Common motifs shared by conserved enhancers of Drosophila midline glial genes.

Coding sequences are usually the most highly conserved sectors of DNA, but genomic regions controlling the expression pattern of certain genes can also be conserved across diverse species. In this study, we identify five enhancers capable of activating transcription in the midline glia of Drosophila melanogaster and each contains sequences conserved across at least 11 Drosophila species. In addition, the conserved sequences contain reiterated motifs for binding sites of the known midline transcriptional activators, Single-minded, Tango, Dichaete, and Pointed. To understand the molecular basis for the highly conserved genomic subregions within enhancers of the midline genes, we tested the ability of various motifs to affect midline expression, both individually and in combination, within synthetic reporter constructs. Multiple copies of the binding site for the midline regulators Single-minded and Tango can drive expression in midline cells; however, small changes to the sequences flanking this transcription factor binding site can inactivate expression in midline cells and activate expression in tracheal cells instead. For the midline genes described in this study, the highly conserved sequences appear to juxtapose positive and negative regulatory factors in a configuration that activates genes specifically in the midline glia, while maintaining them inactive in other tissues, including midline neurons and tracheal cells.

Identification of motifs that are conserved in 12 Drosophila species and regulate midline glia vs. neuron expression.

Functional complexity of the central nervous system (CNS) is reflected by the large number and diversity of genes expressed in its many different cell types. Understanding the control of gene expression within cells of the CNS will help reveal how various neurons and glia develop and function. Midline cells of Drosophila differentiate into glial cells and several types of neurons and also serve as a signaling center for surrounding tissues. Here, we examine regulation of the midline gene, wrapper, required for both neuron-glia interactions and viability of midline glia. We identify a region upstream of wrapper required for midline expression that is highly conserved (87%) between 12 Drosophila species. Site-directed mutagenesis identifies four motifs necessary for midline glial expression: (1) a Single-minded/Tango binding site, (2) a motif resembling a pointed binding site, (3) a motif resembling a Sox binding site, and (4) a novel motif. An additional highly conserved 27 bp are required to restrict expression to midline glia and exclude it from midline neurons. These results suggest short, highly conserved genomic sequences flanking Drosophila midline genes are indicative of functional regulatory regions and that small changes within these sequences can alter the expression pattern of a gene.

Antibiotic susceptibility of bacteria infecting total joint arthroplasty sites.

BACKGROUND: Currently, there is no consensus regarding the principles of empiric antibiotic treatment of suspected periprosthetic infection following total knee and hip arthroplasties. This study was undertaken to attempt to establish such principles. METHODS: We performed a retrospective analysis of 146 patients who had had a total of 194 positive cultures of specimens obtained at the time of a reoperation following a total knee or total hip arthroplasty at one of two institutions. Patient demographic data, comorbid conditions, bacterial species, the antibiotic sensitivity profile, and the postoperative day on which the culture tested positive were recorded. RESULTS: Specimens from 110 hips and eighty-four knees were positive on culture. Seventy percent of the infections were classified as chronic; 17%, as acute postoperative; and 13%, as acute hematogenous. The mean time between the operation and the positive culture results was three days. Gram-positive organisms caused the majority of the infections. In the series as a whole, 88% of the bacteria were sensitive to gentamicin; 96%, to vancomycin; and 61%, to cefazolin. The most antibiotic-resistant bacterial strains were from patients for whom prior antibiotic treatment had failed. Acute postoperative infections had a greater resistance profile than did chronic or hematogenous infections. Bacteria isolated from patients with a hematogenous infection had a high sensitivity to both cefazolin and gentamicin. CONCLUSIONS: Empiric antibiotic treatment for suspected periprosthetic infection should be guided by the class of the infection and the findings of Gram staining. We believe that, until the final culture results are available, acute hematogenous infections should initially be treated by a combination of cefazolin and gentamicin therapy. All chronic and acute postoperative infections with Gram-positive bacteria and all cases in which a Gram stain fails to identify bacteria should be managed with vancomycin. Infections with Gram-negative bacteria should be managed with a third or fourth-generation cephalosporin. Infections with mixed Gram-positive and Gram-negative bacteria should be managed with a combination of vancomycin and a third or fourth-generation cephalosporin. Furthermore, we believe that if culture results and other confirmatory tests are not positive by the fourth postoperative day, termination of empiric antibiotic therapy should be considered.

