Anterior lumbar spine surgery: a systematic review and meta-analysis of associated complications

BACKGROUND CONTEXT

The anterior approach to the lumbar spine is increasingly used to accomplish various surgical procedures. However, the incidence and risk factors for complications associated with anterior lumbar spine surgery (ALS) have not been fully elucidated.

PURPOSE

To identify and document types of complications and complication rates associated with ALS, determine risk factors for these events, and evaluate the effect of measures used to decrease complication rates.

STUDY DESIGN

Systematic review and meta-analysis.

METHODS

A systematic review of the English-language literature was conducted for articles published between January 1992 and December 2013. A MEDLINE search was conducted to identify articles reporting complications associated with ALS. For each complication, the data were combined using a generalized linear mixed model with a binomial probability distribution and a random effect based on the study. Predictors used were the type of procedure (open, minimally invasive, or laparoscopic), the approach used (transperitoneal vs. retroperitoneal), use of recombinant bone morphogenetic protein-2, use of preoperative computed tomography angiography (CTA), and the utilization of an access surgeon. Open surgery was used as a reference category.

RESULTS

Seventy-six articles met final inclusion criteria and reported complication rates in 11,410 patients who underwent arthrodesis and/or arthroplasty via laparoscopic, mini-open, and open techniques. The overall complication rate was 14.1%, with intraoperative and postoperative complication rates of 9.1% and 5.2%, respectively. Only 3% of patients required reoperation or revision procedures. The most common complications reported were venous injury (3.2%), retrograde ejaculation (2.7%), neurologic injury (2%), prosthesis related (2%), postoperative ileus (1.4%), superficial infection (1%), and others (1.3%). Laparoscopic and transperitoneal procedures were associated with higher complication rates, whereas lower complication rates were observed in patients receiving mini-open techniques. Our analysis indicated that the use of recombinant bone morphogenetic protein-2 was associated with increased rates of retrograde ejaculation; however, there may be limitations in interpreting these data. Data regarding the use of preoperative CTA and an access surgeon were limited and demonstrated mixed benefit.

CONCLUSIONS

Overall complication rates with ALS are relatively low, with the most common complications occurring at a rate of 1% to 3%. Complication rates are related to surgical technique, approach, and implant characteristics. Further randomized controlled trials are needed to validate the use of preventative measures including CTA and the use of an access surgeon.

What is new in the diagnosis and prevention of spine surgical site infections

BACKGROUND CONTEXT

Surgical site infection (SSI) after spinal surgery can result in several serious secondary complications, such as pseudoarthrosis, neurological injury, paralysis, sepsis, and death. There is an increasing body of literature on risk factors, diagnosis, and specific intraoperative interventions, including attention to sterility of instrumentation, application of minimally invasive fusion techniques, intraoperative irrigation, and application of topical antibiotics, that hold the most promise for reduction of SSI.

PURPOSE

The purpose of this review is to identify and summarize the recent literature on the incidence, risk factors, diagnosis, prevention, and treatment of SSIs after adult spine surgery.

STUDY DESIGN

The study design included systematic review and literature synthesis.

METHODS

For the systematic reviews, a search was performed in Medline and Scopus using keywords derived from a preliminary review of the literature and Medline MeSH terms. These studies were then manually filtered to meet the study criteria outlined in each section. Studies were excluded via predetermined criteria, and the majority of articles reviewed were excluded.

RESULTS

There are a number of patient- and procedure-specific risk factors for SSI. Surgical site infection appears to have significant implications from the patients' perspective on outcome of care. Diagnosis of SSI appears to rely primarily on clinical factors, while laboratory values such as C-reactive protein are not universally sensitive. Similarly, novel methods of perioperative infection prophylaxis such as local antibiotic administration appear to be modestly effective.

CONCLUSIONS

Surgical site infections are a common multifactorial problem after spine surgery. There is compelling evidence that improved risk stratification, detection, and prevention will reduce SSIs.

Bone substitutes and expanders in Spine Surgery: A review of their fusion efficacies

STUDY DESIGN

A narrative review of literature.

OBJECTIVE

This manuscript intends to provide a review of clinically relevant bone substitutes and bone expanders for spinal surgery in terms of efficacy and associated clinical outcomes, as reported in contemporary spine literature.

