Femoral and tibial component rotation in total knee arthroplasty: methods and consequences.

At least four ways have been described to determine femoral component rotation, and three ways to determine tibial component rotation in total knee replacement (TKR). Each method has its advocates and each has an influence on knee kinematics and the ultimate short and long term success of TKR. Of the four femoral component methods, the author prefers rotating the femoral component in flexion to that amount that establishes a stable symmetrical flexion gap. This judgement is made after the soft tissues of the knee have been balanced in extension. Of the three tibial component methods, the author prefers rotating the tibial component into congruency with the established femoral component rotation with the knee is in extension. This yields a rotationally congruent articulation during weight-bearing and should minimise the torsional forces being transferred through a conforming tibial insert, which could lead to wear to the underside of the tibial polyethylene. Rotating platform components will compensate for any mal-rotation, but can still lead to pain if excessive tibial insert rotation causes soft-tissue impingement.

The evolving incidence and reasons for re-operation after fixed-bearing PCL retaining total knee arthroplasty.

PCL retaining fixed-bearing TKA is a highly successful operation with the need for more surgery occurring at the rate of approximately 0.4% per year over the first 27 years. The most common cause for revision surgery is related to polyethylene insert failure and accounts for approximately 50% of re-operations. Late metastatic infection is the next most frequent cause followed by patellar problems, late instability and component loosening in decreasing frequency. A myriad of rare miscellaneous problems can also occur.

Self-expanding metal stent insertion for inoperable esophageal carcinoma in Belfast: an audit of outcomes and literature review.

Successful palliation of dysphagia in patients with inoperable esophageal carcinoma has a major effect on quality of life. Self-expanding metal stents (SEMS) are currently recommended for rapid symptomatic relief when life expectancy is less than 3 months. We assessed complication and reintervention rates along with survival outcomes in patients with inoperable esophageal carcinoma undergoing stent insertion. A retrospective audit was performed from April 2007 to June 2009 for all inoperable primary esophageal carcinoma patients who had an esophageal stent inserted for dysphagia. Case notes were reviewed for clinical, pathological, stent and complication details, while ICD-10 causes of death were obtained from the Department of Health and Social Services, Northern Ireland. Fifty-six stents were inserted into 53 patients (66.0% male, mean age of 70 years). Inoperability was defined by metastatic spread (n= 34, 64.2%), locally advanced disease (n= 7, 13.2%), and severe medical comorbidities (n= 12, 22.6%). The median time from diagnosis to stent insertion was 109 (interquartile range [IQR] 43-187) days. Fifty stents (94.3%) were successfully deployed, while three patients (5.7%) required an additional stent as the primary stent had not bridged the tumor (proximal deployment = 2, suboptimal stent length = 1). Post-SEMS dysphagia scores were significantly better than pre-SEMS scores (2.90 vs. 1.54, P < 0.001). There were 27 complications identified in 23 (43.4%) patients (major complications = 9, minor complications = 14). Twelve patients (22.6%) required additional endoscopic procedures. The 30-day mortality rate was 11.3% (n= 6). Only one patient (1.9%) remains alive with a cumulative median survival rate of 84 (IQR 38-156) days. Esophageal stent insertion in this group of patients still presents a clinical challenge, with complication and endoscopic reintervention rates of 43.4 and 22.6%, respectively. Our results are comparable with previously published series, and as a palliative modality stent insertion remains appropriate when expected survival is less than 3 months. A range of SEMS is currently available with broadly similar efficacy and safety profiles. Data regarding the newly available fully covered SEMS suggest that they should be avoided.

Identification and characterization of the intracellular poly-3-hydroxybutyrate depolymerase enzyme PhaZ of Sinorhizobium meliloti.

