The use of simvastatin in rabbit posterolateral lumbar intertransverse process spine fusion

A Comparative Evaluation of Commercially Available Cell-Based Allografts in a Rat Spinal Fusion Model

Background

To evaluate the comparative abilities of commercially available, viable, cellular bone allografts to promote posterolateral spinal fusion.

Methods

Human allografts containing live cells were implanted in the athymic rat model of posterolateral spine fusion. Three commercially available allogeneic cellular bone matrices (Trinity Evolution, Trinity ELITE and Osteocel Plus) were compared with syngeneic iliac crest bone as the control. All spines underwent radiographs, manual palpation, and micro-computed tomography (CT) analysis after excision at 6 weeks. Histological sections of randomly selected spines were subjected to semiquantitative histopathological scoring for bone formation.

Results

By manual palpation, posterolateral fusion was detected in 40% (6/15) of spines implanted with syngeneic bone, whereas spines implanted with Trinity Evolution and Trinity ELITE allografts yielded 71% (10/14) and 77% (10/13) fusion, respectively. Only 7% (1/14) of spines implanted with Osteocel Plus allografts were judged fused by manual palpation (statistically significantly less than ELITE, P < .0007, and Evolution, P < .0013). The mineralized cancellous bone component of the allografts confounded radiographic analysis, but Trinity Evolution (0.452 ± 0.064) and Trinity ELITE (0.536 ± 0.109) allografts produced statistically significantly higher bone fusion mass volumes measured by quantitative micro-CT than did syngeneic bone (0.292 ± 0.109, P < .0001 for ELITE and P < .003 for Evolution) and Osteocel Plus (0.258 ± 0.103, P < .0001). Semiquantitative histopathological scores supported these findings because the total bone and bone marrow scores reflected significantly better new bone and marrow formation in the Trinity groups than in the Osteocel Plus group.

Conclusions

The Trinity Evolution and Trinity ELITE cellular bone allografts were more effective at creating posterolateral fusion than either the Osteocel Plus allografts or syngeneic bone in this animal model.

Clinical Relevance

The superior fusion rate of Trinity cellular bone allografts may lead to better clinical outcome of spinal fusion surgeries.

Locally Applied Simvastatin as an Adjunct to Promote Spinal Fusion in Rats

STUDY DESIGN

Basic Science.

OBJECTIVE

To determine if locally delivered simvastatin can enhance bone formation in a rat spinal fusion model.

SUMMARY OF BACKGROUND DATA

The bone-anabolic properties of statins in fracture healing are well established, however, few studies have evaluated the impact of locally delivered statins in spinal fusion.

METHODS

We formulated poly(lactic-co-glycolic acid) (PLGA) nanoparticles by adapting previously published techniques. Two types of nanoparticles were created: simvastatin nanoparticles (SimNP) and nanoparticles without simvastatin (BlankNP). Drug elution from SimNP was characterized. Osteoblastic differentiation was analyzed using MC3T3-E1 cells cultured in differentiation medium containing SimNP or BlankNP. Forty male 12 week old outbred Wistar rats underwent uninstrumented posterolateral fusion using iliac crest bone graft and BlankNP, SimNP or simvastatin drug. X-rays to assess bone formation were obtained at 4 weeks and 9 weeks post-operatively. Spines were explanted at 9 weeks for micro-CT analysis, and a blinded manual assessment of fusion (MAF).

RESULTS

SimNP achieved a release efficiency of 74.1% with ∼50% release occurring in the first day. Simvastatin and SimNP treated cells showed significantly greater expression of osteopontin (OPN) and osteocalcin (OCN). On micro-CT analysis, SimNP animals had higher bone volume and percent bone volume (bone volume/total volume) than control animals. SimNP rats had higher X-ray scores at 4 weeks (p=0.010) and 9 weeks (p<0.001) relative to BlankNP. MAF showed that SimNP had a higher fusion rate than BlankNP (42.9% vs. 0%, p=0.006).

CONCLUSION

We were able to validate that sustained release of simvastatin via a PLGA nanoparticle. SimNP was able to induce an increase in mineralization as well as an increase in markers of bone formation. X-ray analysis, micro-CT quantification, and MAF assessment of SimNP treated rats showed significantly greater bone formation and fusion mass strength relative to vehicle treated animals. Simvastatin may be a safe, cost-effective bone anabolic agent for use in spinal fusion.

LEVEL OF EVIDENCE

N/A.

