Comparison of synthetic bone graft ABM/P-15 and allograft on uninstrumented posterior lumbar spine fusion in sheep

BACKGROUND

Spinal fusion is a commonly used procedure in spinal surgery. To ensure stable fusion, bone graft materials are used. ABM/P-15 (commercial name i-Factor™ Flex) is an available synthetic bone graft material that has CE approval in Europe. This peptide has been shown to improve bone formation when used in devices with fixation or on bone defects. However, the lack of external stability and large graft size make posterolateral lumbar fusion (PLF) a most challenging grafting procedure. This prospective randomized study was designed to evaluate early spinal fusion rates using an anorganic bovine-derived hydroxyapatite matrix (ABM) combined with a synthetic 15 amino acid sequence (P-15)-ABM/P-15 bone graft, and compared with allograft in an uninstrumented PLF model in sheep. The objective of this study was to assess fusion rates when using ABM/P-15 in uninstrumented posterolateral fusion in sheep.

METHODS

Twelve Texas/Gotland mixed breed sheep underwent open PLF at 2 levels L2/L3 and L4/L5 without fixation instruments. The levels were randomized so that sheep received an ABM graft either with or without P15 coating. Sheep were euthanized after 4.5 months and levels were harvested and evaluated with a micro-CT scanner and qualitative histology. Fusion rates were assessed by 2D sections and 3D reconstruction images and fusion was defined as intertransverse bridging.

RESULTS

There was 68% fusion rate in the allograft group and an extensive migration of graft material was noticed with a fusion rate of just 37% in the ABM/P-15 group. Qualitative histology showed positive osteointegration of the material and good correlation to scanning results.

CONCLUSIONS

In this PLF fusion model, ABM/P15 demonstrated the ability to migrate when lacking external stability. Due to this migration, reported fusion rates were significantly lower than in the allograft group. The use of ABM/P15 as i-Factor™ Flex may be limited to devices with fixation and bone defects.

The effect of hyaluronate-carboxymethyl cellulose on bone graft substitute healing in a rat spinal fusion model

OBJECTIVE

The aim of this study was to evaluate the impact of sodium hyaluronate-sodium carboxymethyl cellulose (HA-CMC), an anti-adhesive material for spinal surgery, on bone fusion by applying it to rat spinal models after lumbar posterolateral fusion.

METHODS

Lumbar posterolateral fusion was performed at L4-5 using bone graft substitutes in 30 rats. HA-CMC was injected in 15 rats at a dose of 0.2 cc (HA-CMC group) and a saline solution of 0.2 cc in the other 15 rats (control group). Simple radiographs were taken until postoperative 9 weeks with an interval of one week. At postoperative 4 and 9 weeks, three dimensional computed tomography (3D CT) scanning was performed to observe the process of bone fusion. At 9 weeks, bone fusion was confirmed by gross examination and manual palpation.

RESULTS

There were no statistically significant differences in bone fusion between the two groups. 3D CT scanning did not reveal significant differences between the groups. The gross examination and manual palpation after autopsy performed at 9 weeks confirmed bone union in 93.3% of both groups.

CONCLUSION

The anti-adhesive material used for spinal surgery did not have adverse effects on spinal fusion in rats.

Enhanced bone regenerative properties of calcium phosphate ceramic granules in rabbit posterolateral spinal fusion through a reduction of grain size

Osteoinductivity is a crucial factor to determine the success and efficiency of posterolateral spinal fusion (PLF) by employing calcium phosphate (Ca-P) bioceramics. In this study, three kinds of Ca-P ceramics with microscale to nanoscale gain size (BCP-control, BCP-micro and BCP-nano) were prepared and their physicochemical properties were characterized. BCP-nano had the spherical shape and nanoscale gain size, BCP-micro had the spherical shape and microscale gain size, and BCP-control (BAM®) had the irregular shape and microscale gain size. The obtained BCP-nano with specific nanotopography could well regulate in vitro protein adsorption and osteogenic differentiation of MC3T3 cells. In vivo rabbit PLF procedures further confirmed that nanotopography of BCP-nano might be responsible for the stronger bone regenerative ability comparing with BCP-micro and BCP-control. Collectedly, due to nanocrystal similarity with natural bone apatite, BCP-nano has excellent efficacy in guiding bone regeneration of PLF, and holds great potentials to become an alternative to standard bone grafts for future clinical applications.

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The nanocrystal of porous BCP ceramic spheres is similar to natural bone apatite.

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BCP nanoceramics is conducive to protein adsorption and osteogenic differentiation of MC3T3 cells.

