Alendronate treatment improves bone-pedicle screw interface fixation in posterior lateral spine fusion: an experimental study in a porcine model

Midterm Outcomes of Multimodal Approach to Treating Severe Scoliosis in Patients With Osteogenesis Imperfecta

INTRODUCTION

The surgical management of severe scoliosis in patients with osteogenesis imperfecta (OI) is challenging because of curve rigidity, small stature, and inherent bone fragility. This study evaluated the midterm outcomes of our multimodal approach to address these issues, integrating perioperative bisphosphonate therapy, preoperative/intraoperative traction, various osteotomies, segmental pedicle screw instrumentation with cement augmentation, and bone morphogenetic protein-2 application.

METHODS

A single-center retrospective review of 30 patients (average age 14.1 ± 2.2 years; 18 were female) diagnosed with OI and scoliosis was conducted. These patients underwent posterior spinal fusion between 2008 and 2020 and completed a minimum follow-up of 2 years. We measured radiographic parameters at each visit and reviewed the incidence of complications. A mixed-effects model was used to evaluate changes in radiographic parameters from preoperative measurements to the first and latest follow-ups.

RESULTS

The patient cohort consisted of 2 individuals with type I OI, 20 with type III, 6 with type IV, and 2 with other types (types V and VIII). Surgical intervention led to a notable improvement in the major curve magnitude from 76° to 36°, with no notable correction loss. In addition, the minor curve, apical vertical translation, lowest instrumented vertebra tilt, and pelvic obliquity were also improved. In the sagittal plane, thoracic kyphosis and lumbar lordosis remained unchanged while thoracolumbar kyphosis markedly improved. Two patients experienced proximal junctional kyphosis with screw pullout, one of whom required revision surgery. One patient developed a superficial infection that was successfully treated with oral antibiotics. No instances of neurologic deficits or cement extravasation were observed.

DISCUSSION

This study demonstrated the effectiveness and safety of our multimodal approach to treating scoliosis in patients with OI, achieving a 53% major curve correction with minimal complications over 2-year follow-up. These findings provide notable insights into managing scoliosis in this population.

LEVEL OF EVIDENCE

Level IV (case series).

Osteoporosis treatment in patients undergoing spinal fusion: a systematic review and meta-analysis

OBJECTIVE

Bisphosphonates and teriparatide are the most common therapies used in the treatment of osteoporosis. Their impact on fusion rates in osteoporotic patients following spinal fusion has yet to be concretely defined, with previous systematic reviews focusing heavily on bisphosphonates and lacking clinical insight on the utility of teriparatide. Herein the authors present an updated meta-analysis of the utility of both bisphosphonates and teriparatide in improving spinal fusion outcomes in osteoporotic patients.

METHODS

After a comprehensive search of the English-language literature in the PubMed and Embase databases, 11 clinical studies were included in the final qualitative and quantitative analyses. Of these studies, 9 investigated bisphosphonates, 7 investigated teriparatide, and 1 investigated a combination of teriparatide and denosumab. Odds ratios and 95% confidence intervals were calculated where appropriate.

RESULTS

A meta-analysis of the postoperative use of bisphosphonate demonstrated better odds of successful fusion as compared to that in controls during short-term monitoring (OR 3.33, 95% CI 1.72-6.42, p = 0.0003) but not long-term monitoring (p > 0.05). Bisphosphonate use was also shown to significantly reduce the likelihood of postoperative vertebral compression fracture (VCF; OR 0.07, 95% CI 0.01-0.59, p = 0.01) and significantly reduce Oswestry Disability Index scores (mean difference [MD] = -2.19, 95% CI -2.94 to -1.44, p < 0.00001) and visual analog scale pain scores (MD = -0.58, 95% CI -0.79 to -0.38, p < 0.00001). Teriparatide was found to significantly increase fusion rates at long-term postoperative periods as compared to rates after bisphosphonate therapy, with patients who received postoperative teriparatide therapy 2.05 times more likely to experience successful fusion (OR 2.05, 95% CI 1.17-3.59, p = 0.01).

CONCLUSIONS

The authors demonstrate the benefits of bisphosphonate and teriparatide therapy independently in accelerating fusion during the first 6 months after spinal fusion surgery in osteoporotic patients. In addition, they show that teriparatide may have superior benefits in spinal fusion during long-term monitoring as compared to those with bisphosphonates. Bisphosphonates may be better suited in preventing VCFs postoperatively in addition to minimizing postoperative disability and pain.

Postoperative bisphosphonate do not significantly alter the fusion rate after lumbar spinal fusion: a meta-analysis

Background

To evaluate the effect of postoperative BP treatment on improving the fusion rate after lumbar spinal fusion surgery by performing a meta-analysis of randomized controlled trials (RCTs) and other comparative cohort studies.

