIGATION

Vertebroplasty, which is the percutaneous injection of bone cement into vertebral bodies has recently been used to treat painful osteoporotic compression fractures. Early clinical results have been encouraging, but very little is known about the consequences of augmentation with cement for the adjacent, non-augmented level. We therefore measured the overall failure, strength and structural stiffness of paired osteoporotic two-vertebra functional spine units (FSUs). One FSU of each pair was augmented with polymethylmethacrylate bone cement in the caudal vertebra, while the other served as an untreated control. Compared with the controls, the ultimate failure load for FSUs treated by injection of cement was lower. The geometric mean treated/untreated ratio of failure load was 0.81, with 95% confidence limits from 0.70 to 0.92, (p < 0.01). There was no significant difference in overall FSU stiffness. For treated FSUs, there was a trend towards lower failure loads with increased filling with cement (r2 = 0.262, p = 0.13). The current practice of maximum filling with cement to restore the stiffness and strength of a vertebral body may provoke fractures in adjacent, non-augmented vertebrae. Further investigation is required to determine an optimal protocol for augmentation.

Load shift of the intervertebral disc after a vertebroplasty: a finite-element study.

Infiltrating osteoporotic cancellous bone with bone cement (vertebroplasty) is a novel surgical procedure to stabilize and prevent osteoporotic vertebral fractures. Short-term clinical and biomechanical results are encouraging; however, so far no reports on long-term results have been published. Our clinical observations suggest that vertebroplasty may induce subsequent fractures in the vertebrae adjacent to the ones augmented. At this point, there is only a limited understanding of what causes these fractures. We have previously hypothesized that adjacent fractures may result from a shift in stiffness and load following rigid augmentation. The purpose of this study is to determine the load shift in a lumbar motion segment following vertebroplasty. A finite-element (FE) model of a lumbar motion segment (L4-L5) was used to quantify and compare the pre- and post-augmentation stiffness and loading (load shift) of the intervertebral (IV) disc adjacent to the augmented vertebra in response to quasi-static compression. The results showed that the rigid cement augmentation underneath the endplates acted as an upright pillar that severely reduced the inward bulge of the endplates of the augmented vertebra. The bulge of the augmented endplate was reduced to 7% of its value before the augmentation, resulting in a stiffening of the IV joint by approximately 17%, and of the whole motion segment by approximately 11%. The IV pressure accordingly increased by approximately 19%, and the inward bulge of the endplate adjacent to the one augmented (L4 inferior) increased considerably, by approximately 17%. This increase of up to 17% in the inward bulge of the endplate adjacent to the one augmented may be the cause of the adjacent fractures.

2004 Young Investigator Award Winner: vertebral endplate marrow contact channel occlusions and intervertebral disc degeneration.

Study Design. Intervertebral disc degeneration was evaluated by morphologic appearance, magnetic resonance imaging, and by biochemical matrix composition. Caliber and distribution of openings of the adjacent vertebral osseous endplates were measured. Objectives. Correlation between occlusion of vertebral endplate openings and intervertebral disc degeneration was quantified. Summary of Background Data. Calcifications of vertebral endplates with disease and age have suggested insufficient nutrition as a mechanism for intervertebral disc degeneration. It has been proposed that occlusion of endplate openings, which contain vascular sources for the disc, may limit the transport of nutrients, leading to disc degeneration. Methods. Fresh magnetic resonance images from 39 human lumbar discs were scored. Sectioned discs with endplates were morphologically graded. Samples of nuclear and anular regions were evaluated for proteoglycan and collagen contents. Backlight microscopic images of 4 endplate regions were obtained, and caliber and distribution of endplate openings for each disc were measured. Analysis of variance regression models were used to assess correlation between endplate openings and disc degeneration. Results. The decrease in opening density significantly correlated to morphologic degeneration grade, best for openings with 20 to 50 ìm equivalent diameter and in the nuclear region. Although the density of 20 to 50 ìm openings also significantly indirectly correlated to age, it was not as strong as the correlation to degeneration grade. Opening density was also significantly correlated to proteoglycan content in all regions. However, all other biochemical parameters as well as the T2 intensity score showed only weak or no correlation to opening density. Conclusions. A high indirect correlation between the density of openings in the osseous endplate (particularly of the size of the capillary buds) and the morphologicdegeneration grade of the disc support the hypothesis that occlusion of these openings may deprive the cells of nutrients, leading to insufficient maintenance of the extracellular matrix and disc degeneration.

Theoretical and experimental model to describe the injection of a polymethylmethacrylate cement into a porous structure

A theoretical approach was used to determine the distribution of a poly(methylmethacrylate) cement after its injection into a porous structure. The predictions of the model were then compared to experimental results obtained by injecting a polymethylmethacrylate cement into an open-porous ceramic filter. The goal was to define a model that could predict what factors affect the risk of cement extravasation and hence how the risk of cement extravasation can be minimized. The calculations were based on two important rheological laws: the law of Hagen-Poiseuille and the law of Darcy. The law of Hagen-Poiseuille describes the flow of a fluid in a cylindrical tube. The law of Darcy describes the flow of a fluid through a porous media. The model predicted that the extravasation risk was decreased when the cement viscosity, the bone pore size, the bone permeability and the bone porosity were increased, and when the diameter of the extravasation path and the viscosity of the marrow were decreased. Experimentally, the effect of the marrow viscosity and extravasation path could be evidenced. Therefore, the model was believed to be an adequate approximation of the experimental behavior. In conclusion, the experimental results demonstrated that the model was adequate and that the best practical way to decrease the risk of extravasation is to increase the cement viscosity.

Kyphoplasty for treatment of osteoporotic vertebral fractures: a prospective non-randomized study.

