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PubMedDate not supplied

Mechanical comparison of two external fixator clamp designs.

OBJECTIVE: To compare two external fixation clamp designs for their ability to resist movement of a fixation pin in relation to the connecting rod. STUDY DESIGN: Two designs of external fixator clamps were attached to connecting rods mounted on a jig for mechanical testing. Fixator pins were placed perpendicular to the connecting rod. A mechanical testing machine was used to deflect each 3.2-mm pin at a distance that was 25 mm from the center of the clamp bolt. Both clamp designs were tightened to 4.4, 6.1, and 7.8 newton-meters (N x m) torque, and loads were applied in a position ramp through 4 mm and resisting loads were measured. Two clamp orientations were used during load application, such that the deflection of the pin tended to tighten the clamp bolt or tended to loosen the clamp bolt. The tests were videotaped to determine mode of failure. Comparisons of the load/displacement curves for the two external fixator clamp designs were made using nonlinear equational curve fitting methods. The resultant plateau and rise coefficients were compared using analysis of variance. RESULTS: Slippage of the pin in relation to the clamp occurred with the Kirschner-Ehmer clamp tightened to 4.4, 6.1, and 7.8 N x m, and slipping of the pin in relation to the clamp occurred with the experimental clamp design tightened to 4.4 and 6.1 N x m but not to 7.8 N m. At 7.8 N x m, the 3.2-mm pin deformed plastically with the experimental clamp design. Increasing the torque of the clamp bolt resulted in superior plateau coefficients for both clamp designs. At each level of tightness and in each clamp orientation to applied pin load, the experimental clamp design provided greater plateau coefficients than did the Kirschner-Ehmer clamp design. At 7.8 N x m of tightness, the Kirschner-Ehmer clamp and bolt bent, whereas only slight plastic deformation of the experimental clamp design occurred. CONCLUSIONS: The experimental external fixator clamp was more secure in resisting fixator pin movement at all levels of tightening compared with the Kirschner-Ehmer-type external fixator clamp. At 7.8 N x m of tightening, the new clamp design did not allow slippage of the pin within the clamp. CLINICAL SIGNIFICANCE: The experimental external fixator clamp should result in greater rigidity of fixator configurations, in addition to providing design features that allow addition of a clamp between two installed clamps, sleeved predrilling of pilot holes for all pins, measurement of pin depth, and placement of positive profile pins at all sites.

Animals↗
PubMedDate not supplied

A comparative mechanical study of 3 external fixator clamps.

OBJECTIVE: To compare external fixator clamps from Kirschner-Ehmer (K-E), Synthes, and Meynard with respect to 6 mechanical parameters. Study Design-A bench test of mechanical properties. METHODS: Specially designed fixtures were used to mechanically test 6 clamps of each type at 2.5, 5.0, and 7.5 Newton-Meters of clamp bolt-tightening torque. RESULTS: Components slipped axially and torsionally in the K-E clamp at higher forces for all parameters except for clamp bolt axis pivot. No bolt axis pivot occurred with the Synthes clamp. Instead, the clamp plastically deformed at the fixator-pin interface. This failure occurred at a higher applied torque than the pivot torque for other clamps. The Meynard clamp withstood significantly greater force than the K-E clamp when torsion was applied to the clamp bolt axis in the clockwise direction. Pivot forces for the K-E clamp were significantly higher than the Meynard clamp in the counterclockwise direction. CONCLUSIONS: Overall, the K-E clamp was able to resist higher axial and torsional forces before slipping than the Meynard clamp or the Synthes clamp. The Synthes clamp was best able to resist torsion around the clamp bolt axis. Torsional resistance at the clamp-fixator pin and clamp-connecting bar interface was the weakest parameter of clamp mechanics. CLINICAL RELEVANCE: The ability to resist motion within a clamp is related to fracture-reduction stability. Knowledge of the mechanical properties of fixator clamps will improve a clinician's ability to apply rigid fixation.

Animals↗
PubMed2002

Comparison of insulin sensitivity, clearance, and secretion estimates using euglycemic and hyperglycemic clamps in children.