Role of Simvastatin on fracture healing and osteoporosis: a systematic review on in vivo investigations

Simvastatin is a lipid lowering drug whose beneficial role on bone metabolism was discovered in 1999. Several in vivo studies evaluated its role on osteoporosis and fracture healing, however, controversial results are seen in the literature. For this reason, Simvastatin has not been the focus of any clinical trials as yet. This systematic review clears the mechanisms of action of Simvastatin on bone metabolism and focuses on in vivo investigations that have evaluated its role on osteoporosis and fracture repair to find out (i) whether Simvastatin is effective on treatment of osteoporosis and fracture repair, and (ii) which of the many available protocols may have the ability to be translated in the clinical setting. Simvastatin induces osteoinduction by increasing osteoblast activity and differentiation and inhibiting their apoptosis. It also reduces osteoclastogenesis by decreasing both the number and activity of osteoclasts and their differentiation. Controversial results between the in vivo studies are mostly due to the differences in the route of administration, dose, dosage and carrier type. Local delivery of Simvastatin through controlled drug delivery systems with much lower doses and dosages than the systemic route seems to be the most valuable option in fracture healing. However, systemic delivery of Simvastatin with much higher doses and dosages than the clinical ones seems to be effective in managing osteoporosis. Simvastatin, in a particular range of doses and dosages, may be beneficial in managing osteoporosis and fracture injuries. This review showed that Simvastatin is effective in the treatment of osteoporosis and fracture healing.

Evaluation of a new formulation of demineralized bone matrix putty in a rabbit posterolateral spinal fusion model

BACKGROUND CONTEXT

Alternatives to autologous bone graft (ABG) with osteoconductive, osteoinductive, and osteogenic potential continue to prove elusive. Demineralized bone matrix (DBM) however, with its osteoconductive and osteoinductive potential remains a viable option to ABG in posterolateral spine fusion.

PURPOSE

To compare the efficacy of a new formulation of DBM putty with that of ABG in a rabbit posterolateral spinal fusion model.

STUDY DESIGN

Efficacy of a new formulation of DBM was studied in an experimental animal posterolateral spinal fusion model.

METHODS

Twenty-four male New Zealand White rabbits underwent bilateral posterolateral spine arthrodesis of the L5-L6 intertransverse processes, using either ABG (control group, n=12) or DBM (DBM made from rabbit bone) putty (test group, n=12). The animals were killed 12 weeks after surgery and the lumbar spines were excised. Fusion success was evaluated by manual palpation, high resolution X-rays, microcomputed tomography imaging, biomechanical four-point bending tests, and histology.

RESULTS

Two animals were lost because of anesthetic related issues. Manual palpation to assess fusion success in the explanted lumbar spines showed no statistical significant difference in successful fusion in 81.8% (9/11) of DBM group and 72.7% (8/11) of ABG group (p=.99). Reliability of these assessments was measured between three independent observers and found near perfect agreement (intraclass correlation cofficient: 0.92 and 0.94, respectively). Fusion using high resolution X-rays was solid in 10 of the DBM group and 9 of the ABG group (p=.59). Biomechanical testing showed no significant difference in stiffness between the control and test groups on flexion, extension, and left lateral and right lateral bends, with p values accounting for .79, .42, .75, and .52, respectively. The bone volume/total volume was greater than 85% in the DBM treated fusion masses. Histologic evaluation revealed endochondral ossification in both groups, but the fusion masses were more mature in the DBM group.

CONCLUSIONS

The DBM putty achieved comparable fusion rates to ABG in the rabbit posterolateral spinal fusion model.

Effect of Pentoxifylline on Spinal Fusion: An Experimental Study in Rabbits

STUDY DESIGN

Randomized, double-blinded, animal model.

OBJECTIVE

The objective of this study is to evaluate the effect of pentoxifylline (PTX) on spinal fusion in a rabbit model.

SUMMARY OF BACKGROUND DATA

Previous studies assert that PTX increases new bone formation. Because PTX seems to have these profound effects on bone metabolism, it may be hypothesized that it may enhance spinal fusion.

METHODS

Twenty-four New Zealand white rabbits were randomized and each received single-level posterolateral, inter-transverse process fusion with autologous iliac crest. In group 1, 12 male New Zealand white rabbits were treated with intravenous PTX treatment in 100-mg/kg/day dose after the surgical procedure. In group 2, 12 received no PTX medication and were accepted as the control group. Nine weeks after surgery, the animals were killed. The spines were tested via a manual palpation test, biomechanical testing, plain radiography, computed tomographic scans, and histomorphometric analysis.

