The water jet as a new tool for endoprosthesis revision surgery--an in vitro study on human bone and bone cement

In revision surgeries of endoprostheses, the interface between implant and bone cement or bone must be loosened. Conventional tools have many disadvantages because of their size and limited range. Taking advantage of the selective and athermic cutting process, a plain water jet is already used in order to cut soft tissues. This study investigates the possibilities of both a plain and an abrasive water jet as cutting tools for revision surgery. Samples of the mid-diaphysis of human femora and bone cement (CMW3) were cut with a plain water jet (PWJ) and an abrasive water jet (AWJ) at two different jet-to-surface angles (30 degrees,90 degrees ) and at five different pressure levels (30, 40, 50, 60, 70 MPa). For a PWJ a selective pressure range was identified, where only bone cement was cut. Injecting a bio-compatible abrasive (lactose) to the jet stream resulted in significantly higher cut depths in both materials. Material removal in bone was significantly less at the smaller jet-to-surface angle for both techniques. No clear selectivity between bone and bone cement was observed for application of the AWJ. However, the material removal rate was significantly higher for bone cement than for bone at all pressure levels. The results indicate that an AWJ might be an alternative tool for cement removal. The possibility for localised cutting at interfaces could be an advantage for revision of a non-cemented prosthesis.     

Intrathecal midazolam reduces isoflurane MAC and increases the apnoeic threshold in rats

Canadian Journal of Anesthesia/Journal canadien d'anesthésie - The purpose of this study was to examine the anaesthetic requirement of intrathecal midazolam in a dose-response fashion in...     

Trichodysplasia Spinulosa—A Rare Complication in Immunosuppressed Patients

Abstract: Immunosuppression is necessary in a large number of conditions to modify immune responses and control disease severity. It is a vital part of treatment regimes following organ and bone marrow transplants. However, the use of immunosuppressive drugs has been shown to cause infections with common and unusual pathogens. We present the case of a 5‐year‐old female heart transplant recipient. Nine months after the transplant, she developed a tender acneiform eruption on her face consisting of numerous small yellowish to pink papules and pustules. Many of the lesions had a central, firm, small spinulous excrescence or a central dell. Histopathology demonstrated abnormal maturation of the hair follicles, nucleated eosinophilic cells with trichohyalin granules. The clinical presentation and histological features were in keeping with trichodysplasia spinulosa, a rare complication in immunosuppressed subjects. Treatment trials included reduction of immunosuppression combined with topical and oral retinoids, topical acyclovir, and oral valganciclovir with limited success.     

Transverse fractures of the olecranon: a biomechanical comparison of three fixation techniques

Introduction  

The gold standard for treating transverse olecranon fractures is tension band fixation. A problem with this technique is migration of the K-wires leading to premature hardware removal. The aim of this study is to compare stability provided by two new techniques designed to eliminate the problem with backing out of K-wires, with that of the recommended tension band technique, performed with a biomechanical in vitro investigation. Our hypothesis was that the two new techniques would provide at least equal stability as the traditional tension band fixation.     

Less than additive antinociceptive interaction between midazolam and fentanyl in enflurane-anesthetized dogs

The anesthetic interactions of midazolam and fentanyl were determined in terms of enflurane MAC reduction in dogs. In part 1, 8 animals received an intravenous (iv) loading dose of fentanyl followed by a constant infusion at 0.05 micrograms.kg-1.min-1 to produce a stable enflurane MAC reduction of approximately 20%. Midazolam was then administered in a series of three incremental loading doses and infusions (2.4, 9.6, and 28.8 micrograms.kg-1.min-1 previously determined to produce enflurane MAC reductions of approximately 30, 45, and 60%, respectively. Enflurane MAC was determined for each infusion. Then fentanyl was discontinued; naloxone 1 mg/kg was administered; and enflurane MAC was determined. In part 2, six dogs received a loading dose and a continuous infusion of fentanyl (0.2 micrograms.kg-1.min-1) designed to produce a stable enflurane MAC reduction of approximately 40%. A series of two incremental loading doses and infusions of midazolam (2.4 and 28.8 micrograms.kg-1.min-1) were added, and MAC determinations were repeated at each infusion rate. Then midazolam was discontinued; flumazenil (RO 15-1788) 1.5 mg/kg was administered; and enflurane MAC was determined. The fentanyl concentrations in plasma remained stable at 1.0 +/- 0.3 ng/ml (mean +/- standard deviation [SD], part 1) and 3.1 +/- 0.5 ng/ml (part 2) throughout the study and, in the absence of midazolam, reduced enflurane MAC by 28 +/- 11 and 44 +/- 5%, respectively. The addition of midazolam produced significant further reductions in enflurane MAC, but the reductions were less than those predicted on the basis of an additive interaction. Naloxone returned enflurane MAC reduction to that expected for midazolam alone (part 1).(ABSTRACT TRUNCATED AT 250 WORDS)     

