Spinal Fusion Rates Research Articles

Bone grafting

In recent years our understanding of spinal fusion biology has improved. This includes the continued elucidation of the step-by-step cellular and molecular events involved in the prototypic bone induction cascade, as well as the identification and characterization of the various critical growth factors governing the process of bone formation and bone graft incorporation. Based on these fundamental principles, growth factor technology has been exploited in an attempt to improve rates of spinal fusion, and promising results have been realized in preclinical animal studies and initial clinical human studies. In this article the authors review the recent advances in the biology of bone fusion and provide a perspective on the future of spinal fusion, a future that will very likely include increased graft fusion rates and improved patient outcome as a result of the successful translation of fundamental bone fusion principles to the bedside.

The use of electrical stimulation to enhance spinal fusion

The goal of spinal arthrodesis is a solid osseous union across one or more spinal segments. A solid bone union after arthrodesis is commonly known as a spinal fusion. Surgeons have begun to understand the biomechanical and biological factors that influence the bone-healing process. One of the most commonly used adjuncts is spinal instrumentation. Instrumentation has increased the spinal fusion rate; however, fusion failure (that is, nonunion or pseudarthrosis) remains significant. A less commonly used adjunct is electrical stimulation (ES). Investigators in experimental studies have demonstrated the beneficial effects of ES on increasing the fusion rate. In this review the authors discuss the evidence concerning the benefits of ES as an adjunct to spinal arthrodesis. In addition, the different types of ES devices are described along with the current experimental and clinical evidence for each type of device.

Gene transfer approaches to the healing of bone and cartilage.

Gene transfer approaches to the healing of bone and cartilage.

Update on use of instrumentation in lumbar spine disorders

The past 20 years have witnessed significant changes in the indications for and use of instrumentation in lumbar spine surgery. Absolute indications for surgical instrumentation include cases of clearly defined instability that commonly occur in the setting of trauma, tumour and infection. Relative indications for instrumentation must consider the clinical context and individual patient characteristics but may include cases of spondylolisthesis, junctional stenosis and pseudarthrosis. The use of instrumentation in the surgical treatment of degenerative disc disease is prevalent but remains highly controversial. Pedicle screws and interbody cages represent alternative forms of instrumentation with substantial clinical evidence supporting their safety and efficacy when applied in the correct clinical settings. Minimally invasive and computer-assisted surgical techniques have shown promising early results but must be subject to longer-term scrutiny. The development of prosthetic disc replacements is an exciting area of research, but clinical results have not approached the success currently enjoyed by hip and knee prostheses, and these devices should be considered experimental. One of the goals of instrumentation is to enhance the rate of spinal fusion. However, achievement of solid radiographic fusion does not guarantee a clinically successful outcome and, conversely, excellent results can be obtained in the setting of radiographic pseudarthrosis. The most important determinant of favourable surgical outcome is appropriate patient selection through a sound understanding of surgical indications.

Recombinant human bone morphogenetic protein-4 (rhBMP-4) enhanced posterior spinal fusion without decortication

In posterior spinal fusion, insufficient decortication may decrease the number of bone marrow derived ostoprogenitor stem cells and affect the success of bony fusion. The finding of bone formation through interaction between rhBMP-4 and non-marrow derived mesenchymal cells constituted the basis of the current study. The aim is to investigate the possibility of molecular enhancement of posterior spinal fusion by site-specific application of rhBMP-4 with or without surgical decortication. Eighteen adult rabbits underwent single level bilateral posterior intertransverse process spinal fusion at L5–L6, one side with decortication, and the other side without decortication. Two animals underwent sham operation without bone grafts, the other 16 animals were randomly allocated into three groups, using hydroxyapatite-tricalcium phosphate (HA-TCP) ceramic blocks augmented with 0, 0.125 and 0.5 mg of rhBMP-4 respectively. Spinal fusion morphology was evaluated with sequential X-ray, microradiography and histomorphology. At week 7, complete bony fusion was achieved in none of the groups without rhBMP-4 irrespective of whether the bony contact surface was decorticated or not. In the groups with low dose rhBMP-4, complete fusion occurred in two of six un-decorticated sites (33%) and in three of six (50%) decorticated sites. 100% complete fusion was found in the high dose rhBMP-4 group independent of surgical decortication. The dorsal cortices of the un-decorticated transverse processes were replaced by newly formed trabecular bone through biological remodeling. This study suggested that rhBMP-4 can induce non-marrow derived mesenchymal cells to differentiate into osteogenic cells and thus enhance the high success rate of posterior spinal fusion in both the decorticated and un-decorticated model.