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Osteoindutivity of BCP ceramics is a crucial factor to determine the sucess and efficiency of PLF.

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BCP ceramic spheres with nanotopography hold great potential in clinical PLF applications.

The efficacy of a nanosynthetic bone graft substitute as a bone graft extender in rabbit posterolateral fusion

BACKGROUND CONTEXT

Synthetic bone graft substitutes are commonly used in spinal fusion surgery. Preclinical data in a model of spinal fusion to support their efficacy is an important component in clinical adoption to understand how these materials provide a biological and mechanical role in spinal fusion.

PURPOSE

To evaluate the in vivo response of a nanosynthetic silicated calcium phosphate putty (OstP) combined with autograft compared to autograft alone or a collagen-biphasic calcium phosphate putty (MasP) combined with autograft in a rabbit spinal fusion model.

STUDY DESIGN

Efficacy of a nanosynthetic silicated calcium phosphate putty as an extender to autograft was studied in an experimental animal model of posterolateral spinal fusion at 6, 9, 12 and 26 weeks, compared to a predicate device.

METHODS

Skeletally mature female New Zealand White rabbits (70) underwent single level bilateral posterolateral intertransverse process lumbar fusion, using either autograft alone (AG), a nanosynthetic silicated calcium phosphate putty (OstP) combined with autograft (1:1), or a collagen-biphasic calcium phosphate putty (MasP) combined with autograft (1:1). Iliac crest autograft was harvested for each group, and a total of 2 cc of graft material was implanted in the posterolateral gutters per side. Fusion success was assessed at all time points by manual palpation, radiographic assessment, micro-CT and at 12 weeks only using non-destructive range of motion testing. Tissue response, bone formation and graft resorption were assessed by decalcified paraffin histology and by histomorphometry of PMMA embedded sections.

RESULTS

Assessment of fusion by manual palpation at the 12 week endpoint showed 7 out of 8 (87.5%) bilateral fusions in the OstP extender group, 4 out of 8 (50%) fusions in the MasP extender group, and 6 out of 8 (75%) fusions in the autograft alone group. Similar trends were observed with fusion scores of radiographic and micro-CT data. Histology showed a normal healing response in all groups, and increased bone formation in the OstP extender group at all timepoints compared to the MasP extender group. New bone formed directly on the OstP granule surface within the fusion mass while this was not a feature of the Collagen-Biphasic CaP material. After 26 weeks the OstP extender group exhibited 100% fusions (5 out of 5) by all measures, whereas the MasP extender group resulted in bilateral fusions in 3 out of 5 (60%), assessed by manual palpation, and fusion of only 20 and 0% by radiograph and micro-CT scoring, respectively. Histology at 26 weeks showed consistent bridging of bone between the transverse processes in the Ost P extender group, but this was not observed in the MasP extender group.

CONCLUSIONS

The nanosynthetic bone graft substituted studied here, used as an extender to autograft, showed a progression to fusion between 6 and 12 weeks that was similar to that observed with autograft alone, and showed excellent fusion outcomes, bone formation and graft resorption at 26 weeks.

CLINICAL SIGNIFICANCE

This preclinical study showed that the novel nanosynthetic silicated CaP putty, when combined with autograft, achieved equivalent fusion outcomes to autograft. The development of synthetic bone grafts that demonstrate efficacy in such models can eliminate the need for excessive autograft harvest and results from this preclinical study supports their effective use in spinal fusion surgery.

Long-term (> 10 years) clinical outcomes of instrumented posterolateral fusion for spondylolisthesis

PURPOSE

Despite the rapid increase in instrumented spinal fusions for a variety of indications, most studies focus on short-term fusion rates. Long-term clinical outcomes are still scarce and inconclusive. This study investigated clinical outcomes > 10 years after single-level instrumented posterolateral spinal fusion for lumbar degenerative or isthmic spondylolisthesis with neurological symptoms.

METHODS

Cross-sectional long-term follow-up among the Dutch participants of an international multicenter randomized controlled trial comparing osteogenic protein-1 with autograft. Clinical outcomes were assessed using the Oswestry Disability Index (ODI), EQ-5D-3L and visual analogue scale (VAS) for leg and back pain, as well as questions on satisfaction with treatment and additional surgery.

