The effects of dexamethasone on bone fusion in an experimental model of posterolateral lumbar spinal arthrodesis

General Considerations About Foot and Ankle Arthrodesis. Any Way to Improve Our Results?

Nonunion and adjacent joint osteoarthritis (OA) are known complications after a fusion procedure, and foot and ankle surgeons are commonly exposed to such disabling complications. Determining who is at risk of developing nonunion is essential to reducing nonunion rates and improving patient outcomes. Several evidenced-based modifiable risk factors related to adverse outcomes after foot and ankle arthrodesis have been identified. Patient-related risk factors that can be improved before surgery include smoking cessation, good diabetic control (HbAc1 <7%) and vitamin D supplementation. Intraoperatively, using less invasive techniques, avoiding joint preparation with power tools, using bone grafts or orthobiologics in more complex cases, high-risk patients, nonunion revision surgeries, and filling in bone voids at the arthrodesis site should be considered. Postoperatively, pain management with NSAIDs should be limited to a short period (<2 weeks) and avoided in high-risk patients. Furthermore, early postoperative weight-bearing has shown to be beneficial, and it does not seem to increase postoperative complications. The incidence of surrounding joint OA after foot and ankle fusion seems to increase progressively with time. Owing to its progression and high probability of being symptomatic, patients must be informed consequently, as they may require additional joint fusions, resulting in further loss of ankle/foot motion. In patients with symptomatic adjacent joint OA and unsatisfactory results after an ankle arthrodesis, conversion to total ankle arthroplasty (TAA) has become a potential option in managing these complex and challenging situations.

The effect of local steroid application on bony fusion in a rat posterolateral spinal arthrodesis model

INTRODUCTION

Local steroid administration during anterior cervical spine surgery has been shown to improve postoperative dysphagia. However, concerns over potential complications remain. This study aims to evaluate the effect of local steroid administration on bone regeneration and spine fusion in a preclinical model, as well as the impact on osteogenic differentiation of human bone marrow-derived mesenchymal stem cells (hBM-MSCs) in a 3D culture system.

MATERIALS AND METHODS

Forty-five rats underwent bilateral L4-L5 posterolateral lumbar fusion (PLF) utilizing local delivery of low-dose recombinant human bone morphogenetic protein-2 (rhBMP-2; 0.5 μg/implant). Rats were divided into three groups: no steroid (control), low dose (0.5 mg/kg), and high dose (2.5 mg/kg) of triamcinolone. Bone growth and fusion were assessed using radiography, blinded manual palpation, and micro-CT analysis and were visualized by histology. The impact of triamcinolone exposure on osteogenic differentiation of hBM-MSCs was evaluated by gene expression analysis, alkaline phosphatase activity assay, and alizarin red staining.

RESULTS

No significant differences in fusion scores or rates were seen in the low- or high-dose steroid treatment groups relative to untreated controls. Quantification of new bone formation via micro-CT imaging revealed no significant between-group differences in the volume of newly regenerated bone. Triamcinolone also had no negative impact on pro-osteogenic gene transcript levels, and ALP activity was enhanced in the presence of triamcinolone. Mineral deposition appeared comparable in cultures grown with and without triamcinolone.

CONCLUSIONS

Local steroid application does not seem to inhibit rhBMP-2-mediated spine fusion in rats, though our study may not be adequately powered to detect differences in fusion as measured by manual palpation or bone volume as measured by micro-CT. These findings suggest that local triamcinolone may not increase pseudarthrosis in spine fusion procedures. Further large animal and clinical studies to verify its safety and efficacy are warranted.

Factors important in bone union after posterior lumbar interbody fusion using the cortical bone trajectory technique

Background

The cortical bone trajectory (CBT) technique has developed as an alternative to the traditional pedicle screw fixation technique due to its minimum invasiveness for screw insertion and rigid fixation for posterior lumbar interbody fusion (PLIF). However, the factors contributing to bone union after CBT-PLIF is a controversial subject. The aim of this study was to investigate factors important to bone union after CBT-PLIF.