SUMMARY OF BACKGROUND DATA

Ever since the introduction of allograft as a substitute for autologous bone in spinal surgery, a sea of literature has surfaced, evaluating both established and newly emerging fusion alternatives. An understanding of the available fusion options and an organized evidence-based approach to their use in spine surgery is essential for achieving optimal results.

METHODS

A Medline search of English language literature published through March 2016 discussing bone graft substitutes and fusion extenders was performed. All clinical studies reporting radiological and/or patient outcomes following the use of bone substitutes were reviewed under the broad categories of Allografts, Demineralized Bone Matrices (DBM), Ceramics, Bone Morphogenic proteins (BMPs), Autologous growth factors (AGFs), Stem cell products and Synthetic Peptides. These were further grouped depending on their application in lumbar and cervical spine surgeries, deformity correction or other miscellaneous procedures viz. trauma, infection or tumors; wherever data was forthcoming. Studies in animal populations and experimental in vitro studies were excluded. Primary endpoints were radiological fusion rates and successful clinical outcomes.

RESULTS

A total of 181 clinical studies were found suitable to be included in the review. More than a third of the published articles (62 studies, 34.25%) focused on BMP. Ceramics (40 studies) and Allografts (39 studies) were the other two highly published groups of bone substitutes. Highest radiographic fusion rates were observed with BMPs, followed by allograft and DBM. There were no significant differences in the reported clinical outcomes across all classes of bone substitutes.

CONCLUSIONS

There is a clear publication bias in the literature, mostly favoring BMP. Based on the available data, BMP is however associated with the highest radiographic fusion rate. Allograft is also very well corroborated in the literature. The use of DBM as a bone expander to augment autograft is supported, especially in the lumbar spine. Ceramics are also utilized as bone graft extenders and results are generally supportive, although limited. The use of autologous growth factors is not substantiated at this time. Cell matrix or stem cell-based products and the synthetic peptides have inadequate data. More comparative studies are needed to evaluate the efficacy of bone graft substitutes overall.

Is It Necessary to Extend a Multilevel Posterior Cervical Decompression and Fusion to the Upper Thoracic Spine?

STUDY DESIGN

A retrospective cohort analysis.

OBJECTIVE

The aim of this study was to determine if there is a difference in the revision rate in patients who undergo a multilevel posterior cervical fusions ending at C7, T1, or T2-T4.

SUMMARY OF BACKGROUND DATA

Multilevel posterior cervical decompression and fusion is a common procedure for patients with cervical spondylotic myelopathy, but there is little literature available to help guide the surgeon in choosing the caudal level of a multilevel posterior cervical fusion.

METHODS

Patients who underwent a three or more level posterior cervical fusion with at least 1 year of clinical follow-up were identified. Patients were separated into three groups on the basis of the caudal level of the fusion, C7, T1, or T2-T4, and the revision rate was determined. In addition, the C2-C7 lordosis and the C2-C7 sagittal vertical axis (SVA) was recorded for patients with adequate radiographic follow-up at 1 year.

RESULTS

The overall revision rate was 27.8% (61/219 patients); a significant difference in the revision rates was identified between fusions terminating at C7, T1, and T2-T4 (35.3%, 18.3%, and 40.0%, P = 0.008). When additional variables were taken into account utilizing multivariate linear regression modeling, patients whose construct terminated at C7 were 2.29 (1.16-4.61) times more likely to require a revision than patients whose construct terminated at T1 (P = 0.02), but no difference between stopping at T1 and T2-T4 was identified.

CONCLUSION

Multilevel posterior cervical fusions should be extended to T1, as stopping a long construct at C7 increases the rate of revision.

LEVEL OF EVIDENCE

3.

C1 fractures: a review of diagnoses, management options, and outcomes

The atlas is subject to fracture under axial load, often due to traumatic injuries such as shallow dives and automobile accidents. These fractures account for 2-13 % of injuries to the cervical spine [Marcon RM et al. Clinics (Sao Paulo) 68(11):1455-61, 2013]. Fractures of the C1 vertebra are often difficult to diagnose, as there is often no neurological deficit or easily identifiable findings on radiographs. However, injuries to the atlas can be associated with vertebral artery injury and atlantoaxial or atlanto-occipital instability, making prompt and accurate diagnosis imperative. A detailed understanding of the anatomy, inherent stability, and common injury patterns is essential for any surgeon treating spinal trauma. This chapter explores the diagnosis and management of C1 fractures, as well as outcomes after treatment.

