CT volumetry of intravertebral cement after kyphoplasty. Comparison of polymethylmethacrylate and calcium phosphate in a 12-month follow-up

Biodegradable Cements for Bone Regeneration

Bone cements such as polymethyl methacrylate and calcium phosphates have been widely used for the reconstruction of bone. Despite their remarkable clinical success, the low degradation rate of these materials hampers a broader clinical use. Matching the degradation rate of the materials with neo bone formation remains a challenge for bone-repairing materials. Moreover, questions such as the mechanism of degradation and how the composition of the materials contribute to the degradation property remain unanswered. Therefore, the review provides an overview of currently used biodegradable bone cements such as calcium phosphates (CaP), calcium sulfates and organic-inorganic composites. The possible degradation mechanism and clinical performance of the biodegradable cements are summarized. This paper reviews up-to-date research and applications of biodegradable cements, hoping to provide researchers in the field with inspirations and references.

Does Calcium Phosphate Cement Kyphoplasty Cause Intervertebral Disk Degeneration in Adolescents?

OBJECTIVE

Balloon kyphoplasty with polymethylmethacrylate (PMMA) represents the standard procedure for the treatment of thoracic and lumbar type A compression fractures. However, an increased degeneration in adjacent intervertebral disks following PMMA kyphoplasty has been demonstrated in elderly patients. Calcium phosphate cement (CPC) appears to be superior to PMMA for the intravertebral stabilization in younger patients. It remains unkown whether CPC kyphoplasty causes degeneration of adjacent disks in adolescents.

DESIGN

Seven adolescents with thoracolumbar spine fractures underwent kyphoplasty at a mean age of 14.5 years (range 10-18). At a mean follow-up of 3.7 years (range 1 to 4.8) postoperatively, 3.0 Tesla magnetic resonance imaging (MRI) of the spine was performed to assess intervertebral disk degeneration by quantitative T2 relaxation maps and subjective ratings using modified Pfirrmann scores. A total of 56 intervertebral disks was analyzed. Initial computed tomography (CT) examinations served as basis to assess the severity of adjacent endplate injuries in terms of articular step-offs.

RESULTS

Initial imaging detected 18 thoracolumbar vertebral body fractures of which 9 were treated with CPC kyphoplasty. Quantitative follow-up MRI revealed signs of degeneration in 10 (17.9%) of the examined 56 intervertebral disks, 7 of them adjacent to a previously fractured vertebral body. Signs of disk degeneration were significantly higher in caudal endplates with articular step-offs larger than 5 mm compared to fractured vertebral bodies without endplate step-offs.

CONCLUSIONS

Quantitative MRI follow-ups did not suggest CPC-related intervertebral disk degradations following thoracolumbar kyphoplasty in adolescents, but indicated disk alterations correlating to adjacent endplate fracture severity.

Minimally invasive treatment of tibial plateau depression fractures using balloon tibioplasty: Clinical outcome and absorption of bioabsorbable calcium phosphate cement

The exact reconstruction of the tibial plateau and articular surface is the main operative aim in the treatment of tibial plateau depression fractures. For selected cases, a novel technique with the use of balloon tibioplasty in combination of bioabsorbable calcium phosphate cement is available. In this study, the first objective was to answer the question whether the clinical outcome parameters after balloon tibioplasty are comparable to open reduction procedures described in the literature. Secondly, we asked whether the cement absorption is safe in relation to adverse effects like osteolysis and measured the absorption ability during the bone conversion process in the proximal tibia bone. Eight patients (mean age 54 years; 4 males and 4 females) received the abovementioned surgical procedure. Mean follow-up period was 27 months. This study evaluated clinical outcome and radiological measured cement absorption within the postoperative course. Cement absorption was measured on X-rays and calculated based on the greatest extend on anterior-posterior and lateral view radiographs just after the operation on the latest available follow-up. WOMAC score showed a mean of 93. Radiologic absorption was 1/5 at a mean of 18 months. No osteolysis reaction was seen surrounding the cement. This far, promising clinical and radiological results have been shown with WOMAC scores comparable to the results of noninjured knees. The indication for this relatively new technique is restricted to isolated depression fractures. It is a useful tool to facilitate the reduction of select depressed tibial fractures. The radiologic absorption effect seems to be quite fast in bone remodeling and safe without any osteolysis or osseous reaction.

