Biomechanical performance of different cable and wire cerclage configurations

Purpose

Cerclage technology is regaining interest due to the increasing number of periprosthetic fractures. Different wiring techniques have been formerly proposed and have hibernated over years. Hereby, they are compared to current cerclage technology.

Methods

Seven groups (n = 6) of different cable cerclage (Ø1.7 mm, crimp closure) configurations (one single cerclage looped once around the shells, one single cerclage looped twice, two cerclages each looped once) and solid wire cerclages (Ø1.5 mm, twist closure) (same configurations as cable cerclages, and two braided wires, twisted around each other looped once) fixed two cortical half shells of human femoral shaft mounted on a testing jig. Sinusoidal cyclic loading with constantly increasing force (0.1 N/cycle) was applied starting at 50 N peak load. Cerclage pretension (P), load leading to onset of plastic deformation (D) and load at total failure (T) were identified. Statistical differences between the groups were detected by univariate ANOVA.

Results

Double looped cables (P442N ± 129; D1334N ± 319; T2734N ± 330) performed significantly better (p < 0.05) than single looped cables (P292N ± 56; D646N ± 108; T1622N ± 171) and were comparable to two single cables (P392N ± 154; D1191N ± 334; T2675N ± 361). Double looped wires (P335N ± 49; D752N ± 119; T1359N ± 80) were significantly better (p < 0.05) than single looped wires (P181N ± 16; D343N ± 33; T606N ± 109) and performed similarly to single looped cables. Braided wires (P119N ± 26; D225N ± 55; T919N ± 197) exhibited early loss of pretension and plastic deformation.

Conclusion

Double looped cerclages provided a better fixation stability compared to a single looped cerclage. Double looped wires were comparable to a single looped cable. The use of braided wires could not be recommended mechanically.     

Non-linear dynamics of heart rate variability during incremental cycling exercise

Within the last years complex models of cardiovascular regulation and exercise fatigue have implemented heart rate variability (HRV) as a measure of autonomic nervous system. Using detrended fluctuation analysis (DFA) to assess heart rate correlation properties, the present study examines the influence of exercise intensity on total variability and complexity in non-linear dynamics of HRV. Sixteen cyclists performed a graded exercise test on a bicycle ergometer. HRV time domain measures and fractal correlation properties were analyzed using short-term scaling exponent alpha1 of DFA. Amplitude and complexity of HRV parameters decreased significantly. DFA-alpha1 increased from rest to low exercise intensity and showed an almost linear decrease from higher intensities until exhaustion. These findings support a qualitative change in self-organized heart rate regulation from a complex autonomic control at rest and low intensities towards a breakdown of the interaction in control mechanisms with non-autonomic heart rate control dominating at high intensities.     