Methods

We analyzed 69 consecutive patients who underwent single-level CBT-PLIF from October 2011 to December 2016 and were followed for over two years. Bone union was evaluated using computed tomography (CT) and dynamic assessment in the radiograph within two years after CBT-PLIF. The following factors that may influence bone union were investigated: age, gender, bone mineral density (BMD), cage materials [polyether-ether-ketone (PEEK) or titanium (Ti)], vertebral-slip (neutral), translational motion (flexion/extension), angular motion (flexion/extension), screw depth into the vertebral body (% depth), interval of bilateral screw heads, and cage position.

Results

The bone union rate at the two-year follow-up was 88.4% (61/69). A univariate analysis revealed that variables with values of P<0.20 were age (P<0.01), gender (P=0.07), cage material (P=0.18), vertebral slip (neutral) (P=0.14), % depth (P=0.086), and cage position (P<0.01). Multiple logistic regression analyses revealed that factors related to bone union were young age (P<0.01), Ti cage (P<0.01), small vertebral slip (neutral) (P<0.01), high % depth (P<0.01), and anterior cage position (P<0.01).

Conclusions

For CBT-PLIF, deeper screw insertion into the vertebral body, anterior cage placement, and Ti cage usage may be important surgical techniques to achieve a successful bone union.

Effect of bisphosphonates or teriparatide on mechanical complications after posterior instrumented fusion for osteoporotic vertebral fracture: a multi-center retrospective study

Background

The optimal treatment of osteoporosis after reconstruction surgery for osteoporotic vertebral fractures (OVF) remains unclear. In this multicentre retrospective study, we investigated the effects of typically used agents for osteoporosis, namely, bisphosphonates (BP) and teriparatide (TP), on surgical results in patients with osteoporotic vertebral fractures.

Methods

Retrospectively registered data were collected from 27 universities and affiliated hospitals in Japan. We compared the effects of BP vs TP on postoperative mechanical complication rates, implant-related reoperation rates, and clinical outcomes in patients who underwent posterior instrumented fusion for OVF. Data were analysed according to whether the osteoporosis was primary or glucocorticoid-induced.

Results

A total of 159 patients who underwent posterior instrumented fusion for OVF were included. The overall mechanical complication rate was significantly lower in the TP group than in the BP group (BP vs TP: 73.1% vs 58.2%, p = 0.045). The screw backout rate was significantly lower and the rates of new vertebral fractures and pseudoarthrosis tended to be lower in the TP group than in the BP group. However, there were no significant differences in lumbar functional scores and visual analogue scale pain scores or in implant-related reoperation rates between the two groups. The incidence of pseudoarthrosis was significantly higher in patients with glucocorticoid-induced osteoporosis (GIOP) than in those with primary osteoporosis; however, the pseudoarthrosis rate was reduced by using TP. The use of TP also tended to reduce the overall mechanical complication rate in both primary osteoporosis and GIOP.

Conclusions

The overall mechanical complication rate was lower in patients who received TP than in those who received a BP postoperatively, regardless of type of osteoporosis. The incidence of pseudoarthrosis was significantly higher in patients with GIOP, but the use of TP reduced the rate of pseudoarthrosis in GIOP patients. The use of TP was effective to reduce postoperative complications for OVF patients treated with posterior fusion.

Risk Factors for Pseudarthrosis in Minimally-Invasive Transforaminal Lumbar Interbody Fusion

Study Design

Retrospective cohort study (level of evidence: 4).

Purpose

To describe the potential comorbid, operative, and radiographic risk factors for the development of clinically-relevant pseudarthrosis following minimally-invasive transforaminal lumbar interbody fusion (MIS-TLIF).

Overview of Literature

MIS-TLIF has shown long-term clinical outcomes with decreased perioperative morbidity and earlier return to work, similar to those of open TLIF. However, unsuccessful fusion still remains a concern. The impacts of various patient, operative, and radiographic risk factors have not been evaluated for their potential association with pseudarthrosis related to MIS-TLIF.