The euglycemic clamp is the gold standard for estimating insulin sensitivity. The hyperglycemic clamp is easier to perform and is the gold standard for estimating beta-cell secretion. Reports in adults suggest that hyperglycemic clamps can estimate insulin sensitivity with results equivalent to euglycemic clamps. We investigated whether insulin sensitivity measures from both clamps are equivalent in children. Thirty-one lean and obese children (mean body mass index, 25.1 +/- 4.9 kg/m(2); mean age, 8.7 +/- 1.4 yr; 15 girls and 16 boys; 12 black and 19 white) were studied. All subjects underwent hyperglycemic clamps, then euglycemic clamps 2-6 wk later. Body composition was estimated by dual energy x-ray absorptiometry. Visceral and sc abdominal fat was estimated by abdominal magnetic resonance imaging. Whole-body glucose disposal and insulin sensitivity (SI clamp) derived from both clamps and normalized for total or visceral fat and lean mass were significantly correlated (r, 0.45-0.65; P < 0.05). However, absolute SI clamp values were not equivalent. Bland-Altman comparisons found that SI clamp estimates from hyperglycemic clamps became less precise as SI clamp increased. There were significant correlations between indices of beta-cell secretion from the hyperglycemic clamp and mean C-peptide values from the euglycemic clamp (P < 0.05). However, no correlation was found between measures of total insulin clearance (derived from the euglycemic clamp) and surrogates of hepatic insulin clearance (derived from the hyperglycemic clamp). In this cohort of diverse children, SI clamp values from euglycemic and hyperglycemic clamps were significantly correlated but were not equivalent, whereas the insulin clearance measures were not correlated. It cannot be assumed that the hyperglycemic clamp obviates the need for euglycemic clamp studies to accurately estimate insulin sensitivity in children.

Black People↗
PubMed1996

Loss of endothelium-mediated vascular relaxation as a response to various clamping pressures.

The contraction/relaxation responses of thoracic aortal rings clamped with two clamping pressures to potassium chloride (KC1), noradrenaline and carbachol were studied using a scanning electron microscope (SEM) to ascertain endothelial lacerations. Clamp A had the tip pressure PA = 0.60 N/mm2 and clamp B PB = 5.16 N/mm2. In 15 Wistar albino rats, weighing 328 +/- 19 g (mean +/- SD), the thoracic aorta was occluded for 15 min and then three vascular rings (2 mm wide) were excised. The proximal unclamped ring served as a control. The aorta diameter was calculated from the circumference of distal rings 1.61 +/- 0.01 mm (n = 15, dmin = 1.51 mm, dmax = 1.70 mm). The rings were challenged with cumulative additions of KC1 (10-80 mmol/l) to measure the contraction. Then cumulative relaxation on the administration of carbachol (0.01-100 mumol/l) as a response to noradrenaline precontraction (0.1 mumol/l) was determined. A significant loss (P < 0.05) of vascular relaxation in all clamped rings (clamped with PA and PB clamping pressures) was seen. No significant differences (P > 0.05) were observed for contraction between clamped and control rings clamped with clamp A, however the rings clamped with clamp B showed significantly reduction of contraction (P < 0.05). No significant differences were seen from control rings between groups A and B (P > 0.05), as well as from clamped rings between groups A and B (P > 0.05) for both the contraction and relaxation parts of the experiments. With SEM, great endothelial lacerations with complete disruption of the endothelial layer in the rings clamped with the clamp B were seen, but no disruption in rings clamped with clamp A. Therefore endothelial vascular layers are much more susceptible to pressure injuries than was previously believed. The clamped vessel wall injuries, particularly in endothelial layers, depend on the momentary peak clamping pressure (MPCP) as well as on the lower stationary clamping pressure (SCP).

Adrenergic alpha-Agonists↗
PubMed1980

Advantages of hypothermic potassium cardioplegia and superiority of continuous versus intermittent aortic cross-clamping.

