Bone grafting alternatives in spinal surgery

BONE BANKS

Bone banks are necessary for providing biological material for a series of orthopedic procedures. The growing need for musculoskeletal tissues for transplantation has been due to the development of new surgical techniques, and this has led to a situation in which a variety of hospital services have been willing to have their own source of tissue for transplantation. To increase the safety of transplanted tissues, standards for bone bank operation have been imposed by the government, which has limited the number of authorized institutions. The good performance in a bone bank depends on strict control over all stages, including: formation of well-trained harvesting teams; donor selection; conducting various tests on the tissues obtained; and strict control over the processing techniques used. Combination of these factors enables greater scope of use and numbers of recipient patients, while the incidence of tissue contamination becomes statistically insignificant, and there is traceability between donors and recipients. This paper describes technical considerations relating to how a bone bank functions, the use of grafts and orthopedic applications, the ethical issues and the main obstacles encountered.

Micromechanical Properties of Biocompatible Materials for Bone Tissue Engineering Produced by Direct 3D Printing

Bone implants in form of artificial scaffolds manufactured from poly-lactic acid (PLA) represent an attractive alternative to traditional surgical treatments of defective bones (i.e. autografts and allografts). In this work factors influencing biocompatibility and primary stability of implants manufactured from PLA using direct 3D printing were assessed using nanoindentation. For this reason bulk sample of the PLA material and a printed object were subjected to nanomechanical measurement. Quasi-static nanoindentation was employed to identify elastic modulus and hardness distribution on surface and within volume of the samples. Moreover mechanical properties along scanning direction and interlayer characteristics were also assessed. Gradients in mechanical properties have been identified within volume of the material, within the printing layers and at contact between individual layers.

Comparison of structural allograft and traditional autograft technique in occipitocervical fusion: radiological and clinical outcomes from a single institution

OBJECT The authors' objectives were to compare the rate of fusion after occipitoatlantoaxial arthrodesis using structural allograft with the fusion rate from using autograft, to evaluate correction of radiographic parameters, and to describe symptom relief with each graft technique. METHODS The authors assessed radiological fusion at 6 and 12 months after surgery and obtained radiographic measurements of C1-2 and C2-7 lordotic angles, C2-7 sagittal vertical alignments, and posterior occipitocervical angles at preoperative, postoperative, and final follow-up examinations. Demographic data, intraoperative details, adverse events, and functional outcomes were collected from hospitalization records. Radiological fusion was defined as the presence of bone trabeculation and no movement between the graft and the occiput or C-2 on routine flexion-extension cervical radiographs. Radiographic measurements were obtained from lateral standing radiographs with patients in the neutral position. RESULTS At the University of Utah, 28 adult patients underwent occipitoatlantoaxial arthrodesis between 2003 and 2010 using bicortical allograft, and 11 patients were treated using iliac crest autograft. Mean follow-up for all patients was 20 months (range 1-108 months). Of the 27 patients with a minimum of 12 months of follow-up, 18 (95%) of 19 in the allograft group and 8 (100%) of 8 in the autograft group demonstrated evidence of bony fusion shown by imaging. Patients in both groups demonstrated minimal deterioration of sagittal vertical alignment at final follow-up. Operative times were comparable, but patients undergoing occipitocervical fusion with autograft demonstrated greater blood loss (316 ml vs 195 ml). One (9%) of 11 patients suffered a significant complication related to autograft harvesting. CONCLUSIONS The use of allograft in occipitocervical fusion allows a high rate of successful arthrodesis yet avoids the potentially significant morbidity and pain associated with autograft harvesting. The safety and effectiveness profile is comparable with previously published rates for posterior C1-2 fusion using allograft.

Comparison of a novel oxysterol molecule and rhBMP2 fusion rates in a rabbit posterolateral lumbar spine model

BACKGROUND CONTEXT

The nonunion rate after lumbar spinal fusion is as high as 25%. Recombinant human bone morphogenetic protein 2 (rhBMP2) has been used as a biological adjunct to promote bony fusion. However, recently there have been concerns about BMP2. Oxysterol 133 (Oxy133) has been shown to promote excellent fusion rates in rodent lumbar spine models and offers a potential alternative to rhBMP2.

PURPOSE

The purpose of this study was to compare the fusion rate of rhBMP2 and Oxy133 in a randomized controlled trial using a posterolateral lumbar rabbit spinal fusion model.

STUDY DESIGN

This was a randomized control animal study.

METHODS

Twenty-four male adult white New Zealand rabbits (3-3.5 kg) underwent bilateral posterolateral lumbar spinal fusion at L4-L5. Rabbits were divided into four groups: control (A), 30-μg rhBMP2 (B), 20-mg Oxy133 (C), and 60-mg Oxy133 (D). At 4 weeks, fusion was evaluated by fluoroscopy, and at 8 weeks, the rabbits were sacrificed and fusion was evaluated radiographically, by manual palpation, and with microcomputed tomography.

RESULTS

Fusion rates by radiographic analysis at 8 weeks were Group A, 40.0%; Group B, 91.7%; Group C, 91.7%; and Group D, 100%. Evaluation of fusion masses by manual palpation of excised spines after sacrifice showed the following fusion rates: Group A, 0%; Group B, 83.3%; Group C, 83.3%; and Group D, 90%. Microcomputed tomography scanning confirmed these findings.

CONCLUSIONS

These findings in a rabbit model demonstrate that both 20- and 60-mg Oxy133 doses promote fusion that is equivalent to fusion induced by 30-μg rhBMP2 and significantly greater than the control group. The present findings confirm that Oxy133 is a promising candidate for therapeutic development as an alternative to rhBMP2 to promote spinal fusion.

A Prospective Randomized Clinical Trial Comparing Bone Union Rate Following Anterior Cervical Discectomy and Fusion Using a Polyetheretherketone Cage: Hydroxyapatite/B-Tricalcium Phosphate Mixture versus Hydroxyapatite/Demineralized Bone Matrix Mixture

Study Design

Prospective randomized noninferiority trial.

Purpose

To evaluate whether the union rate of anterior cervical discectomy and fusion (ACDF) using a polyetheretherketone (PEEK) cage filled with a mixture of hydroxyapatite (HA) and demineralized bone matrix (DBM) is inferior to that of a mixture of β-tricalcium phosphate (β-TCP) and HA.

Overview of Literature

There have been no clinical trials investigating the outcomes of a mixture of HA and DBM in a PEEK cage in ACDF.

Methods

Eighty-five eligible patients were randomly assigned to group B (n=43), in which a PEEK cage with a mixture of HA and DBM was used, or group C (n=42), in which a PEEK cage with a mixture of HA and β-TCP was used. The primary study endpoint was the fusion rate, which was assessed with dynamic radiographs and computed tomography (CT) scans. Secondary endpoints included pain intensity using a visual analogue scale, functional outcome using a neck disability index score, laboratory tests of inflammatory profiles, and the infection rate.

Results

Seventy-seven patients (38 in group B and 39 in group C) were included in the final analysis. One year postoperatively, bone fusion was achieved in 87% of group B patients and 87% of group C patients on dynamic radiographs, and 87% of group B patients and 72% of group C patients on CT scans (p=1.00 and 0.16, respectively). There were also no between-groups differences with respect to the secondary endpoints.

Conclusions

A HA/DBM mixture inside a PEEK cage can provide noninferior outcomes compared to a HA/TCP mixture in ACDF.

Permeability study of cancellous bone and its idealised structures

Artificial bone is a suitable alternative to autografts and allografts, however their use is still limited. Though there were numerous reports on their structural properties, permeability studies of artificial bones were comparably scarce. This study focused on the development of idealised, structured models of artificial cancellous bone and compared their permeability values with bone surface area and porosity. Cancellous bones from fresh bovine femur were extracted and cleaned following an established protocol. The samples were scanned using micro-computed tomography (μCT) and three-dimensional models of the cancellous bones were reconstructed for morphology study. Seven idealised and structured cancellous bone models were then developed and fabricated via rapid prototyping technique. A test-rig was developed and permeability tests were performed on the artificial and real cancellous bones. The results showed a linear correlation between the permeability and the porosity as well as the bone surface area. The plate-like idealised structure showed a similar value of permeability to the real cancellous bones.

