Intramedullary fixation of femoral cortical osteotomies with interlocked biodegradable self-reinforced poly-96L/4D-lactide (SR-PLA96) nails.

Femoral diaphyseal osteotomies of adult sheep were fixed with intramedullary (i.m.) biodegradable self-reinforced poly-96L/4D-lactide (SR-PLA96) nails (Phi 10.66-10.78 mmx195-199 mm) that were interlocked with four Phi 1.5 mm metallic Kirschner (K) wires. Hollow i.m. nails used in the pilot study resulted in implant failure and only two of these sheep were followed long term (18 months and 3 years). In the main study, solid nails were used and this resulted in consolidation in 5/6 cases and in one non-union due to failure of both proximal K wires at 3 weeks. Sheep in the main study were followed for 6 and 12 months. Femurs were studied radiographically, microradiographically, histologically and by oxytetracycline labelling. Good bone healing was achieved and histology showed only a mild tissue reaction to the implant at 6-18 months. At 3 years, the implant had almost degraded and numerous foamy macrophages were ingesting the disintegrated material. No accumulations of lymphocytes implying an immunological inflammatory reaction were seen. This investigation demonstrated that absorbable SR-PLA96 i.m. nails can be used together with interlocking metallic K wires in fixation of simple cortical osteotomies in large animals weighing up to 63 kg. The long-term biocompatibility should be studied in a larger population.

Intramedullary fixation of cortical bone osteotomies with absorbable self-reinforced fibrillated poly-96L/4D-lactide (SR-PLA96) rods in rabbits.

Osteotomies of the femoral diaphysis were fixed with absorbable self-reinforced fibrillated poly-96L/4D-lactide (SR-PLA96) intramedullary rods (4.5 mm x 50-60 mm) in 43 adult rabbits. Follow-up times varied from 3 weeks to 3 yr. After sacrifice histological, oxytetracycline-fluorescence and microradiographic studies of the bones were performed. Strength characteristics and changes in crystallinity and molecular weight of the rods were also measured. All osteotomies were evaluated radiographically. Thirty-six osteotomies (84%) healed uneventfully. The implant disappeared almost totally within 3 yr and histology showed only a minor foreign body reaction. From 6 weeks on, the bending force needed to break the osteotomy was comparable to the bending force needed to break the control bone. The shear strength of the rods displayed only minor changes for the first 24 weeks. Subsequently, the rods rapidly lost their strength and at 48 weeks there was practically no shear strength left, which is ideal for healing of an osteotomy. The present investigation demonstrated, that absorbable. fibrillated SR-PLA96-rods can be used for the intramedullar fixation of simple cortical bone osteotomies in rabbits. These results have encouraged us to continue our studies with the fixation of experimental cortical bone osteotomies in larger species.

Material properties of absorbable self-reinforced fibrillated poly-96L/4 D-lactide (SR-PLA96) rods; a study in vitro and in vivo.

A study was carried out to investigate changes in mechanical properties and degradation of self-reinforced fibrillated poly-96L/4D-lactide (SR-PLA96) rods in vitro and in vivo. The viscosity-average molecular weight, Mv, of the intact sterile (gamma irradiated) rods was around 50,000 g mol(-1). The SR-PLA96 rods of diameter 1.1 mm by 30 mm and diameter 4.5 mm by 50 mm were immersed in phosphate-buffered saline or implanted in the dorsal subcutis of rabbits. Bending, shear and torsion strength and bending modulus, together with the changes of viscosity and crystallinity, were measured up to 24 wk. The strength values showed only a slight decrease during the follow-up period with the exception of torsion strength, that decreased to 52% of the initial value during 24 wk. There were no statistically significant differences in the strength retention between in vitro and in vivo groups. Crystallinity increased over time, being 46-49% at 24 wk. The Mv of the rods decreased over 50% by 24 wk. These promising results motivated us to continue the studies with the fixation of experimental cortical bone osteotomies with SR-PLA96 intramedullary rods.

Polylactide screws in the fixation of olecranon osteotomies. A mechanical study in sheep.

We studied absorbable self-reinforced poly-L-lactide screws in the fixation of osteotomies in sheep. A left olecranon osteotomy in 10 sheep was fixed with polylactide screws and in an additional 10 sheep with metallic AO cortical screws. Follow-up times were 6 and 12 weeks. 8 polylactide fixations healed and 2 failed. All metal fixations united; one of them had a fracture of the proximal fragment resulting in malposition. After killing the sheep the olecranons were radiographed and the shear strengths of the osteotomies were compared with those of the non-operated contralateral bones. After 6 weeks the mean comparative strength was 74 percent in the polylactide group and 83 percent in the metallic control group. After 12 weeks the corresponding values were 112 and 47 percent (P less than 0.05). Our study demonstrated that the mechanical weakening of fixed bone can be avoided by using absorbable polylactide screws instead of metallic screws. However, polylactide screws are not recommended for use without external support in places of high mechanical strain.

Comparison of neurologic responses to the use of medetomidine as a sole agent or preanesthetic in laboratory beagles.