The relative effectivenss of hypothermic potassium (K) cardioplegia in conjunction with either continuous or intermittent aortic cross-clamping was evaluated in 20 mongrel dogs. Isovolumetric left ventricular (LV) contractions and myocardial biopsies were obtained before and after a total of 90 minutes of aortic cross-clamping. The dogs were randomly divided into four groups of five dogs each as follows: Group I, continuous 90 minute cross-clamping and multidose K at 4 degrees C (40 mEq/L); Group II, intermittent cross-clamping consisting of six 15 minute periods of cross-clamping separated by 5 minute reperfusion periods and K cardioplegia at 4 degrees C given at the start of each cross-clamping period; Group III, continuous 90 minute cross-clamping and multidose buffered saline at 4 degrees C; Group IV, intermittent cross-clamping, consisting of six 15 minute periods of cross-clamping separated by 5 minute reperfusion periods and buffered saline at 4 degrees C given at the initiation of each cross-clamp period. Group I dogs had the best myocardial performance, with no difference between control values of peak LV pressure and dP/dtmax and those recordings obtained 60 minutes after release of the aortic cross-clamp. Significant depression of LV function was noted in all other groups. Examination of force-velocity and length-tension relationships confirmed better myocardial performance in Groups I and II (multidose K at 4 degrees C) than in Groups III and IV (buffered saline at 4 degrees C). Groups I and III (continuous cross-clamping) had no de-rease in diastolic LV compliance after cross-clamping, whereas compliance was decreased in both Groups II and IV (intermittent cross-clamping) at higher preloads (p less than 0.05 and p less than 0.025, respectively). The wet weight/dry weight myocardial ratios were lower in Groups I and III (continuous cross-clamping) than in Groups II and IV (intermittent cross-clamping). Although creatine phosphate (CP) concentrations were rapidly restored by reperfusion in all groups, adenosine triphosphate (ATP) and glycogen myocardial stores were better preserved at the end of cross-clamping in Groups I and II (multidose K at 4 degrees C). Although LV diastolic compliance was decreased and myocardial water content was increased in Groups II and IV (intermittent cross-clamping), no differences in the minimal extent of subendocardial hemorrhage, edema, and contraction-band necrosis were observed among any of the groups examined electron microscopically. The present study identifies continuous aortic cross-clamping with multidose K at 4 degrees C as a superior method of myocardial protection.

Animals↗
PubMed1997

Supraceliac versus infrarenal aortic cross-clamp for repair of non-ruptured infrarenal and juxtarenal abdominal aortic aneurysm.

Repair of abdominal aortic aneurysms may require aortic occlusion above the renal arteries. Despite fears of renal, hepatic and intestinal ischemia, recent publications have suggested that when repair would be difficult or impossible with infrarenal aortic clamping, supraceliac clamping may not be associated with significantly increased morbidity. Between February 1985 and January 1994, 169 patients underwent elective or urgent (symptomatic but not ruptured) repair of infra- or juxtarenal abdominal aortic aneurysm. Twenty-three patients (14%) required supraceliac clamping for juxtarenal abdominal aortic aneurysm, inflammatory abdominal aortic aneurysm, or other difficult exposure problems. Supraceliac clamping and infrarenal aortic clamping patients were indistinguishable with respect to age, gender, abdominal aortic aneurysm diameter, and other co-morbidities. There was a trend toward more frequent use of supraceliac clamping in urgent operations. Preoperative angiography was used selectively and was obtained more often in supraceliac clamping patients, reflecting suspected juxtarenal or renal involvement based on computed tomography findings, but the decision to employ supraceliac clamping was made at surgery. Mean (s.d.) supraceliac clamping clamp time was 22(5) (range 12-30) min. Similar numbers of supraceliac clamping and infrarenal aortic clamping patients required bifurcated grafts, operative times were comparable, and numbers of early complications were similar in the two groups. Transfusion requirements were slightly greater and length of stay was insignificantly shorter in supraceliac clamping patients (due to a few prolonged hospital stays in infrarenal aortic clamping patients). No supraceliac clamping patient required dialysis or suffered clinically apparent hepatic failure, coagulopathy, or intestinal ischemia. There were no operative deaths and all patients were discharged from the hospital. Supraceliac clamping was not associated with greater perioperative morbidity and may have contributed to a lack of mortality by facilitating repair of difficult abdominal aortic aneurysm. Supraceliac clamping should be considered for elective and urgent abdominal aortic aneurysm repair when there is inadequate length or quality of infrarenal aorta for anastomosis, severe associated pararenal atherosclerosis, inflammatory aneurysm, or previous aortic surgery. It is concluded that selective supraceliac clamping is safe and facilitates repair of difficult aortic problems.

Aortic Aneurysm, Abdominal↗
PubMedDate not supplied

Mechanical comparison of 3 different clamp and 2 different rod types of a new veterinary internal fixation system, 4.5/5.5-mm VetFix.