BACKGROUND: S. meliloti forms indeterminate nodules on the roots of its host plant alfalfa (Medicago sativa). Bacteroids of indeterminate nodules are terminally differentiated and, unlike their non-terminally differentiated counterparts in determinate nodules, do not accumulate large quantities of Poly-3-hydroxybutyrate (PHB) during symbiosis. PhaZ is in intracellular PHB depolymerase; it represents the first enzyme in the degradative arm of the PHB cycle in S. meliloti and is the only enzyme in this half of the PHB cycle that remains uncharacterized. RESULTS: The S. meliloti phaZ gene was identified by in silico analysis, the ORF was cloned, and a S. meliloti phaZ mutant was constructed. This mutant exhibited increased PHB accumulation during free-living growth, even when grown under non-PHB-inducing conditions. The phaZ mutant demonstrated no reduction in symbiotic capacity; interestingly, analysis of the bacteroids showed that this mutant also accumulated PHB during symbiosis. This mutant also exhibited a decreased capacity to tolerate long-term carbon starvation, comparable to that of other PHB cycle mutants. In contrast to other PHB cycle mutants, the S. meliloti phaZ mutant did not exhibit any decrease in rhizosphere competitiveness; however, this mutant did exhibit a significant increase in succinoglycan biosynthesis. CONCLUSIONS: S. meliloti bacteroids retain the capacity to synthesize PHB during symbiosis; interestingly, accumulation does not occur at the expense of symbiotic performance. phaZ mutants are not compromised in their capacity to compete for nodulation in the rhizosphere, perhaps due to increased succinoglycan production resulting from upregulation of the succinoglycan biosynthetic pathway. The reduced survival capacity of free-living cells unable to access their accumulated stores of PHB suggests that PHB is a crucial metabolite under adverse conditions.

The class IId bacteriocin thuricin-17 increases plant growth.

The mechanisms by which many plant growth promoting rhizobacteria (PGPR) affect plants are unknown. We recently isolated a rhizosphere bacterium (Bacillus thuringiensis NEB17), that promotes soybean growth and screened the liquid growth medium in which it grew for plant growth stimulating materials. We have also shown that it produces a bacteriocin (named by us as thuricin-17 and a member of the recently described class IId bacteriocins). Here we show that application of this bacteriocin to leaves (spray) or roots (drench) directly stimulates the growth of both a C(3) dicot (soybean) and a C(4) monocot (corn). This growth stimulation is similar in nature to that previously seen when plants are treated with Nod factors. Strain NEB17 contains three copies of the gene for thuricin 17 that code for identical amino acid sequences. These two lines of evidence suggest that the dual functions of these proteins may have constrained their evolution. This is the first report of direct plant growth enhancement by a bacteriocin.

Mutational analysis of the Sinorhizobium meliloti short-chain dehydrogenase/reductase family reveals substantial contribution to symbiosis and catabolic diversity.

The short-chain dehydrogenase/reductase (SDR) family is one of the largest and most ubiquitous protein families in bacterial genomes. Despite there being a few well-characterized examples, the substrate specificities or functions of most members of the family are unknown. In this study, we carried out a large-scale mutagenesis of the SDR gene family in the alfalfa root nodule symbiont Sinorhizobium meliloti. Subsequent phenotypic analysis revealed phenotypes for mutants of 21 of the SDR-encoding genes. This brings the total number of S. meliloti SDR-encoding genes with known function or associated phenotype to 25. Several of the mutants were deficient in the utilization of specific carbon sources, while others exhibited symbiotic deficiencies on alfalfa (Medicago sativa), ranging from partial ineffectiveness to complete inability to form root nodules. Five of the mutants had both symbiotic and carbon utilization phenotypes. These results clearly demonstrate the importance of the SDR family in both symbiosis and saprotrophy, and reinforce the complex nature of the interaction of S. meliloti with its plant hosts. Further analysis of the genes identified in this study will contribute to the overall understanding of the biology and metabolism of S. meliloti in relation to its interaction with alfalfa.

Modified RP4 and Tn5-Mob derivatives for facilitated manipulation of large plasmids in Gram-negative bacteria.