Risk Factors for Pseudarthrosis After Surgical Site Infection of the Spine

Background

Pseudarthrosis following spinal fusion is a complication that frequently requires revision surgery. Reported rates of pseudarthrosis after surgical site infection (SSI) range from 30% to 85%, but few studies have identified infection as an independent risk factor for its development. The purpose of this study was to determine the incidence of clinically symptomatic pseudarthrosis in patient who developed SSI following lumbar fusion and to identify factors associated with its development.

Methods

This was a retrospective review of a prospectively collected database. Patients who underwent spinal surgery and developed SSI between January 2005 and March 2015 with a minimum 2-year follow-up were included. Patient-specific and procedural characteristics were recorded. Presence of pseudarthrosis was determined clinically by the treating surgeon and was confirmed radiographically. All those in the Pseudarthrosis group required a revision procedure after the eradication of infection. Univariate and multivariate analyses were conducted as appropriate.

Results

A total of 416 patients were included. Of these, 21 (5.0%) developed symptomatic pseudarthrosis following SSI. In this cohort, multivariate regression showed that age, Charlson Comorbidity Index, male sex, and surgical approach were not significant predictors of pseudarthrosis formation. However, number of levels fused was found to be the leading predictor for pseudarthrosis development (odds ratio [OR], 1.356/level, P < .001), followed by body mass index (OR, 1.083/point, P < .009) in this cohort. The number of levels fused was found to be a significant predictor of hardware removal (OR, 1.190/level, P < .001). Of the 21 pseudarthrosis cases, 85.7% found staphylococcal species, of which 27.8% exhibited methicillin-resistant Staphylococcus aureus.

Conclusions

The number of spinal levels fused and body mass index are independent predictors of pseudarthrosis in patients who develop SSI after spinal fusion.

Level of Evidence

Level 4.

Clinical Relevance

This is the first known study to specifically identify risk factors for the development of symptomatic pseudarthrosis.

Diagnosis and neurologic status as predictors of surgical site infection in primary cervical spinal surgery

BACKGROUND CONTEXT

Surgical site infection (SSI) incidence after cervical spinal surgery ranges from 0.1% to 17%. Although the general risk factors for SSI have been discussed, the relationship of neurologic status and trauma to SSI has not been explicitly explored.

PURPOSE

This study aimed to study associated risk factors and to report the incidence of SSI in patients who have undergone cervical spinal surgery with the following four preoperative diagnoses: (1) degenerative disease with no myelopathy (MP), (2) degenerative disease with MP, (3) traumatic cervical injury without spinal cord injury (SCI), (4) traumatic cervical injury with SCI. We hypothesize that SSI incidence would increase from Group (1) to Group (4).

STUDY DESIGN

Retrospective database analysis was carried out.

PATIENTS SAMPLE

We used International Classification of Diseases codes to identify the four groups of patients in the U.S. Nationwide Inpatient Sample (NIS) from the years 2000 to 2011. We complemented this study with a similar search in our institutional database (ID) from the years 2000 to 2013. Patients with concomitant congenital deformity, infection, inflammatory disease, and neoplasia were excluded, as were revision surgeries.

OUTCOME MEASURES

The primary outcome studied was the occurrence of SSI. Statistical analyses included bivariate comparisons and chi-square distribution of demographic data and multivariable regression for demographic, surgical, and outcome variables.

RESULTS

A total of 1,247,281 and 5,540 patients met inclusion criteria in the NIS database and the ID, respectively. Overall SSI incidence was 0.73% (NIS) versus 1.75% (ID). Surgical site infection incidence increased steadily from 0.52% in Group (1) to 1.97% in Group (4) in the NIS data and from 0.88% to 5.54% in the ID. Differences between diagnostic groups and cohorts reached statistical significance. Surgical site infection was predicted significantly by status (odds ratio [OR] 1.69, p<.0001) and trauma (OR 1.30, p=.0003) in the NIS data. Other significant predictors included the following: approach, number of levels fused, female gender, black race, medium size hospital, rural hospital, large hospital, western US hospital and Medicare coverage. In the ID, only trauma (OR 2.11, p=.03) reached significance when accounting for comorbidities.

CONCLUSIONS

Both primary diagnosis (trauma vs. degenerative) and neurologic status (MP or SCI) were found to be strong and independent predictors of SSI in cervical spine surgery.