OBJECTIVE: To compare the gripping force of a standard clamp with click-on and T clamps of the 4.5/5.5-mm VetFix (AO Research Institute, Davos, Switzerland), mounted on smooth and roughened rods. STUDY DESIGN: In vitro mechanical study. METHODS: Rods were mounted on a clamp-holding device. Each clamp type was tested on a materials-testing machine in groups of 6 specimens for torsional and axial load stability on smooth and roughened rods (total, 72 specimens). The variable evaluated was the discontinuity point (DP) as a measure for gliding resistance of the clamp on the rod. Means (+/-SD) were calculated for all groups separately. For statistical comparison, a multiple regression model was fitted with level of significance set at P =.05. RESULTS: The direction of torsion had a significant effect on DP for both asymmetric clamps (standard, click-on). In torsion and axial load, the roughened rod had significantly higher DP levels than the smooth rod for the standard clamp. Rods differed only in axial load for the T clamp, again favoring the roughened rod. The click-on clamp did not reach 10% of the values achieved by the other clamps, independent from the rods and loading conditions. Compared with the T clamp, standard clamp DP values were significantly higher in torsion on the roughened rod as well as in axial load on both rod types. CONCLUSIONS: The roughened rod with a standard clamp was mechanically superior. For the T clamp, the small loss of gripping force may be compensated for by the possibility of inserting 2 more screws. CLINICAL RELEVANCE: The roughened rod may enhance the bending, compressive, and torsional properties of the 4.5/5.5-mm VetFix system by reducing the risk of clamp gliding on the rod. The standard clamp is the clamp of choice, except for the metaphyseal or epiphyseal region, at which use of a T clamp may be indicated to increase the number of screws inserted at the end of the rod.

Animals↗
PubMed1988

The Martin Titanline arterial clamp. A new lightweight alternative.

When haemostatic clamps are applied, evidence of injury at the site of clamp application may be seen when the clamp is removed. Rarely, the intima may be disrupted. When a new arterial clamp became available, a study was designed to compare the Martin Titanline arterial clamp (13-143-35, curved arterial clamp) with several other arterial clamps already in use. The Martin clamp is a modified pivot-point, preset-tension, spring-controlled arterial clamp. The closing pressures of several clamps were measured objectively. The injury produced when the clamps were applied to occlude the blood flow on the carotid artery of a dog was assessed by histological study of the excised segments of the arterial wall. Histological cross-sections were prepared from canine carotid artery which had been perfused for 1 h after the clamp had been applied for 1 h. Histological evidence of injury was limited to disruption of the intimal layer and compression of the medial layer. No significant difference between the amount of damage caused by the DeBakey, Satinsky or Martin clamp was identified. When compared to the other varieties of clamp listed above, the Martin clamp had a significantly lower closing pressure (304 g) compared with 580g (Bulldog), 580 g (Satinsky), and 686 g (DeBakey). The Martin clamp was easier to apply, did not obstruct the operative field as readily and had good clamp-retention characteristics throughout the procedure.

Arteries↗
PubMed1985

Mechanical and metallurgical properties of carotid artery clamps.

The mechanical and metallurgical properties of carotid artery clamps were evaluated. The pressure plate retreat propensity, metallurgical composition, surface morphology, magnetic properties, and corrosion resistance of the Crutchfield, Selverstone, Salibi, and Kindt clamps were tested. None of the clamps showed evidence of pressure plate retreat. The clamps differed significantly in their composition, surface cleanliness, magnetic properties, and corrosion resistance. The Crutchfield clamp was the only one manufactured from an ASTM-ANSI-approved implantable stainless steel (AISI 316) and the only clamp in which the surfaces were clean and free of debris. The Selverstone clamp was made principally from AISI 304 stainless steel, as was one Salibi clamp. The pressure plate on another Salibi clamp was made from a 1% chromium and 1% manganese steel. Machining and surface debris consisting principally of aluminum, silicon, and sulfur was abundant on the Selverstone and Salibi clamps. The Kindt clamp was manufactured from AISI 301 stainless steel with a silicate-aluminized outer coating. The Crutchfield and Selverstone clamps were essentially nonferromagnetic, whereas the Salibi and Kindt clamps were sensitive to magnetic flux. In the pitting potential corrosion test, the Crutchfield clamp demonstrated good corrosion resistance with a pitting potential of 310 mV and no surface corrosion or pitting by scanning electron microscopy examination. The Selverstone clamp had lower pitting potentials and showed various degrees of corrosion and surface pitting by scanning electron microscopy. The Salibi pressure plate had a very low pitting potential of -525 mV and showed severe corrosion. By metallurgical criteria, only the Crutchfield clamp is suitable for long term implantation.

Animals↗