To investigate the effect of omega-3 fatty-acid supplements (n-3FA) on bleeding during posterior spinal arthrodesis.
We reviewed all one- or two-level posterolateral lumbar decompression/fusions with or without interbody fusion by five surgeons within 3 years. Patients taking n-3FA preoperatively were matched 1:2 with controls based on procedure, surgeon and operative time. Patients with abnormal coagulation parameters, known bleeding disorders or other medications that could affect surgical blood loss were excluded.
Twenty-eight patients met inclusion criteria. The n-3FA and control groups were similar with respect to gender, age, body mass index, operative time, and preoperative use of non-steroidal anti-inflammatory drugs. The n-3FAs were stopped an average of 5.2 days before surgery (range 1–10). Mean estimated blood loss (EBL) was 697 ml in the n-3FA group and 771 ml in the control group (p = 0.36). Mean transfused volume of Cell Saver (CS) was 282 ml in the n-3FA group and 321 ml in the control group (p = 0.30). A post hoc power analysis showed that the study was powered to detect a minimum difference of 105 ml for EBL and 50 ml for CS. The multivariate generalized estimating equation did not show a significant difference between groups for EBL or CS (p = 0.35 and p = 0.29, respectively). Secondary outcomes including drop in postoperative hemoglobin, transfusion requirement, complications and surgical drain output were similar between the two groups.
The n-3FA use did not contribute to higher perioperative blood loss during spinal arthrodesis.
Omega-3 fatty acids; Bleeding; Spinal arthrodesis
To compare central venous pressure (CVP) with peripheral venous pressure (PVP) monitoring during the intraoperative and postoperative periods in patients undergoing spine surgery.
Prospective observational study.
University-affiliated teaching hospital.
35 ASA physical status 1, 2, and 3 patients.
A peripheral catheter in the forearm or hand and a central catheter into the internal jugular vein were placed for PVP and CVP monitoring, respectively.
CVP and PVP values were collected simultaneously and recorded electronically at 5-minute intervals throughout surgery and in the recovey room. The number of attempts for catheter placement, ease of use, maintenance, and interpretation were recorded. Patient comfort, frequency of complications, and cost were analyzed.
The correlation coefficient between CVP and PVP was 0.650 in the operating room (P < 0.0001) and 0.388 in the recovery room (P < 0.0001). There was no difference between groups in number of attempts to place either catheter, maintenance, and interpretation with respect to PVP and CVP monitoring in the operating room. In the recovery room, the nurses reported a higher level of difficulty in interpretation of PVP than CVP, but no differences were noted in ease of maintenance. There were no complications related to either central or peripheral catheter placement. Patient comfort and cost efficiency were higher with a peripheral than a central catheter.
During clinically relevant conditions, there was limited correlation between PVP and CVP in the prone position during surgery and postoperatively in the recovery room.
Central venous pressure; correlation study; peripheral venous pressure
Analysis of the Nationwide Inpatient Sample (NIS) from 1998 to 2008.
To analyze the most recent available and nationally representative data for risk factors contributing to in-hospital mortality after primary lumbar spine fusion.
Summary of background data
The total number of lumbar spine fusion surgeries has increased dramatically over the past decades. While the field of spine fusion surgery remains highly dynamic with changes in perioperative care constantly affecting patient care, recent data affecting rates and risk for perioperative mortality remain very limited.
We obtained the NIS from the Hospital cost and utilization project. The impact of patient and health care system related demographics, including various comorbidities as well as postoperative complications on the outcome of in-hospital mortality after spine fusion were studied. Furthermore, we analyzed the timing of in-hospital mortality.
An estimated total of 1,288,496 primary posterior lumbar spine fusion procedures were performed in the US between 1998 and 2008. The average mortality rate for lumbar spine fusion surgery was 0.2 %. Independent risk factors for in-hospital mortality included advanced age, male gender, large hospital size, and emergency admission. Comorbidities associated with the highest in-hospital mortality after lumbar spine fusion surgery were coagulopathy, metastatic cancer, congestive heart failure and renal disease. Most lethal complications were cerebrovascular events, sepsis and pulmonary embolism. Furthermore, we demonstrated that the timing of death occurred relatively early in the in-hospital period with over half of fatalities occurring by postoperative day 9.