Methods

A comprehensive search of PubMed, EMBASE, the Web of Science, and the Cochrane Central Register of Controlled Trials was performed for RCTs and other comparative cohort studies on the effect of BP treatment on improving the fusion rate after lumbar spinal fusion surgery. The primary outcome measures were the number of patients with bone formation grades A, B, and C at 12 months of follow-up; fusion rates at 12 and 24 months of follow-up; vertebral compression fracture (VCF) at 12 and 24 months of follow-up; pedicle screw loosening at 24 months of follow-up; and cage subsidence, the Oswestry disability index (ODI), and the visual analogue score (VAS) at 12 months of follow-up. The final search was performed in July 2020.

Results

Seven studies with 401 patients were included. Compared with the placebo, BP treatment did not significantly alter the number of patients with bone formation grades A, B, and C, or the VAS at the 12-month follow-up or the fusion rates at the 12- and 24-month follow-ups. In addition, compared with the placebo, BPs significantly reduced the risks of VCF at the 12- and 24-month follow-ups, pedicle screw loosening at the 24-month follow-up, and cage subsidence and the ODI at the 12-month follow-up.

Conclusions

Postoperative BPs do not clearly improve bone formation and the fusion rate, but they reduce VCF, cage subsidence, and loosening of pedicle screws after lumbar fusion surgery compared with the control treatment.

Osseointegration Pharmacology: A Systematic Mapping Using Artificial Intelligence

Clinical performance of osseointegrated implants could be compromised by the medications taken by patients. The effect of a specific medication on osseointegration can be easily investigated using traditional systematic reviews. However, assessment of all known medications requires the use of evidence mapping methods. These methods allow assessment of complex questions, but they are very resource intensive when done manually. The objective of this study was to develop a machine learning algorithm to automatically map the literature assessing the effect of medications on osseointegration. Datasets of articles classified manually were used to train a machine-learning algorithm based on Support Vector Machines. The algorithm was then validated and used to screen 599,604 articles identified with an extremely sensitive search strategy. The algorithm included 281 relevant articles that described the effect of 31 different drugs on osseointegration. This approach achieved an accuracy of 95%, and compared to manual screening, it reduced the workload by 93%. The systematic mapping revealed that the treatment outcomes of osseointegrated medical devices could be influenced by drugs affecting homeostasis, inflammation, cell proliferation and bone remodeling. The effect of all known medications on the performance of osseointegrated medical devices can be assessed using evidence mappings executed with highly accurate machine learning algorithms.

Teriparatide and bisphosphonate use in osteoporotic spinal fusion patients: a systematic review and meta-analysis

PURPOSE

Osteoporosis is one of the most common conditions among adults worldwide. It also presents a challenge among patients undergoing spinal surgery. Use of Teriparatide and bisphosphonates in such patients has been shown to improve outcomes after fusion surgery, including successful fusion, decreased risk of instrumentation failure, and patient-reported outcomes. Herein, we performed a systematic review and indirect meta-analysis of available literature on outcomes of fusion surgery after use of bisphosphonates or Teriparatide.

METHODS

We conducted a comprehensive search of all databases (Ovid MEDLINE(R) and Epub Ahead of Print, In-Process & Other Non-Indexed Citations, Ovid Embase, Ovid Cochrane Central Register of Controlled Trials, Ovid Cochrane Database of Systematic Reviews, and Scopus) to identify studies assessing outcomes of spinal fusion among osteoporotic patients after use of Teriparatide or bisphosphonate. Four authors independently screened electronic search results, and all four authors independently performed study selection. Two authors performed independent data extraction and assessed the studies' risk of bias assessment using standardized forms of Revised Cochrane risk-of-bias tool for randomized trials (RoB 2) and Risk Of Bias In Non-randomized Studies of Interventions (ROBINS-I).

RESULTS

Nineteen studies were included in the final analysis. A total of 13 studies evaluated the difference in fusion rate between bisphosphonates and Teriparatide or control group. Fusion rate was higher for bisphosphonates (effect size (ES) 83%, 95% CI 77-89%) compared with Teriparatide (ES 71%, 95% CI 57-85%), with the p value for heterogeneity between groups without statistical significance (p = 0.123). Five studies assessed the impact of using bisphosphonate or Teriparatide on screw loosening. The rate of screw loosening was higher for bisphosphonates (ES 19%, 95% CI 13-25%) compared with Teriparatide (ES 13%, 95% CI 9-16%) without statistical significance (p = 0.52).

CONCLUSION

Our results indicate that while both agents may be associated with positive outcomes, bisphosphonates may be associated with a higher fusion rate, while Teriparatide may be associated with lower screw loosening. The decision to treat with either agent should be tailored individually for each patient keeping in consideration the adverse effect and pharmacokinetic profiles.