Different dose regimens of medetomidine (a potent alpha 2-adrenergic agonist), adding up to a combined dose of 80 micrograms/kg, were administered to laboratory beagles to determine physiologic responses including neurologic. The study was intended to determine EEG responses where sufficient sedative and analgesic effects are reached with medetomidine and in contrast its effects when used with ketamine or halothane. Cardiopulmonary responses were very similar in each dose regimen, showing the characteristic properties of single doses of 80 micrograms/kg of medetomidine. Effective sedative and analgesic duration seemed to be a function of when the largest dose was administered. Adequate additional sedative and analgesic could be gained from injections at doses of half of the initial one. The potent sedative and analgesic effects of medetomidine confirmed by neurologic evaluation supports its potential use as a premedication to general anesthesia in dogs. In this study, 2 different doses of medetomidine were also tested as premedication to both ketamine HCI and halothane anesthesia. Neorologic responses were determined at the same time cardiopulmonary parameters, anesthetic quality, and dose requirements were recorded. Medetomidine was found to have favorable qualities in conjunction with these anesthetics. Cardiopulmonary parameters remained satisfactory in both groups as preanesthetic medication prior to halothane, but no additional benefits could be seen from doses of 40 micrograms/kg medetomidine compared to 20 micrograms/kg, except a significant 30% reduction in halothane requirement. The positive chronotropic and inotropic properties of ketamine restored the medetomidine-induced bradycardia and produced a short anesthetic period of 15 to 30 min depending on the dose of medetomidine. The quality of anesthesia was better when 40 micrograms/kg medetomidine was used, but recovery was quicker with 20 micrograms/kg medetomidine. Medetomidine significantly reduced cerebral activity as demonstrated by recordings of total amplitude and frequency evaluation of the EEG with compressed spectral analysis. This analytical method was effective in confirming clinical signs of sedation, analgesia, and anesthesia in canine subjects.

Biodegradable implants as intramedullary nails. A survey of recent studies and an introduction to their use.

The high stiffness of metallic implants often requires a removal of the implant through a second operation, after fracture healing has occurred, to prevent disuse osteoporosis from occurring. An absorbable implant, lending sufficient strength and stiffness for support of the fracture during the healing period, would then gradually decay, and shift acting forces over to the healing bone. This paper presents a background to the development of such an implant of self-reinforced polylactic acid, and some recent results from different studies using these rod shaped implants for intramedullary nailing of both experimental and clinical fractures on animals. A short description of the operational technique for use of these implants is also given.

Medetomidine as a preanesthetic prior to ketamine-HCL and halothane anesthesia in laboratory beagles.

The potent sedative and analgesic effects of medetomidine confirm its potential use as a premedication to general anesthesia in dogs. In this study two different doses of medetomidine were tested as premedication to both ketamine HCl and halothane anesthesia in groups consisting of 4 laboratory beagles each. Cardiopulmonary parameters, anesthetic quality and dose requirements were recorded. Medetomidine was found to have favorable qualities in conjunction with these anesthetics. Atropine prevented the profound bradycardia and sinus arrhythmia seen with medetomidine alone. Cardiopulmonary parameters remained satisfactory in both groups, but no additional benefits could be seen from doses of 40 micrograms/kg medetomidine compared to 20 micrograms/kg, except a significant 30% reduction in halothane requirement. The positive chronotropic and inotropic properties of ketamine restored the medetomidine induced bradycardia and produced a short anesthetic period of 15-30 min depending on the dose of medetomidine. The quality of anesthesia was good in both groups, but recovery was quicker and smoother in the group with 20 micrograms/kg medetomidine.

Comparison of three different dose regimes of medetomidine in laboratory beagles.

Different dose regimes of medetomidine (a potent alpha 2-adrenergic agonist), adding up to a combined dose of 80 micrograms/kg, were administered to laboratory beagles to determine the possible superiority of any particular regime. The study was intended to mimic a clinical situation where sufficient sedative and analgesic effect was not reached with the initial dose and an additional dose would have to be administered. Cardiopulmonary responses were very similar in each dose regime, showing the characteristic properties of single doses of 80 micrograms/kg of medetomidine as reported in the literature. Effective sedative and analgesic duration seemed to be a function of when the largest dose was administered. Adequate additional sedative and analgesic effect could be gained from the second injection at doses of half of the initial one.

A comparison of xylazine, acepromazine, meperidine and medetomidine as preanesthetics to halothane anesthesia in dogs.

The preanesthetic properties of medetomidine, a novel alpha 2-adrenergic agonist, were compared to the preanesthetic properties of acepromazine, zylazine and meperidine prior to halothane anesthesia. The premedications were given to 23 randomly selected laboratory beagles in doses with sedative effects equal to the 10 micrograms/kg used in the medetomidine group. These dogs also received 0.04 mg/kg of atropine prior to the preanesthetic. A group of 7 dogs with a high medetomidine dose (40 micrograms/kg) was included in the study. Cardiopulmonary and respiratory parameters were recorded at 10 min intervals during surgical stimulus. Dogs receiving 40 micrograms/kg of medetomidine showed bradycardia, but higher blood pressures than dogs in the other groups. Adequate oxygen saturations and perfusion were recorded in all groups. The low 10 micrograms/kg dose of medetomididine had a halothane sparing effect comparable to the other premedications, while the 40 micrograms/kg of medetomidine group showed a clear decrease in halothane consumption. The sedative effect of 10 micrograms/kg of medetomidine was in some instances inadequate for proper manipulation of the dogs, but 40 micrograms/kg produced excessive sedation. Atropine was found to counteract the medetomidine induced bradycardia.