This study provides nationally representative information on risk factors for and timing of perioperative mortality after primary lumbar spine fusion surgery. These data can be used to assess risk for this event and to develop targeted intervention to decrease such risk.
Perioperative mortality; Lumbar spine fusion; Risk factor; Complication; Comorbidity
To evaluate the effect of ventilation strategy on markers of inflammation in patients undergoing spine surgery in the prone position.
Randomized controlled trial.
University-affiliated teaching hospital.
26 ASA physical status 1 and 2 patients scheduled for elective primary lumbar decompression and fusion in the prone position.
Patients were randomized to receive mechanical ventilation with either a tidal volume (VT) of 12 mL/kg ideal body weight with zero positive end-expiratory pressure (PEEP) or VT of 6 mL/kg ideal body weight with PEEP of 8 cm H2O.
Plasma levels of interleukin (IL)-6 and IL-8 were determined at the beginning of ventilation and at 6 and 12 hours later. Urinary levels of desmosine were determined at the beginning of ventilation and on postoperative days 1 and 3.
A significant increase in IL-6, IL-8, and urine desmosine levels was noted over time compared with baseline (P < 0.01). However, no significant difference in the levels of markers was seen between the groups at any time point when controlling for demographics, ASA physical status, body mass index, duration of ventilation, or estimated blood loss.
Although markers of inflammation are increased after posterior spine fusion surgery, ventilation strategy has minimal impact on markers of systemic inflammation.
Lung injury; spine surgery; tidal volume
Lateral lumbar interbody fusion (LLIF) is a minimally invasive technique that has gained growing interest in recent years. We performed a retrospective review of the medical records and operative reports of patients undergoing LLIF between March 2006 and December 2009. We seek to identify the incidence and nature of neurological deficits following LLIF.
New occurring sensory and motor deficits were recorded at 6 and 12 weeks as well as 6- and 12 months of follow-up. Motor deficits were grouped according to the muscle weakness and severity and sensory deficits to the dermatomal zone. New events were correlated to the patient demographics, pre-operative diagnosis, operative levels, and duration of surgery. At each post-operative time-point patients were queried regarding the presence of leg pain.
A total of 235 patients (139 F; 96 M) with a total of 444 levels fused were included. Average age was 61.5 and mean BMI 28.3. At 12 months’ follow-up, the prevalence of sensory deficits was 1.6%, psoas mechanical deficit was 1.6% and lumbar plexus related deficits 2.9%. Although there was no significant correlation between the surgical level L4–5 and an increased psoas mechanical flexion or lumbar plexus related motor deficit, a trend was observed. Independent risk factors for both psoas mechanical hip flexion deficit and lumbar plexus related motor deficit was duration of surgery.
LLIF is a valuable tool for achieving fusion through a minimally invasive approach with little risk to neurovascular structures.
Lateral transpsoatic interbody fusion; Lateral lumbar interbody fusion; Lumbar plexus injury; Anterior thigh pain; Neurologic deficit; Motor deficit
Analysis of the National Inpatient Sample database from 2000 to 2008.
To identify if metabolic syndrome is an independent risk factor for increased major perioperative complications, cost, length of stay and non-routine discharge.
Summary of Background Data
Metabolic syndrome is a combination of medical disorders that has been shown to increase the health risk of the general population. No study has analyzed its impact in the perioperative spine surgery setting.
We obtained the National Inpatient Sample from the Hospital Cost and Utilization Project for each year between 2000 and 2008. All patients undergoing primary posterior lumbar spine fusion were identified and separated into groups with and without metabolic syndrome. Patient demographics and health care system related parameters were compared. The outcomes of major complications, non-routine discharge, length of hospital stay and hospitalization charges were assessed for both groups. Regression analysis was performed to identify if the presence of metabolic syndrome was an independent risk factor for each outcome.
An estimated 1,152,747 primary posterior lumbar spine fusion were performed between 2000 and 2008 in the US. The prevalence of metabolic syndrome as well as the comorbidities of the patients increased significantly over time. Patients with metabolic syndrome had significantly longer length of stay, higher hospital charges, higher rates of non-routine discharges and increased rates of major life-threatening complications compared to patients without metabolic syndrome.