Adjuvant drug-assisted bone healing: Part III - Further strategies for local and systemic modulation

In this third in a series of reviews on adjuvant drug-assisted bone healing, further approaches aiming at influencing the healing process are discussed. Local and systemic modulation of bone metabolism is pursued with use of a number of drugs with completely different indications, which are characterized by a pleiotropic spectrum of action. These include drugs used to treat lipid disorders (HMG-CoA reductase inhibitors), hypertension (ACE inhibitors), osteoporosis (bisphosphonates), cancer (proteasome inhibitors) and others. Potential applications to enhance bone healing are discussed.

Clinical effect observation of intravenous application of zoledronic acid in patients with cervical spondylosis and osteoporosis after anterior cervical discectomy and fusion: A randomized controlled study

OBJECTIVE

To observe the clinical effect of zoledronic acid (ZA) in patients with cervical spondylosis and osteoporosis after anterior cervical discectomy and fusion (ACDF) surgery.

METHODS

All selected patients were divided into the study group and the control group according to the sequence of surgery time. In the study group, 5 mg (100 ml) of ZA was applied intravenously as intervention on the 5 day after ACDF surgery. Patients were followed up regularly after surgery.

RESULTS

Forty-three cases completed the follow-ups (21/22), the neck disability index (NDI) score significantly decreased at the 3rd month after surgery in both groups, it came to a plateau at the 6th month after surgery, and it had some rise at the 12th month after surgery, but the NDI score was lower in the study group at the 12th month after surgery ( p < 0.05). C-telopeptide of type I collagen (CTX) and amino terminal propeptide of type I procollagen of bone turnover markers in the study group showed a downward trend after surgery, among which CTX decreased significantly and no significant changes in the control group. At the 12th month after surgery, the bone mineral density of lumbar spine area in the study group was significantly improved ( p < 0.05). During the 3rd and the 6th month follow-up after surgery, 1/2 osteogenesis rate of the study group was significantly higher ( p < 0.05). However, all patients in the two groups obtained stable fusion at the 12th month follow-up after surgery.

CONCLUSIONS

For patients with cervical spondylosis and osteoporosis, intravenous application of ZA after ACDF surgery can shorten the time of cervical osteogenesis, promote local bone graft fusion, and improve the postoperative clinical effect to some extent.

Feasibility of Endoscopic Inspection of Pedicle Wall Integrity in a Live Surgery Model

Background

Perforations of the pedicle wall during cannulation can occur with experienced surgeons. Direct endoscopic visualization has not been used to inspect pedicles previously due to bone bleeding obscuring the camera visualization. The hypothesis of this study was that endoscopic visualization of pedicle wall integrity was technically feasible and would enable identification of clinically significant pedicle breaches.

Methods

A live porcine model was used. Eight lumbar pedicles were cannulated. Clinically significant breaches were created. An endoscope was introduced and was used to inspect the pedicles.

Results

All lumbar pedicles were endoscopically visible at a systolic pressure of 100 mm Hg. Clinically relevant anatomic structures and iatrogenic pathology, such as medial, lateral, and anterior breaches, were identified. There were no untoward events resulting from endoscopic inspection of the pedicle endosteal canal.

Conclusions

Endoscopic inspection of lumbar pedicles was safe and effective. The findings on endoscopic inspection corresponded with the ball-tip probe palpation techniques. Additional techniques, such as selection between 2 tracts, was possible with the endoscopic technique.

The effects of bisphosphonates on osteoporotic patients after lumbar fusion: a meta-analysis

Purpose

We conducted a meta-analysis of controlled clinical trials to evaluate the efficacy of bisphosphonates in lumbar fusion.

Introduction

Bisphosphonates reduce bone resorption and remodeling by osteoclast activity inhibition, inactivation, and apoptosis. However, it remains controversial whether bisphosphonate therapy affects spinal fusion.

Methods

We searched MEDLINE, Cochrane CENTRAL, ScienceDirect, EMBASE, and Google Scholar to identify studies reporting the effects of bisphosphonates on osteoporotic patients after lumbar fusion. Secondary sources were identified from the references of the included literature. Pooled data were analyzed using RevMan 5.1.

Results

Seven studies met the inclusion criteria. There were significant differences in solid intervertebral fusion (RD=0.07, 95% CI: −0.00 to 0.15, P=0.05), subsequent VCFs (RD=−0.21, 95% CI: −0.30 to −0.12, P<0.00001), pedicle screw loosening (RD=−0.17, 95% CI: −0.28 to −0.05, P=0.006), and cage subsidence (RD=−0.25, 95% CI: −0.42 to −0.07, P=0.005) between two groups. No significant differences between two groups were found regarding implant fixation failure (RD=−0.06, 95% CI: −0.22 to 0.10, P=0.48).

Conclusion

This meta-analysis showed that bisphosphonates may increase solid intervertebral fusion and decrease subsequent VCFs, pedicle screw loosening, and cage subsidence.

