Mechanical stimulation induces pp125(FAK) and pp60(src) activity in an in vivo model of trabecular bone formation.

Utilizing an in vivo model of trabecular bone formation, we demonstrated the temporal and spatial activation of pp125(FAK) in response to specific mechanical load stimuli. Bone chambers equipped with hydraulic actuators were aseptically inserted into each proximal tibial metaphysis of adult, male dogs under general anesthesia. The load stimulus consisted of a trapezoidal waveform, with a maximum compressive load of 17.8 N, loading rate of 89 N/s, at 1 Hz frequency. One chamber was loaded for 2 (120 cycles), 15 (900 cycles), or 30 min (1,800 cycles), whereas the contralateral chamber served as unloaded control. Bone chambers were biopsied at postload time points of 0, 15, and 45 min. Load-induced activation of FAK was rapid, and the duration of activation was dependent on the number of applied load cycles. Mechanical stimulation increased the association of FAK with Src and the time course of complex formation paralleled the temporal activation of FAK. Evaluation of cryosections revealed prominent FAK immunoreactivity among marrow fibroblasts and stromal cells.

An in vivo model for investigations of mechanical signal transduction in trabecular bone.

The premise that bone cells are able to perceive and respond to mechanical forces is well accepted. This article describes the use of an in vivo hydraulic bone chamber for investigations of mechanical signal transduction. The servohydraulic loading mechanism was activated to apply a controlled compressive load to the woven trabecular bone that formed in one chamber, while the contralateral chamber served as an unloaded control. Specimens were harvested at a series of postload time points, and the cellular response to loading was evaluated by cytochemical, histomorphometric, and Northern blot analysis. A repetitive daily load stimulus elicited osteoblast biosynthetic activity characterized by an initial increase in type I procollagen by day 3 and a subsequent rise in alkaline phosphatase (ALP) activity after the sixth daily load episode. Application of a single load episode induced a biphasic pattern of c-fos and zif-268 gene expression with up-regulation at 30 minutes, down-regulation at 12 h, and up-regulation 24 h after the mechanical stimulus. The results show that a synchronized pattern of bone cell activity and gene expression occurs in response to controlled mechanical stimulation and that candidate load-responsive molecular mediators can be evaluated easily by this model.

Mechanical stimulation of tissue repair in the hydraulic bone chamber.

A hydraulically activated bone chamber model was utilized to investigate cellular and microstructural mechanisms of mechanical adaptation during bone repair. Woven trabecular bone and fibrotic granulation tissue filled the initially empty chambers by 8 weeks postimplantation into canine tibial and femoral metaphyses. Without mechanical stimulation, active bone remodeling to lamellar trabecular bone and reconstitution of marrow elements were observed between 8 and 24 weeks. In subsequent loading studies, the hydraulic mechanism was activated on one randomly chosen side of 10 dogs following 8 weeks of undisturbed bone repair. The loading treatment applied an intermittent compressive force (18 N, 1.0 Hz, 1800 cycles/day) for durations of a few days up to 12 weeks. Stereological analysis of three-dimensional microcomputed tomography images revealed an increase in trabecular plate thickness and connectivity associated with the loaded repair tissue microstructure relative to unloaded contralateral controls. These microstructural alterations corresponded to an over 600% increase in the apparent modulus of the loaded bone tissue. A significant increase in the percentage of trabecular surfaces lined by osteoblasts immunopositive for type I procollagen after a few days of loading provided further evidence for mechanical stimulation of bone matrix synthesis. The local principal tissue strains associated with these adaptive changes were estimated to range from approximately -2000 to +3000 mustrain using digital image-based finite element methods. This study demonstrates the sensitivity of bone tissue and cells to a controlled in vivo mechanical stimulus and identifies microstructural mechanisms of mechanical adaptation during bone repair. The hydraulic bone chamber is introduced as an efficient experimental model to study the effects of mechanical and biological factors on bone repair and regeneration.

Trabecular bone adaptation to variations in porous-coated implant topology.

Trabecular bone adaptation adjacent to porous-coated platen implants embedded within canine distal femoral metaphyses was evaluated following 24 weeks of daily compressive loading. The in vivo experimental model delivered controlled loads to five different platen implant topologies with variations in platen shape and porous coating distribution. Adaptive changes were evaluated based on three-dimensional stereological analyses of trabecular bone architecture underneath each platen and non-destructive mechanical tests of platen construct stiffness. Fully coated cylindrical platen designs possessed the highest construct stiffness in both tension and compression. Changes in local trabecular bone morphology were also found to be significantly influenced by platen implant topology. Cylindrical platens with fully coated bottom surfaces were associated with greater decreases in trabecular bone volume and connectivity than cylindrical platens with smooth bottom surfaces or fully coated conical platens. Comparisons to site-matched contralateral control bone volumes across all platen designs indicated significant decreases in the average bone volume fraction, trabecular plate number, and connectivity within experimental samples, but no change in trabecular plate thickness. In addition, analyses of microstructural anisotropy revealed a 20 degrees or 20.2 degrees trabecular reorientation towards the axis of loading in experimental tissue. This study demonstrates that trabecular bone adaptation near porous-coated surfaces is influenced by variations in local implant topology and provides insight into specific mechanisms of implant-mediated microstructural adaptation.