Patients with metabolic syndrome undergoing primary posterior lumbar spinal fusion represent an increasing financial burden on the health care system. Clinicians should recognize that metabolic syndrome represents a risk factor for increased perioperative morbidity.
metabolic syndrome; spinal fusion; lumbar spine; complications; risk factors; perioperative
The rapid growth of spine degenerative surgery has led to unrelenting efforts to define and prevent possible complications, the incidence of which is probably higher than that reported and varies according to the region of the spine involved (cervical and thoracolumbar) and the severity of the surgery. Several issues are becoming progressively clearer, such as complication rates in primary versus revision spinal surgery, complications in the elderly, the contribution of minimally invasive surgery to the reduction of complication rate. In this paper the most common surgical complications in degenerative spinal surgery are outlined and discussed.
Spine surgery; Complication; Failed back surgery; Instability; Disc herniation
Analysis of population based national hospital discharge data collected for the Nationwide Inpatient Sample.
To study perioperative outcomes of circumferential spine surgery performed on either the same or different days of the same hospitalization.
Summary of Background Data
Circumferential spine fusion surgery has been linked to an increased adjusted risk in perioperative morbidity and mortality compared to procedures involving only one site. In order to minimize these risks some surgeons elect to perform the two components of this procedure in separate sessions during the same hospitalization. The value of this approach is uncertain.
Data collected between 1998 and 2006 for the Nationwide Inpatient Sample were analyzed. Hospitalizations during which a circumferential non-cervical spine fusion was performed were identified. Patients were divided into those who had their anterior and posterior portion performed on the same and those performed on different days of the same hospitalization. The prevalence of patient and health care system related demographics were evaluated. Frequencies of procedure-related complications and mortality were determined. Multivariate regression models were created to identify if timing of procedures was associated with an independent increase in risk for adverse events.
We identified a total of 11,265 entries for circumferential spine fusion. Of those, 71.2% (8022) were operated in one session. Complications were more frequent among staged versus same day surgery patients (28.4% vs. 21.7% P<0.0001). The incidence of venous thrombosis, and ARDS was also increased among staged candidates while the trend toward higher mortality (0.5 vs. 0.4%) did not reach significance. In the regression model staged circumferential spine fusions were associated with a 29% increase in the odds morbidity and mortality compared to same day procedures.
Staging circumferential spine surgery procedures during the same hospitalization offers no mortality benefit, and may even expose patients to increased morbidity.
Spinal Fusion; Staged; Simultaneuos; Lumbar spine; Complications; Mortality; Morbidity
Degenerative lumbar scoliosis is a coronal deviation of the spine that is prevalent in the elderly population. Although the etiology is unclear, it is associated with progressive and asymmetric degeneration of the disc, facet joints, and other structural spinal elements typically leading to neural element compression. Clinical presentation varies and is frequently associated with axial back pain and neurogenic claudication. Indications for treatment include pain, neurogenic symptoms, and progressive cosmetic deformity. Non-operative treatment includes physical conditioning and exercise, pharmacological agents for pain control, and use of orthotics and invasive modalities like epidural and facet injections. Operative treatment should be contemplated after multi-factorial and multidisciplinary evaluation of the risks and the benefits. Options include decompression, instrumented stabilization with posterior or anterior fusion, correction of deformity, or a combination of these that are tailored to each patient. Incidence of perioperative complications is substantial and must be considered when deciding appropriate operative treatment. The primary goal of surgical treatment is to provide pain relief and to improve the quality of life with minimum risk of complications.
degenerative scoliosis; adult scoliosis; adult deformity; spinal stenosis; secondary scoliosis
Low back pain as a result of degenerative disc disease imparts a large socioeconomic impact on the health care system. Traditional concepts for treatment of lumbar disc degeneration have aimed at symptomatic relief by limiting motion in the lumbar spine, but novel treatment strategies involving stem cells, growth factors, and gene therapy have the theoretical potential to prevent, slow, or even reverse disc degeneration. Understanding the pathophysiological basis of disc degeneration is essential for the development of treatment strategies that target the underlying mechanisms of disc degeneration rather than the downstream symptom of pain. Such strategies ideally aim to induce disc regeneration or to replace the degenerated disc. However, at present, treatment options for degenerative disc disease remain suboptimal, and development and outcomes of novel treatment options currently have to be considered unpredictable.