Implantable strain sensor to monitor fracture healing with standard radiography

Current orthopaedic clinical methods do not provide an objective measure of fracture healing or weight bearing for lower extremity fractures. The following report describes a novel approach involving in-situ strain sensors to objectively measure fracture healing. The sensor uses a cantilevered indicator pin that responds to plate bending and an internal scale to demonstrate changes in the pin position on plain film radiographs. The long lever arm amplifies pin movement compared to interfragmentary motion, and the scale enables more accurate measurement of position changes. Testing with a human cadaver comminuted metaphyseal tibia fracture specimen demonstrated over 2.25 mm of reproducible sensor displacement on radiographs with as little as 100 N of axial compressive loading. Finite element simulations determined that pin displacement decreases as the fracture callus stiffens and that pin motion is linearly related to the strain in the callus. These results indicate that an implanted strain sensor is an effective tool to help assess bone healing after internal fixation and could provide an objective clinical measure for return to weight bearing.

An implanted pH sensor read using radiography

A biomedical sensor was developed to measure local pH near orthopedic implants to detect and study implant-associated infection. The sensor is read using plain radiography, a technique which is noninvasive, inexpensive, ubiquitously available in medical facilities, and routinely used in diagnosis and follow-up. The sensor comprises a radiopaque tungsten indicator pin embedded within a chemically responsive hydrogel that exhibits a pH-dependent swelling. A stainless steel well holds this hydrogel and attaches to an orthopedic plate. The local pH may be determined from the extent of hydrogel swelling by radiographically measuring the indicator position relative to the well. We calibrated the sensor in a series of standard pH buffers and tested it during bacterial growth in culture. The sensor was robust: its response was negligibly affected by changes in temperature, ionic strength within the normal physiological range, or long-term incubation with reactive oxygen species generated from hydrogen peroxide and copper. Pooled data from several sensors fabricated at different times and tested in different conditions had a root-mean-square deviation from a pH electrode reading of 0.24 pH units. Radiographic measurements were also performed in cadaveric tissue with the sensor attached to an orthopedic plate fixed to a tibia. Pin position readings varied by 100 μm between observers surveying the same radiographs, corresponding to 0.065 pH units precision in the range pH 4-8. The sensor was designed to augment standard radiographs of tissue, bony anatomy, and hardware by also indicating local chemical concentrations.

Allogeneic and Autogenous Bone Grafts Are Affected by Historical Donor Environmental Exposure

BACKGROUND

Bone graft materials are routinely evaluated for infectious agents; however, data regarding contamination of bone graft from environmental exposure of the donors to osteotoxic substances such as lead are not routinely available. In animal models, stored lead in bone has been shown to impair fracture healing and osteocyte function. In clinical studies, lead is linked to skeletal disease at relatively low concentrations. Presumably the levels of lead in allografts mirror the level of lead in bone in the population; however, the degree to which processing might decrease this and the frequency with which potentially osteotoxic levels appear in bone grafts have not been studied.

QUESTIONS/PURPOSES

(1) Does processing of donor bone for allografts result in lower concentrations of lead in commercial allograft when compared with autologous bone graft; and (2) what proportion of bone grafts contain potentially osteotoxic levels of lead from > 2.0 to 20.0 µg/g corresponding to environmental exposure?

METHODS

Allograft from commercial sources and autologous bone graft materials were examined for lead content using ICP- atomic absorption spectrophotometric analysis. We analyzed bone graft specimens from 42 donors, including 26 corticocancellous tibial specimens from commercially available bone graft materials and 16 autograft corticocancellous tibial specimens. Lead levels were determined for the cortical (n = 42) and cancellous (n = 42) portions of each specimen. For quality control, all instruments, plastic and glassware, were regularly tested for lead contamination by atomic absorption spectrophotometry throughout the experiments. In addition, spectrophotometer calibration was verified using Standard Reference Material 1486 bone meal (NIST, Gaithersburg, MD, USA). Descriptive statistical analysis was performed using SPSS 20 (SPSS Inc, Chicago, IL, USA). Using these techniques, a lead level > 2 µg/g to 20 µg/g corresponds to some degree of environmental exposure to lead.