Relative effects of wound healing and mechanical stimulus on early bone response to porous-coated implants.

We hypothesized that early bone adaptation to well fixed porous-coated implants is influenced more by wound healing than by mechanical loading. To test this hypothesis, two groups of dogs with identical, hydraulically controlled porous-coated implants interference fit within distal femoral trabecular bone were used. One group had no load: the other had 35 N of load applied to the implants. At 5 weeks after surgery, the resulting adaptation of bone around the implants was quantified on a cellular basis by cytochemical analysis of type-I procollagen synthesis and on a structural basis using three-dimensional micro-computed tomography imaging. The percentage of trabecular surfaces covered by osteoblasts expressing type-I procollagen was significantly increased in bone surrounding the implant in both groups compared with contralateral control bone tissue. There was no difference between the groups with no load or 35 N of load. In addition, measures of trabecular bone structure did not differ significantly between the load and no-load groups. Taken together, these results suggest that wound healing plays a much greater role in the early response of bone to well fixed porous-coated implants than does mechanical stimulus.

Effects of imposed hindfoot constraint on ankle contact mechanics for displaced lateral malleolar fractures.

Contact stress distributions on the tibial plafond were mapped in a series of eight fresh-frozen cadaver specimens in which displaced lateral malleolar fractures were studied. These included gripping (a) by snugly lacing the foot in an athletic shoe, (b) by polymethylmethacrylate potting of the calcaneus alone, and (c) by potting of the calcaneus plus talus. Each of these three gripping conditions was tested both for rigid and for nearly frictionless transverse external constraint conditions. Across the series, the grip-dependent changes in contact stress distributions were found to be very minor compared with the wide interspecimen variability that was consistently present. Moreover, although contact stresses generally increased with progressive lateral fibular fragment offsets of up to 5 mm, such an effect was far more modest than that seen in previous cadaver work. The present laboratory cadaver findings suggest that the contact stress elevations occurring clinically for displaced lateral malleolar fractures are probably relatively mild and likely not directly responsible for late secondary degeneration.

An algorithm for approximate crinkle artifact compensation in pressure-sensitive film recordings.

An objective, empirically based image-processing technique was devised to compensate for the presence of crinkle artifact in Pressensor pressure-sensitive film recordings. A spherical indentor was used to produce film stains which deliberately included radially directed artifact streaks, superimposed upon otherwise smooth, nearly axisymmetric stain recordings. An interactive, threshold-based search algorithm was developed to delineate explicitly the perimeters of specific artifacts present within manually (cursor) circumscribed regions where crinkle features were visually apparent. Three mathematical artifact transformation operators were parametrically evaluated in terms of their ability to approximate objectively the corresponding artifact-free axisymmetric pressure fields. All three operators were found to reduce substantially the quantitative deviation from the idealized distributions. When appropriately tuned transformation operators were applied to typical in vitro intraarticular contact stains, the visual prominence of crinkle artifact features was markedly reduced.

Dose-finding and pharmacokinetic study of intramuscular midazolam.

Ten healthy male volunteers received intramuscular (IM) doses of 0.050, 0.075, and 0.100 mg/kg midazolam hydrochloride or its vehicle (placebo) in a double-blind manner until a dose producing adequate preanesthetic sedation was administered. Level of sedation, degree of impairment of psychomotor function, existence of antegrade amnesia, and incidence of side effects were evaluated after each dose. An adequate level of sedation (awake/drowsy or asleep/easily responds to verbal command for at least one hour after drug administration) was produced, beginning shortly after drug administration, in eight of the volunteers by 0.075 mg/kg; the dose producing the same effect (the optimal dose) was 0.050 mg/kg for the oldest volunteer, and the other volunteer required 0.100 mg/kg. Sedation lasted no more than four hours after administration of the optimal dose. The optimal dose in each volunteer produced an impairment of psychomotor function that lasted no more than six hours and antegrade amnesia that lasted no more than two hours. Mild erythema at the injection site occurred infrequently. The pharmacokinetic variables describing the absorption and disposition of midazolam were determined in five of the volunteers. Pharmacokinetic studies indicated that midazolam hydrochloride is absorbed rapidly from IM injection sites; this consistent with the observation of a rapid onset of sedation. The relatively high elimination clearance of midazolam after IM administration is similar to that reported after intravenous administration. The results of this study suggest that midazolam hydrochloride 0.075 mg/kg IM provides sedation and amnesia that is satisfactory for preanesthetic medication but does not last too long into the recovery period.

Midazolam kinetics in women of two age groups.

Midazolam kinetics were determined in 11 younger (22 to 30 yr) and 11 older (50 to 60 yr) women to determine age-related differences in the kinetics of this water-soluble benzodiazepine. Midazolam, 0.2 mg/kg, was injected intravenously over 30 sec for induction of anesthesia that was maintained with 67% nitrous oxide in oxygen and intravenous fentanyl doses. There were no differences between the groups with respect to awakening times or plasma concentrations. Midazolam kinetics were described by a three-compartment open mamillary model. The only differences were small increases in the slow and total volumes of distribution in the older women. The kinetics we determined, including the steady-state volume of distribution of 1.23 l/kg and the elimination clearance of 419 ml/min, are in excellent agreement with those reported by others. Our data suggest that midazolam has advantages over other benzodiazepines, not only because of its water solubility and shorter elimination t1/2, but also because of little change in its kinetics with age.