Although anterior (ACDF) and posterior cervical fusion (PCDF) are relatively common procedures and both are associated with certain complications, the relative frequency and severity of these complications is unclear. Since for some patients either approach might be reasonable it is important to know the relative perioperative risks for decision-making.
The purposes of this study were to: (1) characterize the patient population undergoing ACDF and PCDF; (2) compare perioperative complication rates; (3) determine independent risk factors for adverse perioperative events; and (4) aid in surgical decision-making in cases in which clinical equipoise exists between anterior and posterior cervical fusion procedures.
The National Inpatient Sample was used and entries for ACDF and PCDF between 1998 and 2006 were analyzed. Demographics and complication rates were determined and regression analysis was performed to identify independent risk factors for mortality after ACDF and PCDF.
ACDF had a shorter length of stay and their procedures were more frequently performed at nonteaching institutions. The incidence of complications and mortality was 4.14% and 0.26% among patients undergoing ACDF and 15.35% and 1.44% for patients undergoing PCDF, respectively. When controlling for overall comorbidity burden and other demographic variables, PCDF was associated with a twofold increased risk of a fatal outcome compared with ACDF. Pulmonary, circulatory, and renal disease were associated with the highest odds for in-hospital mortality.
PCDF procedures were associated with higher perioperative rates of complications and mortality compared with ACDF surgeries. Despite limitations, these data should be considered in cases in which clinical equipoise exists between both approaches.
Level of Evidence
Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.
Despite increasing utilization of surgical spine fusions, a paucity of literature addressing perioperative complications after revision (RPSF) versus primary posterior spine fusions (PPSF) of the thoracic and lumbar spine exists.
To examine demographics of patients undergoing PPSF and RPSF of the thoracic and lumbar spine, assess the incidence of perioperative morbidity and mortality, and determine independent risk factors for in-hospital death.
Analysis of nationally representative data collected for the National Inpatient Sample (NIS).
All discharges included in the NIS with a procedure code for posterior thoracic and lumbar spine fusion from 1998 to 2006.
In-hospital mortality and morbidity.
Data collected for each year between 1998 and 2006 for the National Inpatient Sample were analyzed. Discharges with a procedure code for thoracic and lumbar spine fusion were included in the sample. The prevalence of patient as well as health care system related demographics were evaluated by procedure type (primary vs. revision). Frequencies of procedure-related complications and in-hospital mortality were analyzed. Independent predictors for in-hospital mortality were determined.
We identified 222,549 PPSF and 12,474 RPSF discharges between 1998 and 2006. Patients undergoing PPSF were significantly younger (51.23 (CI= [51.16, 51.31]) years) and had lower average comorbidity indices (0.40 (CI= [0.39, 0.41]) than those undergoing RPSF (52.69 (CI= [52.43, 52.97]) years and 0.44 (CI=[0.43, 0.45]), P<0.0001). The incidence of procedure related complications was 16.02% among RPSF compared to 13.44% in PPSF patients (P<0.0001). In- hospital mortality rates after PPSF were approximately twice those of RPSF (0.28% vs. 0.15%, P=0.006). Adjusted risk factors for increased in-hospital mortality included PPSF compared to RPSF, male gender, and increasing age. A number of comorbidities, complications, and specific surgical indications increased the risk for perioperative death.
Despite being performed in generally younger and healthier patients, and having lower perioperative morbidity, PPSF procedures are associated with increased mortality compared with RPSF procedures. The findings of this study can be used for risk stratification, accurate patient consultation, and hypothesis formation for future research.
Spinal Fusion; Revision; Lumbar spine; Complications; Mortality; Morbidity
The objective of this prospective observational study was to determine if urine desmosine levels, a marker of lung injury, increase in response to the periopreative insults of anterior and posterior spine surgery. Desmosine, a stable breakdown product of elastin, has been proposed as a surrogate marker of lung injury in patients with COPD, tobacco use, and ARDS. We recently evaluated this marker in patients undergoing knee surgery, but the utility of desmosine as a marker of lung injury in patients undergoing spine surgery remains unstudied. In this study, we enrolled ten consecutive patients, who underwent anterior/posterior spine surgery. Patient demographics and perioperative data were recorded. Urine samples were collected at baseline, 1 day, and 3 days postoperatively and analyzed for levels of desmosine using a previously validated radioimmunoassay. Desmosine levels were 35.9 ± 18.2 pmol/mg creatinine at baseline, 38.7 ± 11 pmol/mg creatinine on postoperative day 1, and 70.5 ± 49.1 pmol/mg creatinine on postoperative day 3, respectively. Desmosine/creatinine ratios measured on day 3 postoperatively were significantly elevated compared to levels at baseline, and represented a 96.3% increase. No difference was seen between levels at baseline and day 1 postoperatively. In conclusion, we were able to show a significant increase in urine desmosine levels associated with anterior/posterior spine surgery. In the context of previous studies, our findings suggest that desmosine may be a marker of lung injury in this setting. However, further research is warranted for validation and correlation of desmosine levels to clinical markers and various degrees of lung injury.