Methods

Between 2012 and 2015, 204 consecutive patients underwent one or two-level MIS-TLIF at St. Joseph's University Medical Center, Paterson, NJ, USA; they had a minimum of 1 year of follow-up. The patients were divided into two cohorts: those who developed clinically-relevant pseudarthrosis and those who did not. Clinically-relevant pseudarthrosis was determined by both evidence on computed tomography and presence of continued clinical symptoms at 1-year follow-up.

Results

Revision surgery was the only identified non-radiographic factor associated with pseudarthrosis. Disc angle had the highest (R²=0.8), followed by anterior disc height (R²=0.79). Although posterior disc height and the ratio of anterior to posterior disc height showed a marked relationship with the outcome, the R²-values were <0.3, thus indicating a less-strong correlation. The overall pseudarthrosis rate was 8%. No statistically significant differences were identified between the two cohorts with respect to mean age, sex, medical comorbidities, smoking status, or number of levels fused.

Conclusions

Clinically-relevant pseudarthrosis is not uncommon following MIS-TLIF. In the current study, undergoing revision surgery, disc angle, and anterior disc height were observed to be associated with clinically-relevant pseudarthrosis. This study demonstrated that the patient population may benefit from an alternate approach.

Glucocorticoid-induced delayed fracture healing and impaired bone biomechanical properties in mice

Background

The objective of the study was to investigate the effects of glucocorticoid (GC) on the fracture healing process in a closed femur fracture mice model.

Materials and methods

Forty 12-week-old female CD-1 mice were randomly allocated into four groups: healthy control and mice with prednisone exposure (oral gavage), 6 mg/kg/day (GC-L), 9 mg/kg/day (GC-M) and 12 mg/kg/day (GC-H). Three weeks after the initiation of prednisone dosing, closed femur fractures were created on prednisone-exposed mice and the healthy control. Prednisone administration was continued for 9 weeks post-fracture, and X-ray imaging was performed weekly to monitor the fracture healing process until the mice were euthanized. Necropsy was performed after 9 weeks and the fractured femurs were isolated and processed at necropsy for micro-CT and biomechanical property analysis. Another 20 mice (control and GC-H, 10 mice/group) were used for histology and micro-CT analysis at early time point (2-week post fracture) with continued prednisone exposure.

Results

The results showed that oral administration of prednisone for 3 months in this strain of mice could inhibit endochondral ossification and delay the healing process, especially hard callus formation (woven bone) and bone remodeling during healing. It also could significantly decrease bone biomechanical properties.

Conclusion

Long-term GC administration leads to significantly delayed fracture healing and impaired bone biomechanical properties. This mouse model may be used to systematically study the cellular and molecular mechanisms underlying fracture healing with GC treatment background and may also be used to study the influence of different therapeutic interventions for bone fracture healing.

Limited post-operative dexamethasone use does not affect lumbar fusion: a single institutional experience

Background

The use of exogenous dexamethasone during and after lumbar spine surgery remains controversial. The preponderance of studies on this topic is primarily from animal models and little is known about the effects of exogenous dexamethasone use on fusion outcomes in human subjects undergoing lumbar arthrodesis. The aim of this study is to investigate the effect of limited exogenous dexamethasone use on bone fusion after instrumented lumbar arthrodesis.

Methods

Consecutive adult patients (18 years and older) undergoing one and two level lumbar decompression and fusion between January 2013 and December 2014 were reviewed. Patients were dichotomized into one of two groups (A & B) based on whether they received dexamethasone-Group (A) dexamethasone; and Group (B) no dexamethasone. Baseline characteristics, operative details, length of hospital stay, rates of wound infection, and fusion rates at 1 year were gathered by direct medical record review. All patients enrolled in this study were followed for a minimum of 12 months after surgery.