Fixation of periprosthetic femoral shaft fractures associated with cemented femoral stems: a biomechanical comparison of locked plating and conventional cable plates.

UNLABELLED: To determine which of 2 techniques for the treatment of periprosthetic femoral shaft fractures is of greater stiffness. DESIGN: A laboratory study using 8 pairs of matched, embalmed femurs. METHODS: Femurs implanted with a cemented total hip prosthesis had a simulated periprosthetic femur fracture created distal to the implant. Fractures were fixed with a plate with locked screws or a plate with cables (Ogden construct). Fixation stability was compared in various loading modalities before and after cycling. Failure in torsional loading was then determined. The cement mantle was tested for crack propagation that may have occurred secondary to locked screw insertion and loading. OUTCOME MEASUREMENTS: Fixation stiffness (the ratio of applied load to displacement at the fracture site), torsional strength, mode of failure for each system, and cement mantle evaluation for cracks after screw insertion. RESULTS: Locked plating was stiffer than the Ogden construct in pre- and post-cyclic axial loading and torsion. There was no difference in lateral bending stability or torsional failure loads. CONCLUSIONS: Locked plating constructs were stiffer than the Ogden construct in axial loading and torsion. Although no differences in loads to failure during torsion were noted, locked plating constructs exhibited catastrophic failure not observed with the Ogden construct.

The consistency between scientific papers presented at the Orthopaedic Trauma Association and their subsequent full-text publication.

OBJECTIVES: To determine the consistency of conclusions/statements made in podium presentations at the annual meeting of the Orthopaedic Trauma Association (OTA) with those in subsequent full-text publications. Also, to evaluate the nature and consistency of study design, methods, sample sizes, results and assign a corresponding level of evidence. DATA SOURCES: Abstracts of the scientific programs of the OTA from 1994 to 1997 (N = 254) were queried by using the PubMed database to identify those studies resulting in a peer-reviewed, full-text publication. STUDY SELECTION: Of the 169 articles retrieved, 137 studies were the basis of our study after the exclusion criteria were applied: non-English language, basic science studies, anatomic dissection studies, and articles published in non-peer-reviewed journals. DATA EXTRACTION/SYNTHESIS: Information was abstracted onto a data form: first from the abstract published in the final meeting program, and then from the published journal article. Information was recorded regarding study issues, including the study design, primary objective, sample size, and statistical methods. We provided descriptive statistics about the frequency of consistent results between abstracts and full-text publications. The results were recorded as percentages and a 95% confidence interval was applied to each value. Study results were recorded for the abstract and full-text publication comparing results and the overall conclusion. A level of scientific-based evidence was assigned to each full-text publication. RESULTS: The final conclusion of the study remained the same 93.4% of the time. The method of study was an observational case series 52% of the time and a statement regarding the rate of patient follow-up was reported 42% of the time. Of the studies published, 18.2% consisted of a sample size smaller than the previously presented abstract. When the published papers had their level of evidence graded, 11% were level I, 16% level II, 17% level III, and 56% level IV. CONCLUSIONS: Authors conclusions were consistent with those in full-text publications. Most studies were observational, less than half reported on the rate of patient follow-up. Many abstracts followed by publication had a smaller sample size in the published paper. Half of all studies were graded level IV evidence.

Osteotomy about the knee: applications, techniques, and results.

Varus or valgus malalignment of the knee may be either a cause or a consequence of unicompartmental knee arthritis in young, active adults. Proximal tibial osteotomy for the varus knee and distal femoral osteotomy for the valgus knee have been used for decades to manage this condition; however, their use has decreased significantly in recent years as the popularity of unicompartmental and total knee arthroplasty has grown. With the advent of biologic resurfacing techniques for focal full-thickness articular cartilage injury, combined or staged high tibial osteotomy is becoming increasingly popular. In addition, in the face of cruciate ligamentous instability with or without posterolateral corner instability coupled with varus malalignment, high tibial osteotomy with and without ligament reconstruction provides a solution to complex orthopedic problems. Recent long-term follow-up studies have concluded osteotomy allows for improved function and pain relief in properly selected young patients.