urine desmosine; spine; surgery; lung injury; biomarkers; perioperative
We present a case of a revision spinal fusion in which successful bone graft reharvesting was performed from the posterior iliac crest 4 years after initial intracortical harvesting. To date, only anterior iliac crest regeneration has been reported in orthopedic trauma patients. A 70-year-old man with a history of two prior instrumented lumbar fusion operations developed thoracolumbar kyphosis junctional to the lumbosacral fusion mass. His first operation was an instrumented posterolateral lumbar fusion L1 to L5, where bone graft was harvested from the right iliac crest using the intracortical harvesting technique. The second procedure was performed 18 months later and consisted of an extension of the fusion to the sacrum due to L5–S1 level derived symptoms. The bone graft for this procedure was taken with the same technique from the left iliac crest. The development of thoracolumbar junctional kyphosis necessitated the third operation, which consisted of a same-day anterior–posterior extension of the fusion to T10. Prior to this third procedure, a spinal computer tomography was performed that documented regeneration of the cancellous bone in the right iliac crest. This permitted reharvesting of almost 40 ml of cancellous bone using the intracortical bone harvesting technique from the right iliac crest. Histological analysis showed mature bone. Cancellous bone regeneration and restoration of the local anatomy of the ilium are possible after intracortical bone harvesting. This regeneration can provide autologous bone graft to assist fusion in subsequent operations.
posterior iliac crest bone graft; intracortical technique; bone harvesting; reharvesting; complications
Intraspinous and pedicle screw-based (PSB) dynamic instrumentation systems have been in use for a decade now. By direct or indirect decompression, these devices theoretically establish less painful segmental motion by diminishing pathologic motion and unloading painful disks. Ideally, dynamics should address instability in the early stages of degenerative spondylolisthesis before excessive translation occurs. Evidence to date indicates that Grade II or larger slips requiring decompression should be fused. In addition, multiple segment listhesis, severe coronal plane deformities, increasing age, and osteoporosis have all been listed as potential contraindications to dynamic stabilization. We reviewed the exclusion and inclusion criteria found in various dynamic stabilization studies and investigational drug exemption (IDE) protocols. We summarize the reported limitations for both pedicle- and intraspinous-based systems. We then conducted a retrospective chart and imaging review of 100 consecutive cases undergoing fusion for degenerative spondylolisthesis. All patients in our cohort had been indicated for and eventually underwent decompression of lumbar stenosis secondary to spondylolisthesis. We estimated how many patients in our population would have been candidates for dynamic stabilization with either interspinous or pedicle-based systems. Using the criteria for instability outlined in the literature, 32 patients demonstrated translation requiring fusion surgery and 24 patients had instability unsuitable for dynamic stabilization. Six patients had two-level slips and were excluded. Two patients had coronal imbalance too great for dynamic systems. Twelve patients were over the age of 80 and 16 demonstrated osteoporosis as diagnosed by bone scan. Finally, we found two of our patients to have vertebral compression fractures adjacent to the site of instrumentation, which is a strict exclusion criteria in all dynamic trials. Thirty-four patients had zero exclusion criteria for intraspinous devices and 23 patients had none for PSB dynamic stabilization. Therefore, we estimate that 34 and 23% of degenerative spondylolisthesis patients indicated for surgery could have been treated with either intraspinous or pedicle-based dynamic devices, respectively.
Dynamic stabilization; Degenerative spondylolisthesis; Dynamics; Spinal fusion
Subgroup analyses according to treatment received.
To evaluate whether baseline radiographic findings predicted outcomes in patients with degenerative spondylolisthesis (DS).