RESULTS

With the numbers available in the present study, there were no differences in mean lead level between commercial bone graft materials and autogenous bone graft, 2.1 µg/g (95% confidence interval [CI], 1.6-3.3 µg/g) versus 2.0 µg/g (95% CI, 1.0-4.5 µg/g; p = 0.86). The range for all tested samples varied from < 0.1 to 5.0 µg/g. Likewise, there were no differences in mean lead level between cortical bone grafts, which contained 2.2 µg/g (95% CI, 1.5-3.7 µg/g), and cancellous grafts, which contained 1.9 µg/g (95% CI, 1.2-3.4 µg/g; p = 0.58). Thirty-eight percent (16 of 42) of the specimens had levels between 2.0 µg/g and 20 µg/g within a range expected for individuals with known environmental exposure to lead.

CONCLUSIONS

This study demonstrates that lead is present in up to one-third of tibial allograft and autograft bone specimens at potentially osteotoxic levels regardless of the source or screening. Further research is needed to delineate the relationship with nonunion or pseudoarthrosis after procedures in which allograft is used. In addition, further study would examine concentrations of lead and other environmental contaminants in other graft types.

CLINICAL RELEVANCE

Comparable levels of lead exposure have been associated with toxic effects on skeletal tissue. Further study of bone graft used in fusion procedures and other procedures is necessary to define the magnitude of osteotoxic effects in the setting of fracture care or fusion procedures.

Management of West Nile Encephalitis: An Uncommon Complication of West Nile Virus

West Nile virus disease (WNVD) is a mosquito-borne disease that affects the meninges and central nervous system, causing West Nile virus (WNV) encephalitis, a debilitating, life-threatening condition, especially in the elderly. While there is a lot of research discussing different aspects of the disease, the treatment is mainly unknown. We conducted a literature review to explore the wide variety of treatment options that consolidate the knowledge about the most recent management of WNV encephalitis. We did a combined advanced search and Medical Subject Headings (MeSH) search on PubMed. Inclusion criteria included papers written in the English language and human subjects research for the past 25 years. We initially gather 110 papers, and after applying the inclusion/exclusion criteria, we end up with 30 articles for the paper's discussion. This review aims to provide clinicians with an overview of the latest approach in treating and managing hospitalized WNVD patients. It discusses case reports and the outcome of different treatment regimens done in vitro and in vivo. The study discusses all the advancements in treatment and prophylaxis and compares their effectiveness. However, more research is warranted to gain further insight to develop a single guideline for the management of this disease. This review discusses the following treatment modalities: ribavirin, interferon-alpha, intravenous immunoglobulin (IVIG), and other less-used drugs. More studies about ribavirin are needed to know if the drug is useful for WNV encephalitis. Interferon-alpha has been shown to have both protective and disease limiting properties. At the moment, there are no guidelines for the treatment of WNV encephalitis, nor is there a single Food and Drug Administration (FDA)-approved drug. For the time being, IVIG offers the best results in treating WNV encephalitis

Babesiosis: Appreciating the Pathophysiology and Diverse Sequela of the Infection

Babesiosis is a blood-borne disease found mainly in the United States caused by a parasitic piroplasm. While most infections are mild to moderate in immunocompetent hosts, life-threatening complications can occur in those with significant comorbidities like congestive heart failure (CHF) or chronic obstructive pulmonary disease (COPD). There is sparse literature discussing the complications of Babesia microti infection or the pathophysiology and management thereof. A literature review was conducted to consolidate the current knowledge about the disease, pathophysiology, and proposed management of all potential complications based on risk factors and other clinical information. A MeSH cross-references strategy was employed in PubMed using the search terms “babesia” and “babesiosis” and the established associated conditions, and the search expanded to increase capture. Only papers written in the English language and discussing human subjects in the North American patient population were included. The initial search yielded 315 papers and, after applying the inclusion/exclusion criteria, a final number of 18 was reviewed. The various complications and pathophysiology thereof are then discussed according to organ system. Babesia is a subversive parasite associated with a variety of conditions. We hope a better appreciation of all potential presentations and complications will help clinicians manage this increasingly common zoonosis and reduce adverse effects. More research is recommended into the pathophysiology and prevention of complications following this and other tick-borne illnesses.