The effect of varied electrical current densities on lumbar spinal fusions in dogs

Background context: The use of electrical stimulation has been shown to increase the rate of successful spinal fusions. It is possible that increasing the current density of these stimulators may increase the speed and success rate of these fusions. Purpose: This study evaluated the effects of varied current densities on the speed and success rate of spinal fusion in dogs. Study design/setting: Three different current densities (0.83 μA/cm, 4 μA/cm and 10 μA/cm) were used to stimulate spinal fusions in a canine model over a 12-week period. Outcome measures: Radiographic and histologic assessments were used to determine the degree of facet fusions at each time period. Methods: Fifteen dogs underwent spinal facet fusion bilaterally at the level of L1–2 and L4–5. Each fusion site was electrically stimulated using one of three current densities. At 6, 9 and 12 weeks, the specimens were evaluated using high-resolution radiography and routine histology. The fusion masses were graded and then statistically evaluated. Results: The results demonstrate a dose response of fusion mass scores to increasing current density. The highest current density (10 μA/cm) demonstrated a statistically higher fusion scores than the lowest currently density (0.83 μA/cm) at 6 weeks and statistically greater than both the middle (4 μA/cm) and lowest (0.83 μA/cm) current densities at 9 weeks. No differences were noted at 12 weeks, because all groups showed complete fusion. Conclusions: This controlled study suggests that speed of fusion may be further improved by increasing the current density of the electrical stimulation.

Low-intensity pulsed ultrasound improves spinal fusion

Background context: Increasing the incidence of solid bony fusion is a primary goal in spine surgery. Daily low-intensity pulsed ultrasound therapy has been shown to improve and accelerate the bone healing process. Purpose: The purpose of this study was to evaluate the efficacy of daily low-intensity pulsed ultrasound therapy to improve the rate and quality of spinal fusion. Study design: Canine fusion model prospective study. Patient sample: Fourteen adult male dogs were used. Outcome measures: Radiographic grading of plain films, computed tomography (CT) and magnetic resonance imaging (MRI), gross palpation, torsional stiffness and histologic grading were used to determine the presence or absence of fusion. Methods: Posterior noninstrumented bilateral fusions were evaluated at the L2–L3 and L5–L6 levels. Treatment with low-intensity pulsed ultrasound for 20 minutes per day over the fusion site (stimulated) was compared with fusion sites that received no stimulation (nontreated controls) at 6 and 12 weeks after surgery. Plain film radiographs, CT and MRI, mechanical torsion testing and histologic examination were performed. Results: At 6 weeks, ultrasound treated sites were more frequently fused compared with nontreated controls, although the difference in fusion rate was not statistically significant. At 12 weeks after surgery complete radiographic and histologic fusion occurred in 100% of ultrasound-treated sites. In the nontreated control sites 78% had achieved complete radiographic fusion and 44% had complete histologic fusion. Compared with control sites, the histological and mechanical fusion rate was significantly greater in ultrasound-treated sites ( P<.05) at 12 weeks. A statistically significant increase in mechanical stiffness in ultrasound-treated sites was also found at 12 weeks after surgery. Conclusions: Low-intensity pulsed ultrasound therapy may be a useful means to ensure successful spine fusion.

Shared decision-making and the orthopaedic workforce.

Studies of physician workforce need a standard of an appropriately sized workforce to compare projections. Although many studies use average rates of healthcare use as a standard, regional benchmarks provide a pragmatic alternative approach to estimating a reasonably sized physician workforce and avoid many of the problems of needs- and demand-based planning. Wide geographic variations in the rates of many procedures, unexplained by differences in population characteristics, suggest that supply-induced demand or physician practice style or both may be the major determinates of the rates for these procedures. In the current study, the authors explore some of these differences in orthopaedic procedure rates and their implications for workforce planning. For example, the rates of hip fracture are fairly uniform across geographic regions, whereas the rates of spine surgery vary sixfold and the rates of spinal fusion vary 10-fold. Shared decision-making is the process of giving patients informed choices about their treatment options based on current best evidence. Careful studies of treatment effectiveness and shared decision-making hold the promise of allowing patients' preferences and values to determine the right rate of healthcare use. These rates could allow workforce projections to be compared with optimal benchmarks for future planning.

Radiographic assessment of anterior titanium mesh cages.