We have constructed a set of RP4 (NmS/TcS) and Tn5-Mob derivatives which have applications in experiments involving mobilization of replicons in many Gram-negative organisms. The different selection markers of the RP4 and Tn5-Mob derivatives include streptomycin, chloramphenicol, gentamicin, and spectinomycin resistance as well as mercury resistance, and a constitutively expressed lacZ gene. This choice of markers allows the use of these derivatives in bacteria which are naturally resistant to many antibiotics, and in strains which contain pre-existing resistance plasmids, transposons, or antibiotic cassette insertions. In addition, a RP4 derivative carrying the sacB gene of Bacillus subtilis was constructed. This allows the selection for the loss of RP4 after it has been used to mobilize other plasmids. A Tn5-Mob-sacB derivative with a new marker (Gm) was also developed, as were vectors which take advantage of the sacB gene to facilitate replacement of existing Tn5 inserts with other Tn5 derivatives. As an example of the use of these tools, three Rhizobium leguminosarum bv. viciae VF39 plasmids which have been shown to be involved in symbiosis were differentially tagged and mobilized (individually and in various combinations) to the plasmid-free Agrobacterium tumefaciens strain UBAPF2. None of the resultant Agrobacterium strains was able to fix nitrogen in symbiosis with peas.

Green and red fluorescent protein vectors for use in biofilm studies of the intrinsically resistant Burkholderia cepacia complex.

Cystic fibrosis isolates of the Burkholderia cepacia complex (BCC) have demonstrated a propensity to associate intimately with Pseudomonas aeruginosa in mixed community biofilms, which may impact on their overall pathogenicity during infection of the lungs in cystic fibrosis. Here, we describe the construction and use of novel green and red fluorescent protein expression vectors suitable for labeling biofilm cells of multi-resistant clinical isolates of the BCC for microscopic analysis of both single species biofilms and mixed community associations with P. aeruginosa. Antimicrobial susceptibility testing established that tetracycline and/or trimethoprim were suitable selective agents for widespread use in BCC. The green and red fluorescent protein genes, driven by constitutively active promoters, were cloned into two mobilizable plasmids pBBR1MCS-3 and pBBR1Tp, carrying tetracycline and trimethoprim resistance cassettes, respectively. The fluorescence of transformed BCC and P. aeruginosa planktonic cells was detectable using fluorescence microscopy and/or fluorometry. The plasmids were stable in the absence of selection for at least 3 days in planktonic and biofilm cultures, and fluorescence was still visible in a 4-day glass coverslip flow cell biofilm. The plasmids functioned well to distinguish the two species in a mixed community biofilm, with no indications of plasmid transfer between species or cross-talk of the fluorescent signals. These vectors represent the first green and red fluorescent vectors to be constructed and analyzed specifically for wide spread use in BCC and P. aeruginosa single and mixed biofilm cultures.

The glcB locus of Rhizobium leguminosarum VF39 encodes an arabinose-inducible malate synthase.

In the course of a study conducted to isolate genes upregulated by plant cell wall sugars, we identified an arabinose-inducible locus from a transcriptional fusion library of Rhizobium leguminosarum VF39, carrying random insertions of the lacZ transposon Tn5B22. Sequence analysis of the locus disrupted by the transposon revealed a high similarity to uncharacterized malate synthase G genes from Sinorhizobium meliloti, Agrobacterium tumefaciens, and Mesorhizobium loti. This enzyme catalyzes the condensation of glyoxylate and acetyl-CoA to yield malate and CoA and is thought to be a component of the glyoxylate cycle, which allows microorganisms to grow on two carbon compounds. Enzyme assays showed that a functional malate synthase is encoded in the glcB gene of R. leguminosarum and that its expression is induced by arabinose, glycolate, and glyoxylate. An Escherichia coli aceB glcB mutant, complemented with the R. leguminosarum PCR-amplified gene, recovered malate synthase activity. A very similar genome organization of the loci containing malate synthase and flanking genes was observed in R. leguminosarum, S. meliloti, and A. tumefaciens. Pea plants inoculated with the glcB mutant or the wild-type strain showed no significant differences in nitrogen fixation. This is the first report regarding the characterization of a mutant in one of the glyoxylate cycle enzymes in the rhizobia.

Unicompartmental knee arthroplasty: long-term results.