Biological and mechanical performance and degradation characteristics of calcium phosphate cements in large animals and humans

Calcium phosphate cements (CPCs) have been used to treat bone defects and support bone regeneration because of their good biocompatibility and osteointegrative behavior. Since their introduction in the 1980s, remarkable clinical success has been achieved with these biomaterials, because they offer the unique feature of being moldable and even injectable into implant sites, where they harden through a low-temperature setting reaction. However, despite decades of research efforts, two major limitations concerning their biological and mechanical performance hamper a broader clinical use. Firstly, achieving a degradation rate that is well adjusted to the dynamics of bone formation remains a challenging issue. While apatite-forming CPCs frequently remain for years at the implant site without major signs of degradation, brushite-forming CPCs are considered to degrade to a greater extent. However, the latter tend to convert into lower soluble phases under physiological conditions, which makes their degradation behavior rather unpredictable. Secondly, CPCs exhibit insufficient mechanical properties for load bearing applications because of their inherent brittleness. This review places an emphasis on these limitations and provides an overview of studies that have investigated the biological and biomechanical performance as well as the degradation characteristics of different CPCs after implantation into trabecular bone. We reviewed studies performed in large animals, because they mimic human bone physiology more closely in terms of bone metabolism and mechanical loading conditions compared with small laboratory animals. We compared the results of these studies with clinical trials that have dealt with the degradation behavior of CPCs after vertebroplasty and kyphoplasty.

Strontium-modified premixed calcium phosphate cements for the therapy of osteoporotic bone defects

In this study a premixed strontium-containing calcium phosphate bone cement for the application in osteoporotic bone defects has been developed and characterised regarding its material and in vitro properties as well as minimally invasive applicability in balloon kyphoplasty. Strontium was introduced into the cement by substitution of one precursor component, CaCO₃, with its strontium analogue, SrCO₃. Using a biocompatible oil phase as carrier liquid, a cement paste that only set upon contact with aqueous environment was obtained. Strontium modification resulted in an increased strength of set cements and radiographic contrast; and the cements released biologically relevant doses of Sr²⁺-ions that were shown to enhance osteoprogenitor cell proliferation and osteogenic differentiation. Finally, applicability of strontium-containing cement pastes in balloon kyphoplasty was demonstrated in a human cadaver spine procedure. The cement developed in this study may therefore be well suited for minimally invasive, osteoporosis-related bone defect treatment.

STATEMENT OF SIGNIFICANCE

Strontium-releasing calcium phosphate bone cements are promising materials for the clinical regeneration of osteoporosis-related bone defects since they have been shown to stimulate bone formation and at the same time limit osteoclastic bone resorption. Today clinical practice favours minimally invasive surgical techniques, e.g. for vertebral fracture treatment, posing special demands on such cements. We have therefore developed a premixed, strontium-releasing bone cement with enhanced mechanical properties and high radiographic visibility that releases biologically relevant strontium concentrations and thus stimulates cells of the osteogenic lineage. In a pilot experiment we also exemplify its excellent suitability for minimally invasive balloon kyphoplasty procedures.

Osteointegration and Resorption of Intravertebral and Extravertebral Calcium Phosphate Cement

STUDY DESIGN

Eleven patients with painful osteoporotic vertebral fractures who underwent kyphoplasty using calcium phosphate (CaP) cement were followed up for 1 week, 1, 2, and 3 years in a monocentric, nonrandomized, noncontrolled retrospective trial.