Complications in Craniovertebral Junction Instrumentation: Hardware Removal Can Be Associated with Long-Lasting Stability. Personal Experience

BACKGROUND

The causes of craniovertebral junction (CVJ) instabilities include trauma, rheumatological diseases, tumors, infections, congenital malformations, and degenerative disease processes; these complex pathologies often require CVJ instrumentation. Hardware complications were analyzed in a personal series of 48 treated patients. In light of the analysis of very unusual radiological and clinical findings, the authors tried to better investigate the related mechanisms and to reach possible useful conclusions.

METHODS

In a series of 48 patients who underwent CVJ instrumentation and fusion procedures in our Institution, we describe three cases of hardware failure, due to: (1) infection; (2) radio- and chemotherapy; and (3) incorrect surgical procedure.

RESULTS

1. A stable bone CVJ fusion can occur after instrumentation removal for infection, since this removal can enhance bone fusion mechanisms; 2. Radio- and chemotherapy can cause hardware failure due to interference with local bone metabolism; 3. Although old-fashioned, wiring techniques still deserve consideration, mostly in CVJ re-do surgery after screwing technique failures; nevertheless, although the procedure is simple, safe, and effective, care must be taken in the preparation of the cranial holes in order to avoid sliding complications of the U-shaped rods.

CONCLUSIONS

CVJ instrumentations provide reasonably good mechanical stabilization with a high rate of bony fusion. Complications, such as dislocation or rupture of the fixation system, screw loosening, dural fistula, neural or vascular damage, and wound infection, are relatively infrequent. Knowledge and prevention of these complications is fundamental to improve surgical results and outcomes.

Bisphosphonate's and Intermittent Parathyroid Hormone's Effect on Human Spinal Fusion: A Systematic Review of the Literature

There has been a conscious effort to address osteoporosis in the aging population. As bisphosphonate and intermittent parathyroid hormone (PTH) therapy become more widely prescribed to treat osteoporosis, it is important to understand their effects on other physiologic processes, particularly the impact on spinal fusion. Despite early animal model studies and more recent clinical studies, the impact of these medications on spinal fusion is not fully understood. Previous animal studies suggest that bisphosphonate therapy resulted in inhibition of fusion mass with impeded maturity and an unknown effect on biomechanical strength. Prior animal studies demonstrate an improved fusion rate and fusion mass microstructure with the use of intermittent PTH. The purpose of this study was to determine if bisphosphonates and intermittent PTH treatment have impact on human spinal fusion. A systematic review of the literature published between 1980 and 2015 was conducted using major electronic databases. Studies reporting outcomes of human subjects undergoing 1, 2, or 3-level spinal fusion while receiving bisphosphonates and/or intermittent PTH treatment were included. The results of relevant human studies were analyzed for consensus on the effects of these medications in regards to spinal fusion. There were nine human studies evaluating the impact of these medications on spinal fusion. Improved fusion rates were noted in patients receiving bisphosphonates compared to control groups, and greater fusion rates in patients receiving PTH compared to control groups. Prior studies involving animal models found an improved fusion rate and fusion mass microstructure with the use of intermittent PTH. No significant complications were demonstrated in any study included in the analysis. Bisphosphonate use in humans may not be a deterrent to spinal fusion. Intermittent parathyroid use has shown early promise to increase fusion mass in both animal and human studies but further studies are needed to support routine use.

Effects of zoledronic acid on bone fusion in osteoporotic patients after lumbar fusion

Treatment with zoledronic acid in osteoporotic patients with spinal fusion shortens the duration of time to fusion, improves the fusion rate, prevents the subsequent adjacent vertebral compression fractures, improves the clinical outcomes, and prevents immobilization-induced bone loss in the hip.

INTRODUCTION

The objective of the study was to explore the effects of zoledronic acid on the healing process in osteoporotic patients following spinal fusion in a randomized, placebo-controlled, and triple-blinded study.

METHODS

Seventy-nine osteoporotic patients with single-level degenerative spondylolisthesis were randomly assigned to receive either zoledronic acid infusion (zoledronic acid group) or saline infusion (controls) after spinal fusion. Functional radiography and CT scans were used to evaluate fusion status. Bone formation was graded into three categories: Grade A (bridging bone bonding with adjacent vertebral bodies), Grade B (bridging bone bonding with either superior or inferior vertebral body), or Grade C (incomplete bony bridging). A solid fusion was defined as less than 5° of angular motion with Grade A or B bone formation. Adjacent vertebral compression fractures (VCF) were assessed on MRI at 12 months after surgery. Serum level of carboxy terminal cross-linked telopeptide of type I collagen (β-CTX) and amino-terminal propeptide of type I procollagen (PINP) was measured. Bone mineral density (BMD) was measured by DXA. Oswestry Disability Index (ODI) was used to assess the clinical outcomes.