Clinical outcomes and fusion rates following anterior lumbar interbody fusion with bone graft substitute i-FACTOR, an anorganic bone matrix/P-15 composite

Object

Despite limited availability and the morbidity associated with autologous iliac crest bone graft (ICBG), its use in anterior lumbar interbody fusion (ALIF) procedures remains the gold standard to achieve arthrodesis. The search for alternative grafts yielding comparable or superior fusion outcomes with fewer complications continues. In particular, i-FACTOR, a novel bone graft substitute composed of anorganic bone matrix (ABM) with P-15 small peptide, is one example currently used widely in the dental community. Although preclinical studies have documented its usefulness, the role of i-FACTOR in ALIF procedures remains unknown.

The authors' goal was to determine the safety and efficacy of i-FACTOR bone graft composite used in patients who underwent ALIF by evaluating fusion rates and clinical outcomes.

Methods

A nonblinded cohort of patients who were all referred to a single surgeon's practice was prospectively studied. One hundred ten patients with degenerative spinal disease underwent single or multilevel ALIF using the ABM/P-15 bone graft composite with a mean of 24 months (minimum 15 months) of follow-up were enrolled in the study. Patient's clinical outcomes were assessed using the Oswestry Disability Index for low-back pain, the 12-Item Short Form Health Survey, Odom's criteria, and a visual analog scale for pain. Fine-cut CT scans were used to evaluate the progression to fusion.

Results

All patients who received i-FACTOR demonstrated radiographic evidence of bony induction and early incorporation of bone graft. At a mean of 24 months of follow-up (range 15–43 months), 97.5%, 81%, and 100% of patients, respectively, who had undergone single-, double-, and triple-level surgery exhibited fusion at all treated levels. The clinical outcomes demonstrated a statistically significant (p < 0.05) difference between preoperative and postoperative Oswestry Disability Index, 12-Item Short Form Health Survey, and visual analog scores.

Conclusions

The use of i-FACTOR bone graft substitute demonstrates promising results for facilitating successful fusion and improving clinical outcomes in patients who undergo ALIF surgery for degenerative spinal pathologies.

Combined use of low-intensity pulsed ultrasound and rhBMP-2 to enhance bone formation in a rat model of critical size defect

BACKGROUND

Bone repair is regulated by biological factors and the local mechanical environment. We hypothesize that the combined use of low-intensity pulsed ultrasound (LIPUS) and recombinant human bone morphogenetic protein-2 (rhBMP-2) will synergistically or additively enhance bone regeneration in a model simulating the more difficult scenarios in orthopaedic traumatology.

METHODS

Femoral defects in rats were replaced with absorbable collagen sponges carrying rhBMP-2 (0, 1.2, 6, or 12 μg; n = 30). Each group was divided equally to receive daily treatment of either LIPUS or sham stimulation. At 4 weeks, new bone formation was assessed using quantitative (radiography and microcomputed tomography), qualitative (histology), and functional (biomechanical) end points.

RESULTS

LIPUS with 1.2 μg of rhBMP-2 significantly improved the radiographic healing as compared with its sham control starting as early as 2 weeks. Quantitatively, the use of LIPUS with 6 μg of rhBMP-2 significantly increased the bone volume. However, using LIPUS with 12 μg of rhBMP-2 indicated a reduction in callus size, without compromising the bone volume, which was also observable histologically, showing organized lamellar bone and repopulated marrow in the original defect region. Histologically, 1.2 μg of rhBMP-2 alone showed the presence of uncalcified cartilage in the defect, which was reduced with LIPUS treatment. Biomechanically, LIPUS treatment significantly increased the peak torsion and stiffness in the 6- and 12 μg rhBMP-2 groups.

CONCLUSIONS

LIPUS enhances rhBMP-2-induced bone formation at lower doses (1.2 and 6 μg) and callus maturation at 12-μg dose delivered on absorbable collagen sponge for bone repair in a rat critical-sized femoral segmental defect.

Short-term adverse events, length of stay, and readmission after iliac crest bone graft for spinal fusion

STUDY DESIGN

Retrospective cohort study of 13,927 patients, 820 of whom received iliac crest bone graft (ICBG).

OBJECTIVE

To compare adverse events, length of stay (LOS), and readmission for patients receiving ICBG with those who did not using multivariate analysis to control for potentially confounding factors.

SUMMARY OF BACKGROUND DATA

The use of ICBG in spinal fusion has been associated with increased surgical time, LOS, and donor site morbidity. Development of expensive bone graft substitutes has been predicated on these issues. Data on the effect of bone graft harvest on LOS and readmission rate are sparse, and multivariate analysis has not been used to control for confounding factors.

METHODS

Prospectively collected data from the American College of Surgeons National Surgical Quality Improvement Project 2010-2012 database were retrospectively reviewed. This includes demographics, comorbidities, surgical data, and hospital and 30-day follow-up outcomes data including adverse events, LOS, and readmission.

RESULTS

Only 5.9% of spinal fusions use ICBG. Bivariate logistic regression (used for categorical variables) found the ICBG cohort was more likely to have a postoperative blood transfusion (11.6% vs. 5.5%, P < 0.001). Bivariate linear regression (used for continuous variables) found the ICBG cohort to have an extended operative time (+36.0 min, P < 0.001) and extended LOS (+0.6 d, P < 0.001).Multivariate analyses controlling for comorbidities, demographics, and approach-determined postoperative blood transfusion (odds ratio, 1.5), extended operative time (+22.0 min, P < 0.001), and LOS (+0.2 d, P = 0.037) to be significantly associated with ICBG use.No other adverse event was significantly associated with ICBG use. Readmission rates were not significantly different.

CONCLUSION

This study used a large national database cohort and identified increased postoperative blood transfusion, extended operative time, and increased LOS as short-term outcomes associated with ICBG on multivariate analysis. Other short-term morbidities were not significantly associated with ICBG. Readmission rates were not affected.

LEVEL OF EVIDENCE

4.

Trends in bone graft use in the United States

Bone graft and bone graft substitutes are used to provide structural support and enhance bone healing. Autogenous, allogeneic, and artificial bone grafts each have advantages and drawbacks. The development of allografts, synthetic bone grafts, and new operative techniques may have influenced the use of bone grafts in recent years. The goal of this study was to analyze the use of bone grafts and bone graft substitutes in the United States during a 16-year period. Using data from the National Hospital Discharge Survey, the authors analyzed the use of autogenous and artificial bone grafts in almost 2 million patients in the United States between 1992 and 2007 using International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) codes in 4 periods (1992-1995, 1996-1999, 2000-2003, and 2004-2007). Among an estimated almost 2 million bone graft procedures (83% autogenous, 17% artificial), the use of both types of grafts decreased. The main diagnoses for which bone grafts were used did not change; however, cervical spine diseases and lower-limb fractures decreased more remarkably. Although sex (52% male in the early 1990s to 47% in 2000-2003) and discharge status (more discharges to a short-term or long-term-care facility) significantly changed, age increased from 47 to 53 years and inpatient days decreased significantly from 6 to 5 days during the study period. The use of bone grafts and bone graft substitutes is decreasing in the United States, with a slight shift from autogenous to substitute grafts.

A novel osteogenic oxysterol compound for therapeutic development to promote bone growth: activation of hedgehog signaling and osteogenesis through smoothened binding

Osteogenic factors are often used in orthopedics to promote bone growth, improve fracture healing, and induce spine fusion. Osteogenic oxysterols are naturally occurring molecules that were shown to induce osteogenic differentiation in vitro and promote spine fusion in vivo. The purpose of this study was to identify an osteogenic oxysterol more suitable for clinical development than those previously reported, and evaluate its ability to promote osteogenesis in vitro and spine fusion in rats in vivo. Among more than 100 oxysterol analogues synthesized, Oxy133 induced significant expression of osteogenic markers Runx2, osterix (OSX), alkaline phosphatase (ALP), bone sialoprotein (BSP), and osteocalcin (OCN) in C3H10T1/2 mouse embryonic fibroblasts and in M2-10B4 mouse marrow stromal cells. Oxy133-induced activation of an 8X-Gli luciferase reporter, its direct binding to Smoothened, and the inhibition of Oxy133-induced osteogenic effects by the Hedgehog (Hh) pathway inhibitor, cyclopamine, demonstrated the role of Hh pathway in mediating osteogenic responses to Oxy133. Oxy133 did not stimulate osteogenesis via BMP or Wnt signaling. Oxy133 induced the expression of OSX, BSP, and OCN, and stimulated robust mineralization in primary human mesenchymal stem cells. In vivo, bilateral spine fusion occurred through endochondral ossification and was observed in animals treated with Oxy133 at the fusion site on X-ray after 4 weeks and confirmed with manual assessment, micro-CT (µCT), and histology after 8 weeks, with equal efficiency to recombinant human bone morphogenetic protein-2 (rhBMP-2). Unlike rhBMP-2, Oxy133 did not induce adipogenesis in the fusion mass and resulted in denser bone evidenced by greater bone volume/tissue volume (BV/TV) ratio and smaller trabecular separation. Findings here suggest that Oxy133 has significant potential as an osteogenic molecule with greater ease of synthesis and improved time to fusion compared to previously studied oxysterols. Small molecule osteogenic oxysterols may serve as the next generation of bone anabolic agents for therapeutic development.