OBJECTIVE

This study investigates long-term radiomorphologic features of intraosseous CaP cement implants and of extraosseous CaP cement leakages for up to 3 years after implantation by kyphoplasty.

SUMMARY OF BACKGROUND DATA

Kyphoplasty is frequently used for the treatment of painful osteoporotic fractures. Of the materials available, CaP is frequently used as a filling material. Resorption of this material is frequently observed, although clinical outcome is comparable with other cements.

METHODS

Kyphoplasty utilizing CaP cement was performed in 11 patients with painful osteoporotic vertebral fractures. All patients received a pharmacological antiosteoporosis treatment consisting of calcium, vitamin D, and a standard dose of oral bisphosphonates. Radiomorphologic measurements, pain, and mobility were assessed.

RESULTS

Intraosseous and extraosseous CaP cement volumes decreased significantly over 3 years. However, vertebral stability as determined by a constant vertebral body height and the sagittal index was not impaired. Pain improved significantly 2 years after implantation and the mobility scores 1 year after kyphoplasty at least until the third year.

CONCLUSIONS

Intravertebral CaP cement implants are resorbed slowly over time without jeopardizing stability and clinical outcomes most likely because of a slowly progressing osseous replacement. Extraosseous CaP cement material because of leakages during the kyphoplasty procedure is almost completely resorbed as early as 2 years after the leakage occurred. Therefore, CaP cement is an important alternative to PMMA-based cement materials utilized for kyphoplasty of osteoporotic vertebral fractures.

Biocompatibility of calcium phosphate bone cement with optimised mechanical properties: an in vivo study

This work establishes the in vivo performance of modified calcium phosphate bone cements for vertebroplasty of spinal fractures using a lapine model. A non-modified calcium phosphate bone cement and collagen-calcium phosphate bone cements composites with enhanced mechanical properties, utilising either bovine collagen or collagen from a marine sponge, were compared to a commercial poly(methyl methacrylate) cement. Conical cement samples (8 mm height × 4 mm base diameter) were press-fit into distal femoral condyle defects in New Zealand White rabbits and assessed after 5 and 10 weeks. Bone apposition and tartrate-resistant acid phosphatase activity around cements were assessed. All implants were well tolerated, but bone apposition was higher on calcium phosphate bone cements than on poly(methyl methacrylate) cement. Incorporation of collagen showed no evidence of inflammatory or immune reactions. Presence of positive tartrate-resistant acid phosphatase staining within cracks formed in calcium phosphate bone cements suggested active osteoclasts were present within the implants and were actively remodelling within the cements. Bone growth was also observed within these cracks. These findings confirm the biological advantages of calcium phosphate bone cements over poly(methyl methacrylate) and, coupled with previous work on enhancement of mechanical properties through collagen incorporation, suggest collagen-calcium phosphate bone cement composite may offer an alternative to calcium phosphate bone cements in applications where low setting times and higher mechanical stability are important.

Reconstruction of difference in sequential CT studies using penalized likelihood estimation

Characterization of anatomical change and other differences is important in sequential computed tomography (CT) imaging, where a high-fidelity patient-specific prior image is typically present, but is not used, in the reconstruction of subsequent anatomical states. Here, we introduce a penalized likelihood (PL) method called reconstruction of difference (RoD) to directly reconstruct a difference image volume using both the current projection data and the (unregistered) prior image integrated into the forward model for the measurement data. The algorithm utilizes an alternating minimization to find both the registration and reconstruction estimates. This formulation allows direct control over the image properties of the difference image, permitting regularization strategies that inhibit noise and structural differences due to inconsistencies between the prior image and the current data. Additionally, if the change is known to be local, RoD allows local acquisition and reconstruction, as opposed to traditional model-based approaches that require a full support field of view (or other modifications). We compared the performance of RoD to a standard PL algorithm, in simulation studies and using test-bench cone-beam CT data. The performances of local and global RoD approaches were similar, with local RoD providing a significant computational speedup. In comparison across a range of data with differing fidelity, the local RoD approach consistently showed lower error (with respect to a truth image) than PL in both noisy data and sparsely sampled projection scenarios. In a study of the prior image registration performance of RoD, a clinically reasonable capture ranges were demonstrated. Lastly, the registration algorithm had a broad capture range and the error for reconstruction of CT data was 35% and 20% less than filtered back-projection for RoD and PL, respectively. The RoD has potential for delivering high-quality difference images in a range of sequential clinical scenarios including image-guided surgeries and treatments where accurate and quantitative assessments of anatomical change is desired.