RESULTS

Grade A or B bridging bone was more frequently observed in zoledronic acid group at 3, 6, and 9 months post-operation compared to the control group (p < 0.05). At 12 -months post-operation, bridging bone and solid fusion were not significantly different between groups. No patients in zoledronic acid group showed aVCF, whereas six patients (17 %) in the control group did (p < 0.05). Both β-CTX and PINP were suppressed in zoledronic acid group. BMD at the femoral neck decreased rapidly and did not return to the preoperative level in the controls at 3 (-1.4 %), 6 (-2.5 %), and 12 (-0.8 %) months after surgery. Zoledronic acid prevented this immobilization-induced bone loss and increased BMD. ODI showed the improved clinical outcomes compared with controls at 9 and 12 months post-surgery.

CONCLUSION

Treatment with zoledronic acid in osteoporotic patients with spinal fusion shortens the time to fusion, improves the fusion rate, prevents subsequent aVCFs, and improves clinical outcomes.

A novel lateral lumbar integrated plate-spacer interbody implant: in vitro biomechanical analysis

BACKGROUND CONTEXT

Lateral spacers (LSs) are the standard of care for a lateral lumbar interbody fusion. However, various types of fixation, such as bilateral pedicle screws (BPSs), unilateral pedicle screws (UPSs), bilateral facet screws (BFSs), and lateral plates (LPs) have been reported to increase the stability of LSs. The biomechanics of a novel lateral interbody implant, which is an interbody spacer with an integrated plate and two bone screws (lateral integrated plate-spacer [IPS-L]), has not been investigated yet.

PURPOSE

To compare the biomechanical stability of IPS-L and LS with and without supplemental instrumentation.

STUDY DESIGN

Human lumbar cadaveric study evaluating the biomechanical stability of an IPS-L.

METHODS

Each of the six (L2-L5) spines was sequentially tested in intact; IPS-L; IPS-L+UPS; IPS-L+BPS; IPS-L+BFS; LS+BFS; LS+UPS; LS+BPS; LS; and LS+LP, using a load-control protocol in which a ±8 Nm moment was applied, for three cycles each, in flexion-extension (FE), lateral bending (LB), and axial rotation (AR). Data results were obtained from the third cycle.

RESULTS

The IPS-L construct significantly reduced the range of motion (ROM) by 75% in FE, 70% in LB, and 57% in AR, compared with intact. Lateral integrated plate-spacer demonstrated similar biomechanical stability as LS+LP, and higher stability than the LS-alone construct, but the difference was not statistically significant.

CONCLUSIONS

The IPS-L evaluated in the present study demonstrated equivalent biomechanical stability compared with standard lateral interbody fusion constructs. The addition of BPSs to the IPS-L showed significant reduction in ROM in FE, and the addition of BFSs showed significant reduction in ROM in FE and AR, compared with the integrated plate-spacer alone construct. The IPS-L with supplemental fixation may be a viable option for lateral interbody fusion. Long-term clinical studies are further required to confirm these results.

The effect of zoledronic acid on the volume of the fusion-mass in lumbar spinal fusion

Background

Few studies have explored the effects of bisphosphonates on bony healing in patients undergoing spinal fusion surgery. Most previous studies used animal models and found that bisphosphonate shows negative effects on spinal fusion consolidation. We intended to evaluate the effect of a single-dose of zoledronic acid on the volume of the fusion-mass in lumbar spinal fusion.

Methods

A retrospective review was carried out on 44 patients with symptomatic degenerative lumbar spinal stenosis who underwent one or two-level posterolateral fusion from January 2008 and January 2011. They were divided into 4 groups: group 1, autograft and zoledronic acid; group 2, allograft and zoledronic acid; group 3, autograft alone; and group 4, allograft alone. Functional radiography and three-dimensional computed tomography scans were used to evaluate and quantify the volume of the fusion-mass. The visual analog scale (VAS), the Oswestry disability index (ODI), and the short form 36 (SF-36) were used to evaluate the clinical outcomes.

Results

The mean volume of the fusion-mass per level was 8,814 mm³, 8,035 mm³, 8,383 mm³, and 7,550 mm³ in groups 1, 2, 3, and 4, respectively, but there were no significant differences between the groups (p = 0.829). There were no significant decreases in the volume of the fusion-mass (p = 0.533) in the zoledronic acid groups (groups 1 and 2). The VAS, the ODI, and the SF-36 at the 6-month follow-up after surgery were not significantly different (p > 0.05) among the 4 groups. The VAS, the ODI, and the SF-36 were not correlated with the volume of the fusion-mass (p = 0.120, 0.609, 0.642).

Conclusions

A single dose of zoledronic acid does not decrease the volume of the fusion-mass in patients undergoing spinal fusion with osteoporosis. Therefore, we recommend that zoledronic acid may be used after spinal fusion in osteoporotic patients.

Pharmacophysiology of bone and spinal fusion

BACKGROUND CONTEXT

In recent years, the number of complex spinal surgeries has increased significantly in the elderly population, where the prevalence of low bone density is highest. Consequently, spine surgeons often treat osteoporotic patients who are associated with higher rates of instrumentation failure. Therefore, establishing a successful fusion requires an appropriate substrate for bone formation and local bone remodeling. The fusion process can be supported by therapies that seek to shift the balance of bone homeostasis to increased formation and reduced resorption.