A retrospective study of iliac crest bone grafting techniques with allograft reconstruction: do patients even know which iliac crest was harvested? Clinical article

OBJECT

Considerable biological research has been performed to aid bone healing in conjunction with lumbar fusion surgery. Iliac crest autograft is often considered the gold standard because it has the vital properties of being osteoconductive, osteoinductive, and osteogenic. However, graft site pain has been widely reported as the most common donor site morbidity. Autograft site pain has led many companies to develop an abundance of bone graft extenders, which have limited proof of efficacy. During the surgical consent process, many patients ask surgeons to avoid harvesting autograft because of the reported pain complications. The authors sought to study postoperative graft site pain by simply asking patients whether they knew which iliac crest was grafted when a single skin incision was made for the fusion operation.

METHODS

Twenty-five patients underwent iliac crest autografting with allograft reconstruction during instrumented lumbar fusion surgery. In all patients the autograft was harvested through the same skin incision but with a separate fascial incision. At various points postoperatively, the patients were asked if they could tell which iliac crest had been harvested, and if so, how much pain did it cause (10-point Numeric Rating Scale).

RESULTS

Most patients (64%) could not correctly determine which iliac crest had been harvested. Of the 9 patients who correctly identified the side of the autograft, 7 were only able to guess. The 2 patients who confidently identified the side of grafting had no pain at rest and mild pain with activity. One patient who incorrectly guessed the side of autografting did have significant sacroiliac joint degenerative pain bilaterally.

CONCLUSIONS

Results of this study indicate the inability of patients to clearly define their graft site after iliac crest autograft harvest with allograft reconstruction of the bony defect unless they have a separate skin incision. This simple, easily reproducible pilot study can be expanded into a larger, multiinstitutional investigation to provide more definitive answers regarding the ideal, safe, and cost-effective bone graft material to be used in spinal fusions.

Demineralized bone matrix, as a graft enhancer of auto-local bone in posterior lumbar interbody fusion

Study Design

A case controlled study with prospective data collection.

Purpose

To evaluate the early influence and the final consequence of demineralized bone matrix (DBM) on auto-local bone as a graft enhancer in posterior lumbar interbody fusion (PLIF).

Overview of Literature

DBM is known as an osteoinductive material; however, it has not been clearly recognized to enhance auto-local bone with a small amount.

Methods

Patients who had a PLIF were allocated into two groups. Group I (70 cases) used auto-local bone chips and group II (44 cases) used DBM as an additive to auto-local bone, 1 mL per a segment. Group selection was alternated. Early assessment was performed by computed tomography at 6 months and final assessment was done by simple radiography after 24 months at least. The degree of bone formation was assessed by 4 grade scale.

Results

The subjects of both groups were homogenous and had similar Oswestry Disability Index at final assessment. The ratio of auto-local bone chips and DBM was 6:1. The degree of bone formation at 6 months after surgery was superior in group II. However, there was no significant difference between the two groups at the final assessment.

Conclusions

DBM was not recognized to enhance auto-local bone with small amount.

Micro-computed tomography-based three-dimensional kinematic analysis during lateral bending for spinal fusion assessment in a rat posterolateral lumbar fusion model

Rat posterolateral lumbar fusion (PLF) models have been used to assess the safety and effectiveness of new bone substitutes and osteoinductive growth factors using palpation, radiography, micro-computed tomography (μCT), and histology as standard methods to evaluate spinal fusion. Despite increased numbers of PLF studies involving alternative bone substitutes and growth factors, the quantitative assessment of treatment efficacy during spinal motion has been limited. The purpose of this study was to evaluate the effect of spinal fusion on lumbar spine segment stability during lateral bending using a μCT-based three-dimensional (3D) kinematic analysis in the rat PLF model. Fourteen athymic male rats underwent PLF surgery at L4/5 and received bone grafts harvested from the ilium and femurs of syngeneic rats (Isograft, n=7) or no graft (Sham, n=7). At 8 weeks after the PLF surgery, spinal fusion was assessed by manual palpation, plain radiography, μCT, and histology. To determine lumbar segmental motions at the operated level during lateral bending, 3D kinematic analysis was performed. The Isograft group, but not the Sham group, showed spinal fusion on manual palpation (6/7), solid fusion mass in radiographs (6/7), as well as bone bridging in μCT and histological images (5/7). Compared to the Sham group, the Isograft group revealed limited 3D lateral bending angular range of motion and lateral translation during lateral bending at the fused segment where disc height narrowing was observed. This μCT-based 3D kinematic analysis can provide a quantitative assessment of spinal fusion in a rat PLF model to complement current gold standard methods used for efficacy assessment of new therapeutic approaches.

Adult mesenchymal stem cells and impaction grafting: a new clinical paradigm shift

The demographic challenges of an increasingly aging population emphasize the need for innovative approaches to skeletal reconstruction to augment and repair skeletal tissue lost as a consequence of implant loosening, trauma, degeneration or in situations involving revision surgery requiring bone stock. These clinical imperatives to augment skeletal tissue loss have brought mesenchymal stem cells to the fore in combination with the emerging discipline of tissue engineering. To date, impaction bone grafting for revision hip surgery is a recognized technique to reconstitute bone utilizing morselized allograft to provide a good mechanical scaffold, although with little osteoinductive biological potential. This review details laboratory and clinical examples of a paradigm shift in the application of mesenchymal stem cells with allograft to produce a living composite using the principles of tissue engineering. This step change creates a composite that offers a biological and mechanical advantage over the current gold standard of allograft alone. This translation of tissue engineering concepts into clinical practice offers enormous input into the field of bone regeneration and has implications for translation and future change in skeletal orthopedic practice in an increasingly aging population.

Bone graft substitutes for anterior lumbar interbody fusion

The procedure of anterior lumbar interbody fusion (ALIF) is commonly performed on patients suffering from pain and/or neurological symptoms associated with disorders of the lumbar spine caused by disc degeneration and trauma. Surgery is indicated when prolonged conservative management proves ineffective. Because an important objective of the ALIF procedure is solid arthrodesis of the degenerative spinal segment, bone graft selection is critical. Iliac crest bone grafts (ICBG) remain the "gold standard" for achieving lumbar fusion. However, patient dissatisfaction stemming from donor site morbidity, lengthier operating times and finite supply of ICBG has prompted a search for better alternatives. Here presented is a literature review evaluating available bone graft options assessed within the clinical setting. These options include autografts, allograft-based, synthetic and cell-based technologies. The emphasis is on the contentious use of recombinant human bone morphogenetic proteins, which is in widespread use and has demonstrated both significant osteogenic potential and risk of complications.

Factors influencing arthrodesis rates in a rabbit posterolateral spine model with iliac crest autograft

PURPOSE

The rabbit posterolateral intertransverse spine arthrodesis model has been widely used to evaluate spinal biologics. However, to date, the validity and reproducibility of performance of iliac crest bone graft, the most common and critical control group, has not been firmly established. We evaluated original research publications that utilized this model, identified which experimental conditions affected fusion rates, and developed an algorithm to predict fusion rates for future study designs.

