Femoral strength after induced lesions in rats (Rattus norvegicus)

Rats are a common model for the study of bone healing, with the cranium, femur, and tibia being the bones studied most frequently. This study examines noncritical-sized lesions that would allow rats to continue to bear weight without the need for fixation but that are sufficiently large to enable characterization of the healing process. We compared the femoral bone strength associated with 3 lesion sizes selected for use in future studies. Sprague-Dawley rats (age, 10 to 16 wk) were used to assess the ultimate breaking strength, stress, and break force of normal, unmanipulated femurs. We then created lesions of 3 different sizes in the mid- to distal diaphysis of the left and right femurs and characterized the associated decreases in bone strength. Femurs (n = 85) for this study were collected through tissue sharing from rats used in other acute surgical procedures and were tested by using a 3-point bending flexural materials-testing machine. Our hypothesis was that, as a model for bone healing, 3 induced lesions of different sizes would show incremental and proportional decreases in femoral strength, with the intermediate-sized (1.5-mm) lesion demonstrating a decrease of 20% to 40%. A lesion of 1.5 mm yielded a decrease in strength of 17% for both the left and right femurs. The strength of left femurs carrying intermediate lesions was significantly less than that of control, uninjured femur bones. In addition to providing validation for our own future bone-healing project, these data are a useful baseline for other investigators studying bone healing in a rat femur model.

Evaluation of medicated gel as a supplement to providing acetaminophen in the drinking water of C57BL/6 mice after surgery

After surgery, rodents frequently receive acetaminophen-treated drinking water for pain relief, but the effectiveness of this practice is often questioned. Gel products are now available to facilitate the delivery of oral medication to rodents after surgery. We sought to compare consumption of flavored medicated gel and medicated water after surgery and to determine whether providing supplemental acetaminophen in gel form ensures the ingestion of a therapeutic dose of an analgesic after surgery. Male C57BL/6 mice were allocated into 3 groups after surgery: those that received acetaminophen-treated water and untreated gel (MW group); those that received medicated gel and untreated water (MG group); and those that received acetaminophen in both forms (MWG group). Total water and gel consumption were monitored daily from the day before surgery until 2 d thereafter. Mice in the MG group consumed significantly less gel than water, and consequently, the total acetaminophen dose per mouse in the MG group (49 mg/kg) was significantly less than that of the MWG group (347 mg/kg). Although the dose consumed by mice in the MW group (158 mg/kg) approached the targeted acetaminophen dose of 200 mg/kg, only mice in the MWG group actually achieved the desired dose. The results of this study indicate that flavored acetaminophen-containing gel can be used in combination with medicated water to ensure that rodents ingest the targeted dose of medication.

Assessment of postoperative analgesia after application of ultrasound-guided regional anesthesia for surgery in a swine femoral fracture model

Management of pain in research swine used for studies involving painful procedures is a considerable challenge. Here we assessed whether a regional anesthesia method is effective for pain control of hindlimb injuries in pigs used for research in bone fracture healing. For this randomized controlled study, we administered regional anesthesia before an experimental femoral injury was produced. Using ultrasound guidance, we placed sterile infusion catheters near the sciatic and femoral nerves and administered local anesthetic (bupivacaine) for the first 24 h after surgery. We evaluated various behavioral and physiologic parameters to test the hypothesis that this regional anesthesia would provide superior analgesia compared with systemic analgesia alone. We also collected blood samples to evaluate serum levels of cortisol and fentanyl postoperatively. At the end of the study period, we collected sciatic and femoral nerves and surrounding soft tissues for histopathologic evaluation. Treatment pigs had lower subjective pain scores than did control animals. Control pigs had a longer time to first feed consumption and required additional analgesia earlier in the postoperative period than did treatment pigs. Ultrasound-guided regional anesthesia is a viable and effective adjunct to systemic analgesics for providing pain control in swine with experimental femoral fractures.

Comparison of fibrinogen- and collagen-based treatments for penetrating wounds with comminuted femur fractures in a Swine model

INTRODUCTION

Military servicemembers in combat operations often sustain injuries to the extremities from highspeed projectiles, resulting in bleeding and comminuted open fractures. Severe injury with bone fragmentation can result in limb amputation. Surgical treatment options include materials that promote osteogenesis and bone proliferation, such as growth hormones, stem cells, or mineralized matrix adjuncts. However, none of these are amenable to use by the first responder, nor do they address the question of hemorrhage control, which is a common problem in traumatic injuries.

HYPOTHESIS

Our hypothesis was that treatment with a fibrinogen-based protein mixture at the time of the bone injury will provide both hemostasis and a supportive environment for preservation of injured bone.

METHODS

A comminuted femur fracture was produced in 28 female Yorkshire swine, and one of four treatments was instilled into the wound immediately after injury. Each animal was evaluated for the following parameters: inflammation, new bone growth, osteoclast proliferation, callus formation, and femur wound cavity fill, using post-mortem computed tomography and analysis of histological sections.

RESULTS

Overall, salmon fibrinogen?thrombin and porcine fibrinogen?thrombin showed a trend for improved healing based on bone filling and calcification. However, statistically significant differences could not be established between treatment groups.

CONCLUSIONS

These findings indicate that a fibrinogen?thrombin matrix may be a useful as an immediate response product to enhance fracture healing. Salmon fibrinogen?thrombin has the advantages of cost and a pathogen profile compared to mammalian fibrinogens.

The effect of daily repeated sedation using ketamine or ketamine combined with medetomidine on physiology and anesthetic characteristics in rhesus macaques

BACKGROUND

Non-human primates are frequently sedated to permit handling that can alter physiological values. The purpose of this study was to identify the effects of daily serial sedation using ketamine (K) or ketamine combined with medetomidine (KM). We hypothesized KM would reduce observed effects of repeated sedation.

METHODS

Eight rhesus macaques were anesthetized for three consecutive days. Physiological data were recorded daily at 5-minute intervals. Time intervals from injection to ataxia, recumbency, first movement and recovery were recorded. Depth of anesthesia was evaluated.

RESULTS

Data showed an 11.7% increased heart rate at 5 minutes between the first and third day of injection with K and 17.9% with KM. Time from injection to ataxia increased 13.7% with K and 14.3% with KM. Time to recumbency increased 34.7% with K and 37.1% with KM.

CONCLUSION

These findings demonstrate repeated anesthesia with ketamine can initiate changes suggesting a tolerance effect.

Effects of serial anesthesia using ketamine or ketamine/medetomidine on hematology and serum biochemistry values in rhesus macaques (Macaca mulatta)

BACKGROUND

This study aimed at determining the cumulative effect of daily anesthesia, using two drug regimens, over hematological and biochemical parameters.

METHODS

Blood samples were obtained from rhesus monkeys 20 minutes after intramuscular administration of ketamine or ketamine/medetomidine combination for three consecutive days and results were evaluated to determine their effect on hematological and serum biochemistry values. Statistical significance of drug, day, and interaction of these two variables were evaluated.

RESULTS

Drug effect resulted in a dramatic increase of aspartate aminotransferase and creatine kinase values. Day effect resulted in decreases of RBC, HCT, Hgb, and alkaline phosphatase but an increase of other biochemical parameters evaluated. The drug/day interaction effect was found to be -significant for RBC, platelets, aspartate aminotransferase, alanine aminotransferase, and creatine kinase values.

CONCLUSION

The results of our study suggest a cumulative effect of serial anesthesia and should be an important consideration when interpreting hematology and serum biochemistry in rhesus macaques.