A pharmacokinetically designed etomidate infusion regimen for hypnosis.

An etomidate infusion regimen for hypnosis as part of balanced, totally intravenous anesthesia was designed to maintain plasma etomidate concentrations above the awakening concentration of 300 ng/ml while avoiding dose-related side effects. The etomidate infusion regimen of 0.1 mg/kg/min for 3 min, 0.02 mg/kg/min for 27 min, and 0.01 mg/kg/min for the remainder of the anesthesia was used together with intravenous bolus doses of fentanyl, droperidol, and pancuronium. This was evaluated in 11 patients and the kinetics of etomidate were reexamined. The anesthetic technique seemed clinically satisfactory for the infusion periods of 30-109 min. The average time and plasma concentration at the end of the infusion was 59.5 min and 583 ng/ml, at awakening was 9.3 min and 307 ng/ml, and at alertness was 19.5 min and 227 ng/ml. The main difference between the kinetics observed in the present study and those of previous studies is in the elimination clearance. The average plasma elimination clearance of the present study was 1210 ml/min and the whole-blood clearance was estimated to be 1357 ml/min, giving an apparent hepatic extraction ratio of approximately 0.90. The negative correlation of patient mass and elimination clearance normalized for body mass suggests that the terminal infusion should not be adjusted to body mass.

Intramuscularly administered ciramadol for management of postoperative pain: a comparative study.

Efficacy and safety of the analgesic ciramadol in the management of postoperative pain was evaluated in 139 healthy patients given single, double-blind, intramuscular injections of either 30 mg ciramadol, 60 mg ciramadol, 10 mg morphine or 0.9% saline on the first or second postoperative day. Differences in pain intensity and relief of pain, changes from baseline on a pain analog scale, percentage of patients with moderate or greater pain relief, and cumulative treatment failures were measured for 6 hours after injection. Morphine proved to be superior to all other treatments. Neither dose of ciramadol could be statistically differentiated from placebo. During the first hour after administration, some measurements showed that 30 mg ciramadol was superior to 60 mg ciramadol. Patients experienced little or no drowsiness in any of the four groups, and other side effects were transient and required no specific therapy. Some patients experienced an acute increase in pain intensity after administration of 60 mg ciramadol; this possibly represents antagonism of the residual effect of the previous narcotic. This study must be interpreted with the knowledge that ciramadol, an agonist-antagonist analgesic, was administered to patients who had been receiving narcotic analgesics before entering the study. Future studies of ciramadol given as the sole analgesic may more clearly define its efficacy in the management of postoperative pain.

Comparison of three doses of oral ciramadol and placebo for the treatment of moderate to severe postoperative pain.

Ciramadol, 20, 40, or 60 mg, or a placebo was administered orally, double blind, to patients complaining of moderate (N = 89) or severe (N = 80) postoperative pain to determine the lowest effective dose. The highest dose used for moderate pain, 40 mg, was statistically more effective than placebo as measured by pain intensity differences and pain relief scores. The highest dose used to treat severe pain, 60 mg, was also more effective statistically than placebo and the lower doses of ciramadol at certain points during the 6-hour observation period. Drowsiness was minimal, and side effects were infrequent and mild in intensity. We conclude that 40 mg ciramadol for moderate postoperative pain and 60 mg ciramadol for severe postoperative pain would be the minimal oral doses to compare with standard analgesics in future studies.

Awakening characteristics following anesthesia induction with midazolam for short surgical procedures.

8-Chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazol[1,5-a][1,4]benzodiazepine (midazolam maleate, Ro 21-3981, Dormicum) or thiopental were administered to 99 women undergoing short gynecological surgical procedures for induction and maintenance of anesthesia along with 67% nitrous oxide. Either fentanyl 1.5 microgram kg-1 or a saline placebo were given i.v. as acute premedication 5 min before induction. We measured the quality of induction and maintenance. Induction was more rapid after thiopental but thiopental produced more apnea especially when combined with fentanyl. Fentanyl premedication reduced the dose of hypnotics necessary to keep patients asleep. It was difficult to keep patients from moving during the procedure when only the hypnotics and nitrous oxide were used, so the use of these drugs for both induction and maintenance is recommended only when combined with narcotics or other analgesics. Although recovery after midazolam was slower than after thiopental, it was without untoward reactions such as hallucinations or excitement. Vomiting was less frequent after midazolam. Midazolam produced a profound period of amnesia for 1-2 h, so important instructions could not be given to patients during this time. All patients were awake enough to discharge from the hospital 200 min after the last dose of hypnotic was given. We would recommend a combination of midazolam, fentanyl and nitrous oxide for induction and maintenance of anesthesia for short surgical procedures except when a rapid induction is desired, then thiopental is preferred as the hypnotic.