Luminescent Spectral Rulers for Noninvasive Displacement Measurement through Tissue

A luminescent spectral ruler was developed to measure micrometer to millimeter displacements through tissue. The spectral ruler has two components: a luminescent encoder patterned with alternating stripes of two spectrally distinct luminescent materials and an analyzer mask with periodic transparent windows the same width as the encoder stripes. The analyzer mask is placed over the encoder and held so that only one type of luminescent stripe is visible through the window; sliding the analyzer over the encoder modulates the luminescence spectrum acquired through the analyzer windows, enabling detection of small displacements without imaging. We prepared two types of spectral rulers, one with a fluorescent encoder and a second with an X-ray excited optical luminescent (XEOL) encoder. The fluorescent ruler used two types of quantum dots to form stripes that were excited with 633 nm light and emitted at 645 and 680 nm, respectively. Each ruler type was covered with chicken breast tissue to simulate implantation. The XEOL ruler generated a strong signal with negligible tissue autofluorescence but used ionizing radiation, while the fluorescence ruler used non-ionizing red light excitation but required spectral fitting to account for tissue autofluorescence. The precision for both types of luminescent spectral rulers (with 1 mm wide analyzer windows, and measured through 6 mm of tissue) was <2 μm, mostly limited by shot noise. The approach enabled high micrometer to millimeter displacement measurements through tissue and has applications in biomechanical and mechanochemical measurements (e.g., tracking postsurgical bone healing and implant-associated infection).

Calcium-Alkali Syndrome: Historical Review, Pathophysiology and Post-Modern Update

Milk-alkali syndrome or calcium-alkali syndrome (CAS) is the triad of hypercalcemia, metabolic alkalosis and renal impairment. It is often related to ingestion of high amounts of calcium carbonate, which was used historically for the treatment of peptic ulcer disease. The incidence of the syndrome decreased dramatically after the introduction of newer peptic ulcer medications such as proton pump inhibitors and histamine blocking agents. However, a resurgence was seen in the late 1980s with the wide use of over-the-counter calcium supplements, mainly by females for osteoporosis prophylaxis. The modern version of the syndrome continues to evolve along with medical management. This review focuses on the historical context of CAS, pathogenesis, resurgence of the condition with variable presentations, and contemporary management.

Delayed Bone Infarct in the Ilium Following a Pelvic Crush Injury and Embolization: A Case Report

CASE

We present a case of delayed osteonecrosis of the ilium. After receiving embolization and multiple orthopaedic procedures following a complex pelvic crush injury, the patient subsequently developed posterior pelvic pain and tenderness over the posterior superior iliac spine, along with pain on sacroiliac joint compression. Magnetic resonance imaging of the pelvis demonstrated a bone infarction in the left ilium adjacent to the sacroiliac joint.

CONCLUSION

The symptoms from osteonecrosis of the ilium may simulate sacroiliitis or other conditions. It is important to keep the differential diagnosis in mind when considering additional management for posterior pelvic pain in the setting of prior trauma and preexisting hardware.

Prevalence of Fabry Disease in Patients With Cryptogenic Strokes: A Systematic Review

Fabry disease (FD) is an X-linked disorder involving multiple organs. Stroke is a serious and frequent complication of FD. Cryptogenic stroke is a common presentation of FD, especially in the young population. The etiology of cryptogenic stroke is highly variable and difficult to assess, frequently leaving patients without a primary diagnosis. We conducted a systematic review to investigate the pooled prevalence of FD among patients with cryptogenic stroke, or patients with FD in whom a stroke was the presenting condition. English-language studies involving humans published in the last 20 years were included in this systematic review. FD was more common in male patients and tended to present at an earlier age. The frequency of hemorrhagic and ischemic strokes in this population was similar to that in the general population. There was a high rate of stroke recurrence in the study sample, even among patients undergoing enzyme replacement therapy. We conclude that screening for FD in patients with cryptogenic stroke is low yield and not cost-effective. However, it may be worthwhile to screen for FD among patients with recurrent strokes.

LITE-1 mediates behavioral responses to X-rays in Caenorhabditis elegans

Rapid sensory detection of X-ray stimulation has been documented across a wide variety of species, but few studies have explored the underlying molecular mechanisms. Here we report the discovery of an acute behavioral avoidance response in wild type Caenorhabditis elegans to X-ray stimulation. The endogenous C. elegans UV-photoreceptor protein LITE-1 was found to mediate the locomotory avoidance response. Transgenic expression of LITE-1 in C. elegans muscle cells resulted in paralysis and egg ejection responses to X-ray stimulation, demonstrating that ectopic expression of LITE-1 can confer X-ray sensitivity to otherwise X-ray insensitive cells. This work represents the first demonstration of rapid X-ray based genetically targeted (X-genetic) manipulation of cellular electrical activity in intact behaving animals. Our findings suggest that LITE-1 has strong potential for use in this minimally invasive form of neuromodulation to transduce transcranial X-ray signals for precise manipulation of neural activity in mammals, bypassing the need for invasive surgical implants to deliver stimulation.