Carbon fiber and titanium cage implantation for anterior column support during spinal fusions is an alternative to the use of more traditional structural allografts and autografts. The authors report instrumentation and cage failure for patients who underwent spinal fusion with structural titanium mesh cages implanted into the anterior column a minimum of 2 years after surgery. They wanted to determine whether plain radiographic techniques can be used to critically assess disk space and corpectomy fusions after implantation of these radioopaque cages. Fifty patients having undergone spinal fusions using structural titanium mesh cages in the anterior column had 99 anterior levels fused with at least 1 (maximum of 2) titanium mesh cage, resulting in a total of 131 cages used. The cages were examined for evidence of settling, migration, or failure. The anterior and posterior instrumentation was assessed for evidence of failure, and the spine was examined for evidence of successful fusion. Radiographic cage settling (>2 mm) into the vertebral body end plates was observed, but cage migration or failure were not. An average lordotic correction of 10 degrees was observed, with loss of correction into kyphosis from immediately after operation to final follow-up averaging 2 degrees. As an average of all reviewers, using a strict radiographic fusion assessment, definite or probable anterior fusion was graded at 81% of the levels, probably not or no at 5% of the levels, and could not be assessed at 14% of the levels. Definite or probable posterior fusion as an average of all reviewers was graded at 44% of the posterior fusion levels, questionable at 4%, no at 5%, and could not be assessed at 47%. The use of anterior-only, posterior-only, or anterior and posterior instrumentation with structural titanium mesh cages in the anterior spine along with proper autogenous bone grafting techniques provided anterior column support with a low rate of radiographic complications. Acceptable anterior spinal fusion rates, as assessed by a consensus agreement of reviewers, were observed primarily by evaluation of the fusion mass around the cages (extracage fusion), because intracage fusion was difficult to assess.

LAPAROSCOPIC LUMBAR INTERBODY SPINAL FUSION

Laparoscopic ALIF is an evolving technique requiring the participation of a laparoscopic surgeon experienced in advanced laparoscopic techniques and knowledgeable in anterior lumbar spinal exposures. Initial enthusiasm for this technique was fostered by the development of interbody fusion devices and a method of exposing the anterior lumbar spine, which takes advantage of the ability of minimally invasive surgeries to improve exposure and visualization while minimizing collateral tissue damage and injury to healthy tissue. Preliminary studies have demonstrated laparoscopic ALIF feasibility. These same studies have been able to prove only minor advantages with the laparoscopic versus open technique using the current implants and bone grafting techniques for single-level disc disease. General acceptance of laparoscopic ALIF awaits further investigation. Reasons for a lack of general acceptance include the expense of the interbody fusion devices and laparoscopic equipment, the unfamiliarity of this advanced laparoscopic technique to spine and general surgeons, and the steep learning curve of the procedure. Intraoperative complications that arise are often severe, such as vascular injuries. Many skeptics appropriately believe that initial enthusiasm and zealousness must be tempered with scientific effort that provides data from long-term follow-up. For laparoscopic ALIF to gain general acceptance, randomized comparisons of laparoscopic ALIF to open ALIF and posterior lumbar spinal fusion and controlled studies with long-term follow-up documenting symptomatic outcome variables and spinal fusion rates must be completed. As new modalities are developed, minimally invasive techniques may facilitate their utility. The indications, procedures, and surgical principles of ALIF are unchanged, and physicians must not invent indications to justify the technique; however, eventually we may be able to redefine the indications to take full advantage of the endoscopic techniques and biological advances.

In vitro flexibility of an experimental pedicle screw and plate instrumentation system on the porcine lumbar spine

The positive correlation between spinal construct stiffness and fusion rate has led to the use of increasingly rigid surgical spinal instrumentation systems. Unfortunately, however, these rigid systems have also been correlated with sub-optimal fusion quality measures. To date, in vivo studies to explore these relationships have involved the use of different implants and surgical procedures to influence the biomechanical environment at the fusion site. In order to avoid these confounding variables, a novel experimental instrumentation system has been developed which is capable of independently controlling spinal construct flexibility (inverse of stiffness). In the present study, this experimental pedicle screw and plate system was subjected to rigorous pure moment flexibility testing in flexion–extension and lateral bending using an in vitro porcine lumbar spine model. Analysis of the data showed that the system provided a reproducible, stepwise-modulated spinal construct flexibility as measured by neutral zone flexibility, laxity angle and range of motion parameters. Differences in flexibility were most evident using the neutral zone parameters (neutral zone flexibility and laxity angle). This is of particular interest given that the clinical instability of a spinal segment may be related to its behaviour within the neutral zone. This information will ultimately guide the design of improved human spinal instrumentation systems.

Review: evidence supports surgery for lumbar disc prolapse but is insufficient for degenerative lumbar spondylosis

(1999) Spine 24, 1820. Gibson JN, Grant IC, Waddell G. . The Cochrane review of surgery for lumbar disc prolapse and degenerative lumbar spondylosis. . Sep 1; . : ....

Use of ultrasound in spinal arthrodesis. A rabbit model.