Demineralization after balloon kyphoplasty with calcium phosphate cement: a histological evaluation in ten patients

PURPOSE

Balloon kyphoplasty (BKP) with calcium phosphate cement (CPC) is increasingly being used for spinal surgery in younger patients. In routinely performed follow-up CT scans we observed considerable areas of demineralization in CPC processed vertebrae in several patients. To rule out infections or inflammations histological examinations were planned for these patients.

METHODS

Ten patients (23-54 years; six men) with significant demineralization areas in CT scans after CPC balloon kyphoplasty were selected. Punch biopsies from these areas were taken in local anesthesia using a biopsy needle. One half of the specimen was decalcified and embedded in paraffin, and sections were examined histologically using hematoxylin and eosin, Van Gieson, and trichrome staining. The second half of the specimen was cast directly in methyl methacrylate and sections were examined by Paragon and von Kossa/Safranin staining. Stained slides were viewed under light microscopy.

RESULTS

Bone-punch specimens were taken at 17.5 months (mean) after BKP with CPC. In most cases, the cement was well surrounded by newly formed lamellar bone with very tight connections between the cement and new bone. Unmineralized areas were observed sporadically at the cement surface and adjacent to the implant. There were no pronounced signs of inflammation or osteolysis of adjacent bone. No complications were observed during or following patients' biopsy procedures.

CONCLUSIONS

CPC demonstrated good biocompatibility and osseointegration in clinical use, with no evidence of inflammation or osteonecrosis. Demineralized areas in CT scans could be a result of remodeling of the cancellous bone in vertebral bodies.

Calcium-phosphate and polymethylmethacrylate cement in long-term outcome after kyphoplasty of painful osteoporotic vertebral fractures

STUDY DESIGN

A comparative prospective trial evaluating 3-year outcome.

OBJECTIVE

To compare clinical and morphologic outcomes as well as follow-up fractures after kyphoplasty of painful osteoporotic vertebral fractures with calcium-phosphate (CaP) cement (group 1) and with polymethylmethacrylate (PMMA)-cement (group 2).

SUMMARY OF BACKGROUND DATA

CaP cements seem to be an alternative material for usage in kyphoplasty of vertebral fractures. CaP cements are biodegradable and replaceable by newly formed bone after implantation. Concerns have been raised with regard to the stability of resorbable CaP-cements after implantation into vertebrae post kyphoplasty. Calcibon is a possible CaP cement, which exhibited adequate stability in short-term observations.

MATERIALS AND METHODS

Kyphoplasty was performed in 40 consecutive patients with primary osteoporosis and painful vertebral fractures, 20 received CaP-cement, 20 were treated with PMMA-cement. All patients received a pharmacological antiosteoporosis treatment (1000 mg calcium, 1000 IU vitamin D3, and oral aminobisphosphonate), pain medication, and physiotherapy. Pain (visual analog scale [VAS]; range, 0-100), mobility (EVOS-score; range, 0-100) and radiomorphologic measurements were assessed at baseline and after 6, 12, and 36 months.

RESULTS

There were no statistically significant differences between the CaP and PMMA-cement group regarding VAS-scores, EVOS-scores, or height-restoration at any time point. Furthermore, there was no significant difference in the occurrence of vertebral follow-up fractures between both groups during the 3-year follow-up period.