Biomechanics of locked plates and screws.

OBJECTIVE: To review the biomechanical principles that guide fracture fixation with plates and screws; specifically to compare and contrast the function and roles of conventional unlocked plates to locked plates in fracture fixation. We review basic plate and screw function, discuss the design rationale for the new implants, and examine the biomechanical evidence that supports the use of such implants. DATA SOURCES: Systematic review of the per reviewed English language orthopaedic literature listed on PubMed (National Library of Medicine online service). STUDY SELECTION: Papers selected for this review were drawn from peer review orthopaedic journals. All selected papers specifically discussed plate and screw biomechanics with regard to fracture fixation. PubMed search terms were: plates and screws, biomechanics, locked plates, PC-Fix, LISS, LCP, MIPO, and fracture fixation. DATA SYNTHESIS: The following topics are discussed: plate and screw function-neutralization plates and buttress plates, bridge plates; fracture stability-specifically how this effects gap strain and fracture union, conventional plate biomechanics, and locking plate biomechanics. CONCLUSIONS: Locked plates and conventional plates rely on completely different mechanical principles to provide fracture fixation and in so doing they provide different biological environments for healing. Locked plates may increasingly be indicated for indirect fracture reduction, diaphyseal/metaphyseal fractures in osteoporotic bone, bridging severely comminuted fractures, and the plating of fractures where anatomical constraints prevent plating on the tension side of the bone. Conventional plates may continue to be the fixation method of choice for periarticular fractures which demand perfect anatomical reduction and to certain types of nonunions which require increased stability for union.

Review: acute compartment syndrome of the foot.

Foot compartment syndrome is a serious potential complication of foot crush injury, fractures, surgery, and vascular injury. The purpose of this article is to summarize and review the existing literature on this entity. Long-term sequelae of foot compartment syndrome (FCS) include contractures, deformity, weakness, paralysis, and sensory neuropathy. These complications are poorly tolerated, and often necessitate multiple procedures for rehabilitation. Therefore, the threshold for considering compartment syndrome and performing fasciotomy must be low to minimize such outcomes. The existence of nine foot compartments and frequent presence of complicating injuries necessitate multi-stick needle catheterization for direct measurement of compartment pressures. Fasciotomy is indicated when compartment pressure exceeds 30 mmHg, or if compartment pressure is greater than 10-30 mmHg below diastolic pressure. The approaches for compartment decompression generally include two dorsal incisions for access to forefoot compartments, and one medial incision for decompression of the calcaneal, medial, superficial, and lateral compartments.

Traumatic superficial temporal artery pseudoaneurysms in a minor league baseball player: a case report and review of the literature.

Traumatic STA aneurysm is a rare complication of facial trauma occuring typically in young men. We present the case of a minor league baseball player who developed 2 pseudoaneurysms after being struck by a baseball and review all cases associated with sports activities. Reports associated with sports activities are increasing and may represent an increasing incidence. The team physician should suspect this condition when a player presents with a new temporal mass after facial trauma. Diagnosis is typically made on history and physical examination, but can be confirmed by duplex ultrasound. Definitive treatment is surgical resection of the aneurysm after proximal and distal ligation of the vessel.

A comparison of midline and tracheal gene regulation during Drosophila development.

Within the Drosophila embryo, two related bHLH-PAS proteins, Single-minded and Trachealess, control development of the central nervous system midline and the trachea, respectively. These two proteins are bHLH-PAS transcription factors and independently form heterodimers with another bHLH-PAS protein, Tango. During early embryogenesis, expression of Single-minded is restricted to the midline and Trachealess to the trachea and salivary glands, whereas Tango is ubiquitously expressed. Both Single-minded/Tango and Trachealess/Tango heterodimers bind to the same DNA sequence, called the CNS midline element (CME) within cis-regulatory sequences of downstream target genes. While Single-minded/Tango and Trachealess/Tango activate some of the same genes in their respective tissues during embryogenesis, they also activate a number of different genes restricted to only certain tissues. The goal of this research is to understand how these two related heterodimers bind different enhancers to activate different genes, thereby regulating the development of functionally diverse tissues. Existing data indicates that Single-minded and Trachealess may bind to different co-factors restricted to various tissues, causing them to interact with the CME only within certain sequence contexts. This would lead to the activation of different target genes in different cell types. To understand how the context surrounding the CME is recognized by different bHLH-PAS heterodimers and their co-factors, we identified and analyzed novel enhancers that drive midline and/or tracheal expression and compared them to previously characterized enhancers. In addition, we tested expression of synthetic reporter genes containing the CME flanked by different sequences. Taken together, these experiments identify elements overrepresented within midline and tracheal enhancers and suggest that sequences immediately surrounding a CME help dictate whether a gene is expressed in the midline or trachea.