RESULTS

The fusion rates of manual palpation were 40% in the control group and 80% in the PTX group (P = 0.17). Using a 5-grade radiographical system, the mean fusion grade was 2.4 in the control group and 3.1 in PTX group (P = 0.012). Total displacement of the fused level for the control group under flexion and extension was 0.2515 mm and was lower for the PTX-treated group: 0.1266 mm (P = 0.012). In the control group, the mean bone volume of the fusion mass determined from computed tomographic analysis was 4.0678 cm, whereas in the PTX group it was 4.7802 cm (P = 0.009). The mean trabecular bone area was 14% and 19% for the control and PTX groups, respectively (P = 0.002).

CONCLUSION

The differences between groups was statistically significant in terms of radiological fusion grading, biomechanical testing, volume of the fusion mass, and percentage of trabecular bone area. These results suggest that PTX may have a beneficial effect on spinal fusion.

LEVEL OF EVIDENCE

2.

Delivery of small molecules for bone regenerative engineering: preclinical studies and potential clinical applications

Stimulation of bone regeneration using growth factors is a promising approach for musculoskeletal regenerative engineering. However, common limitations with protein growth factors, such as high manufacturing costs, protein instability, contamination issues, and unwanted immunogenic responses of the host reduce potential clinical applications. New strategies for bone regeneration that involve inexpensive and stable small molecules can obviate these problems and have a significant impact on the treatment of skeletal injury and diseases. Over the past decade, a large number of small molecules with the potential of regenerating skeletal tissue have been reported in the literature. Here, we review this literature, paying specific attention to the prospects for small molecule-based bone-regenerative engineering. We also review the preclinical study of small molecules associated with bone regeneration.

Statins, bone metabolism and treatment of bone catabolic diseases

The discovery that statins had bone anabolic properties initiated many investigations into their use for treatment of bone catabolic diseases, such as osteoporosis. This paper reviews the molecular basis of statin's role in bone metabolism, and animal and human studies on the impact of systemic statins on osteoporosis-induced bone fracture incidence and healing, and on bone density. Limitations of systemic statins are described along with alternative dosing strategies, including local applications and bone-targeting systemic preparations. The principal findings of this review are: (1) traditional oral dosing with statins results in minimal efficacy in the treatment of osteoporosis; (2) local applications of statins show promise in the treatment of accessible bony defects, such as periodontitis; and (3) systemically administered statins which can target bone or inflammation near bone may be the safest and most effective strategy in the treatment of osseous deficiencies.

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.

The design and use of animal models for translational research in bone tissue engineering and regenerative medicine

This review provides an overview of animal models for the evaluation, comparison, and systematic optimization of tissue engineering and regenerative medicine strategies related to bone tissue. This review includes an overview of major factors that influence the rational design and selection of an animal model. A comparison is provided of the 10 mammalian species that are most commonly used in bone research, and existing guidelines and standards are discussed. This review also identifies gaps in the availability of animal models: (1) the need for assessment of the predictive value of preclinical models for relative clinical efficacy, (2) the need for models that more effectively mimic the wound healing environment and mass transport conditions in the most challenging clinical settings (e.g., bone repair involving large bone and soft tissue defects and sites of prior surgery), and (3) the need for models that allow more effective measurement and detection of cell trafficking events and ultimate cell fate during the processes of bone modeling, remodeling, and regeneration. The ongoing need for both continued innovation and refinement in animal model systems, and the need and value of more effective standardization are reinforced.

In vivo performance of simvastatin-loaded electrospun spiral-wound polycaprolactone scaffolds in reconstruction of cranial bone defects in the rat model

Reconstruction of large bone defects is still a major problem. Tissue-engineering approaches have become a focus in regeneration of bone. In particular, critical-sized defects do not ossify spontaneously. The use of electrospinning is attracting increasing attention in the preparation of tissue-engineering scaffolds. Recently, acellular scaffolds carrying bioactive agents have been used as scaffolds in "in situ" tissue engineering for soft and hard tissue repair. Poly(epsilon-caprolactone) (PCL) with two different molecular weights were synthesized, and the blends of these two were electrospun into nonwoven membranes composed of nanofibers/micropores. To stimulate bone formation, an active drug, "simvastatin" was loaded either after the membranes were formed or during electrospinning. The matrices were then spiral-wound to produce scaffolds with 3D-structures having both macro- and microchannels. Eight-millimeter diameter critical size cranial defects were created in rats. Scaffolds with or without simvastatin were then implanted into these defects. Samples from the implant sites were removed after 1, 3, and 6 months postimplantation. Bone regeneration and tissue response were followed by X-ray microcomputed tomography and histological analysis. These in vivo results exhibited osseous tissue integration within the implant and mineralized bone restoration of the calvarium. Both microCT and histological data clearly demonstrated that the more successful results were observed with the "simvastatin-containing PCL scaffolds," in which simvastatin was incorporated into the PCL scaffolds during electrospinning. For these samples, bone mineralization was quite significant when compared with the other groups.