METHODS

A MEDLINE search was performed for publications through December, 2011 that utilized this model to evaluate fusion rates elicited by iliac crest autograft. All study parameters were recorded, and logistic regression analyses were performed to determine the effects of these variables on fusion rates as determined by either manual palpation or radiographs.

RESULTS

Seventy studies with 959 rabbits in 102 groups met the inclusion criteria. Excluding studies that measured fusion at 4 or fewer weeks or intentionally tried to decrease the fusion rate, the overall fusion rate for autograft was 58.3 ± 16.3 % (mean ± SD) as determined by manual palpation and 66.4 ± 17.8 % by plain radiographs. Regression analysis demonstrated a difference between these outcome measures with a trend towards significance (p = 0.09). Longer time points and larger volumes of autograft resulted in significantly greater reported fusion rates (p < 0.0001 and p < 0.05, respectively). Neither strain, age, weight, nor vertebral level significantly affected fusion rates.

CONCLUSIONS

Although experimental conditions varied across studies, time point evaluation and autograft volume significantly affected fusion rates. Despite some variability demonstrated across certain studies, we demonstrated that when the time point and volume of autograft were controlled for, the iliac crest control group of the rabbit posterolateral spinal arthrodesis model is both reliable and predictably affected by different experimental conditions.

Tissue engineering strategies in spinal arthrodesis: the clinical imperative and challenges to clinical translation

Skeletal disorders requiring the regeneration or de novo production of bone present considerable reconstructive challenges and are one of the main driving forces for the development of skeletal tissue engineering strategies. The skeletal or mesenchymal stem cell is a fundamental requirement for osteogenesis and plays a pivotal role in the design and application of these strategies. Research activity has focused on incorporating the biological role of the mesenchymal stem cell with the developing fields of material science and gene therapy in order to create a construct that is not only capable of inducing host osteoblasts to produce bone, but is also osteogenic in its own right. This review explores the clinical need for reparative approaches in spinal arthrodesis, identifying recent tissue engineering strategies employed to promote spinal fusion, and considers the ongoing challenges to successful clinical translation.

Management of clavicle nonunion and malunion

BACKGROUND

Clavicle fractures are common injuries of the shoulder girdle and occasionally result in nonunion or symptomatic malunion. When present, these chronic injuries can result in considerable shoulder dysfunction. A number of surgical techniques have been described for the management of these injuries. Current literature suggests that supplemental bone grafting may not be necessary in all cases but should be considered in the setting of atrophic nonunion. However, optimal treatment is controversial, as discussed in the literature. This article highlights the current treatment options based on the existing literature and describes our preferred techniques.

METHODS

We carried out a comprehensive review of the PubMed and Medline databases using multiple keywords (eg, clavicle fracture, clavicle nonunion, and clavicle malunion) to identify the relevant literature regarding this topic. Reference lists of the relevant articles were reviewed for additional important articles.

CONCLUSION

Nonunion and malunion of the clavicle remain challenging problems. Reliable bony union and improved shoulder function can be expected with thoughtful surgical planning, appropriate implant choice, and meticulous surgical technique.

Role of biomechanics in intervertebral disc degeneration and regenerative therapies: what needs repairing in the disc and what are promising biomaterials for its repair?

BACKGROUND CONTEXT

Degeneration and injuries of the intervertebral disc (IVD) result in large alterations in biomechanical behaviors. Repair strategies using biomaterials can be optimized based on the biomechanical and biological requirements of the IVD.

PURPOSE

To review the present literature on the effects of degeneration, simulated degeneration, and injury on biomechanics of the IVD, with special attention paid to needle puncture injuries, which are a pathway for diagnostics and regenerative therapies and the promising biomaterials for disc repair with a focus on how those biomaterials may promote biomechanical repair.

STUDY DESIGN

A narrative review to evaluate the role of biomechanics on disc degeneration and regenerative therapies with a focus on what biomechanical properties need to be repaired and how to evaluate and accomplish such repairs using biomaterials. Model systems for the screening of such repair strategies are also briefly described.

METHODS

Articles were selected from two main PubMed searches using keywords: intervertebral AND biomechanics (1,823 articles) and intervertebral AND biomaterials (361 articles). Additional keywords (injury, needle puncture, nucleus pressurization, biomaterials, hydrogel, sealant, tissue engineering) were used to narrow the articles down to the topics most relevant to this review.

RESULTS

Degeneration and acute disc injuries have the capacity to influence nucleus pulposus (NP) pressurization and annulus fibrosus (AF) integrity, which are necessary for an effective disc function and, therefore, require repair. Needle injection injuries are of particular clinical relevance with the potential to influence disc biomechanics, cellularity, and metabolism, yet these effects are localized or small and more research is required to evaluate and reduce the potential clinical morbidity using such techniques. NP replacement strategies, such as hydrogels, are required to restore the NP pressurization or the lost volume. AF repair strategies including cross-linked hydrogels, fibrous composites, and sealants offer promise for regenerative therapies to restore AF integrity. Tissue engineered IVD structures, as a single implantable construct, may promote greater tissue integration due to the improved repair capacity of the vertebral bone.

CONCLUSIONS

IVD height, neutral zone characteristics, and torsional biomechanics are sensitive to specific alterations in the NP pressurization and AF integrity and must be addressed for an effective functional repair. Synthetic and natural biomaterials offer promise for NP replacement, AF repair, as an AF sealant, or whole disc replacement. Meeting mechanical and biological compatibilities are necessary for the efficacy and longevity of the repair.

Substitutes of structural and non-structural autologous bone grafts in hindfoot arthrodeses and osteotomies: a systematic review

Background

Structural and non-structural substitutes of autologous bone grafts are frequently used in hindfoot arthrodeses and osteotomies. However, their efficacy is unclear.

The primary goal of this systematic review was to compare autologous bone grafts with structural and non-structural substitutes regarding the odds of union in hindfoot arthrodeses and osteotomies.

Methods

The Medline and EMBASE and Cochrane databases were searched for relevant randomized and non-randomized prospective studies as well as retrospective comparative chart reviews.

Results

10 studies which comprised 928 hindfoot arthrodeses and osteotomies met the inclusion criteria for this systematic review. The quality of the retrieved studies was low due to small samples sizes and confounding variables. The pooled random effect odds for union were 12.8 (95% CI 12.7 to 12.9) for structural allografts, 5.7 (95% CI 5.5 to 6.0) for cortical autologous grafts, 7.3 (95% CI 6.0 to 8.6) for cancellous allografts and 6.0 (95% CI 5.7 to 6.4) for cancellous autologous grafts. In individual studies, the odds of union in hindfoot arthrodeses achieved with cancellous autologous grafts was similar to those achieved with demineralised bone matrix or platelet derived growth factor augmented ceramic granules.

Conclusion

Our results suggest an equivalent incorporation of structural allografts as compared to autologous grafts in hindfoot arthrodeses and osteotomies. There is a need for prospective randomized trials to further clarify the role of substitutes of autologous bone grafts in hindfoot surgery.

Developing a new model for the invention and translation of neurotechnologies in academic neurosurgery

BACKGROUND

There is currently an acceleration of new scientific and technical capabilities that create new opportunities for academic neurosurgery. To engage these changing dynamics, the Center for Innovation in Neuroscience and Technology (CINT) was created on the premise that successful innovation of device-related ideas relies on collaboration between multiple disciplines. The CINT has created a unique model that integrates scientific, medical, engineering, and legal/business experts to participate in the continuum from idea generation to translation.

OBJECTIVE

To detail the method by which this model has been implemented in the Department of Neurological Surgery at Washington University in St. Louis and the experience that has been accrued thus far.

METHODS

The workflow is structured to enable cross-disciplinary interaction, both intramurally and extramurally between academia and industry. This involves a structured method for generating, evaluating, and prototyping promising device concepts. The process begins with the "invention session," which consists of a structured exchange between inventors from diverse technical and medical backgrounds. Successful ideas, which pass a separate triage mechanism, are then sent to industry-sponsored multidisciplinary fellowships to create functioning prototypes.

RESULTS

After 3 years, the CINT has engaged 32 clinical and nonclinical inventors, resulting in 47 ideas, 16 fellowships, and 12 patents, for which 7 have been licensed to industry. Financial models project that if commercially successful, device sales could have a notable impact on departmental revenue.