Mastermind mutations generate a unique constellation of midline cells within the Drosophila CNS.

BACKGROUND: The Notch pathway functions repeatedly during the development of the central nervous system in metazoan organisms to control cell fate and regulate cell proliferation and asymmetric cell divisions. Within the Drosophila midline cell lineage, which bisects the two symmetrical halves of the central nervous system, Notch is required for initial cell specification and subsequent differentiation of many midline lineages. METHODOLOGY/PRINCIPAL FINDINGS: Here, we provide the first description of the role of the Notch co-factor, mastermind, in the central nervous system midline of Drosophila. Overall, zygotic mastermind mutations cause an increase in midline cell number and decrease in midline cell diversity. Compared to mutations in other components of the Notch signaling pathway, such as Notch itself and Delta, zygotic mutations in mastermind cause the production of a unique constellation of midline cell types. The major difference is that midline glia form normally in zygotic mastermind mutants, but not in Notch and Delta mutants. Moreover, during late embryogenesis, extra anterior midline glia survive in zygotic mastermind mutants compared to wild type embryos. CONCLUSIONS/SIGNIFICANCE: This is an example of a mutation in a signaling pathway cofactor producing a distinct central nervous system phenotype compared to mutations in major components of the pathway.

Timing issues in fracture management: a review of current concepts.

The timing of operative fracture care is often confounded by multisystem injuries, conflicting or absent literature, and lack of communication between orthopaedic surgeons and other physicians providing care to the patient. Much has been published regarding the proper sequence of events in providing care to patients with multisystem injuries. Only recently has the role of complex musculoskeletal injuries and the timing of fixation in multiply-injured patients been explored in detail. Timing of care for pelvic injuries is frequently determined by the presence of injury to other organ systems, the presence of open wounds, and hemodynamic status. There is likely an optimal time window for fixation. However, existing data is often difficult to compare, given varying definitions and protocols. Furthermore, reports are often conflicting, making the determination of an optimal time-window difficult. Similar concerns are present with lower extremity long bone fractures. Injury to other organ systems must be considered with timing of femur fixation, particularly in the presence of lung injury. Tibia fractures are frequently complicated by the presence of a tenuous soft tissue envelope and other injury factors that often alter the timing of fixation. These issues and, last, the timing of care for calcaneus and talus injuries are reviewed, as risk of avascular necrosis and quality of articular reduction are related to the timing of fixation.

Management of periprosthetic femur fractures with a first generation locking plate.

Periprosthetic femoral fractures associated with well-fixed total hip or total knee prostheses present a challenging management problem as these injuries typically occur in osteoporotic bone. Conventional management entails extensive periosteal stripping to allow for plate fixation. We reviewed a consecutive series of patients who sustained fractures associated with a well fixed total knee prosthesis, a total hip prosthesis, or both. Twenty four patients with a mean age of 69.4 years were included. All patients underwent fixation via percutaneous insertion techniques with a first generation locking plate and screws (LISS--Less Invasive Skeletal Stabilization, Synthes, Paoli, PA). Three patients sustained fractures distal to a well-fixed total hip prosthesis, eighteen fractures occurred above a well-fixed total knee femoral component, and three were interprosthetic. The mean length of time from the index procedure to fracture was 76 months, range (2-172 months). Blood loss was minimal in each case, with a mean operative time of 90 min (range 60-120 min). Twenty one of twenty four went on to unite at a mean 6.2 months (range 3-19 months). Three patients underwent further surgery. One failure of fixation was encountered. Percutaneous fixation is technically demanding as it requires stable fixation without direct visualisation of the fracture site or the entire fixation device. Our results suggest percutaneous fixation with the LISS plate is an effective although technically demanding method of treatment. Complication rates were comparable to existing reports of this treatment method, and appear to be improved over traditional methods of fixation.