The biomechanical and histologic characteristics of posterolateral spinal fusion in a rabbit model with and without the application of low-intensity ultrasound were analyzed. To evaluate the use of ultrasound to improve the spinal fusion rate and biomechanical characteristics of the fusion mass in a rabbit model. This is the first study in which the benefits of ultrasound in spinal fusion have been assessed. Posterolateral intertransverse process fusion in the rabbit has a pseudarthrosis rate similar to that recorded in humans (5-40%). Fourteen New Zealand White rabbits were randomly assigned to each of two groups to undergo spinal fusion using autologous bone with ultrasound or autologous bone without ultrasound. A specially designed plastic constraint was used to focus the ultrasound over the rabbits' lumbar spine 20 minutes per day. Animals were killed at 6 weeks for biomechanical and histologic testing. The rate of pseudarthrosis, evaluated radiographically and manually in a blinded fashion, decreased at a statistically significant rate (from 35% to 7%) with ultrasound. Biomechanical analysis of the fusion mass showed that ultrasound resulted in statistically significant increases in stiffness (33%; P = 0.03), area under the load displacement curve (25%; P = 0.05), and load to failure of the fusion mass (24%; P = 0.04). Qualitative histologic assessment showed increased bone formation in those fusions exposed to ultrasound. Lumbar spinal fusion is a complex biologic process. The results of the current study demonstrate the reproducibility of a rabbit fusion model and the ability of ultrasound to induce a statistically significant increase in fusion rate, stiffness, area under the load displacement curve, and load to failure of the fusion mass. These results provide a basis for continued evaluation of biologic improvement of spinal arthrodesis with the use of ultrasound.

An experimental study of a combination method using a pedicle screw and laminar hook for the osteoporotic spine.

Using human cadaver spines, the authors compared the effect of using a combination of pedicle screw and laminar hook on the same vertebra with that of using a pedicle screw alone in reference to bone mineral density of the vertebra under nondestructive cyclic loading. To quantify stiffness obtained by pedicle screw alone and by the combination method and to clarify a relationship between stiffness obtained by each instrumentation method and bone mineral density of the vertebra. The use of pedicle screws apparently improves the union rate of spinal fusion. Instrumentation failures sometimes occur, however, such as loosening or loss of correction of the spine, especially in patients with osteoporosis. Some augmentation method in instrumentation is necessary to overcome bone fragility in the osteoporotic spine. Thirteen cadaver lumbar vertebrae were used for this study. Bone mineral density was measured by dual-energy X-ray absorptiometer. After separating each vertebrae, the pedicle screw was screwed into a vertebra. Five cycles of cephalocaudal loading were performed to the shank of the screw with a cross-head speed of 3 mm/min under a maximum load control of 29.4 N using an Instron type testing machine, and the stiffness obtained with the pedicle screw (Kj) was calculated from the load-deformation curve. Then, a laminar hook was set and connected to the screw via a rod. Mechanical testing was performed in the same way, and the stiffness obtained with the combination method (Kf) was determined. Kj and Kf were compared using the paired t test. The relationship between Kj, Kf, or the stiffness improvement ratio ([Kf-Kj]/Kj) by the combination method and bone mineral density was analyzed by linear regression analysis. Stiffness obtained by the combination method was significantly greater than that obtained by pedicle screw alone (89.8 +/- 35.0 N/mm by the combination method, 60.2 +/- 19.6 N/mm by pedicle screwing alone; P < 0.0001). Stiffness, whether obtained by pedicle screw alone or by the combination method, was positively correlated with bone mineral density (with pedicle screw alone, R2 = 0.614, P < 0.0001; with the combination method, R2 = 0.645, P < 0.0001). However, there was no significant correlation between stiffness improvement ratio and bone mineral density. Instrumentation stiffness obtained by the combination method was significantly greater than that obtained by the use of pedicle screw alone. There was no significant correlation between the improvement ratio by the combination method and bone mineral density. These results suggest that the combination method is valuable irrespective of the presence of spinal osteoporosis.

Lumbar Spinal Fusion

Regional variations in lumbar spinal fusion rates suggest a poor consensus on surgical indications. Therefore, complications, costs, and reoperation rates were compared for elderly patients undergoing surgery with or without spinal fusion. Subjects were Medicare recipients who underwent surgery in 1985, with 4 years of subsequent follow-up. There were 27,111 eligible patients, of whom 5.6% had fusions. Mean age was 72 years. Patients undergoing fusion had a complication rate 1.9 times greater than those who had surgery without fusion. The blood transfusion rate was 5.8 times greater, nursing home placement rate 2.2 times greater, and hospital charges 1.5 times higher (all P < 0.0005). Six-week mortality was 2.0 times greater for patients undergoing fusions (P = 0.025). Reoperation rates at 4 years were no lower for patients who had fusion surgery and results were similar in most diagnostic subgroups. Indications for fusion among older patients require better definition, preferably based on outcomes from prospective controlled studies.