CONCLUSION

The CINT is a model that supports an integrated approach from the time an idea is created through its translational development. To date, the approach has been successful in creating numerous concepts that have led to industry licenses. In the long term, this model will create a novel revenue stream to support the academic neurosurgical mission.

Recombinant human bone morphogenetic protein-2 versus autogenous iliac crest bone graft for lumbar fusion: a meta-analysis of ten randomized controlled trials

BACKGROUND

Recombinant human bone morphogenetic protein-2 (rhBMP-2) as a substitute for iliac crest bone graft (ICBG) has been increasingly widely used in lumbar fusion. It has been proven non-inferior in fusion success and clinical outcomes when compared with ICBG. However, increasingly, some potentially uncommon and serious complications associated with the use of rhBMP-2 have been of great concern to surgeons. The purpose of this study was to determine whether rhBMP-2 could be considered an effective and, more importantly, a relatively safe substitute for ICBG in lumbar fusion.

METHODS

Randomized controlled trials that compared rhBMP-2 with ICBG for lumbar fusion were identified by computer and manual searching. The risk of bias and clinical relevance of the included studies were assessed. Publication bias was explored using funnel plot and statistical tests (Egger's test and Begg's test). Meta-analyses were performed using the Cochrane systematic review methods.

RESULTS

Ten randomized controlled trials (1,342 patients) met the inclusion criteria. Compared with ICBG, the use of rhBMP-2 significantly decreased the risk of fusion failure at all time intervals (6 months: p < 0.0001, RR = 0.55, 95 % CI = 0.42-0.72; 12 months: p = 0.0003, RR = 0.53, 95 % CI = 0.37-0.75; 24 months: p < 0.00001, RR = 0.31, 95 % CI = 0.21-0.46) and the rate of reoperation (p = 0.0001, RR = 0.52, 95 % CI = 0.37-0.72). There was no statistical difference in clinical improvement on the Oswestry Disability Index, although a favorable trend in the rhBMP-2 group was found (p = 0.12, RR = 0.73, 95 % CI = 0.49-1.08). Subgroup analyses stratified by the type of surgical procedure yielded similar results. Owing to the different data formats, meta-analysis on adverse events was not performed.

CONCLUSION

RhBMP-2 was superior to the ICBG for achieving fusion success and avoiding reoperation. However, evidence from the Food and Drug Administration document and subsequent independent studies has demonstrated that original, industry-sponsored trials underestimated rhBMP-2-related adverse events. There are still security risks in the use of rhBMP-2.

A review of demineralized bone matrices for spinal fusion: the evidence for efficacy

BACKGROUND AND PURPOSE

Autologous Iliac Crest Bone Grafting (ICBG) is considered the gold-standard graft choice for spinal arthrodesis; however, it is associated with donor site morbidity and a limited graft supply. Bone graft alternatives to replace autograft and augment arthrodesis are a topic of ongoing research. This article will review properties of Demineralized Bone Matrix (DBM) and review the evidence for its use, including animal models and human clinical trials.

METHODS

A systematic and critical review of the English-language literature was conducted on Pubmed, Cochrane, CINAHL, and Google Scholar using search key terms such as 'Demineralized Bone Matrix', 'Spine' and 'Fusion'. Papers that were included were original research articles in peer-reviewed journals that investigated fusion outcomes. Scientific validity of articles was appraised using the PRISMA methodology. Articles were critically examined and compared according to study design, DBM type, outcomes, and results. Primary outcome of interest was fusion rate. Secondary outcomes included Oswestry Disability Index; Short Form-36 survey; Odom's criteria; Visual Analog Scale neurologic pain score; Japanese Orthopedic Association myelopathy score; Neck Disability and Ishihara Curvature Indices; and pseudarthrosis and surgical failure rates.

RESULTS

Demineralized Bone Matrix has been evaluated in animal models and human clinical trials of spine fusion. Results of animal studies indicate variation in performance within and among DBM products. The majority of human clinical trials report high fusion rates when DBM is employed as a graft extender or a graft enhancer. Few prospective randomized controlled trials have been performed comparing DBM to autologous iliac crest bone graft in spine fusion.

CONCLUSIONS

Although many animal and human studies demonstrate comparable efficacy of DBM when combined with autograft or compared to autograft alone, additional high level of evidence studies are required to clearly define the indications for its use in spine fusion surgeries and the appropriate patient population that will benefit from DBM.

The effect of iliac crest autograft on the outcome of fusion in the setting of degenerative spondylolisthesis: a subgroup analysis of the Spine Patient Outcomes Research Trial (SPORT)

BACKGROUND

There is considerable controversy about the long-term morbidity associated with the use of posterior autologous iliac crest bone graft for lumbar spine fusion procedures compared with the use of bone-graft substitutes. The hypothesis of this study was that there is no long-term difference in outcome for patients who had posterior lumbar fusion with or without iliac crest autograft.

METHODS

The study population includes patients enrolled in the degenerative spondylolisthesis cohort of the Spine Patient Outcomes Research Trial who underwent lumbar spinal fusion. Patients were divided according to whether they had or had not received posterior autologous iliac crest bone graft.

RESULTS

There were 108 patients who had fusion with iliac crest autograft and 246 who had fusion without iliac crest autograft. There were no baseline differences between groups in demographic characteristics, comorbidities, or baseline clinical scores. At baseline, the group that received iliac crest bone graft had an increased percentage of patients who had multilevel fusions (32% versus 21%; p=0.033) and L5-S1 surgery (37% versus 26%; p=0.031) compared with the group without iliac crest autograft. Operative time was higher in the iliac crest bone-graft group (233.4 versus 200.9 minutes; p<0.001), and there was a trend toward increased blood loss (686.9 versus 582.3; p=0.057). There were no significant differences in postoperative complications, including infection or reoperation rates, between the groups. On the basis of the numbers available, no significant differences were detected between the groups treated with or without iliac crest bone graft with regard to the scores on Short Form-36, Oswestry Disability Index, Stenosis Bothersomeness Index, and Low Back Pain Bothersomeness Scale or the percent of patient satisfaction with symptoms averaged over the study period.

CONCLUSIONS

The outcome scores associated with the use of posterior iliac crest bone graft for lumbar spinal fusion were not significantly lower than those after fusion without iliac crest autograft. Conversely, iliac crest bone-grafting was not associated with an increase in the complication rates or rates of reoperation. On the basis of these results, surgeons may choose to use iliac crest bone graft on a case-by-case basis for lumbar spinal fusion.

The efficacies of 2 ceramic bone graft extenders for promoting spinal fusion in a rabbit bone paucity model

STUDY DESIGN

Prospective, randomized, controlled animal study.

OBJECTIVE

To determine the efficacies of 2 ceramic composite bone graft extenders for promoting spinal fusion.

SUMMARY OF BACKGROUND DATA

Although autogenous bone is still considered the "gold standard" graft material for fusion procedures, its use is associated with a number of limitations. Synthetic ceramic composites represent a class of osteoconductive materials that may be employed as supplements or even alternatives to autograft. In this study, we compared the fusion rates generated by 2 ceramic composite bone graft extenders (MasterGraft and Mozaik Strips) with that obtained with autograft in a rabbit bone paucity model.

METHODS

Thirty-two New Zealand white rabbits undergoing noninstrumented posterolateral lumbar fusion were randomized to 1 of the following 4 groups: 100% autograft, 50% autograft, 50% autograft with Mozaik Strip, and 50% autograft with MasterGraft Strip. The rabbits were followed postoperatively for 8 weeks at which time the spinal segments were explanted and assessed for the presence of a solid fusion.

RESULTS

The arthrodesis rates by manual palpation of the 100% and 50% autograft controls were 75% (6 of 8 animals) and 12.5% (1 of 8), respectively (P < 0.01). In the 50% autograft/Mozaik and 50% autograft/MasterGraft groups, 3/8 and 1/8 of the rabbits were determined to have fused successfully, respectively (P = 0.569). However, there were no significant differences between the fusion rate of the 50% autograft cohort and those exhibited by the Mozaik or MasterGraft animals (P = 0.569 and 1.00, respectively).