The pharmacokinetics and pharmacodynamics of ketamine in dogs anesthetized with enflurane

The plasma concentration vs. anesthetic effect relationships for ketamine are not well known. It is desirable to establish stable and predictable drug concentrations in plasma (and brain) in order to define such relationships. As a prelude to pharmacodynamic studies, we investigated ketamine pharmacokinetics in eight dogs anesthetized with enflurane and correlated ketamine concentration in plasma (KET) with its ability to reduce the enflurane concentration required for anesthesia (enflurane EC50: MAC--the end-tidal concentration at which half the dogs moved in response to clamping of the tail and half did not move). Four dogs (Group 1) received ketamine 10 mg/kg iv over 30 sec. Blood for determination of KET was collected repeatedly over the 5-h period following injection. Based on the pharmacokinetic parameters determined for Group 1, four dogs in Group 2 received ketamine as a continuous infusion of 300 micrograms.kg-1.min-1 for 5 hr accompanied by an initial loading dose (26 mg/kg administered over 20 min) designed to produce a stable KET of 20 micrograms/ml of plasma. Enflurane MAC and KET were determined regularly during the infusion and for 5 hr after discontinuation of the infusion. There were no significant differences in the following pharmacokinetic parameters determined for Group 1 vs. Group 2: t1/2 beta = 122 +/- 9 vs. 141 +/- 40 min (mean +/- SD) and CL = 18.1 +/- 5.9 vs. 13.9 +/- 2.5 ml.kg-1.min-1, respectively. When administered as a continuous infusion (Group 2), KET remained relatively stable at 22.1 +/- 4.6 micrograms/ml for 5 hr. The degree of MAC reduction remained relatively stable at 73% during the continuous infusion. Finally, the enflurane MAC reduction vs. KET was established over a wide range of plasma concentrations in 4 additional dogs (Group 3). This study determined that the pharmacokinetics of ketamine were consistent under two different experimental conditions and demonstrated the relationship between plasma concentration and anesthetic effect in the dog.     

The locking attachment plate for proximal fixation of periprosthetic femur fractures-a biomechanical comparison of two techniques

Purpose

Mechanical properties of a locking attachment plate construct (LAP-LCP), allowing bicortical screw placement laterally to the prosthesis stem, are compared to a cerclage-LCP construct.

Methods

Eight right synthetic femora with implanted uncemented hip endoprosthesis were cut distally and fixed with LCP, monocortical locking screws and either LAP (n = 4) or cerclage (n = 4). Cyclic testing was performed with monotonically increasing sinusoidal load until failure. Relative movements at the plate–femur interface were registered by motion tracking. Statistical differences were detected by unpaired t-test and general linear model repeated measures.

Results

Stiffness of the LAP-LCP was significantly higher at the beginning (875.4 N/mm ± 29.8) and after 5000 cycles (1213.0 N/mm ± 101.1) compared to the cerclage-LCP (644.96 N/mm ± 50.1 and 851.9 N/mm ± 81.9), with p = 0.013. Relative movements for AP-bending (B) and axial translation (T) of the LAP-LCP at the beginning (0.07° ± 0.02, 0.20 mm ± 0.08), after 500 cycles (0.16° ± 0.10, 0.26 mm ± 0.07) and after 5000 cycles (0.26° ± 0.11, 0.31 mm ± 0.07) differed significantly from the cerclage-LCP (beg.: 0.26° ± 0.04, 0.28 mm ± 0.05; 500 cyc: 0.47° ± 0.03, 0.53 mm ± 0.07; 5000 cyc.: 0.63° ± 0.18, 0.79 mm ± 0.13), with B: p = 0.02, T: p = 0.04. Relative movements for medial bending were not significantly different between the two constructs. Cycles to failure (criterion 1 mm axial translation) differed significantly between LAP-LCP (19,519 ± 1,758) and cerclage-LCP (11,265 ± 2,472), with p = 0.035.

Conclusions

Biomechanically, the LAP-LCP construct improves proximal fixation of periprosthetic fractures compared to the cerclage-LCP construct.