Spatial Resolution for X-ray Excited Luminescence Chemical Imaging (XELCI)

Measuring chemical concentrations at the surface of implanted medical devices is important for elucidating the local biochemical environment, especially during implant infection. Although chemical indicator dyes enable chemical measurements in vitro, they are usually ineffective when measuring through tissue because the background obscures the dye signal and scattering dramatically reduces the spatial resolution. X-ray excited luminescent chemical imaging (XELCI) is a recent imaging modality which overcomes these limitations using a focused X-ray beam to excite a small spot of red light on scintillator-coated medical implants with well-defined location (because X-rays are minimally scattered) and low background. A spectrochemical indicator film placed over the scintillator layer, e.g., a polymer film containing pH-indicator dyes, absorbs some of the luminescence according to the local chemical environment, and this absorption is then detected by measuring the light intensity/spectrum passing through the tissue. A focused X-ray beam is used to scan point-by-point with a spatial resolution mainly limited by the X-ray beam width with minimum increase from X-ray absorption and scattering in the tissue. X-ray resolution, implant surface specificity, and chemical sensitivity are the three key features of XELCI. Here, we study spatial resolution using optically absorptive targets. For imaging a series of lines, the 20-80% knife-edge resolution was ∼285 (±15) μm with no tissue and 475 ± 18 and 520 ± 34 μm, respectively, through 5 and 10 mm thick tissue. Thus, doubling the tissue depth did not appreciably change the spatial resolution recorded through the tissue. This shows the promise of XELCI for submillimeter chemical imaging through tissue.

Do Inflammatory Cytokines Affect Patient Outcomes After ACDF?

STUDY DESIGN

Prospective cohort study.

OBJECTIVE

The aim was to determine the relationship between serum inflammatory mediators, preoperative cervical spine disease severity, and clinical outcomes after anterior cervical discectomy and fusion (ACDF).

SUMMARY OF BACKGROUND DATA

Given the role of the inflammatory cascade in spinal degenerative disease, it has been hypothesized that inflammatory markers may serve as a predictor of patient outcomes after surgery.

MATERIALS AND METHODS

All patients over age 18 who underwent ACDF for cervical spondylosis with associated radiculopathy and/or myelopathy between 2015 and 2017 from a single institution were prospectively recruited. Preoperative serum inflammatory markers including interleukin (IL)-6, IL-8, tumor necrosis factor-α, high-mobility group box-1 (HMGB1), and white blood cells were measured and correlated to patient demographics, surgical characteristics, duration of symptoms, previous opioid use, and preoperative and 1-year postoperative patient-reported outcomes measures (PROMs) including the neck disability index (NDI), visual analog scale neck pain, visual analog scale arm pain, and Physical and Mental Component Scores of the Short Form-12 (PCS and MCS, respectively) using spearman's rho coefficient.

RESULTS

A total of 77 patients were enrolled with follow-up PROMs available for 62% (n=48) of patients at a minimum of 1-year after ACDF. The absolute concentrations of IL-6 and tumor necrosis factor-α were found to be weakly correlated with one another (ρ=0.479). Preoperative symptoms lasting <1-year were weakly correlated with elevation in HMGB1 (ρ=0.421). All other patient demographics exhibited negligible correlation with the preoperative inflammatory markers. Lower preoperative PCS (ρ=0.355) and higher preoperative NDI (ρ=0.336) were weakly correlated with elevated HMGB1. Lower MCS (ρ=0.395) and higher NDI (ρ=0.317) preoperatively were weakly correlated with elevated white blood cells. Postoperative improvement in MCS (ρ=0.306) and MCS recovery ratio (ρ=0.321) exhibited a weakly positive correlation with IL-6.

CONCLUSION

Preoperative cytokine levels demonstrated minimal correlation with preoperative symptoms or clinical improvement, suggesting that profiling of patient cytokines has limited utility in predicting outcomes after ACDF.

LEVEL OF EVIDENCE

Level III.