Unicompartmental knee arthroplasty has been controversial since its introduction in the early 1970s. Some initial reports suggested that medial compartment replacement did not yield good enough early results to be a viable long-term option, although lateral compartment replacement seemed to be promising. By the early 1980s, however, good initial results were being published for medial and lateral replacements and enthusiasm for the procedure began to increase. Refinements were made in patient selection, surgical technique, and prosthetic design. Ten-year followup studies were reported that showed survivorship was slightly less than that reported for total knee arthroplasty but acceptable considering the theoretically conservative nature of unicompartmental surgery. Unicompartmental knee arthroplasty now can be characterized as a procedure with a reliable 8- to 10-year outcome in properly selected patients with osteoarthritis who receive a skillfully implanted proper design. Unicondylar knee arthroplasty can be an attractive alternative to osteotomy or total knee arthroplasty especially some middle-aged women. Approximately all studies with followups of 10 years or greater show that unicompartmental knee arthroplasty will have inferior survivorship to total knee arthroplasty whether from loosening, prosthetic wear, or secondary degeneration of the opposite compartment in the second decade. Recently published 10-year results from two centers (one using a mobile-bearing design, the other using a fixed-bearing design) are comparable with those of total knee arthroplasty. This suggests that enhanced second-decade survivorship and therefore an expansion of the indications for unicompartmental knee arthroplasty are possibilities.

Measuring the economic costs of antimicrobial resistance in hospital settings: summary of the Centers for Disease Control and Prevention-Emory Workshop.

Health systems administrators and clinicians need refined calculations of the attributable cost of infections due to drug-resistant microorganisms to develop and assess cost-effective prevention strategies that deal with these infections. To date, however, efforts to provide this information have yielded widely variable and often conflicting estimates. This lack of reproducibility is largely attributable to problems in study design and in the methods used to identify and measure costs. Addressing these methodological issues was the focus of a workshop that included participants from a broad range of backgrounds, including economics, epidemiology, health care management, health care outcomes research, and clinical care. This workshop summary presents the advantages and disadvantages of various research designs as well as particular methodological issues related to the measurement of the economic cost of resistance in health care settings. Suggestions are made for needed common definitions and approaches, study areas for future research are considered, and priority investigations are identified.

Applying economic principles to health care.

Applying economic thinking to an understanding of resource use in patient care is challenging given the complexities of delivering health care in a hospital. Health-care markets lack the characteristics needed to determine a "market" price that reflects the economic value of resources used. However, resource allocation in a hospital can be analyzed by using production theory to determine efficient resource use. The information provided by hospital epidemiologists is critical to understanding health-care production processes used by a hospital and developing economic incentives to promote antibiotic effectiveness and infection control.

Persistent limp after total hip replacement: one step at a time.

A limp can be a significant sign of serious pathology about the hip. The source of the limp can be the hip or remote from the hip. Careful evaluation of each individual patient can lead to the discovery of the cause and, hopefully, its resolution.

A comparison of 4 intraoperative methods to determine femoral component rotation during total knee arthroplasty.

A total of 100 consecutive posterior cruciate-retaining total knee arthroplastics were performed in 81 patients with an average age of 69 years by 1 surgeon. Diagnoses included osteoarthritis in 93 knees and rheumatoid arthritis in 7 knees. The femoral alignment necessary to create a rectangular flexion gap was determined and compared with Whiteside's line, the transepicondylar axis, and a line in 3 degrees of external rotation relative to the posterior condyles of the femur. The transepicondylar axis most consistently recreated a balanced flexion space, whereas 3 degrees of external rotation off the posterior condyles was least consistent, especially in valgus knees.

Tibial osteotomy coincident with long stem total knee arthroplasty: a surgical technique.

Tibial deformity secondary to previous fracture or osteotomy requires corrective osteotomy in some patients undergoing total knee arthroplasty (TKA). This can be performed in either two stages or coincident with the arthroplasty. Literature on coincident tibial osteotomy and TKA has been published previously, but details of the complicated surgical technique are lacking for surgeons performing this procedure for the first time. This article details the preoperative planning involved and the intraoperative technique used in tibial osteotomy coincident with TKA.

The Ranawat Award. Femoral component rotation during total knee arthroplasty.

One-hundred consecutive posterior cruciate retaining total knee arthroplasties were performed by one surgeon in 81 patients with an average age of 69 years. Diagnoses included osteoarthritis in 93 knees and rheumatoid arthritis in seven. The femoral alignment necessary to create a rectangular flexion gap was determined and compared with Whiteside's line, the transepicondylar axis, and a line in 3 degrees external rotation relative to the posterior condyles of the femur. The transepicondylar axis most consistently recreated a balanced flexion space whereas 3 degrees external rotation off the posterior condyles was least consistent especially in knees in valgus.