CONCLUSION

This study provides further evidence that the quantity of autograft may influence the process of spinal fusion such that the arthrodesis rate was significantly lower when less bone was implanted. Neither of the ceramic composite scaffolds seemed to enhance the fusion response compared to an equivalent amount of autograft alone, suggesting that these substances may need to be combined with other osteogenic materials to optimize bone production.

Current trends and future perspectives of bone substitute materials - from space holders to innovative biomaterials

An autologous bone graft is still the ideal material for the repair of craniofacial defects, but its availability is limited and harvesting can be associated with complications. Bone replacement materials as an alternative have a long history of success. With increasing technological advances the spectrum of grafting materials has broadened to allografts, xenografts, and synthetic materials, providing material specific advantages. A large number of bone-graft substitutes are available including allograft bone preparations such as demineralized bone matrix and calcium-based materials. More and more replacement materials consist of one or more components: an osteoconductive matrix, which supports the ingrowth of new bone; and osteoinductive proteins, which sustain mitogenesis of undifferentiated cells; and osteogenic cells (osteoblasts or osteoblast precursors), which are capable of forming bone in the proper environment. All substitutes can either replace autologous bone or expand an existing amount of autologous bone graft. Because an understanding of the properties of each material enables individual treatment concepts this review presents an overview of the principles of bone replacement, the types of graft materials available, and considers future perspectives. Bone substitutes are undergoing a change from a simple replacement material to an individually created composite biomaterial with osteoinductive properties to enable enhanced defect bridging.

Characterization of the inflammatory response to four commercial bone graft substitutes using a murine biocompatibility model

Bone grafting is utilized in nearly all orthopedic subspecialties and in most anatomic regions. Bone graft substitutes have the potential to offer similar efficacy as autogenous grafts without the morbidity of harvest. Several studies have noted the efficacy of new-generation bone substitute products, but few studies have evaluated their safety. This study characterizes and quantifies the inflammatory reaction to four different commercially available bone graft substitutes, which were examined using the in vivo murine air pouch biocompatibility model. One coralline hydroxyapatite product was chosen as an example of a purely osteoconductive material. Three demineralized bone matrix products were chosen to represent products that are both osteoconductive and osteoinductive. Samples were implanted in a murine air pouch and harvested after 14 days in situ. Pouch fluid was extracted, mRNA isolated, and reverse transcription polymerase chain reactions carried out to detect interleukin-1 gene expression as a marker for inflammation. In addition, multiple histological characteristics were examined to quantify cellular responses to the implanted materials. All bone graft substitutes induced a significant inflammatory response compared with negative controls. Histology and polymerase chain reaction data indicated that the level of inflammatory reaction was elevated in materials with a higher demineralized bone matrix to carrier proportion. The hydroxyapatite product generated a low inflammatory reaction. In conclusion, this study used an in vivo model of biocompatibility to demonstrate that a significant inflammatory reaction occurs when using implanted bone graft substitutes. When choosing a bone grafting method, surgeons should consider both the efficacy and safety of methods and materials used. Further studies are necessary to determine the ideal bone graft material to maximize efficacy while minimizing morbidity.

Mechanical and microarchitectural analyses of cancellous bone through experiment and computer simulation

The relationship between microarchitecture to the failure mechanism and mechanical properties can be assessed through experimental and computational methods. In this study, both methods were utilised using bovine cadavers. Twenty four samples of cancellous bone were extracted from fresh bovine and the samples were cleaned from excessive marrow. Uniaxial compression testing was performed with displacement control. After mechanical testing, each specimen was ashed in a furnace. Four of the samples were exemplarily scanned using micro-computed tomography (μCT) and three dimensional models of the cancellous bones were reconstructed for finite element simulation. The mechanical properties and the failure modes obtained from numerical simulations were then compared to the experiments. Correlations between microarchitectural parameters to the mechanical properties and failure modes were then made. The Young's modulus correlates well with the bone volume fraction with R² = 0.615 and P value 0.013. Three different types of failure modes of cancellous bone were observed: oblique fracture (21.7%), perpendicular global fracture (47.8%), and scattered localised fracture (30.4%). However, no correlations were found between the failure modes to the morphological parameters. The percentage of error between computer predictions and the actual experimental test was from 6 to 12%. These mechanical properties and information on failure modes can be used for the development of synthetic cancellous bone.

Novel oxysterols have pro-osteogenic and anti-adipogenic effects in vitro and induce spinal fusion in vivo

Stimulation of bone formation by osteoinductive materials is of great clinical importance in spinal fusion surgery, repair of bone fractures, and in the treatment of osteoporosis. We previously reported that specific naturally occurring oxysterols including 20(S)-hydroxycholesterol (20S) induce the osteogenic differentiation of pluripotent mesenchymal cells, while inhibiting their adipogenic differentiation. Here we report the characterization of two structural analogues of 20S, Oxy34 and Oxy49, which induce the osteogenic and inhibit the adipogenic differentiation of bone marrow stromal cells (MSC) through activation of Hedgehog (Hh) signaling. Treatment of M2-10B4 MSC with Oxy34 or Oxy49 induced the expression of osteogenic differentiation markers Runx2, Osterix (Osx), alkaline phosphatase (ALP), bone sialoprotein (BSP), and osteocalcin (OCN), as well as ALP enzymatic activity and robust mineralization. Treatment with oxysterols together with PPARγ activator, troglitazone (Tro), inhibited mRNA expression for adipogenic genes PPARγ, LPL, and aP2, and inhibited the formation of adipocytes. Efficacy of Oxy34 and Oxy49 in stimulating bone formation in vivo was assessed using the posterolateral intertransverse process rat spinal fusion model. Rats receiving collagen implants with Oxy 34 or Oxy49 showed comparable osteogenic efficacy to BMP2/collagen implants as measured by radiography, MicroCT, and manual inspection. Histological analysis showed trabecular and cortical bone formation by oxysterols and rhBMP2 within the fusion mass, with robust adipogenesis in BMP2-induced bone and significantly less adipocytes in oxysterol-induced bone. These data suggest that Oxy34 and Oxy49 are effective novel osteoinductive molecules and may be suitable candidates for further development and use in orthopedic indications requiring local bone formation.

Technique, challenges and indications for percutaneous pedicle screw fixation

Minimally invasive techniques in spinal surgery are increasing in popularity due to numerous potential advantages, including reduced length of stay, blood loss and requirements for post-operative analgesia as well as earlier return to work. This review discusses guidelines for safe implantation of percutaneous pedicle screws using an image intensifier technique. As indications for percutaneous pedicle screw techniques expand, the nuances of the minimally invasive surgery technique will also expand. It is paramount that experienced surgeons share their collective knowledge to assist surgeons at their early attempts of these complex, and potentially dangerous, procedures. Technical challenges of percutaneous pedicle screw fixation techniques are also discussed including: small pedicle cannulation, percutaneous rod insertion for multilevel constructs, incision selection for multilevel constructs, changing direction with percutaneous pedicle screw placement, L5/S1 screw head proximity and sclerotic pedicles with difficult Jamshidi placement. We discuss potential indications for minimally invasive fusion techniques for complex spinal surgery and support these with descriptions of illustrative patients.

Bone graft harvesting using the RIA (reaming irrigation aspirator) system - a quantitative assessment

INTRODUCTION

Autologous bone graft is still considered to be the gold standard for treating non-unions in trauma and orthopedic surgery. Intramedullary bone graft harvest appears to be an alternative to other bone graft options such as iliac crest bone graft and synthetic bone substitutes. A one-step reamer-irrigator-aspirator (RIA) system has been developed to reduce the intramedullary pressure and, as a consequence, minimize the risk of fat embolization. The purpose of this study was to determine whether the quantity of harvested intramedullary bone graft is comparable to the quantity of graft that was harvested from the iliac crest in other studies. The aim of the present study was to quantify harvested bone marrow and to compare our results to already published data.

METHODS

Eight human cadavers (7 males, 1 female, and 16 limbs) with an average age of 68 years (range, 49-79 years) were obtained for this study. Intramedullary reaming was performed in the tibiae and femora of each cadaver. Two different sizes (12- and 14-mm diameter) of the RIA system were used. After a medial parapatellar incision was made at the knee, antegrade and retrograde reaming were performed in the tibiae and femur to harvest bone graft.

RESULTS

A significantly greater quantity of bone graft was harvested from the femora (27 ± 12 g) than the tibiae (17 ± 9 g) (p = 0.007).