PURPOSE

Thorough understanding of the physiology of bone formation and adjunctive therapies can help improve fusion rates. Therefore, we present a thorough review of the latest pharmacologic agents used to enhance bone strength and surgical spinal fusion.

METHODS

Systematic review of literature.

RESULTS

Current knowledge on bone physiology has led to the development of several pharmacologic agents that enhance bone formation and strengthen the human skeleton. At present, natural supplements of vitamin D and calcium or synthetic medications like bisphosphonates are widely used before and after spine surgeries to enhance bone fusion. Additional physiologic agents, including testosterone, parathyroid hormone, calcitonin, and growth hormone, have been shown to improve bone mass density or spinal fusion in both animal and human studies. As in other medical fields, gene therapy has shown viability and promise with the use of both viral and nonviral vectors.

CONCLUSIONS

Through the understanding of bone physiology, numerous natural and synthetic pharmacologic agents have been developed to enhance the body's skeleton and to improve outcomes of spinal fusion surgery.

Effect of pilot hole on biomechanical and in vivo pedicle screw-bone interface

PURPOSE

To experimentally study the influence of pilot hole diameter (smaller than or equal to the internal (core) diameter of the screw) on biomechanical (insertion torque and pullout strength) and histomorphometric parameters of screw-bone interface in the acute phase and 8 weeks after pedicle screw insertion.

METHODS

Fifteen sheep were operated upon and pedicle screws inserted in the L1-L3 pedicles bilaterally. The pilot hole was smaller (2.0 mm) than the internal diameter (core) of the screw on the left side pedicle and equal (2.8 mm) to the internal diameter (core) of the screw on the right side pedicle. Ten animals were sacrificed immediately (five animals were assigned to pullout strength tests and five animals were used for histomorphometric bone-screw interface evaluation). Five animals were sacrificed 8 weeks after pedicle screw insertion for histomorphometric bone-screw interface evaluation.

RESULTS

The insertion torque and pullout strength were significantly greater in pedicle screws inserted into pilot holes smaller than internal (core) diameter of the screw. Histomorphometric evaluation of bone-screw interface showed that the percentage of bone-implant contact, the area of bone inside the screw thread and the area of bone outside the screw thread were significantly higher for pilot holes smaller than the internal (core) diameter of the screw immediately after insertion and after 8 weeks.

CONCLUSION

A pilot diameter smaller than the internal (core) diameter of the screw improved the insertion torque and pullout strength immediately after screw insertion as well the pedicle screw-bone interface contact immediately and 8 weeks after screw placement in sheep with good bone mineral density.

The effect of therapies for osteoporosis on spine fusion: a systematic review

BACKGROUND CONTEXT

Fusion of the spine requires de novo bone formation and remodeling, processes that rely heavily on the action of the osteoblast and osteoclast. Bisphosphonate drugs and intermittent parathyroid hormone (PTH) therapy are widely prescribed to treat osteoporosis and act on the osteoblast/osteoclast complex. The impact of these medications on spine fusion is not known.

PURPOSE

To evaluate the available evidence on the potential impact of bisphosphonates and PTH on fusion rate and fusion quality in spinal arthrodesis.

STUDY DESIGN

A systematic review of the literature.

PATIENT SAMPLE

All available literature regarding the impact of bisphosphonates and PTH on spinal fusion.

OUTCOME MEASURES

Fusion rate and histologic, microstructural, or biomechanical measures of fusion quality.

METHODS

A systematic review of the literature published between 1980 and 2011 was conducted using major electronic databases. The results of studies meeting criteria for inclusion were then aggregated and examined for consensus on the effect of these medications on spine fusion.

RESULTS

The literature contained 18 animal studies and one clinical trial investigating the impact of these medications on spine fusion. Most animal studies evaluating the impact of bisphosphonates on fusion rate have not found statistically significant changes with treatment, although this fact may be attributable to low statistical power. The animal literature does suggest that bisphosphonate therapy results in a less histologically mature fusion mass; however, the impact of these changes on fusion mass biomechanics is unclear. The only available human study suggests that these bisphosphonates may increase the radiographically defined fusion rate but did not demonstrate an impact on clinical outcome. In animals, PTH improves the fusion rate and fusion mass microstructure, but data on its effect on fusion mass biomechanics are lacking. No studies have evaluated the impact of PTH on spine fusion in humans.

CONCLUSIONS

In animals, bisphosphonate therapy appears to impede maturation of the fusion mass, with an unclear effect on mechanical strength. This effect was not seen in the lone human study, which suggested that these medications improved the radiographically defined fusion rate. The available animal studies on intermittent PTH treatment suggest that it may improve fusion rate and fusion mass microstructure. Given the widespread use of these agents, further investigation into their impact on human spine fusion is necessary to inform the care of patients with osteoporosis who are undergoing spine surgery.