CONCLUSION

CaP cement, e.g., Calcibon, is as effective and safe as conventional PMMA-cement with regard to immediate and sustained pain reduction and improvement of mobility after kyphoplasty of patients with painful osteoporotic vertebral fractures. CaP cement has the potential of being resorbed and replaced by newly formed bone tissue; thus, it seems to be a promising alternative for PMMA also in younger patients with painful vertebral fractures.

Biomechanical in vitro testing of human osteoporotic lumbar vertebrae following prophylactic kyphoplasty with different candidate materials

STUDY DESIGN

Biomechanical study of human osteoporotic lumbar vertebrae following prophylactic kyphoplasty.

OBJECTIVES

To evaluate the potential benefits of different resorbable candidate materials for use in prophylactic kyphoplasty compared with the behavior of polymethylmethacrylate cement.

SUMMARY OF BACKGROUND DATA

Kyphoplasty using PMMA bone cement for the stabilization of fractured osteoporotic vertebrae has been established as a useful clinical tool. In several studies, consecutive compression fractures have been reported in vertebrae caudal or cranial to those augmented with bone cement. Consequently, some physicians have begun to treat adjacent vertebrae by means of prophylactic augmentation.

METHODS

Biomechanical in vitro testing was performed on 40 human osteoporotic nonfractured lumbar vertebrae. Three types of bone cement (PMMA, 2 different calcium phosphate cements) and one silicon derivative were assessed during compressive and cyclic sinusoidal testing. Each candidate material was applied bipedicularly under fluoroscopic control.

RESULTS

Differing processing qualities of the materials led to substantial differences during cement injection, in particular in the amount of cement filling of the vertebrae. However, in comparison to native vertebrae, augmented specimens showed significantly higher compressive failure. No significant differences between vertebral bodies treated with PMMA and those treated with either type of calcium phosphate cement were documented. The biomechanical properties of the vertebrae could not be significantly improved by the silicon derivative.

CONCLUSION

This study demonstrated that calcium phosphate cements displayed identical behavior to PMMA cement with respect to in vitro mechanical qualities. Consequently, from a mechanical viewpoint, calcium phosphate cements may be used in addition to PMMA cement for kyphoplasty and prophylactic kyphoplasty. Silicon derivatives are apparently not recommendable as candidate materials for kyphoplasty.

The intravertebral vacuum phenomen as specific sign of osteonecrosis in vertebral compression fractures: results from a radiological and histological study

This study investigated the prevalence of the intravertebral vacuum phenomenon (IVP) and osteonecroses in vertebral compression fractures (VCFs). We therefore performed an histological analysis of biopsies obtained from VCFs prior to balloon kyphoplasty. Computed tomography (CT) scans were reviewed regarding the presence of an IVP (i.e. cleft sign, Kümmell disease). We reviewed the data of 266 consecutive patients treated by balloon kyphoplasty in 501 procedures from 2002 to 2004. From 180 patients (68%) we obtained adequate bone tissue for histological evaluation. Biopsy specimens were analysed regarding the presence of osteoporosis, infection, malignancy and osteonecrosis. CT scans of all 180 patients were reviewed for presence of an IVP. Histological examination revealed 135 (75%) osteoporoses, 20 (11%) neoplasms, 12 (7%) trauma cases and 13 (7%) osteonecroses. An IVP was present in 12 (7%) patients. There was a significant association of osteonecrosis and IVP (P < 0.0001). Eleven of 12 patients with a vacuum phenomenon showed an osteonecrosis on histology, whereas 11 of 13 patients with osteonecrosis showed an IVP on CT. The IVP is a specific sign of osteonecrosis in vertebral compression fractures (sensitivity 85%, specificity 99%, positive predictive value 91%). Our findings strongly support the thesis that an IVP indicates local bone ischemia associated with a non-healing vertebral collapse and pseudarthrosis.