SUMMARY OF BACKGROUND DATA
The SPORT combined randomized and observational DS cohorts.
The Meyerding listhesis grade was determined on the neutral radiograph (n=222). Patients were classified as having low disk height if disk height was less than 5 mm. Flexion-extension radiographs (n=185) were evaluated for mobility. Those with greater than 10° rotation or 4mm translation were considered Hypermobile. Changes in outcome measures were compared between listhesis (Grade 1 vs. Grade 2), disk height (Low vs. Normal) and mobility (Stable vs. Hypermobile) groups using longitudinal regression models adjusted for potential confounders. Outcome measures included SF-36 bodily pain (BP) and physical function (PF) scales, Oswestry disability index (ODI), stenosis bothersomeness index (SBI), and low back pain bothersomeness scale.
Overall, 86% had a Grade 1 listhesis, 78% had Normal disk height, and 73% were Stable. Baseline symptom severity was similar between groups. Overall, surgery patients improved more than patients treated non-operatively. At one year, outcomes were similar in surgery patients across listhesis, disk height, and mobility groups (ODI: Grade 1 -23.7 vs. Grade 2 -23.3, p=0.90; Normal disk height-23.5 vs. Low disk height -21.9, p=0.66; Stable -21.6 vs. Hypermobile -25.2, p=0.30). Among those treated nonoperatively, Grade 1 patients improved more than Grade 2 patients (BP +13.1 vs. -4.9, p=0.019; ODI -8.0 vs. +4.8, p=0.010 at 1 year), and Hypermobile patients improved more than Stable patients (ODI -15.2 vs -6.6, p=0.041; SBI -7.8 vs -2.7, p=0.002 at 1 year).
Regardless of listhesis grade, disk height or mobility, patients who had surgery improved more than those treated non-operatively. These differences were due, in part, to differences in non-operative outcomes, which were better in patients classified as Grade 1 or Hypermobile.
radiograph; surgery; degenerative spondylolisthesis; outcomes; non-operative
Low-back pain is a common, disabling medical condition, and one of the major causes is disc degeneration. Total disc replacements are intended to treat back pain by restoring disc height and re-establishing functional motion and stability at the index level. The objective of this study was to determine the effect on range of motion (ROM) and stiffness after implantation of the ProDisc®-L device in comparison to the intact state. Twelve L5–S1 lumbar spine segments were tested in flexion/extension, lateral bending, and axial rotation with axial compressive loads of 600 N and 1,200 N. Specimens were tested in the intact state and after implantation with the ProDisc®-L device. ROM was not significantly different in the implanted spines when compared to their intact state in flexion/extension and axial rotation but increased in lateral bending. Increased compressive load did not affect ROM in flexion/extension or axial rotation but did result in decreased ROM in lateral bending and increased stiffness in both intact and implanted spine segments. The ProDisc®-L successfully restored or maintained normal spine segment motion.
total disc replacement; biomechanics; lumbar spine; ProDisc®-L
Sophisticated and newer imaging capabilities have resulted in increased reporting and treatment options of spinal lumbar synovial cysts (LSS). Most of the patients with lumbar cysts tend to be in their sixth decade of life with a slight female predominance. The incidence of LSS is thought to be less than 0.5% of the general symptomatic population. They may be asymptomatic and found incidentally or the epidural growth of cysts into the spinal canal can cause compression of neural structures and hence associated clinical symptoms. Most of the symptomatic LSS patients present with radicular pain and neurological deficits. Spinal synovial cysts are commonly found at L4-5 level, the site of maximum mobility. They may be unilateral or bilateral and at one or multilevel. MRI is considered the tool of choice for its diagnosis. The etiology of LSS is still unclear, but underlying spinal instability, facet joint arthropathy and degenerative spondylolisthesis has a strong association for worsening symptoms and formation of spinal cysts. Synovial cysts resistant to conservative therapy should be treated surgically. Resection and decompression with or without fusion and instrumentation remains an appropriate option. Synovial cysts may recur following surgery. The optimal approach for patients with juxtafacet LSS remains unclear. The best surgical treatment option for each particular individual should be tailored depending upon the symptoms, radiological findings and other co morbidities.
Lumbar synovial cysts; Spondylolisthesis; Conservative treatment; Surgical treatment; Resection and decompression; Spinal fusion