CONCLUSIONS

On the basis of our present results, harvesting intramedullary bone graft with the RIA system appears to be an innovative technique for bone grafting in limb reconstruction. A significantly greater quantity of bone graft was harvested from the femora than the tibiae (p = 0.007). No significant differences among age, sex, body weight, bone length, or BMI were observed. Our results showed that a sufficient quantity in weight of autogenous bone graft could be obtained using the RIA system.

Generating 3D tissue constructs with mesenchymal stem cells and a cancellous bone graft for orthopaedic applications

Bone matrix (BM) is an acellular crosslinked porcine-derived cancellous bone graft, and therefore may provide advantages over other synthetic and naturally derived materials for use in orthopaedic surgery. Here, we analysed the potential of BM to support the growth and differentiation of primary human multipotent stromal cells/mesenchymal stem cells (MSCs) in order to predict in vivo bone regeneration events. Imaging with laser scanning confocal microscopy and scanning electron microscopy showed that 1 day after static seeding, a dense population of viable MSCs could be achieved on scaffolds suggesting they could be used for in vivo delivery of cells to the implant site. Long-term growth analysis by confocal imaging and histology demonstrated that BM was permissive to the growth and the 3D population of primary MSCs and an enhanced green fluorescent protein expressing osteosarcoma cell line, eGFP.MG63s, over several days in culture. Measurement of alkaline phosphatase (ALP) activities and mRNA expression levels of osteogenic markers (Runx-2, ALP, collagen type I, osteonectin, osteocalcin and osteopontin) indicated that BM supported osteogenesis of MSCs when supplemented with osteogenic stimulants. Upregulation of some of these osteogenic markers on BM, but not on tissue culture plastic, under non-osteogenic conditions suggested that BM also had osteoinductive capacities.

Preparation of combined β-TCP/α-CSH artificial bone graft and its performance in a spinal fusion model

To evaluate α-calcium sulfate hemihydrate (α-CSH)/β-tricalcium phosphate (β-TCP) combined artificial bone graft (COB) in an animal model of posterolateral spinal fusion, α-CSH and β-TCP were combined in a 3 : 7 weight ratio. A rabbit model of posterolateral spinal fusion was produced ( N = 36); one side was implanted with the COB, and the other with local autogenous bone. Rabbits were killed on the 4th, 8th, or 12th week after surgery and fusion, COB degradation, mineralization, and new bone formation were evaluated. Scanning electron microscopy revealed that the COB retained the porous spatial structure of β-TCP and α-CSH crystals were adhered to the surface and pores of β-TCP. At the 12th week after surgery, the fusion rate was 75.0% on the 12th week after the operation, which was higher than the fusion rate of 54.4% the autogenous bone side ( p = 0.073). Bone volume fraction of the COB was 0.49 ± 0.08 for the 4th week and 0.16 ± 0.05 for the 12th week after surgery. The mineralization rate of the new bone was greater on the side implanted with autogenous bone than on the side implanted with COB at all the three time points after surgery. At each time point after surgery, the difference in mineralization rate between the autogenous bone side and the COB side was statistically significant ( p < 0.001); α-CSH/β-TCP in a 3 : 7 weight ratio was as effective as local autogenous bone in producing spinal fusion in a rabbit model. Used in this ratio, the speed of material degradation and new bone formation are relatively equivalent, and the rate of new bone mineralization is similar to that of autogenous bone graft.

Effects on growth and osteogenic differentiation of mesenchymal stem cells by the zinc-added sol-gel bioactive glass granules

Responses of mesenchymal stem cells (MSCs) cultured with zinc-added (2 and 5%) bioactive glass granules were evaluated in terms of cell growth and osteogenic differentiation. MSCs were cultured with different quantities (3, 10 and 30) of glass granules for up to 21 days in the osteogenic medium. Cell growth was stimulated by a small quantity of glasses, particularly those that contained zinc. Osteogenic differentiation, as assessed by alkaline phosphatase activity (ALP) activity, was significantly enhanced by the glasses, particularly with large quantities of glass and for prolonged culturing. Expression of bone-sialo protein (BSP) was significantly up-regulated around the bioactive glass granules. Moreover, the zinc addition significantly altered the ALP and BSP depending on the culture time and glass quantity. Cellular mineralization was improved in all glass samples, and particularly in the 2% zinc-glass. Taken together, the zinc addition to bioactive glass induced the MSCs growth and their osteogenic differentiation, at least to the level of zinc-free glass, and with even higher level observed depending on the quantity and culture time. These findings indicate that the zinc addition to bioactive glass may be useful in development of biomaterials for the stimulation of adult stem cell in bone tissue engineering.

Autogenous bone marrow stromal cell sheets-loaded mPCL/TCP scaffolds induced osteogenesis in a porcine model of spinal interbody fusion

This study was designed to investigate whether a tissue-engineered construct composed of autogenous cell sheets and a polycaprolactone-based bioresorbable scaffold would enhance bone regeneration and spinal interbody fusion in a large animal model. Porcine-derived autogenous bone marrow stromal cells (BMSCs) cultured into multilayered cell sheets were induced into osteogenic differentiation with dexamethasone, l-ascorbic acid, and β-glycerol phosphate. These cell sheets were assembled with bioresorbable scaffolds made from medical-grade poly(epsilon-caprolactone) incorporating 20% β-tricalcium phosphate (mPCL/TCP) as tissue-engineered BMSC constructs. L2/3, L4/5 discectomies and decortication of the vertebral end plates were performed on 16 SPF Yorkshire pigs through an anterolateral approach. The tissue-engineered BMSC constructs were transplanted into the prepared intervertebral disc spaces of half of the pigs (n = 8), whereas cell-free mPCL/TCP served as controls in the remaining pigs. New bone formation and spinal fusion were evaluated at 3 and 6 months using microcomputed tomography, histology, fluorochrome bone labeling, and biomechanical testing. New bone formation was evident as early as 3 months in the BMSC group. At 6 months, bony fusion was observed in >60% (5/8) of segments in the BMSC group. None of the control animals with cell-free scaffold showed fusion at both time points. Biomechanical evaluation further revealed a significantly increased segmental stability in the BMSC group compared with the cell-free group at 6 months postimplantation (p < 0.01). These findings suggest that mPCL/TCP scaffolds loaded with in vitro differentiated autogenous BMSC sheets could induce bone formation and interbody fusion. This in turn resulted in enhanced segmental stability of the lumbar spine.

Mineralization of hydrogels for bone regeneration

Hydrogels are an important class of highly hydrated polymers that are widely investigated for potential use in soft tissue engineering. Generally, however, hydrogels lack the ability to mineralize, preventing the formation of chemical bonds with hard tissues such as bone. A recent trend in tissue engineering involves the development of hydrogels that possess the capacity to mineralize. The strategy that has attracted most interest has been the incorporation of inorganic phases such as calcium phosphate ceramics and bioglasses into hydrogel matrices. These inorganic particles act as nucleation sites that enable further mineralization, thus improving the mechanical properties of the composite material. A second route to create nucleation sites for calcification of hydrogels involves the use of features from the physiological mineralization process. Examples of these biomimetic mineralization strategies include (1) soaking of hydrogels in solutions that are saturated with respect to calcium phosphate, (2) incorporation of enzymes that catalyze deposition of bone mineral, and (3) incorporation of synthetic analogues to matrix vesicles that are the initial sites of biomineralization. Functionalization of the polymeric hydrogel backbone with negatively charged groups is a third mechanism to promote mineralization in otherwise inert hydrogels. This review summarizes the main strategies that have been developed in the past decade to calcify hydrogel matrices and render these hydrogels suitable for applications in bone regeneration.