Magnetresonanztomographische Diagnostik der peripheren Durchblutung*

PURPOSE: This article describes the potential of dynamic contrast- enhanced magnetic resonance tomography (DCE-MRT) for the visualization and quantification of blood flow of lower leg muscles at rest and after individually adjusted muscular exercise. PATIENTS AND METHODS: Five cases were chosen to exemplify the qualitative and semi-quantitative blood flow evaluation in the lower leg muscles. The crural muscle state was determined with an isometric maximal strength measurement from a female patient with peripheral arterial occlusive disease (pAVK), a male patient with coronary heart disease (KHK) without clinical signs of a pAVK, a volunteer with sufficient physical activity in accordance with the Freiburg Questionnaire of Physical Activity and two professional athletes. After calibration of the plantarflexion ergometer MR-PEDALO (Figures 2a and 2b) for the execution of auxotonic muscle work a 1- minute alternating foot extension and flexion exercise on MRPEDALO was performed in the MR machine. Instead of the lower leg splint shown in Figures 2a and 2b the MR coil fits exactly in MR-PEDALO used for DCE-MRT. Mechanical work performed during the 1-minute exercise ranged from 52 watt seconds (Ws) to 244 Ws (0.65 W to 4.07 W), indicating similar interindividual work loads in relation to the individual maximum isometric strength. DCE-MRT was performed at rest and immediately after auxotonic exercise test (T1w 2DFLASH- GE sequence with TR/TE/alpha: 100 ms/6 ms/70 degrees; field of view: 400; matrix: 81 x 256; slice thickness: 10 mm; acquisitions: 73 at 8.3 s each; total examination time: 9.24 min; bolus application of Magnevist, Schering, 0.02 ml/kg kg, 20 ml bolus NaCl, flow 2 ml/s, 22G cannula in a cubital vein). Signal intensity (SI) curves were analyzed with DynaVision (MeVis gGmbH, Bremen, Germany). RESULTS: Measuring peripheral blood flow needs appropriate muscular stress tests. The SI-curves of the region of interest (ROI) representing the peroneus, tibialis anterior and gastrocnemius muscle run almost parallel at rest. Workloads between 52 Ws and 244 Ws (0.65 W and 4.07 W), similar in relation to the individual maximum isometric strength, induce distinctive changes of the upslope, wash-in, peak and washout of SI-curves preferably for the peroneus muscle and less predominant also for the tibialis anterior muscle and gastrocnemius muscle respectively. The first case, a 55-year-old female patient with peripheral arterial occlusive disease (pAVK) stage Fontaine IIb before (Figure 3a) and after (Figure 3b) percutaneous transluminal angioplasty (PTA) of a right femoral artery stenosis shows after interventional treatment a rapid post-exercise SI-increase in the peroneus muscle. The steeper SI-curve indicates a better contrast medium inflow due to an improved perfusion. The second case, a 65-year-old man suffering from coronary heart disease without clinical signs of pAVK (Figure 4) exercised with a workload of 92 Ws. After stress test the ROI for the peroneus muscle shows a clear intensity increase. After exercise the SI-curve for the tibialis anterior muscle shows a similar, but less predominant change while the shape of the SI-curve of the gastrocnemius muscle remains mainly identical. A 23-year-old male person with average physical activity (Figure 5) performed DCE-MRT of the left lower leg after stress test with 172 Ws demonstrating a rapid signal increase in the peroneus muscle while the synergistic tibialis anterior muscle and antagonistic gastrocnemius muscle show a comparatively slow contrast-medium wash-in. A 26-year-old male athlete (Figure 6) exercised with 196 Ws showing a rapid contrast medium inflow in the peroneus muscle and initially also in the synergistic tibialis anterior muscle. A contrast-medium wash-out appears in both muscles, while the shape of the gastrocnemius muscle SI-curve remains substantially unchanged. A 26-year-old female athlete (Figure 7) exercised with 244 Ws. Post exercise SI-curves show a distinctive and rapid increase of contrast medium wash-in with a sharp peak particularly in the peroneus muscle and similarly in the tibialis anterior and gastrocnemius muscle. After exercise all SI-curves show a wash-out phase. CONCLUSION: SI-curves show relative increase in correlation with Time-to-Peak (TTP) decrease and Mean-Intensity to Time Ratio (MITR) increase indicating blood flow reserve mobilization after exercise. Individual muscle state seems to be linked to muscle recruitment and muscle coordination reflected by post-exercise SI-curves. The gastrocnemius muscle shows comparatively low SI-curve changes after muscular load test. Further methodological standardization and optimization of the stress test is mandatory to assure intra- and interindividual comparisons. Due to direct visualization and quantitative evaluation of the peripheral microcirculation DCE-MRT has a diagnostic potential for monitoring therapeutic response in peripheral circulation disorders and sports medicine.     

Early identification of peritonitis by peritoneal cytokine measurement

PURPOSE: The assessment of plasma cytokine levels adds a useful tool to the diagnostic measures in severe inflammatory diseases. Proinflammatory cytokine levels in abdominal fluid after abdominal surgery have been shown to far exceed plasma cytokine levels. Thus, we investigated the local release of interleukin 1, interleukin 6, and tumor necrosis factor- in patients after colorectal surgery during the early postoperative period to evaluate whether it may serve as an indicator of evolving peritonitis. METHOD: In a prospective, observational pilot study, the first 12 consecutive patients who did not develop any postoperative complications (Group I), and the first 12 patients with secondary peritonitis caused by an anastomotic leakage (Group II), were included in the study. Interleukin 6, interleukin 1, and tumor necrosis factor- levels were determined in the abdominal exudate and compared between the groups within the first four days after colorectal surgery. RESULTS: Abdominal fluid interleukin 6 levels in Group II patients were higher (162,500 ± 105,800 pg/ml) as early as the first postoperative day compared with Group I (27,940 ± 13,860 pg/ml; P < 0.0001); this lasted for the whole observation period. The same applies to tumor necrosis factor- levels (461.4 ± 167.8 pg/ml vs. 175.8 ± 178.6 pg/ml on day 1; P = 0.0007). The difference in interleukin 1 cytokine levels became statistically significant on the third postoperative day. Moreover, abdominal fluid cytokine levels rose in Group II, whereas they remained virtually unchanged or even tended to decrease over time in Group I. CONCLUSION: We suggest that the estimation of the peritoneal cytokine levels might be an additional diagnostic tool that can support the early recognition of peritonitic complications in colorectal surgery.     