Posterolateral Spinal Fusion in Rabbits Using a RP-based PLGA/ TCP/Col/BMSCs-OB Biomimetic Grafting Material

Three-dimensional highly porous poly(DL-lactic-co-glycolic acid)/ tricalcium phosphate (PLGA/TCP) scaffolds were fabricated using a rapid prototyping technique (RP). The 3D rhombic lamellar PLGA/TCP carriers (20 mm × 20 mm × 3 mm) subsequently were coated with collagen type I (Col) to produce PLGA/TCP/Col composites. Both the RP-based PLGA/TCP scaffolds and the PLGA/TCP/Col composites were observed by scanning electron microscopy. Forty New Zealand white rabbits were equally randomized into 2 groups (group A and group B) and bilaterally underwent posterolateral intertransverse process arthrodesis at the L4—L5 level using the following graft materials: In group A, PLGA/TCP/Col/BMSCs-OB composites (on the right side, group A1, n = 20) and autogenous iliac bone grafts (on the left side, group A2, n = 20) were used; In group B, PLGA/TCP scaffolds plus fresh autogenous bone marrow (on the right side, group B1, n = 20) and PLGA/TCP scaffolds alone (on the left side, group B2, n = 20) were utilized. In group A1, rabbit bone marrow stromal cells (BMSCs) were isolated and cultured under the osteogenic conditions (BMSCs-OB). Structural PLGA/TCP/Col composites then were efficiently loaded with BMSCs-OB and cultured 5 days to make PLGA/TCP/ Col/BMSCs-OB biomaterials. Rabbits were sacrificed after 12-week follow-up and the spinal fusion were evaluated by a general observation, a manual palpation test, histological analyses and radiography. As a result, RP established PLGA/TCP scaffolds with appropriate biomaterial properties including satisfactory microstructure, inter-connectivity and porosity. Modifications to the structural highly porous PLGA/TCP scaffolds with Col (PLGA/TCP/Col) essentially increased the affinity of the carriers to seeding cells. In group A1, radiological evaluation revealed strong ability of new bone formation and bony fusion in the implanted sites and histological analyses showed highly cellular bone marrow between the newly formed trabecular bone was present in the fusion mass. In group A2, there was a reduced amount of newly formed bone. In group B1, only a few bony fusions were obtained. In group B2, PLGA/TCP scaffolds were biocompatible and biodegradable; whereas, no newly formed bone or bony fusion was found. Twelve weeks after surgery, spinal fusion rates in groups of A1, A2, B1, and B2 were 70.0%(14/20), 45.0%(9/20), 15.8%(3/19), and 0%(0/19), respectively. The rates of fusion were significantly higher in groups of A1 and A2 compared with groups of B1 and B2 (p<0.01), and there was no significant difference of fusion rate between group A1 and group A2 (p>0.05). Therefore, RP-based 3D PLGA/TCP/Col/BMSCs-OB biomaterial holds promise as a bone grafting substitute for spinal fusion. Our attempts may provide a novel method for biofabrication of the bionic construct.

The effect of risedronate on posterior lateral spinal fusion in a rat model

OBJECTIVE

To evaluate the potential effects of risedronate (RIS) which shows a higher anti-resorptive effect among bisphosphonates, after a posterolateral lumbar intertransverse process spinal fusion using both autograft and allograft in a rat model.

METHODS

A totoal of 28 Sprague-Dawley rats were randomized into 2 study groups. A posterolateral lumbar intertransverse process spinal fusion was peformed using both autograft and allograft in a rat model. Group I (control) received 0.1 mL of steril saline (placebo) and Group II (treatment) received risedronate, equivalent to human dose (10 microg/kg/week) for 10-weeks period.

RESULTS

The fusion rates as determined by manual palpation were 69% in the group I and 46% in the group II (p = 0.251). According to radiographic score, the spinal segment was considered to be fused radiographically in 7 (53%) of the 13 controls and 9 (69%) of the 13 rats treated with RIS (p = 0.851). The mean histological scores were 5.69 +/- 0.13 and 3.84 +/- 0.43 for the control and treatment groups, respectively. There was a significant difference between the both groups (p = 0.001). The mean bone density of the fusion masses was 86.9 +/- 2.34 in the control group and 106.0 +/- 3.54 in the RIS treatment group. There was a statistical difference in mean bone densities of the fusion masses comparing the two groups (p = 0.001).

CONCLUSION

In this study, risedronate appears to delay bone fusion in a rat model. This occurs as a result of uncoupling the balanced osteoclastic and osteoblastic activity inherent to bone healing. These findings suggest that a discontinuation of risedronate postoperatively during acute fusion period may be warranted.