Results

One hundred sixty-five consecutive patients undergoing 1- and 2-level fusions were included in the study. Fifty eight patients received dexamethasone and 107 patients did not. The mean ± SD age was similar between both cohorts ("dexamethasone": 58.12±16.25 years vs. "no dexamethasone": 61.00±12.95, P=0.24). The was no difference in the prevalence of smoking (P=0.72) between both cohorts. Length of in-hospital stay was similar between cohorts ("dexamethasone": 4.08±3.44 days vs. "no dexamethasone": 4.50±2.85 days, P=0.43). The incidence of post-operative infections was similar between cohorts. At 12 months after surgery, 70% of patients in the dexamethasone cohort had radiographic evidence of bony fusion compared to 73% of patients in the no-dexamethasone cohort (P=0.68).

Conclusions

Our study suggests that a limited exposure to exogenous dexamethasone after lumbar spine fusion may not be associated with a lower fusion rate. Prospective randomized control trials are needed to corroborate our findings.

Instrumented Spinal Stabilization without Fusion for Spinal Metastatic Disease

OBJECTIVES

Spinal stabilization surgery is an integral part of the treatment of spinal metastatic disease. Bony fusion is the hallmark of spinal stabilization in non-oncology patients. Spinal oncology patients are unlikely to achieve bony fusion because of their overall prognosis and concurrent therapies. Stabilization surgery without fusion may be a reasonable approach for these patients. Literature evaluating the effectiveness of this approach is limited. The object of this study was to investigate the rate of instrumentation failure in patients undergoing posterior spinal instrumented stabilization without fusion for spinal metastatic disease.

METHODS

Data from consecutive cases of spinal surgery at our institution during an 81-month period were reviewed. Demographics, clinical notes, and computed tomography findings were recorded and used to evaluate instrumentation failures. Patients who underwent separation surgery that included laminectomy and posterior spinal instrumentation without fusion for spinal metastatic disease and had follow-up computed tomography scans >3 months postoperatively were selected for the study.

RESULTS

Twenty-seven patients were included in the study. Mean age was 64.85 ± 6.53 years. Nine patients were women. A mean of 1.61 ± 0.96 laminectomy levels was performed. A mean of 8.26 ± 1.48 screws was inserted. The mean postoperative discharge date was 5.07 ± 1.47 days. Mean follow-up duration was 12.17 ± 11.73 months. None of the patients had a change in instrumentation position, pedicle screw pullout, change in spinal alignment, or progressive deformity. No patient required reoperation or instrumentation revision or replacement.

CONCLUSIONS

Our experience suggests that instrumented spinal stabilization without fusion is an acceptable approach for patients with spinal metastatic disease.

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.

Vascular endothelial growth factor: an essential component of angiogenesis and fracture healing

Fractures require adequate stability and blood supply to heal. The vascular supply to long bones is compromised in a fracture, and the ability to heal hinges on the ability of new blood vessels to proliferate from surrounding vessels in a process known as angiogenesis. This process is largely driven by the growth factor, vascular endothelial growth factor (VEGF), whose levels are increased locally and systemically during fracture healing. VEGF is involved in many steps throughout the fracture healing cascade, from initially being concentrated in fracture hematoma, to the promotion of bone turnover during the final remodeling phase. This article reviews the current literature surrounding the role of VEGF and other growth factors in reestablishing vascular supply to fractured bone, as well as medications and surgical techniques that may inhibit this process.

The effects of the short-term administration of low therapeutic doses of anti-COX-2 agents on the healing of fractures

We have evaluated the effect of the short-term administration of low therapeutic doses of modern COX-2 inhibitors on the healing of fractures.

A total of 40 adult male New Zealand rabbits were divided into five groups. A mid-diaphyseal osteotomy of the right ulna was performed and either normal saline, prednisolone, indometacin, meloxicam or rofecoxib was administered for five days. Radiological, biomechanical and histomorphometric evaluation was performed at six weeks.