Percutaneous vertebroplasty and kyphoplasty for the stand-alone augmentation of osteoporosis-induced vertebral compression fractures: Present status and future directions

Enormous research efforts are being expended on two minimally invasive procedures: percutaneous vertebroplasty (VP) and kyphoplasty (KP). The present report, which is a detailed critical review of VP and KP that emphasizes their biomechanics aspects, is divided into six parts. In the first two parts, succinct descriptions are given of osteoporosis-induced vertebral body (VB) compression fractures as the underlying pathology to be treated with VP and KP, the theory of VP and KP, and the techniques used in performing these procedures. Concerns about VP and KP, such as the high radiation exposure burden that may be imposed on both patient and medical personnel and extravasation of the injectable bone cement, are discussed in the third part. Detailed discussions of fourteen issues/questions, such as the extent to which VP or KP affects various biomechanical measures of the augmented VB and those adjacent to it and the appropriate volume of the cement to use, are presented in the fourth part. Ideas for future research, such as development of a new generation of injectable bone cements and identification of an appropriate animal model, are covered in the fifth part. The final section contains a summary of the most salient points/observations made in the report.

Osseous integration of calcium phosphate in osteoporotic vertebral fractures after kyphoplasty: initial results from a clinical and experimental pilot study

INTRODUCTION

This study evaluated the radiological changes at the bone-cement interface of calcium phosphate cement (CPC) and polymethylmethacrylate (PMMA) 12 months after kyphoplasty. In a pilot experiment, we additionally performed a histomorphometric analysis in osteopenic foxhounds to analyze the process of osseous integration of CPC and PMMA.

METHODS

Twenty postmenopausal female patients with 46 vertebral compression fractures (VCF) were treated by kyphoplasty, utilizing CPC (N=28) or PMMA (N=18) for intravertebral stabilization. After a 12-month follow-up, we measured the density changes of border voxels at the bone-cement interface by computed tomography (CT) using dedicated software algorithms. We defined the border-voxel density (BVD) as a parameter of cement resorption at the interface. We also investigated the bone-implant interface in three osteopenic foxhounds by histomorphometry 3, 6, and 12 months after cement implantation.

RESULTS

Twelve months after kyphoplasty, only CPC showed a significant decrease of the BVD compared to PMMA (p<0.01), indicating a slow progress of resorption at the interface. Histomorphometry of the dog vertebrae showed near total bone coverage of CPC implants, whereas the PMMA surface exhibited only 30% direct bone contact (p<0.01). We also observed a time-dependent increase in the number of discernable osteons close to the interface of CPC, but no bone tissue within PMMA (p<0.01).

CONCLUSIONS

The decrease of the BVD 12 months after kyphoplasty may indicate osseous integration of CPC by: (1) the ingrowth of bone tissue and (2) osteonal penetration close to the interface.

Kyphosis reduction and the rate of cement leaks after vertebroplasty of intravertebral clefts

To assess the results of vertebroplasty in patients with intravertebral clefts compared to patients with normal osteoporotic fractures, we evaluated the pre- and postoperative images and pain scores (VAS) of 114 patients with 192 vertebroplasty procedures treated between March 2002 and February 2005. Intravertebral clefts were identified on conventional radiographs, MR or CT images as gas- or fluid-filled spaces adjacent to an endplate of a fractured vertebra. Forty-four vertebrae showed intravertebral clefts. All clefts were filled with PMMA showing a typical filling pattern. Due to the prone positioning of the patient during vertebroplasty, a significant reduction of the kyphosis angle was achieved in the cleft group. Cement leakage occurred in 18.2% of clefts and 46% of regular osteoporotic fractures. In all patients, good filling of the cleft was achieved no matter where the needle tip was placed in the vertebra. The VAS score was 9.1 preoperatively, 3.6 before discharge and 3.9 6 months postoperatively, showing no significant difference between both groups. Patients with intravertebral clefts show a significant reduction of the kyphosis angle compared to non-cleft patients and have a significantly lower risk of experiencing cement leakage during vertebroplasty. Pain reduction is the same in both groups.