BackgroundMinimally invasive augmentation techniques of vertebral bodies have been advocated to treat osteoporotic vertebral body compression fractures (VBCFs). Kyphoplasty is designed to address both fracture-related pain as well as kyphotic deformity usually associated with fracture. Previous studies have indicated the potential of this technique for reduction of vertebral body height, but there has been little investigation into whether this has a lasting effect. The current study reports on our experience and the one-year results in 27 kyphoplasty procedures (24 patients) for osteoporotic VBCFs.ResultsAll but one patient experienced pain relief following the procedure (on VAS 1–10)—with a lasting effect over the follow-up period in 25 cases. An average vertebral kyphosis reduction of 47.7% was achieved with no loss of reduction after one year. The potential for reduction was statistically related to the pre-operative amount of kyphosis, the level treated, and the age of the fracture, but not to the age of the patient. During follow-up, one fracture adjacent to a treated level was observed. Pain relief was not related to the amount of reduction.ConclusionKyphoplasty is an effective treatment of VBCFs in terms of pain relief and durable reduction of deformity. Whether spinal realignment results in an improved long-term clinical outcome remains to be investigated.

Bone substitutes in vertebroplasty

Abstract. Vertebroplasty – percutaneous cement augmentation of vertebral bodies – is an efficient procedure for the treatment of painful vertebral fractures in osteoporosis. At the present time, polymethylmethacrylate (PMMA) is the only available cement with reports of clinical application and experience. The material is easy to handle, the radiopacity can be adapted by adding contrast dye, and it is mechanically efficient. Composite cements (acrylic cements in conjunction with ceramics) are bioactive, highly radiopaque, and feature excellent mechanical properties. One such cement, Cortoss, is currently undergoing clinical trials for vertebroplasty and has so far been shown to be a potentially valuable alternative to PMMA. Several in vitro studies with injectable calcium phosphate (CaP) cements show their feasibility and mechanical effectiveness. Animal studies confirm their biocompatibility and osteoconductivity. However, handling problems and the limited radiopacity of these cements currently preclude their clinical use.

Kyphoplasty for treatment of osteoporotic vertebral fractures

Cement reinforcement for the treatment of osteoporotic vertebral fractures is efficient mean with high success in pain release and prevention of further sintering of the reinforced vertebrae; however, the technique does not allow to address the kyphotic deformity. Kyphoplasty was designed to address the kyphotic deformity and help to realign the spine. It involves the percutaneous placement of an inflatable bone tamp into a vertebral body. Restoration of VB height and kyphosis correction is achieved by inflation of the bone tamp with liquid. After deflation, a cavity is created that eases the cement application. The potential of kyphosis reduction is given in fresh fractures with a range of 0–90% for height restoration and absolute correction of the kyphotic angle of 8.5°. The cavity formation, on one hand, and the different cementing technique leads to lower risk for cement extravasation. An alternative method for kyphosis correction represents the so-called lordoplasty where the adjacent vertebrae are reinforced first and with the cannulas in place acting as a lever the reduction of the collapsed vertebra can be performed. The results with respect to kyphosis correction are superior in comparison with a kyphoplasty procedure.

Adjacent vertebral failure after vertebroplasty

Vertebroplasty, which is the percutaneous injection of bone cement into vertebral bodies has recently been used to treat painful osteoporotic compression fractures. Early clinical results have been encouraging, but very little is known about the consequences of augmentation with cement for the adjacent, non-augmented level.We therefore measured the overall failure, strength and structural stiffness of paired osteoporotic two-vertebra functional spine units (FSUs). One FSU of each pair was augmented with polymethyl-methacrylate bone cement in the caudal vertebra, while the other served as an untreated control.Compared with the controls, the ultimate failure load for FSUs treated by injection of cement was lower. The geometric mean treated/untreated ratio of failure load was 0.81, with 95% confidence limits from 0.70 to 0.92, (p < 0.01). There was no significant difference in overall FSU stiffness. For treated FSUs, there was a trend towards lower failure loads with increased filling with cement (r2 = 0.262...

Immunophenotypic changes of human articular chondrocytes during monolayer culture reflect bona fide dedifferentiation rather than amplification of progenitor cells

In this study, a time‐course comparison of human articular chondrocytes (HAC) and bone marrow‐derived mesenchymal stem cells (MSC) immunophenotype was performed in order to determine similarities/differences between both cell types during monolayer culture, and to identify HAC surface markers indicative of dedifferentiation. Our results show that dedifferentiated HAC can be distinguished from MSC by combining CD14, CD90, and CD105 expression, with dedifferentiated HAC being CD14+/CD90bright/CD105dim and MSC being CD14‐/CD90dim/CD105bright. Surface markers on MSC showed little variation during the culture, whereas HAC showed upregulation of CD90, CD166, CD49c, CD44, CD10, CD26, CD49e, CD151, CD51/61, and CD81, and downregulation of CD49a, CD54, and CD14. Thus, dedifferentiated HAC appear as a bona fide cell population rather than a small population of MSC amplified during monolayer culture. While most of the HAC surface markers showed major changes at the beginning of the culture period (Passage 1–2), CD26 was upregulated and CD49a downregulated at later stages of the culture (Passage 3–4). To correlate changes in HAC surface markers with changes in extracellular matrix gene expression during monolayer culture, CD14 and CD90 mRNA levels were combined into a new differentiation index and compared with the established differentiation indices based on the ratios of mRNA levels of collagen type II to I (COL2/COL1) and of aggrecan to versican (AGG/VER). A correlation of CD14/CD90 ratio at the mRNA and protein level with the AGG/VER ratio during HAC dedifferentiation in monolayer culture validated CD14/CD90 as a new membrane and mRNA based HAC differentiation index. J. Cell. Physiol. 214:75–83, 2008.