Comparison of fixation methods for scaphoid nonunions: a biomechanical model.

The purpose of this study was to analyze the relative bio- mechanical stability of three types of internal ixation with cancellous bone graft in a cadaveric, scaphoid nonunion model. A scaphoid nonunion model was created by remov- ing a volar wedge of bone from the waist of the scaphoid in 18 fresh frozen human cadavers. Cancellous sawbone graft was inserted into the osteotomy site and three groups of six cadavers each were then internally ixed with a pair of parallel 0.045-inch K-wires, Mini-Acutrak screws, or Standard Acutrak screws, respectively for each group. The potted specimens were tested using an Instron(R) tensile testing machine by applying force to the distal pole of the scaphoid. The load and stiffness were calculated at 2 mm and 4 mm of displacement. Results showed that both the Mini-Acutrak screw and the Standard Acutrak screw were statistically stronger and stiffer at 2 mm displacement than the pair of parallel 0.045-inch K-wires. No statistically sig- niicant difference between the Standard and Mini-Acutrak screws was noted at 2 mm displacement. At higher loads (4 mm displacement), the Standard Acutrak became statisti- cally stronger and stiffer than the Mini-Acutrak screw. It was concluded that the Standard Acutrak screw followed by the Mini-Acutrak screw may be a better option than a pair of parallel 0.045-inch K-wires when treating scaphoid nonunions. The screws have increased strength of ixation and stiffness when compared to K-wires. Also, unlike the K wires, the Acutrak screws enhance fracture healing by achieving interfragmentary compression. Even in a cancel- lous bone graft model, interfragmentary compression was achieved and our concern that the bone graft would "spit out" was allayed.

Fixation of diaphyseal fractures with a segmental defect: a biomechanical comparison of locked and conventional plating techniques.

BACKGROUND: Locking plates are an alternative to conventional compression plate fixation for diaphyseal fractures. The objective of this study was to compare the stability of various plating with locked screw constructs to conventional nonlocked screws for fixation of a comminuted diaphyseal fracture model using a uniform, synthetic ulna. Locked screw construct variables were the use of unicortical or bicortical screws, and increasing bone to plate distance. METHODS: This biomechanical study compared various construct groups after cyclic axial loading and three-point bending. Results were analyzed via one-way analysis of variance. Displacements after cyclical axial loading and number of cycles to failure in cyclic bending were used to assess construct stability. RESULTS: The constructs fixed by plates with bicortical locked screws withstood significantly more cycles to failure than the other constructs (p < 0.001). Significantly less displacement occurred after axial loading with bicortical locked screws than with bicortical nonlocked screws. Increased distance of the plate from the bone surface, and use of unicortical locked screws led to early failure with cyclic loading for constructs with locked screws. CONCLUSIONS: These results support the use of plating with bicortical locked screws as an alternative to conventional plating for comminuted diaphyseal fractures in osteoporotic bone. Bicortical locked screws with minimal displacement from the bone surface provide the most stable construct in the tested synthetic comminuted diaphyseal fracture model. The results of this study suggest use of plates with unicortical screws for the described fracture is not recommended.

Podium versus poster publication rates at the Orthopaedic Trauma Association.

Original studies at orthopaedic meetings are presented on the podium and in poster format. Publication of those studies in peer-reviewed journals is the standard of communicating scientific data to colleagues. Investigators of previous studies have reported publication rates, but never differentiated between the modes of presentation. We evaluated the annual meeting of the Orthopaedic Trauma Association from 1994-1998 and found that studies presented on the podium were 1.3 times more likely to be published than those presented in a poster format (67% versus 52%). The mean time to publication was similar, 21.6 months for poster presentations and 24.8 months for podium presentations. Podium presentations were more likely to be published in the Journal of Orthopaedic Trauma, Clinical Orthopaedics and Related Research, and the Journal of Bone and Joint Surgery (American and British editions). Our findings suggest different rates and distribution of publication between podium and poster presentations at an international trauma meeting. These findings should be considered when evaluating studies of interest at the Orthopaedic Trauma Association meeting.