In the group in which the highly selective anti-COX-2 agent, rofecoxib, was used the incidence of radiologically-incomplete union was similar to that in the control group. All the biomechanical parameters were statistically significantly lower in both the prednisolone and indometacin (p = 0.01) and in the meloxicam (p = 0.04) groups compared with the control group. Only the fracture load values were found to be statistically significantly lower (p = 0.05) in the rofecoxib group. Histomorphometric parameters were adversely affected in all groups with the specimens of the rofecoxib group showing the least negative effect.

Our findings indicated that the short-term administration of low therapeutic doses of a highly selective COX-2 inhibitor had a minor negative effect on bone healing.

Bone morphogenetic protein gene therapy using a fibrin scaffold for a rabbit spinal-fusion experiment

OBJECTIVE

To observe the feasibility of using fibrin gel as a scaffold during rabbit spinal fusion with rat kidney cells carrying bone morphogenetic protein-2 (BMP-2) expression vector.

METHODS

Normal Rattusnorvegicus (rat) kidney (NRK) cells were transfected with pCMV-BMP2 vectors by using a nonviral reagent (FuGENE6), following which the transfected cells (1.5 x 10(7)) were encapsulated and evenly suspended in a fibrin scaffold, and implanted to either side of the L5-L6 intertransverse space for six test rabbits. For the control group (six rabbits), the transfected cells (1.5 x 10(7)) were added on and absorbed in a surgical gelatin sponge, and implanted in an analogous location. Radiographs of the spine of all animals were taken at six, ten, and 12 weeks subsequent to fusion surgery. Gross and histological examination of the fusion masses for all the animals were performed subsequent to animals having been sacrificed at 12 weeks.

RESULTS

Expression of BMP-2 was verified in the pCMV-BMP2 transfected NRK cells which were used for the subsequent rabbit experiment. For all 12 rabbits, no evidence of implanted-tissue rejection was seen during the postoperative course. Neither residual scaffold nor inflammatory granulation tissue was seen in the harvested spinal segments. For the six study-group rabbits, radiographic examinations revealed that four individuals (67%) featured prominent new-bone formation (good fusion), and two (33%) revealed moderate new-bone formation (fair fusion) at the implanted sites, whereas all six control-group rabbits revealed no evidence of new-bone formation (nonfusion) at the implanted sites. For the histological examinations, all animals in the study group revealed the presence of osseous tissue at the sites corresponding to the sites of radiographically demonstrated new-bone formation, whereas for the control group, no osseous tissue was seen at the implanted sites for any animal

CONCLUSION

Fibrin gel, being a biocompatible and biodegradable matrix, can encapsulate pCMV-BMP2 transfected NRK cells and adhere to the intertransverse lumbar-spine spaces of test rabbits. With the above characteristics, it plays an important role in the successful delivery of pCMV-BMP2-transfected cells for this rabbit spinal-fusion experiment. Being a natural matrix and able to be obtained readily from patients' own blood, fibrin gel seems to be a promising scaffold for future gene therapy in human trials.

Revision Deformity Surgery

Revision deformity surgery may be necessary for several reasons. Symptomatic pseudarthrosis, implant failure or pull-out, or loss of correction may mandate reoperation. The keys to a successful revision procedure are a careful analysis of the problem, particularly the mode of failure and the contributing biomechanical factors, and the development of an appropriate surgical plan.

Bone healing and spinal fusion

Bone is a tissue that constantly undergoes deposition, resorption of stromal matrix, and remodeling. These processes may be altered by a variety of chemical, mechanical, cellular, and pathological mechanisms. Understanding the physiology of bone healing and the mechanisms affecting this process is important not only when evaluating normal skeletal development but also when initiating fracture repair. Because the ultimate success of spinal fusions involves creation of an osseous union, we focus this review on the anatomy and physiology of bone under physiological conditions, normal bone healing and mechanisms that alter it, and available adjuvant therapies that may enhance healing potential in a clinical setting.