Occipito-cervical instrumentation failure after radio-chemotherapy for axis solitary plasmacytoma: a case-based update

INTRODUCTION

Axis solitary plasmacytoma is a rare cause of cranio-vertebral junction instability and atlanto-axial subluxation. Occipito-cervical instrumentation through lateral mass screws fixation is commonly used to obtain an internal stabilisation through a posterior approach in the management of axis tumours. Although radiotherapy and chemotherapy have been strongly advocated for treatment of spinal solitary plasmacytoma, their role in determining failure of instrumented fusion has not yet been emphasised.

CASE REPORT

A 52-year-old man affected by an axis solitary plasmacytoma underwent occipito-cervical instrumentation through lateral mass screws fixation and subsequent radio-chemotherapy. Bone resorption and failure of instrumented fusion were observed at 6-month follow-up. New instrumented surgery by using Songer titanium sublaminar wires was then performed. Post-operatively, a Halo-Vest system was applied for 3-months and administration of oral bisphosphonates was started. The patient quickly regained walking ability. Computed tomography scan demonstrated the correct position of the sublaminar wires, as the initial bone fusion too. A 30-month follow-up computed tomography scan documented the maintenance of spinal stability and alignment due to successful fusion.

DISCUSSION

Despite the effect of radio-chemotherapy on bony metabolism has been widely discussed, its role in influencing the failure of instrumented fusion has not yet been definitively analysed, especially when glucocorticoids are chosen as chemotherapic agent. Moreover, the most appropriate technique of instrumented fusion to be used after radio-chemotherapy is not established. Also the role of bisphosphonates in preventing the failure of instrumented surgery has not yet documented. All these aspects are discussed by the authors along with a literature review, taking a cue from the management of this case.

Short-term alendronate treatment does not maintain a residual effect on spinal fusion with interbody devices and bone graft after treatment withdrawal: an experimental study on spinal fusion in pigs

PURPOSE

Whether alendronate treatment has a residual effect on bone ingrowth into porous biomaterial in humans or experimental animals after treatment withdrawal is still unknown. The purpose of this study was to investigate bone ingrowth into porous tantalum and carbon fiber interbody implants after discontinuing alendronate treatment in experimental spinal fusion in pigs.

METHODS

Twenty-four pigs were randomly divided into two groups of each 12 pigs. The pigs underwent anterior intervertebral lumbar arthrodeses at L2-3, L4-5 and L6-7. Each level was randomly allocated to one of the three implants: a porous tantalum ring with pedicle screw fixation, a porous tantalum ring or a carbon fiber cage with anterior staple fixation. The central hole of implants was packed with an autograft. Alendronate was given orally for the first 3 months to one of the two groups. The pigs were observed for 6 months postoperatively. Histology and micro-CT scans were done at the endpoint.

RESULTS

The spinal fusion rates of each implant showed no differences between two treatment groups. Furthermore, no differences were found between two groups as for bone ingrowth into the central holes of implants and bone-implant interface in each implant, or as for the pores of tantalum implants. Trabecular bone microarchitecture in the central hole of the carbon fiber cage did not differ between two treatment groups.

CONCLUSION

The application of ALN, with a dose equivalent to that given to humans during the first 3 months after surgery, does not maintain a residual effect on spinal fusion with porous tantalum ring and autograft after treatment withdrawal in a porcine ALIF model.

Does alendronate disturb the healing process of posterior lumbar interbody fusion? A prospective randomized trial

Object

Bisphosphonate medications are widely used for the treatment of osteoporosis, but they might disturb the healing process of spinal fusion. The object of this prospective randomized controlled study was to evaluate the effect of bisphosphonate medication on spinal fusion through radiographic, clinical, and biological assessments.

Methods

A total of 40 patients with osteoporosis who were candidates for single-level posterior lumbar interbody fusion were randomly assigned to the alendronate group (alendronate sodium 35 mg/week) or the control group (vitamin D, alfacalcidol 1 μg/day). Pedicle screw fixation and carbon polyetheretherketone cages were used for all the patients. Bone graft material was prepared as a mixture of local bone and β-tricalcium phosphate in a ratio of 2:1. Functional radiography and CT scans were used to evaluate fusion status and cage subsidence. The incidence of vertebral compression fractures (VCFs) occurring after surgery (subsequent VCFs) was assessed by means of MR imaging. Bridging bone formation was graded into 3 categories: Grade A (bridging bone through bilateral cages), Grade B (bridging bone through a unilateral cage), or Grade C (incomplete bony bridging). A solid fusion was defined as less than 5° of angular motion in flexion-extension radiographs and the presence of bridging bone through the cage (Grade A or B). Clinical outcome was evaluated by means of the Oswestry Disability Index. Bone metabolic markers (serum bone alkaline phosphatase, serum and urine Type I collagen cross-linked N-telopeptides) were measured to investigate the biological effects of alendronate on spinal fusion.