Antiinfective therapy with a small molecule inhibitor of Staphylococcus aureus sortase

Methicillin-resistant Staphylococcus aureus (MRSA) is the most frequent cause of hospital-acquired infection, which manifests as surgical site infections, bacteremia, and sepsis. Due to drug-resistance, prophylaxis of MRSA infection with antibiotics frequently fails or incites nosocomial diseases such as Clostridium difficile infection. Sortase A is a transpeptidase that anchors surface proteins in the envelope of S. aureus, and sortase mutants are unable to cause bacteremia or sepsis in mice. Here we used virtual screening and optimization of inhibitor structure to identify 3-(4-pyridinyl)-6-(2-sodiumsulfonatephenyl)[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole and related compounds, which block sortase activity in vitro and in vivo. Sortase inhibitors do not affect in vitro staphylococcal growth yet protect mice against lethal S. aureus bacteremia. Thus, sortase inhibitors may be useful as antiinfective therapy to prevent hospital-acquired S. aureus infection in high-risk patients without the side effects of antibiotics.The gram-positive bacterium Staphylococcus aureus colonizes the human skin and nares yet also causes invasive diseases such as skin and soft tissue infections, osteomyelitis, pneumonia, bacteremia, sepsis, and endocarditis (1). Methicillin-resistant S. aureus (MRSA) acquired resistance against many different drugs, including β-lactam, cephalosporin, fluoroquinolone, aminoglycoside, tetracycline, macrolide, trimethoprim-sulfamethoxazole, and vancomycin antibiotics (2). In the United States, MRSA isolates are responsible for >50% of S. aureus infections in hospitals and long-term care facilities (3). Individuals at high risk of MRSA infection include very-low-birth-weight neonates, elderly, and patients with indwelling catheters, endotracheal intubation, medical implantation of foreign bodies (prosthetic joints, implants and heart valves), trauma, surgical procedures, diabetes, dialysis, and immunosuppressive or cancer therapy (4). Antibiotic prophylaxis is designed to mitigate the risk of S. aureus infection, especially in surgical patients; however, this frequently fails due to drug resistance (5). Importantly, antibiotic therapy suppresses human microbiota and promotes Clostridium difficile infection, which is also associated with increased morbidity and mortality (6, 7). Several trials for vaccines and immune therapeutics were designed to prevent MRSA infection in hospital settings; these efforts have thus far failed to meet their study end points (4).Surface proteins of S. aureus are secreted as precursors with C-terminal sorting signals that are cleaved by sortase A (SrtA) between the threonine (T) and the glycine (G) residues of their LPXTG motif (8, 9). The active site cysteine residue of sortase forms an acyl enzyme intermediate that is relieved by the nucleophilic attack of the amino group (pentaglycine crossbridge) in peptidoglycan synthesis precursors (10). Surface proteins attached to peptidoglycan precursors are subsequently incorporated into the cell wall envelope and displayed on the staphylococcal surface (9). Genome sequencing revealed that all S. aureus isolates encode 17–21 surface proteins with LPXTG sorting signals, which fulfill diverse functions during the infectious process (11). SrtA mutants cannot assemble surface proteins into their envelope and are unable to form abscess lesions in organ tissues or cause lethal bacteremia when inoculated into the bloodstream of mice (12, 13). In contrast, mutations that abrogate the expression of secreted virulence factors may cause attenuation but do not abrogate the ability of S. aureus to cause infectious diseases (12).We reasoned that small molecule inhibitors blocking SrtA may be useful as antiinfectives to prevent S. aureus infection without affecting the growth of other bacteria. If so, such compounds could be used to reduce the incidence of MRSA infections without the side effects of antibiotics.