RESULTS

The follow-up rate was 73% (41 patients). At mean 11.8 (range 10.1-13.7) years after surgery, a non-significant deterioration of clinical outcomes compared to 1-year follow-up was observed. The mean ODI was 20 ± 19, mean EQ-5D-3L index score 0.784 ± 0.251 and mean VAS for leg and back pain, respectively, 34 ± 33 and 31 ± 28. Multiple regression showed that diagnosis (degenerative vs. isthmic spondylolisthesis), graft type (OP-1 vs. autograft) and 1-year fusion status (fusion vs. no fusion) were not predictive for the ODI at long-term follow-up (p = 0.389). Satisfaction with treatment was excellent and over 70% of the patients reported lasting improvement in back and/or leg pain. No revision surgeries for non-union were reported.

CONCLUSION

This study showed favourable clinical outcomes > 10 years after instrumented posterolateral spinal fusion and supports spondylolisthesis with neurological symptoms as indication for fusion surgery.

Ketogenic diet delays spinal fusion and decreases bone mass in posterolateral lumbar spinal fusion: an in vivo rat model

BACKGROUND

Ketogenic diet (KD), a low-carbohydrate-and-high-fat diet, causes a metabolic state of ketogenesis and has been used to treat drug-resistance epilepsy. Our recent studies showed KD neuroprotective after spinal cord injury and causing bone loss. Effects of KD on spinal fusion were still unknown. This study was aimed to evaluate effects of KD on spinal fusion in rats.

METHODS

Thirty-two Sprague-Dawley rats were randomly divided into KD and standard diet (SD) groups. The KD group was fed with food of 1:4 carbohydrates to fat. All rats were subjected to L4/5 posterolateral lumbar spinal fusion. The blood ketone, and serum calcium, phosphorus, and insulin-like growth factor-1 (IGF-1) were measured, as well as the fusion rates, bone mass (BV), and bone mineral contents (BMC) of fusion sites were estimated at 4 and 8 weeks.

RESULTS

There was no significant difference in serum calcium or phosphorus levels between groups at 4 or 8 weeks. However, there was a significant increase of blood ketone (1.02 mmol/L vs 0.38 mmol/L at 4 weeks; 0.83 mmol/L vs 0.32 mmol/L, at 8 weeks) and decrease of serum IGF-1 (339.4 ng/mL vs 630.6 ng/mL at 4 weeks; 418.8 ng/mL vs 628.6 ng/mL, at 8 weeks) in the KD group compared with the SD group. The spinal fusion occurred less in the KD group (1/16 vs 6/16 at 4 weeks; 7/16 vs 10/16, at 8 weeks), particularly at 4 weeks after surgery. The BV and BMC were lower in the KD group than that in the SD group at 4 weeks, but not different between groups at 8 weeks.

CONCLUSIONS

This study demonstrated that KD delayed spinal fusion and decreased bone mass in posterolateral lumbar spinal fusion in rats.

Spinal fusion of biodegradable poly(propylene fumarate) and poly(propylene fumarate-co-caprolactone) copolymers in rabbits

Background

Autologous bone grafts are currently the standard in orthopedic surgery despite limited donor sources and the prevalence of donor site morbidity. Other alternatives such as allografts are more readily available than autografts but have lower rates of graft incorporation.

Methods

Here, we propose a novel graft alternative consisting of an injectable poly(propylene fumarate) (PPF) and poly(propylene fumarate-co-caprolactone) P(PF-co-CL) copolymer with a recombinant human bone morphogenetic protein-2 (rhBMP-2)/vascular epithelial growth factor (VEGF) release system accompanied by hydroxyapatite (HA). The efficacy of scaffold formulations was studied using a standard, bilateral, L-level (L5-L6) posterolateral transverse spinal fusion using New Zealand white rabbits. Rabbits were divided into 4 experimental groups: group I, negative control; group II, autograft (positive control); group III, injectable PPF scaffold with rhBMP-2/VEGF release system and HA; group IV, injectable P(PF-co-CL)scaffold with rhBMP-2/VEGF release system and HA. Spines were harvested at 6 weeks and 12 weeks after surgery, and spinal fusions were assessed using manual palpation, radiographic analysis, micro-computed tomography (μCT) assessment, and histologic analysis.

Results

Of the 4 experimental groups, the injectable P(PF-co-CL) scaffold displayed superior initial strength and faster degradation than scaffolds constructed from PPF alone and facilitated the fusion of lateral processes in the rabbit standard posterolateral spinal fusion model. The results obtained from manual palpation, radiology, and μCT showed no difference between the P(PF-co-CL) group and the PPF group. However, histologic sections showed more osteogenesis with the new injectable P(PF-co-CL) scaffold.

Conclusion

Injectable P(PF-co-CL) polymers showed promising spine fusion abilities in rabbits after 12 weeks of posterolateral implantation.