Results

Bridging bone formation (Grade A or B) was more frequently observed in the alendronate group at all postoperative assessment periods. At 1-year postoperative follow-up, a solid fusion was achieved in 95% of the patients in the alendronate group and 65% of those in the control group. Cage subsidence (> 2 mm) was observed in 5% of the alendronate group and 29% of the control group. No vertebral fractures were observed in the alendronate group, whereas 24% of patients in the control group showed subsequent VCFs. There was no statistically significant between-groups difference in clinical outcomes, but poor clinical results in the control group were associated with pseudarthrosis and subsequent VCFs. Biochemical analysis of bone turnover demonstrated that alendronate inhibited bone resorption from the early phase of the fusion process and also suppressed bone formation after 6 months postoperatively.

Conclusions

Favorable mechanical circumstances provided by alendronate overcame its detrimental biological effect on the healing process of spinal fusion. The authors recommend that osteoporosis patients undergoing spinal fusion take bisphosphonates throughout the postoperative period.

[Degeneration and osteoporosis of the spine. Is there a modified procedure?]

Reduced bone quality due to osteoporosis poses a fundamental problem in spine surgery instrumentation. The consequences observed most often are insufficient implant anchoring and adjacent fractures. In cases of manifest osteoporosis, several modern anchoring possibilities are at our disposal that, to differing degrees, increase the stability of the instrumentation. Cement augmentation of a fractured vertebra by means of kyphoplasty or vertebroplasty verifiably leads to significantly better pain reduction than conservative treatment does, at least in the short-term postoperative course. A difference between these two techniques has not yet been substantiated. The rate of adjacent fractures occurring after cement augmentation is not higher than in conservatively treated patients.

Effect of a single dose of pamidronate administered at the time of surgery in a rabbit posterolateral spinal fusion model

Spinal fusion is usually performed on patients who receive bisphosphonates (BP); however, limited data on their action on spinal fusion are available. Previous studies in animal models have shown that chronic administrations of BP reduced spinal fusion rates, and only one study has shown that a single dose administration of zolendronic acid increased fusion rate. The objective of the present study was to evaluate if pamidronate (PA), which was previously demonstrated to reduce spinal fusion rate when administered continuously for 8 weeks, would increase the spinal fusion rate if administered in a single dose at the time of surgery in a rabbit model. Thirty-two New Zealand rabbits underwent an L5-L6 posterolateral intertransverse fusion with iliac crest autograft. Animals were randomized to receive either PA 3 mg/kg in a single dose immediately after surgery, or normal saline. Animals were killed 8 weeks after surgery and fusion was determined by manual palpation and radiographic analysis. Fusion healing was obtained in eight rabbits (50%) in the PA group and in four animals (25%) in the control group, p = 0.137. In a rabbit model, a single dose of PA did not decrease lumbar spinal arthrodesis consolidation rates, but it obtained a nonsignificant higher spinal fusion rate.

Pharmacological agents and bone healing

Osteoporosis is the most common alteration of bone metabolism. It derives from an increase in bone resorption with respect to bone formation and is characterized by microarchitectural alterations, decreased bone mass and increased risk of fracture. The coupling between bone formation and resorption is a fundamental concept in skeletal metabolism, and it explains how a certain amount of removed tissue can be replaced by the same amount of new bone. Various substances used to treat osteoporosis may also be used for orthopaedic conditions such as fracture healing, implant fixation, bone grafts and osteonecrosis. Fracture healing consists in the replacement of the lost bone by a tissue that has the same biomechanical properties as those preceding the fracture. The repair process is triggered by the local response to the tissue injury that damaged the continuity of bone. The duration of each phase of the healing process can vary significantly, depending on the site and characteristics of the fracture, on patient related factors and on the treatment choice. While most of the fractures heal with conventional treatment, they can also cause permanent damage and complications, especially in a certain kind of patients. Osteoporosis and old age may contribute in delaying or impairing the reparative process. In animal models the healing process is slower in older and/or ovariectomized animals. Biomechanical tests have also shown that bone strength is compromised in human osteoporotic cadaver bone. The same problems were highlighted in the surgical treatment of fractures in osteoporotic patients. Mainly in the treatment of hip fractures there is an increased risk of cut-out, re-fractures and implant failure in patients with osteoporosis. Preclinical studies have shown that certain pharmacological agents (bisphosphonates, strontium ranelate, teriparatide) may enhance osseointegration and stimulate reparative processes. They may be administered systemically and/or used locally at the fracture site on the implant surface. The aim of fracture treatment is to restore bone biomechanical properties and to allow restoring normal function at the affected site. If the new pharmacological approaches could be translated into clinical benefit and offered to patients with osteoporosis or other factors that put at risk the process of healing (subjects with severe loss of substance or fractures at high risk of complications), they could represent a valuable aid in the treatment of fractures.