OP-1 (BMP-7) stimulates osteoprogenitor cell differentiation in the presence of polymethylmethacrylate particles

Polymethylmethacrylate (PMMA) particles have been shown to inhibit the differentiation, proliferation, and mineralization of osteoprogenitor cells in vitro. In this study, we investigated the effects of OP-1 (BMP-7) on the osteogenesis of MC3T3-E1 osteoprogenitor cells exposed to PMMA particles in vitro. MC3T3-E1 cells challenged with PMMA particles on the 1st day of differentiation in osteogenic culture showed a significant dose-dependent decrease in mineralization and alkaline phosphatase expression over a 20-day culture period. Exposure of these cells to OP-1 (200 ng/mL) during days 1-4, 1-20, and 4-20 in the presence of PMMA particles resulted in significant increases in mineralization and alkaline phosphatase expression at all particle doses. Addition of OP-1 to MC3T3-E1 cultures challenged with PMMA particles on the 4th day of differentiation in osteogenic media also resulted in significant increases in mineralization and alkaline phosphatase expression. This study has shown that OP-1 stimulates osteogenesis in MC3T3-E1 osteoprogenitor cells that have been inhibited by PMMA particles. Local administration of OP-1 to the site of osteolysis may be a potential adjunctive therapy to reverse the bone destruction due to wear particles.

Engineering embryonic stem-cell aggregation allows an enhanced osteogenic differentiation in vitro

Pluripotent embryonic stem (ES) cells hold great promise for the field of tissue engineering, with numerous studies investigating differentiation into various cell types including cardiomyocytes, chondrocytes, and osteoblasts. Previous studies have detailed osteogenic differentiation via dissociated embryoid body (EB) culture in osteoinductive media comprising of ascorbic acid, beta-glycerophosphate, and dexamethasone. It is hoped that these osteogenic cultures will have clinical application in bone tissue repair and regeneration and pharmacological testing. However, differentiation remains highly inefficient and generates heterogeneous populations. We have previously reported an engineered three-dimensional culture system for controlled ES cell-ES cell interaction via the avidin-biotin binding complex. Here we investigate the effect of such engineering on ES cell differentiation. Engineered EBs exhibit enhanced osteogenic differentiation assessed by cadherin-11, Runx2, and osteopontin expression, alkaline phosphatase activity, and bone nodule formation. Results show that cultures produced from intact EBs aggregated for 3 days generated the greatest levels of osteogenic differentiation when cultured in osteoinductive media. However, when cultured in control media, only engineered samples appeared to exhibit bone nodule formation. In addition, polymerase chain reaction analysis revealed a decrease in endoderm and ectoderm expression within engineered samples. This suggests that engineered ES cell aggregation has increased mesoderm homogeneity, contributing to enhanced osteogenic differentiation.

Bone grafting options in children

STUDY DESIGN

Retrospective review of the literature.

OBJECTIVE

To review the current literature as well as recent trends in bone grafting techniques available for children.

SUMMARY OF BACKGROUND DATA

The currently accepted gold standard in bone grafting for adolescent idiopathic scoliosis (AIS) is autogenous iliac crest. Due to questions concerning complications such as donor site pain, other options have been explored, including various allograft sources, demineralized bone matrix, and bone morphogenetic protein.

METHODS

A review of the current medical literature was completed and additional case examples are presented.

RESULTS

A review of the literature reveals that up to 31% of patients have persistent pain at 2 years post surgery when autogenous iliac crest bone graft is harvested. Allograft supplementation of local autograft has been demonstrated in the literature to be as effective as autogenous iliac crest bone grafting in contributing to a successful posterior spinal fusion in patients with AIS. Modern demineralized bone matrix formulations have been found in both animal models as well as in a recent retrospective clinical review to contribute to a successful posterior spinal fusion in AIS. Bone morphogenetic protein has been shown to contribute to a successful posterior spinal fusion in complex pediatric spinal deformity patients. At 2 years follow-up, patients who underwent a posterior instrumented spinal fusion that was not augmented with any bone graft appear to have successful spinal fusions.

CONCLUSION

Although autogenous iliac bone graft remains the benchmark to which bone grafting materials are compared, other options including the placement of no bone graft at all provides similar fusion rates in patients with AIS.

Bone morphogenetic protein (BMP) for fracture healing in adults

BACKGROUND

Delay in fracture healing is a complex clinical and economic issue for patients and health services.

OBJECTIVES

To assess the incremental effectiveness and costs of bone morphogenetic protein (BMP) on fracture healing in acute fractures and nonunions compared with standards of care.

SEARCH STRATEGY

We searched The Cochrane Library (2008, Issue 4), MEDLINE, and other major health and health economics databases (to October 2008).

SELECTION CRITERIA

Randomised controlled trials (RCTs) and full or partial economic evaluations of BMP for fracture healing in skeletally mature adults.

DATA COLLECTION AND ANALYSIS

All clinical and economic data were extracted by one author and checked by another.

MAIN RESULTS

Eleven RCTs, all at high risk of bias, and four economic evaluations were included. Apart from one study, the times to fracture healing were comparable between the BMP and control groups. There was some evidence for increased healing rates, without requiring a secondary procedure, of BMP compared with usual care control in acute, mainly open, tibial fractures (risk ratio (RR) 1.19, 95% CI 0.99 to 1.43). The pooled RR for achieving union for nonunited fractures was 1.02 (95% CI 0.90 to 1.15). One study found no difference in union for patients who had corrective osteotomy for radial malunions. Data from three RCTs indicated that fewer secondary procedures were required for acute fracture patients treated with BMP versus controls (RR 0.65, 95% CI 0.50 to 0.83). Adverse events experienced were infection, hardware failure, pain, donor site morbidity, heterotopic bone formation and immunogenic reactions. The evidence on costs for BMP-2 for acute open tibia fractures is from one large RCT. This indicates that the direct medical costs associated with BMP would generally be higher than treatment with standard care, but this cost difference may decrease as fracture severity increases. Limited evidence suggests that the direct medical costs associated with BMP could be offset by faster healing and reduced time off work for patients with the most severe open tibia fractures.

AUTHORS' CONCLUSIONS

This review highlights a paucity of data on the use of BMP in fracture healing as well as considerable industry involvement in currently available evidence. There is limited evidence to suggest that BMP may be more effective than controls for acute tibial fracture healing, however, the use of BMP for treating nonunion remains unclear. The limited available economic evidence indicates that BMP treatment for acute open tibial fractures may be more favourable economically when used in patients with the most severe fractures.

Osteoblast response to polymethyl methacrylate bioactive glass composite

Polymethylmethacrylate (PMMA) has been used in many orthopedic and dental applications since the 1960s. Biocompatibility of newly developed surface porous fiber reinforced (SPFR) PMMA based composite has not been previously proven in cell culture environment. Analysis of rat bone marrow stromal cells grown on the different test materials showed only little difference in normalized cell activity or bone sialoprotein (BSP) production between the test materials, but the osteocalcin (OC) levels remained higher (P < 0.015-0.005) through out the test with SPFR-material when compared to tissue culture poly styrene (TCPS). The cells grown on SP-FRC material also showed highest calcium depletion from the culture medium (P < 0.026-0.001) when compared to all other test substrates. SEM images of the cultured samples confirmed that all the materials enabled cell spreading and growth on their surface, but the roughened surface remarkably enhanced this process of cell attachment, division and calcified nodule formation. This study shows that the SP-FRC composite material does not elicit harmful/toxic reactions in cell cultures more than neutral TCPS and can be considered biocompatible. The material possesses good capabilities to form new mineralized tissue onto its surface, and through that a possibility to bond directly to bone. Rough surface seems to enhance osteoblast proliferation and formation of mineralized extracellular matrix.

Spinal Fusion of an Unstable Atlantoaxial Fracture in a Completely Tetraplegic Patient Using Silicate-Substituted Calcium Phosphate

Bone graft harvesting from the iliac crest constitutes the gold standard in spinal surgery due to its osteogenic, osteoconductive and osteoinductive properties. Large amounts of autograft can provoke complications like donor site morbidity, pain and the need for a second operation. Therefore, research into bone graft substitutes is of great interest. Silicate-substituted calcium phosphate (Actifuse(TM) Synthetic Bone Graft, ApaTech Ltd, London) was used in combination with morselized corticocancellous graft in a transarticular stabilization (modified Magerl) of a completely tetraplegic patient with an unstable atlantoaxial fracture. Computed tomography showed bone bridging between the segment C1/C2, the surface of the implant and the remodeled bone at follow-up at 8 months. The use of silicate-substituted calcium phosphate as a bone graft extender in spinal surgery could be an alternative to autografting from the iliac crest. Vegetative symptoms are often underestimated but can be triggered by donor site morbidity or pain in patients after spinal cord injury.